JP2013246396A - Image forming apparatus, image forming method, program, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a reduction in color reproducibility due to a change in the adhesion amount of transparent toner.SOLUTION: An image area separation unit 503a performs determination of character/non-character, chromatic/non-chromatic, dot/non-dot, and low-density dots for each pixel of an input image, and outputs a determination result as an image area separation result X. A glossiness addition unit 504a determines a glossiness addition amount T of transparent toner to be added to each pixel on the basis of image data and the image area separation result X, and an adhesion amount of chromatic color toner according to the adhesion amount of the transparent toner.

Description

  The present invention relates to an image forming apparatus, an image forming method, a program, and a recording medium that form an image using colored toner and transparent toner.

  Conventionally, there is a technique for changing the glossiness of a printed matter by attaching colorless toner (transparent toner, clear toner). For example, in Patent Document 1, the amount (development amount) of the transparent toner is adjusted according to the color of the input image signal.

  However, in the conventional techniques as described above, the amount of the transparent toner attached is determined according to the color of the input image signal. Since the adhesion amount of the transparent toner is the same, the gloss cannot be changed by changing the adhesion amount of the transparent toner.

  In addition, in the printed matter to which the above technique is applied, there is a problem that even if the amount of the colored toner is the same, the color reproducibility is lowered due to the amount of the colorless toner deposited on the colored toner.

The present invention has been made in view of the above problems,
An object of the present invention is to provide an image forming apparatus, an image forming method, a program, and a recording medium that do not deteriorate color reproducibility due to a change in the adhesion amount of the transparent toner when the gloss is changed by changing the adhesion amount of the transparent toner. There is.

  The present invention is an image forming apparatus that forms an output image on a predetermined medium using colored toner and transparent toner based on image data obtained by reading a document, and adds gloss to each pixel of the image data. Determining means for determining whether or not to add the gloss to the pixel determined to add gloss, and a determination means for determining the amount of color toner attached according to the gloss addition amount based on the gloss addition amount. The most important feature.

  According to the present invention, it is possible to prevent a decrease in color reproducibility due to a difference in the amount of transparent toner attached.

The configuration of the entire copying machine is shown. The control system built in the copying machine is shown. 1 shows an overall configuration of an image processing unit of the present invention. 2 shows a configuration of an image area separation / ACS circuit. The structure of an image area separation part is shown. The processing flowchart of a glossiness addition part is shown. The processing flowchart of gloss addition amount [type 1] is shown. The relationship between gloss addition amount and the dispersion | variation in background data is shown. The relationship between the adhesion amount of transparent toner and image density is shown. The processing flowchart of gloss addition amount [type 2] is shown. The relationship between the gloss addition amount and the image density of the target pixel is shown. The processing flowchart of gloss addition amount [type 3] [type 4] is shown. The correspondence relationship between the type of paper used for the original and the gloss addition amount used for the printed material is shown. 5 shows a processing flowchart of determination (first determination) of variation and smoothness of image data. Indicates the variation in the background of the document. The processing flowchart of the determination (2nd determination) of the dispersion | variation and smoothness of image data is shown. The processing flowchart of the determination (3rd determination) of the dispersion | variation and smoothness of image data is shown. 9 shows a processing flowchart of determination (fourth determination) of variation and smoothness of image data. An example of an adaptive edge enhancement circuit is shown. Specific examples of a Laplacian filter and an edge amount detection filter are shown. An example of conversion to a filter coefficient corresponding to the edge degree is shown. The color space explaining a color correction process is shown. The color space explaining a color correction process is shown. The code table of a hue area is shown. The color plane explaining a color correction process is shown. The processing flowchart of a hue area | region determination part is shown. A calibration chart is shown. The relationship between transfer paper (coated paper) and color gamut is shown. The relationship between the transfer paper (plain paper) and the color gamut is shown. The relationship between the saturation of the document and the toner adhesion amount is shown. The relationship between the printed document and the read value is shown. The structure of a gradation processing part is shown. The structure of a quantization threshold is shown. The structure of a feature-value extraction part is shown. An error diffusion matrix and a dither threshold matrix are shown. Shows screen angle and line growth direction. It is a figure explaining feature-value extraction. An operation part is shown. It is a figure explaining automatic gradation correction. The processing flowchart of automatic gradation correction is shown. It is a figure explaining automatic gradation correction. It is a figure explaining the production | generation of a gradation conversion table. The flowchart of the arithmetic processing in automatic gradation correction is shown.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  An embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter simply referred to as a copying machine) as an image forming apparatus will be described below. FIG. 1 shows the configuration of the entire copying machine.

  In FIG. 1, around the organic photosensitive member (OPC) drums 102a-102 having a diameter of 30 [mm], which are arranged side by side at the center of the copying machine main body 101, are arranged as photosensitive drums 102a-102. electrification chargers 103a to 103e for charging the surface of e, laser optical systems 104a to 104e for irradiating semiconductor laser light onto the surfaces of the uniformly charged photoreceptor drums 102a to 102e to form an electrostatic latent image, electrostatic Three color developing devices 105c, 105d of transparent toner T developing device 105a, black developing device 105b, yellow Y, magenta M, and cyan C are obtained by supplying each color toner to the latent image and developing the toner image for each color. 105e, an intermediate transfer belt 109 that sequentially transfers toner images for each color formed on the photosensitive drums 102a to 102e, and a bias roller that applies a transfer voltage to the intermediate transfer belt 109 10a to 10e, cleaning devices 111a to 111e for removing the toner remaining on the surface of the photosensitive drum 102 after transfer, and a charge eliminating unit for removing charges remaining on the surface of the photosensitive drum 102a to 102e after transfer Has been.

  Further, the intermediate transfer belt 109 is provided with a transfer bias roller for applying a voltage for transferring the transferred toner image to the transfer material, and a belt cleaning device for cleaning the toner image remaining on the transfer material after transfer. Has been.

  A fixing device 116 that heats and pressurizes and fixes the toner image is disposed at an end portion on the exit side of the conveyance belt that conveys the transfer material peeled off from the intermediate transfer belt 109, and an exit portion of the fixing device 116. A paper discharge tray 117 is attached.

  The upper part of the laser optical system 104 has a contact glass as an original placement table arranged on the upper part of the copying machine main body 101, an exposure lamp for irradiating the original on the contact glass with scanning light, and a reflection mirror for reflecting light from the original. Then, the light is guided to an imaging lens and is incident on a CCD image sensor array which is a photoelectric conversion element. An image signal converted into an electrical signal by the CCD image sensor array passes through an image processing device (not shown) and controls laser oscillation of the semiconductor laser in the laser optical system 104.

  Next, a control system built in the copying machine will be described. As shown in FIG. 2, the control system includes a main control unit (CPU) 130, a predetermined RAM 131 and ROM 132 are attached to the main control unit 130, and the main control unit 130 has an interface I. / O 133 through the laser optical system control unit 134, the power supply circuit 135, the optical sensor 136 installed in each image forming unit of YMCK, the toner density sensor 137 installed in each developing unit of YMCK, the environment sensor 138, the surface of the photoreceptor The potential sensors 139a to 139e, the toner supply circuit 140, the intermediate transfer belt driving unit 141, and the operation unit 142 are connected to each other.

  The laser optical system control unit 134 adjusts the laser output of the laser optical systems 104a to 104d, and the power supply circuit 135 supplies a predetermined discharge voltage for charging to the charging chargers 113a to 113e and a developing device. A development bias having a predetermined voltage is applied to 105a to 105e, and a predetermined transfer voltage is applied to the bias rollers 110a to 110e and the transfer bias roller.

  The optical sensor 136 is opposed to the photoconductors 102a to 102e, respectively, and is opposed to the optical sensor 136a and the transfer belt 109 for detecting the toner adhesion amount on the photoconductors 102a to 102e. An optical sensor 136b for detecting the amount and an optical sensor 136c for detecting the amount of toner adhering to the conveyance belt while facing the conveyance belt are illustrated. In practice, detection may be performed at any one of the optical sensors 136a to 136c.

  The optical sensors 136 (a to c) include a light emitting element such as a light emitting diode and a light receiving element such as a photo sensor that are disposed in proximity to the areas after transfer of the photosensitive drums 102 a to 102 e, and are formed on the photosensitive drum 102. The toner adhesion amount in the toner image of the detection pattern latent image and the toner adhesion amount in the background portion are detected for each color, and the so-called residual potential after the charge elimination on the photosensitive member is detected.

  Detection output signals from the photoelectric sensors 136 (a to c) are applied to a photoelectric sensor control unit (not shown). The photoelectric sensor control unit obtains a ratio between the toner adhesion amount in the detection pattern toner image and the toner adhesion amount in the background portion, compares the ratio value with a reference value, detects a change in image density, and detects the toner density of each color of YMCK. The control value of the sensor 137 is corrected.

  Further, the toner concentration sensor 137 detects the toner concentration based on a change in magnetic permeability of the developer present in the developing devices 105a to 105e. The toner density sensor 137 compares the detected toner density value with a reference value, and when the toner density falls below a certain value and becomes a toner shortage state, a toner replenishment signal having a magnitude corresponding to the shortage is supplied to the toner. A function of applying to the supply circuit 140 is provided.

  The potential sensor 139 detects the surface potential of each of the photoconductors 102a to 102e, which are image carriers, and the intermediate transfer belt driving unit 141 controls the driving of the intermediate transfer belt.

  A developer containing black toner and a carrier is accommodated in the black developing device 105b. The developer is agitated by the rotation of the developer agitating member, and the amount of the developer pumped up on the sleeve by the developer regulating member on the developing sleeve is reduced. adjust. The supplied developer is magnetically carried on the developing sleeve and rotates as a magnetic brush in the rotation direction of the developing sleeve.

  FIG. 3 shows the overall configuration of the image processing unit of the present invention. 3, 400a is a scanner that uses a CCD as a reading device, 400b is a scanner that uses a CIS (Contact Image Sensor) as a reading device, 401a is a shading correction circuit for the scanner (CCD) 400a, and 401b is a scanner (CIS). 400b shading correction circuit, 430 an FL correction processing circuit for the scanner (CCD) 400a, 431 an inter-chip pixel interpolation circuit for the scanner (CIS) 400b, 432 a memory controller (1), 433 an image memory, 402 Is a scanner γ conversion circuit, 403 is an image area separation / ACS determination (1) circuit, 404 is a spatial filter (1) circuit, 405 is an automatic density adjustment (ADS) level detection / removal circuit, 406 is a hue determination (1) circuit, 407 is a color correction UCR processing (1) circuit, 408 is a scaling process (1) circuit, 409 is a γ conversion (2) circuit, 410 is a gradation processing (1) circuit, 411 Is an editing process (1) circuit, 412 is a Multilayer BUS, 413 is a pattern generation (2) circuit, 414 is a γ conversion (3) circuit, and 415 is a printer.

  439 is an image area separation / ACS determination (2) circuit, 425 is a gray / RGB conversion circuit, 426 is an RGB synthesis circuit, 427 is an internal pattern generation circuit, 428 is a spatial filter (2) circuit, and 429 is an ADS removal circuit. 430 is a hue determination processing (2) circuit, 431 is a color correction / UCR processing (2) circuit, 432 is a pattern generation (1) circuit, 433 is a scaling process (2) circuit, 434 is a total amount regulation circuit, and 422 is Feature extraction circuit 423 γ conversion (2) circuit 424 gradation processing (2) circuit 435 editing (2) circuit 416 compression / decompression circuit 418 HDD I / F 419 HDD (Hard Disk), 420 is a rotation processing circuit, 421 is an external interface I / F, 436 is a memory controller (2) circuit, 437 is a main memory, and 438 is a CPU.

  When the user designates double-sided simultaneous reading, the original to be copied is separated into R, G, and B by a color scanner (CCD) 400a with one side of the original as the front and is read as a 10-bit signal as an example. Then, both sides of the document are simultaneously read by a single conveyance by the color scanner (CIS) with the opposite side of the document as the back side.

  The image signal read by the scanner (CCD) 400a is corrected for unevenness in the main scanning direction by the shading correction circuit 401a and output as an 8-bit signal. Similarly, the image signal read by the scanner (CIS) 400b is corrected for unevenness in the main scanning direction by the shading correction circuit 401b and output as an 8-bit signal. The FL correction processing circuit 430 corrects a sensitivity difference (tone difference) between two sets of CCDs arranged in the main scanning direction. The inter-chip pixel interpolation circuit 431 interpolates the image data of the gap between the chips of the CIS device arranged in the main scanning direction from the adjacent pixels.

  The memory controller 432 is read by the scanner (CCD) 400a and is read by the image data 1 after processing by the shading correction circuit 401a and the FL correction circuit 430 or by the scanner (CIS) 400b, and the shading correction circuit 401b and the inter-chip pixel are read. This is a DDR memory controller for temporarily storing image data 2 processed by the interpolation circuit 431 in an image memory 433 using a DDR memory.

  The image area separation / ACS (1) circuit 403 is, for each pixel of the image data (signals R, G, B), an image area separation determination result (signal X) such as a character area, a photographic area, or a color original. A color determination result ACS Result and gloss addition amount T as to whether the document is a black and white document are output.

  FIG. 4A shows the configuration of the image area separation / ACS (1) circuit 403. 4A, reference numeral 501 denotes an input image I / F (interface), which performs logical inversion of image data (signals R, G, B) in accordance with the processing of 503 to 505. Reference numeral 502 denotes a delay adjustment memory unit that delays and outputs image data and various output results in accordance with the processing of 503 to 505. Reference numeral 503a denotes an image area separation unit that performs character / non-character, chromatic / achromatic, halftone / non-halftone, low density halftone, etc. for each pixel of the input image, Output. Reference numeral 504a denotes a gloss adding unit, which determines a gloss addition amount T (transparent toner adhesion amount) based on the transparent toner added to each pixel of the image data based on the image data and the image area separation result X. An ACS (automatic color selection) unit 505 determines whether the image data is a monochrome document or a color document, and outputs a determination result ACS Result. Reference numeral 506 denotes an output image I / F. The image data logically inverted by the input image I / F 501 is subjected to logical determination, and the image data input to the image area separation / ACS (1) processing circuit 403 is combined with the monochrome logic. A process of matching (whether white is 0 or black is 0) is performed.

  FIG. 4B shows the configuration of the image area separation / ACS (2) circuit 439. When the image area separation result X and the gloss addition amount T are output from the image area separation / ACS (1) circuit shown in FIG. 4A, the image area separation / ACS (2) circuit 439 The X and T are output as an input signal Xin and a signal Tin, respectively, as an output signal X (= Xin) and an output signal T (= Tin) without being processed. For this reason, the image area separation unit 503b and the gloss adding unit 504b respond to requests to output the input signals Xin and Tin as signals X (= Xin) and T (= Tin) without processing them.

  On the other hand, for image data to which the image area separation signal Xin and the gloss addition signal Tin are not added, such as print data input from an external computer, the image area separation unit 503b and the gloss addition unit 504b respectively This corresponds to the generation request from.

  FIG. 5 shows the configuration of the image area separation units 503a and 503b. In FIG. 5, 511 is an MTF correction unit, 512 is an edge separation unit, 513 is a white background separation unit, 514 is a halftone separation unit, 515 is a color determination unit, 516 is a pattern detection unit, 517 is an overall determination unit, and 518 is It is an image area separation result packing unit.

  The MTF correction unit 511 performs edge enhancement on the image data in order to detect an edge or a white background, and corrects the deterioration of the MTF characteristic. The edge separation unit 512 separates characters and photographs (including high line number halftone dots) from the continuity of white pixels and black pixels. The halftone dot separation unit 514 separates halftone dots based on the presence or absence of peaks in the image data. The white background separation unit 513 determines the white background pixel based on whether or not the white pixel exists in the surrounding area. The color determination unit 515 determines whether the pixel is an achromatic color or a chromatic color based on the difference in RGB signal. The comprehensive determination unit 517 determines the pattern line as a non-character by examining the inside of the character edge.

  The pattern detection unit 516 detects a predetermined pattern on the background and outputs a pattern detection result. The image area separation result packing unit 518 reflects the determination results of the MTF correction unit 511 to the pattern detection unit 516 in the corresponding predetermined bits and outputs them as the subsequent image area separation determination result X.

  FIG. 6 shows a processing flowchart of the gloss adding unit 504. In step S101, image data is read out, and in step S102, the image area separation result X of the image area separation unit 503a is acquired for the pixel data of the target pixel and the peripheral pixels in the read image data. If the image area separation result X is a background determination pixel in step S103 (Yes), it is compared with a predetermined background density threshold in step S104. When the pixel data is brighter than the background density threshold (that is, the image density is low) (Yes), it is determined in step S112 that the pixel is a gloss added pixel [type 1]. In step S113, the gloss added amount T [type 1].

  If the background determination pixel is darker (the image density is higher) than the predetermined background density threshold value in step S104 (No), it is determined in step S114 as a glossy addition pixel [type 2], and in step S115, gloss addition is performed. The quantity T [type 2] is acquired.

  If the image area separation result X of the image area separation unit 503a is a halftone dot determination pixel in step S105 (Yes), it is compared with a predetermined background density threshold value in step S106. When the image density is lower (brighter) than the predetermined background density threshold (Yes), it is determined in step S116 that it is a gloss added pixel [type 3], and in step S117, the gloss added amount T [type 3] is obtained. .

  If the image area separation result X of the image area separation unit 503a is a character determination pixel in step S107 (Yes), it is compared with a predetermined background density threshold value in step S108. When the image density is lower (brighter) than the predetermined background density threshold (Yes), the processes after step S112 are performed. When the image density is higher (darker) than the predetermined background density threshold (No), in step S109, the image density is lower (brighter) than the character pixel density threshold compared with the predetermined character pixel density threshold. (Yes), in step S118, it is determined that the pixel is a gloss added pixel [type 4], and in step S119, the gloss added amount T [type 4] is acquired. If the image density is higher (darker) than the predetermined character pixel density threshold (No), it is determined in step S120 that the pixel is not glossy added, and the gloss addition amount T is set to 0 in step S121.

  In step S107, when the image area separation result X of the image area separation unit 503a is not a character determination pixel (No), it is compared with a predetermined background density threshold value in step S110. When the image density is lower (brighter) than the predetermined background density threshold (Yes), the processes after step S112 are performed.

  In step S110, if the image density is higher (darker) than the predetermined background density threshold (No), in step S111, the density is lower than the predetermined photographic pixel density threshold compared with the predetermined photographic pixel density threshold. If it is bright (Yes), the processing from step S118 is performed. In step S111, if the density is higher (darker) than the predetermined photographic pixel density threshold (No), the processes in and after step S120 are executed.

  FIG. 7 shows a processing flowchart of the gloss addition amount T [type 1] executed by the gloss adding unit. In step S201, when the target pixel (x0, y0) is background data or image data with brightness close to the background, the processing from step S202 is executed. Do not use toner.

A method for determining that the pixel of interest (x0, y0) is background data or image data with brightness close to the background will be described below. Assume that the image data S (x0, y0) of the pixel of interest (x0, y0) is composed of signals (R (x0, y0), G (x0, y0), B (x0, y0)). That is,
Assume that S (x0, y0) = (R (x0, y0), G (x0, y0), B (x0, y0)). When S (x0, y0) is proportional to reflectance or proportional to lightness, the larger the value is, the brighter it is, and the background data is compared with the background determination threshold Sgth = (Rgth, Ggth, Bght). do it,
S (x0, y0) ≧ Sgth or R (x0, y0) ≧ Rgth and G (x0, y0) ≧ Ggth and B (x0, y0) ≧ Bgth
Holds.

  A moving average (Save (x0, y0)) is obtained from the pixel of interest (x0, y0) and the surrounding pixels (x, y). For each of the RGB components of the image data S (x0, y0) (signals R (x0, y0), G (x0, y0), B (x0, y0)) of the pixel of interest (x0, y0), the region of interest A ( The average value Save (x0, y0) (moving average) is obtained for the image data S (x, y) of x, y) (as an example, Px pixels in the main scanning direction × Py pixels in the sub scanning direction).

Save (x0, y0) = (Rave (x0, y0), Gave (x0, y0), Bave (x0, y0))
this,

Is written. here,

Represents the sum of the coordinates (x, y) of the pixels included in the attention area A. Here, x, yεA represents a pixel included in the region A, and Σ represents the sum of xεA and yεA.

Assuming that the number of pixels px and py are odd numbers and the coordinates (x0, y0) are the center pixel of the area A, the coordinates (x, y) included in the area A are, for example, x0− (px / 2) ≦ x ≦ x0 + (Px / 2),
y0− (py / 2) ≦ y ≦ y0 + (py / 2) (Formula 2)
Included in the range. When the end region of the image data is the target pixel, the target pixel (x0, y0) may not be the center pixel of the target region S without being limited to the range shown in (Expression 2).

  Also, px and py are

It can be expressed as.
The average value of (Expression 1) can be used when all the pixels in the attention area A (x, y) are background data, but the pixels other than the background data are in the attention area A (x, y). Is included, pixels other than the background data are excluded and an average value is obtained. Notation of attention area A (background) (x, y) excluding background data,
A (background) (x, y) ⊆ A (x, y) (Formula 4)
There is a relationship. Here, A (background) ⊆A indicates that the area A (background) having only the background data is equal to or included in the area A.

From (Equation 1), the average value Save (background) (x0, y0) of only the background data of the region A including the target pixel (x0, y0) is
From (Formula 3) and (Formula 4),

It can be expressed as.

  In step S202, the unbiased variance V (background) (x0, y0) is obtained from the difference between the image data S (x0, y0) of the target pixel (x0, y0) and the moving average Save (background) (x0, y0). That is, when the unbiased variance V (background) (x0, y0) is obtained from the difference between each pixel of the attention area A (background) (x0, y0) and the average value Save (background) (x0, y0),

It can be expressed as. Here, [x] ^ 2 represents the square of x.

  In (Expression 6), an effective value cannot be obtained unless two or more pixels satisfy A (background). Further, in obtaining the variation of the background data, the number of pixels p (A (background)) of the background data in the attention area A (x0, y0).

Is a predetermined number of pixels Pth greater than 2 p (A (background)) ≧ pth
is necessary. Therefore, when p (A (background)) <pth, the transparent toner is not used.

  In step S203, it is determined whether or not the unbiased variance V (background) (x0, y0) is equal to or less than a predetermined value Vth. If the unbiased variance V (background) (x0, y0) is equal to or less than the predetermined value Vth, the image is smooth and the unbiased variance V is determined in step S204. Based on (background) (x0, y0), the gloss addition amount T (x0, y0) is determined. In step S205, when the unbiased variance V (background) (x0, y0) is equal to or greater than the predetermined value Vth, the gloss addition amount T (x0, y0) is set to zero.

When the value of unbiased variance V (background) (x0, y0) is less than or equal to a predetermined value Vth V (background) (x0, y0) ≦ Vth
In this case, the pixel of interest (x0, y0) is determined to be image data in a background area with little variation, and transparent toner is used. When V (background) (x0, y0)> Vth, the transparent toner is not used.

Further, the gloss addition amount T is changed according to the value of (background) (x0, y0) or [V (background) (x0, y0)] ² with the maximum value Tmax of the gloss addition amount as an upper limit. As the value of (background) (x0, y0) or [V (background) (x0, y0)] ² is smaller, the gloss addition amount T is increased. The gloss addition amount Tmax is set to the smaller value of the gloss addition amount that maximizes the gloss or the upper limit value of the allowable gloss addition amount.

FIG. 8 shows the relationship between the gloss addition amount T and the variance of the background data (dispersion V (background)). The horizontal axis is the uneven variance V (background) (x0, y0) or the square value of the unbiased variance [V (background) (x0, y0)] ² as the variation of the background data, and the vertical axis is glossy. The quantity T. The smaller the unbiased variance V (background), the smaller the variance of the background data. Therefore, the smoothness of the image data is high, or the background data is smooth. On the other hand, as the unbiased variance V (background) or its square value [V (background) (x0, y0)] ² is larger, the background data is more scattered, and the smoothness of the background data is lower or rougher. Yes (not smooth).

  As shown in FIG. 8, the gloss addition amount T is set to a predetermined upper limit value Tmax, and the gloss addition amount T is decreased as the unbiased variance V (background) of the background data increases.

  FIG. 9 shows the relationship between the adhesion amount (M / A) T of the transparent toner and the image density D (color toner adhesion amount (M / A) Color, Color = Y, M, C, or K). The horizontal axis represents the image density D or the adhesion amount (M / A) of the color toner (KCMY) per unit area, and the vertical axis represents the adhesion amount (M / A) T of the transparent toner per unit area. As the amount of colored toner deposited on the transfer paper increases, the amount of transparent toner deposited decreases.

  Even when the pixel of interest (x0, y0) is not background data, when the transparent toner is used for the adjacent pixel, it is determined that the transparent toner is used. The X-axis, Y-axis, and Z-axis are orthogonal to each other, the background data variation is assigned to the X-axis, the color toner application amount is assigned to the Y-axis, and the transparent toner adhesion amount is assigned to the Z-axis. The adhesion amount of the transparent toner is determined according to the toner adhesion amount.

  FIG. 10 shows a processing flowchart of the gloss addition amount T [type 2] executed by the gloss adding unit. In step S301, the interval between halftone pixels is acquired. Here, the interval between the halftone pixels is a resolution of 600 dpi to 1200 dpi, and the number of lines of 50 lines to 300 lines is detected as an example. In step S302, the number of peripheral pixels excluding halftone pixels is obtained. In step S303, when the number of surrounding pixels is greater than or equal to a predetermined value, a moving average is obtained from the surrounding pixels excluding halftone pixels in step S304. A halftone pixel excludes a pixel whose image density is higher (darker) than the threshold value for determining the background density.

  In step S305, the unbiased variance is obtained from the difference between the pixels used for obtaining the moving average and the moving average or from the difference. In step S306, when the difference or unbiased variance obtained in step S305 is equal to or smaller than a predetermined value, the gloss addition amount T is obtained based on the difference or unbiased variance in step S307. In step S308, it is determined whether or not the halftone pixel interval acquired in step S301 is equal to or smaller than a predetermined value. If it is equal to or smaller than the predetermined value, the gloss addition amount T is set in step S309 according to the halftone pixel interval. adjust. Here, as the interval between the halftone pixels is shorter, the gloss addition amount T is decreased (see FIG. 8). This is because the overlap of the colored toner and the colorless toner prevents an increase in the total toner amount and reduces the occurrence of dust and the like during transfer. In step S306, if the difference or unbiased variance is not less than the predetermined value, the gloss addition amount T is set to zero.

  In step S303, when the number of surrounding pixels is not equal to or larger than the predetermined value, in step S311, it is checked whether or not the surrounding pixels of the target pixel are glossy attached, and the gloss addition amount T of the surrounding pixels is determined as the coordinates of the surrounding pixels. The initial value of the gloss addition amount T of the target pixel is acquired by extrapolation or interpolation with respect to the coordinate position of the target pixel. At this time, if the surrounding pixels are background data, positional interpolation or extrapolation is performed.

  If the peripheral pixel to which the gloss is added is not the background density, the gloss application amount T at the background density is calculated from the image density ID of the peripheral pixel to which the gloss addition amount T is added based on the relationship of FIG. By estimating, the gloss addition amount T of the target pixel is obtained.

  In step S312, the gloss addition amount T of the target pixel is obtained by reducing the gloss addition amount according to the halftone dot density of the target pixel from the gloss addition amount T of the target pixel based on the relationship of FIG. When the glossiness addition amount T of the background density of the surrounding pixels cannot be acquired, the glossiness addition amount T of the halftone density of the surrounding pixels is estimated.

The gloss addition amount T (x0, y0) of the pixel of interest (x0, y0) has the horizontal axis as the main scanning direction, and the coordinates of the left and right pixels are (x0-1, y0) and (x0 + 1, y0), respectively. If
T (x0, y0) = {w (-1, 0) * T (x0-1, y0) + w (+1, 0) * T (x0 + 1, y0) / {w (-1, 0) + w (1, 0)}
As described above, the gloss addition amount T (x0, y0) is acquired as the weighted average process.

  With the sub-scanning direction as the vertical axis, the coordinates of the preceding and following pixels are (x0, y0-1) and (x0, y0 + 1), respectively, and the coordinates of the eight pixels around the pixel of interest (x0, y0) (x0-1) , Y0-1),..., (X0 + 1, y0 + 1) as region S, the gloss addition amounts T (x0-1, y0-1) to T (x0 + 1, y0 + 1) of the respective pixels are obtained. The weighted average of the pixels of

The gloss addition amount T (x0, y0) of the target pixel (x0, y0) is acquired.

  FIG. 12A shows a processing flowchart of the gloss addition amount T [type 3] executed by the gloss adding unit. In step S401, an interval between halftone pixels is acquired. Here, the interval between the halftone pixels is a resolution of 600 dpi to 1200 dpi, and the number of lines from 50 lines to 300 lines is detected as an example. In step S402, a moving average is obtained from surrounding pixels excluding halftone pixels. A halftone pixel excludes a pixel whose image density is higher (darker) than the threshold value for determining the background density. In step S403, unbiased variance is obtained from the difference or difference between the pixel used for obtaining the moving average and the moving average. In step S404, if the difference or unbiased variance obtained in step S403 is equal to or smaller than a predetermined value, the gloss addition amount T is obtained based on the difference or unbiased variance in step S405.

  In step S407, it is determined whether or not the halftone pixel interval acquired in step S401 is equal to or smaller than a predetermined value. If it is equal to or smaller than the predetermined value, the gloss addition amount T is set in step S408 according to the halftone pixel interval. adjust. Here, as described above, the gloss addition amount T is decreased as the interval between the halftone pixels is shorter. In step S404, if the difference or unbiased variance is not less than the predetermined value, the gloss addition amount T is set to zero.

  FIG. 12B shows a processing flowchart of the gloss addition amount T [type 4] executed by the gloss adding unit. In step S501, it is investigated whether or not the peripheral pixels of the target pixel are glossed, and the gloss addition amount T of the peripheral pixel is extrapolated from the coordinate position of the target pixel using the coordinates of the peripheral pixel, or An initial value of the gloss addition amount T of the target pixel is acquired by interpolation. At this time, if the surrounding pixels are background data, positional interpolation or extrapolation is performed.

  When the peripheral pixel to which the gloss is added is not the background density, the gloss addition amount T at the background density is estimated from the image density ID of the peripheral pixel to which the gloss addition amount T is added, and the gloss addition amount of the target pixel is calculated. Find T.

  In step S502, the gloss addition amount T of the target pixel is obtained by reducing the gloss addition amount according to the halftone dot density of the target pixel from the gloss addition amount T of the background density of the target pixel.

  Note that the halftone pixel density threshold and the character density threshold shown in FIG. 6 are switched according to a color material such as a printed document, a document using toner, or ink used in an inkjet printer. In addition, even for a printed document, an ink different from the process ink that is normally used, such as a map, is used. Therefore, it can be adjusted to the user's preference by switching according to the map or spot color ink. is there.

  FIG. 13B shows the relationship between the characteristics of the background data and the paper (estimated) used in the document. Based on the relationship shown in FIG. 13B, the type of paper corresponding to the RGB value of the background data extracted from the image data is determined.

  FIG. 13A shows the correspondence between the type of paper used in the original and the gloss addition amount T used for the printed material. A transparent toner is used for the above-described paper, particularly for paper having good glossiness, smooth surface, and good glossiness. It should be noted that the relationship between the type of paper used in the document and the gloss addition amount T shown in FIG. 13A can be selected by the user. In addition, the setting 1 * 1 and setting 2 * 1 of the mat (silk) photographic paper for silver salt photography and the mat paper for the inkjet printer in FIG. Indicates that is possible.

  In FIG. 8, the smaller the background variation, the greater the amount of transparent toner attached. However, depending on the user's choice, the amount of transparent toner attached is increased for a document with a large background variation. It is also possible to set.

FIG. 14 shows a processing flowchart of determination (first determination) of variation and smoothness of image data executed by the gloss adding unit 504. In step S601, a histogram is obtained for each of RGB components of pixels brighter than a predetermined value within a predetermined area. In step S602, normalized by the number of pixels from the obtained histogram.
1. 1. Peak value Peak width (eg half width)
3. Find the number of peaks.

In step S603, it is determined whether any of the following is satisfied.
1. 1. The peak value is below a predetermined value 2. The peak width is larger than a predetermined value. If there are a plurality of peaks or one of the above is true, it is determined that the images are dispersed, and no transparent toner is used in step S605. If not, transparent toner is used in step S604.

  FIG. 15 shows an example of the histogram of the background area of the document. The horizontal axis represents the reflectance linear data of the image data (RGB components). The larger the value is, the brighter the data is, and the smaller the value is, the darker the data is. The vertical axis represents the histogram frequency. The sample in the figure shows the peak value, the half-value width, and the average value (in the figure, it matches the peak value). Further, the respective histograms of the RGB components for the background area having the same number of pixels of the original document a and the original document b are shown as Ra, Ga, Ba for the original document a, and Rb, Gb, Bb for the original document b.

  The document a has a relationship of Ra <Ga <Ba, and the document b has a relationship of Bb <Gb <Rb. The peak of the histogram of the document “a” is higher than that of the document “b”, and the half-value width of the document “a” is smaller in the document “b”. From this, it is determined that the variation of the background of the document “a” is larger than the variation of the background of the document “b”. Further, it is determined that the original a is higher or smoother than the original b, and the amount of transparent toner attached is increased.

  FIG. 16 shows a process flowchart of determination (second determination) of variation and smoothness of image data of a printed document. In step S701, a (low density) halftone dot is detected. In steps S702 to S704, the frequency component of the halftone dot is detected for the pixel determined to be a halftone dot, and the frequency component is removed. In step S705, a moving average is obtained from the target pixel and surrounding pixels. In step S706, the difference between the pixel of interest and the moving average, or the (unbiased) variance is obtained from the difference. In steps S707 to S710, it is determined whether or not the difference or variance is equal to or smaller than a predetermined value. If the difference or variance is equal to or smaller than the predetermined value, the image is smooth and transparent toner is used. If it exceeds the predetermined value, the transparent toner is not used.

  In step S709, even when the value is equal to or larger than the predetermined value, when the transparent toner is used in the adjacent pixel, the transparent toner is used. If a halftone dot is not detected in step S711, the image data variation / smoothness determination process (third determination) shown in FIG. 17 is executed. The processing in steps S801 to S805 in FIG. 17 is the same as the processing in steps S201 to S205 in FIG.

  FIG. 18 shows a process flowchart of determination (fourth determination) of variation and smoothness of image data of a printed document. In step S901, a moving average is obtained from the target pixel and surrounding pixels. In step S902, an autocorrelation function is obtained using the difference between the target pixel and the moving average. In step S903, Fourier transform is performed to obtain a power spectrum. In step S904, the halftone dot frequency component is removed. In step S905, the power spectrum is integrated.

  In steps S906 to S908, it is determined whether or not the value is equal to or smaller than a predetermined value. If the value is equal to or smaller than the predetermined value, it is determined that the image is smooth, and transparent toner is used. do not use.

  As described above, in the present invention, a character area, a halftone dot area, and a background area are extracted from image data obtained by reading a document, and variations in pixels determined to be a background area are calculated. It discriminate | determines from the area | region which adds a toner, and the area | region which does not add transparent toner. Further, in an area where it is determined that transparent toner is to be added, the amount of transparent toner attached is determined according to the degree of variation in the background data. Accordingly, it is possible to determine whether or not transparent toner is added according to the type of paper used as the document.

  Returning to FIG. 3, the scanner γ conversion circuit 402 converts the read signal from the scanner from reflectance data to brightness data. The image memory 433 stores the image signal after the scanner γ conversion, and the image area separation circuit 403 determines a character portion and a photograph portion, and determines a chromatic color and an achromatic color.

  In the spatial filter 404, in addition to processing for changing the frequency characteristics of the image signal, such as edge enhancement and smoothing according to the user's preference, such as a sharp image or a soft image, the edge according to the edge degree of the image signal Perform enhancement processing (adaptive edge enhancement processing). For example, so-called adaptive edge enhancement is performed on each of the R, G, and B signals, in which edge enhancement is performed on a character edge and edge enhancement is not performed on a halftone image.

  FIG. 19 shows an example of an adaptive edge enhancement circuit. The image signal converted from the reflectance linearity to the lightness linearity by the scanner γ conversion circuit 402 is smoothed by the smoothing filter circuit 1101. The differential component of the image data is extracted by the 3 × 3 Laplacian filter 1102 at the next stage. FIG. 20A shows a specific example of a Laplacian filter.

  Of the 10-bit image signal not subjected to γ conversion by the scanner γ conversion, an edge is detected by the edge amount detection filter 1103 from, for example, an upper 8-bit component. 20B to 20E show specific examples of edge amount detection filters. Among the edge amounts obtained by the edge detection filters of FIGS. 20B to 20E, the maximum value is used as the edge degree in the subsequent stage. The edge degree is smoothed by the subsequent smoothing filter 1104 as necessary. This reduces the influence of the sensitivity difference between the even and odd pixels of the scanner. FIG. 20F shows an example of coefficients of the smoothing filter.

  A table conversion circuit 1105 converts the obtained edge degree into a table. The values of this table specify the darkness of lines and dots (including contrast and density) and the smoothness of the halftone dots. FIG. 21 shows an example of conversion to a table value corresponding to the edge degree. The edge degree is the largest with black lines or dots on a white background, and the edge degree becomes smaller as the pixel boundaries become smoother, such as finely printed halftone dots, silver halide photographs, and thermal transfer originals.

  The product (image signal D) of the edge degree (image signal C) converted by the table conversion circuit 1105 and the output value (image signal B) of the Laplacian filter 1102 becomes the smoothed image signal (image signal A). The signals are added and transmitted as an image signal E to a subsequent image processing circuit.

  The color correction process is performed in the color correction / UCR process (1) circuit 407 and the color correction / UCR process (2) circuit 431 described above. The color correction UCR processing (1) circuit 407 and the color correction / UCR processing (2) circuit 431 correct the difference between the color separation characteristics of the input system and the spectral characteristics of the color material of the output system, and are necessary for faithful color reproduction. The color correction processing unit calculates the amount of the color material YMCT, and the UCR processing unit replaces the portion where the three colors of YMC overlap with Bk (black). The color correction process will be described with reference to FIGS.

  As shown in FIG. 22, the color correction processing is performed by dividing the color space (R, G, B) on a plane extending radially around the achromatic color axis (R = G = B (≡N axis)). Is called. The saturation Cr changes along the distance Ln from the N axis. Further, the hue H changes along the rotation direction H around the N axis on a plane perpendicular to the N axis. That is, all the points on the surface formed in parallel with the N axis in the predetermined rotation direction H are color points indicating a hue determined by the rotation direction H.

  Points C (T), M (T), and Y (T) are points at which the saturation becomes maximum at CMY and the transparent toner amount T, which are the primary colors of the printer, respectively. Here, the transparent toner amount T varies depending on the values of R, G, and B, and T (R, G, B) ≡T. Points C (0), M (0), and Y (0) are points where the saturation becomes maximum when the transparent toner amount T = 0, that is, when the transparent toner is not overlaid on the primary color CMY of the printer. is there. Points R (T), G (T), and B (T) are points where the saturation is maximized by superimposing the transparent toner amount T on RGB that is the secondary color of the printer. The printer color reproduction area 672 includes these points C (T), M (T), Y (T), R (T), G (T), B (T), point W (T) and point K ( This is a substantially spherical region formed by connecting T) with a curve. That is, the inside of the printer color reproduction area 672 is a color area that can be output by the printer. The signal color region 660 is a color region that can be taken by the signal color for the color image signal.

  In addition, when correcting the signal color in this color space, the printer color reproduction area 670 is regarded as the printer color reproduction area 672 in order to simplify the processing. Here, the printer color reproduction area 670 includes points C (T), M (T), Y (T), R (T), G (T), B (T), points corresponding to the maximum values of eight colors. This is a dodecahedron-like region formed by connecting W (T) and point K (T) with a straight line. In this way, by regarding the printer color reproduction area 670 as the printer color reproduction area 672, no substantial error occurs in the correction amount X (T).

  Next, the hue area will be described with reference to FIG. FIG. 23 shows a color space divided into a plurality of hue regions. The C boundary surface 633 is a plane determined by points C (T), W (T), and K (T). Similarly, i boundary surfaces 634 to 638 (i = M, Y, R, G, B) are planes determined by points i, W, K (i = M, Y, R, G, B), respectively. . The color space is divided by these boundary surfaces 633 to 638. In the color space divided by the boundary surfaces 633 to 638, a CB hue region 640, a BM hue region 641, an MR hue region 642, an RY hue region 643, a YG hue region 644, and a GC hue region 645 are formed.

  A hue determination method for image data by the hue determination (1) circuit 406 and the hue determination (2) circuit 430 will be described. First, a method for determining a hue in a three-dimensional space will be described, and then a method for determining a hue in a two-dimensional color plane will be described.

  In the hue determination of the three-dimensional space, each hue evaluation value Fx is calculated from the image data, and the hue area code of the hue area including the signal color is determined based on the hue evaluation value Fx. Here, a theoretical derivation method of the hue evaluation value Fx will be described. The color coordinates indicating the points C (T), M (T), Y (T), R (T), G (T), B (T), W (T), and K (T) shown in FIG. These are respectively represented as (Dir, Dig, Dib) (i = c, m, y, r, g, b, w, k). For example, the color coordinates corresponding to the point C (T) are (Dcr, Dcg, Dcb).

In this case, for example, the C boundary surface 633 is expressed by the following equation.
(Dcg−Dcb) · Dr + (Dcb−Dcr) · Dg + (Dcr−Dcg) · Db = 0 (Expression 7)
It becomes. Similarly, the boundary surfaces 634 to 638 are represented by the following equations, respectively.
(Dmg−Dmb) · Dr + (Dmb−Dmr) · Dg + (Dmr−Dmg) · Db = 0 (Equation 8)
(Dyg−Dyb) · Dr + (Dyb−Dyr) · Dg + (Dyr−Dyg) · Db = 0 (Equation 9)
(Drg−Drb) · Dr + (Drb−Drr) · Dg + (Drr−Drg) · Db = 0 (Equation 10)
(Dgg−Dgb) · Dr + (Dgg−Dgr) · Dg + (Dgr−Dgg) · Db = 0 (Equation 11)
(Dbg−Dbb) · Dr + (Dbb−Dbr) · Dg + (Dbr−Dbg) · Db = 0 (Equation 12)
For example, the color space is divided by the boundary surface 633 into two regions, a region including the C (T) B (T) hue region 640 and a region including the G (T) C (T) hue region 645. Hereinafter, in order to simplify the description of the C (T) B (T) hue region and the G (T) C (T) hue region, the description will be omitted as a CB hue region and a GC hue region. Similarly, the color space is divided into two regions by each boundary surface 634-638. Therefore, in which hue region the color image signal is included can be determined based on which region of the two regions formed by the boundary surfaces 633 to 638 is included in the color image signal. . That is, the hue region including the color image signal is determined based on the sign of the value obtained by substituting the color image signal (Dr, Dg, Db) for each of (Expression 7) to (Expression 12). Can do. Therefore, the hue evaluation value Fx is determined based on (Expression 7) to (Expression 12). That is, the left sides of (Expression 7) to (Expression 12) are respectively Fc, Fm, Fy, Fr, Fg, and Fb.
Fc = (Dcg−Dcb) · Dr + (Dcb−Dcr) · Dg + (Dcr−Dcg) · Db (Formula 13)
Fm = (Dmg−Dmb) · Dr + (Dmb−Dmr) · Dg + (Dmr−Dmg) · Db (Formula 14)
Fy = (Dyg−Dyb) · Dr + (Dyb−Dyr) · Dg + (Dyr−Dyg) · Db (Expression 15)
Fr = (Drg−Drb) · Dr + (Drb−Drr) · Dg + (Drr−Drg) · Db (Expression 16)
Fg = (Dgg−Dgb) · Dr + (Dgb−Dgr) · Dg + (Dgr−Dgg) · Db (Expression 17)
Fb = (Dbg−Dbb) · Dr + (Dbb−Dbr) · Dg + (Dbr−Dbg) · Db (Expression 18)

  That is, in the hue determination in the three-dimensional space, each hue evaluation value Fx defined in (Expression 13) to (Expression 18) is calculated. For example, if Fc and Fg calculated from an arbitrary point (Dr, Dg, Db) in the color space satisfy “Fc ≦ 0 and Fb> 0”, it is indicated that this point is included in the CB hue region. ) Thus, each hue region is defined by the hue evaluation value Fx. That is, in the hue area code table shown in FIG. 24A, the condition of the hue evaluation value Fx associated with the hue area code is a condition determined from the above formula.

  In the hue area code table shown in FIG. 24A, the color coordinates on the N-axis are included in the GC hue area for convenience, but may be included in other hue areas. The hue evaluation value Fx varies depending on the actual value of (Dir, Dig, Div) (i = c, m, y, r, g, b, w, k). Accordingly, the condition of the hue evaluation value to be associated with each hue area code in the hue area code table (FIG. 24A) may be changed according to the value of the hue evaluation value.

  Next, a method for mapping a three-dimensional color space to a two-dimensional plane and using the color coordinates of the color image signal in the two-dimensional plane to determine a hue region including the color image signal will be described with reference to FIG. ) And a flowchart of FIG. 26, the operation of the hue judgment circuit will be described.

  In step S1001 of FIG. 26, first, when a color image signal is input to the hue determination circuit, the value of the color image signal is two-dimensionalized. That is, the difference GR and the difference BG are obtained by substituting the values of the color image signal into the following (Expression 19) and (Expression 20). As a result, the values (Dr, Dg, Db) in the color space of the color image signal are converted into values (GR, BG) in the color plane.

FIG. 25A shows a two-dimensional plane on which a color image signal is to be mapped. In this two-dimensional plane, a straight line corresponding to “Dg−Dr” is a GR axis, and a straight line corresponding to “Db−Dg” is a BG axis. The GR axis and the BR axis are orthogonal to each other. The point (Dr, Dg, Db) on the color space is mapped to the color plane shown in FIG.
GR = Dg−Dr (Equation 19)
BG = Db−Dg (Equation 20)

Further, the point (Dnr, Dng, Dnb) on the N axis in the color space is mapped to the point (Dng-Dnr, Dnb-Dng) on the color plane shown in FIG. Since Dnr = Dng = Dnb,
(Dng−Dnr, Dnb · Dng) = (0, 0) (Equation 21)
It becomes. That is, all points on the N axis are mapped to the origin n on the plane shown in FIG. Further, the points C, M, Y, R, G, and B in the color space are arranged around the origin n as shown in FIG. Therefore, the six hue regions 640 to 645 shown in FIG. 23 are mapped to regions 740 to 745 divided by straight lines connecting the N axis and the points C, M, Y, R, G, and B on the color plane. Is done.

  FIG. 25B shows the same color plane as the color plane of FIG. The hue angle HUE is a rotation angle around the point n with the GR axis as 0 °. Further, the eight equally divided regions 700 to 712 are regions having a boundary with a straight line having a hue angle HUE that is a multiple of 45 °. A value that monotonously increases in accordance with the hue angle HUE, that is, the upper pseudo hue angle Ha is determined for each equally divided region. Specifically, in the equal area 700, the upper pseudo hue angle Ha = 0, Ha = 1 in the equal area 702, Ha = 2 in the equal area 704, Ha = 3 in the equal area 706, and the equal area. In 708, Ha = 4, in the equally divided area 710, Ha = 5, in the equally divided area 712, Ha = 6, and in the equally divided area 714, Ha = 7.

  Next, in step S1002, a difference GR, a difference BG, and each hue evaluation value Fx ′ (x = c, m, y, r, g, b) are calculated from the values of the respective colors of the input color image signal. In step S1003, based on each hue evaluation value Fx ′, difference GR, and difference BG, the hue area code of the hue area including the signal color is determined using the hue area code table (FIG. 24B). .

A method for deriving the hue evaluation value Fx ′ will be described. In the color plane shown in FIG. 25A, straight lines connecting the point N and the points C, M, Y, R, G, and B, that is, a straight line NC, a straight line NM, a straight line NY, a straight line NR, and a straight line. NG and straight line NB are respectively expressed as follows.
BG = (Dcb−Dcg) / (Dcg−Dcr) · GR (where Dcg−Dcr ≠ 0) (Equation 22)
BG = (Dmb−Dmg) / (Dmg−Dmr) · GR (where Dmg−Dmr ≠ 0) (Equation 23)
BG = (Dyb−Dyg) / (Dyg−Dyr) · GR (where Dyg−Dyr ≠ 0) (Equation 24)
BG = (Drb−Drg) / (Drg−Drr) · GR (where Drg−Drr ≠ 0) (Equation 25)
BG = (Dgb−Dgg) / (Dgg−Dgr) · GR (where Dgg−Dgr ≠ 0) (Equation 26)
BG = (Dbb−Dbg) / (Dbg−Dbr) · GR (where Dbg−Dbr ≠ 0) (Equation 27)

  A straight line determined by each equation from the magnitude relationship between the BG value obtained by substituting the GR value of the color image signal for each of (Equation 22) to (Equation 27) and the BG value of the actual color image signal; The positional relationship with the point corresponding to the color image signal is known. Therefore, in which hue region the color image signal is included is determined by substituting the BG value of the color image signal into (Equation 22) to (Equation 27), the BG value of the color image signal, and It can be determined based on the magnitude relationship of.

Therefore, the hue evaluation value Fx ′ is determined as follows based on (Expression 22) to (Expression 27). That is, the left sides of (Expression 22) to (Expression 27) are respectively Fc ′, Fm ′, Fy ′, Fr ′, Fg ′, and Fb ′.
Fc ′ = (Dcb−Dcg) / (Dcg−Dcr) · GR (Formula 28)
Fm ′ = (Dmb−Dmg) / (Dmg−Dmr) · GR (formula 29)
Fy ′ = (Dyb−Dyg) / (Dyg−Dyr) · GR (Expression 30)
Fr ′ = (Drb−Drg) / (Drg−Drr) · GR (Formula 31)
Fg ′ = (Dgb−Dgg) / (Dgg−Dgr) · GR (Formula 32)
Fb ′ = (Dbb−Dbg) / (Dbg−Dbr) · GR (Expression 33)

  For example, when Fc ′ and Fb ′ calculated from an arbitrary point (GR, BG) in the color plane satisfy “BG ≦ Fc′andBG> Fb ′”, this point may be included in the CB hue region. Recognize. That is, the condition of the hue evaluation value Fx ′ associated with the hue area code in the hue area code table shown in FIG. 24B is a condition determined from the above formula. As described above, the condition of the hue evaluation value Fx ′ is set in advance in the hue area code table of FIG. Therefore, the hue determination circuit determines that the BG and the hue evaluation value Fx ′ are selected from the conditions of the hue evaluation value Fx ′ associated with each hue area code, as in the hue area code table of FIG. A condition to be satisfied may be specified, and a hue area code associated with this condition may be selected in the hue area code table (FIG. 24B).

  In the hue area code table shown in FIG. 24B, the color coordinates on the N-axis are included in the GC hue area, but may be included in other hue areas. The hue evaluation value Fx ′ varies depending on the actual value of (Dir, Dig, Div) (i = c, m, y, r, g, b, w, k). Therefore, the condition of the hue evaluation value to be associated with each hue area code in the hue area code table (FIG. 24B) may be changed according to the value of the hue evaluation value Fx ′.

The color image signals (Dr, Dg, Db) are converted into values (GR, BG) on the color plane by the conversion formulas shown in (Equation 19) and (Equation 20). You may convert by a conversion type | formula.
GR = Ri · Dr + Gi · Dg + Bi · Db (Formula 34)
BG = Rj · Dr + Gj · Dg + Bj · Db (Formula 35)
Here, Ri = Gi = Bi = 0 and Rj = Gj = Bj = 0.

  As described above, the hue determination circuit determines where the input image signal (R, G, B) belongs to the divided space, and then a masking coefficient (preliminarily set for each space) Color correction processing is performed using (color correction coefficient) (formula 36). At that time, linear processing of the masking coefficient is performed as necessary, such as density adjustment and color balance adjustment. In the following description, the dividing point is a point where a boundary surface and a side intersect, for example, a point G (Green) in FIG.

When the hue hue is G (Green), the following equation is obtained.

  Here, the left side P (hue) (P = C, M, Y, K; hue = hue R, G, B, Y, M, C, K, W, etc.) is the printer vector, and the right side S (hue) (S = B, G, R; hue = hue R, G, B, Y, M, C, K, W, etc.) is a scanner vector, aPS (hue) (P = C, M, Y, K; S = B, G, R) is called a linear masking coefficient for each hue.

  Normally, the linear masking coefficient aPS (hue) (P = Y, M, C, K; S = R, G, B, constant) in each space is different from two points on the achromatic color axis as shown in FIG. R1, G1, B1) and (R2, G2, B2) and two points (R3, G3, B3) and (R4, G4, B4) on the two boundary surfaces that are not on the achromatic axis. , G, B values and C, M, Y, and K recorded values (C1, M1, Y1, K1), (C2, M2, Y2, K2), (C3, M3) of the developing unit that are optimal for color reproduction , Y3, K3) and (C4, M4, Y4, K4) are determined in advance and obtained by the following calculation.

Inverse matrix on both sides of (Equation 38)

, And replace both sides,

As a result, a linear masking coefficient aPS (hue) (P = Y, M, C, K; S = R, G, B) is obtained.

Here, aXY (3-4) represents a masking coefficient that is established in a color region between hue 3 and hue 4. The recorded values of C, M, Y, and K at each point are equivalent achromatic color density converted values before UCR (under color removal). In the following, in order to simplify the description, two points on the achromatic color axis are set as a white point and a black point. In this case, if the maximum value that can be taken by the equivalent achromatic color density conversion value is Xmax, each value has the following relationship.
In the case of a white point R1 = G1 = B1 = C1 = M1 = Y1 = 0 ≧ K1
In the case of a black dot R1 = G1 = B1 = C1 = M1 = Y1 = Xmax ≧ K2
In addition, two points on the boundary surface are points where the minimum value of the recorded values of C, M, Y and K of the developing portion is 0 and the maximum value of the recorded value is Xmax, that is, recording is possible on each boundary surface. It should be the point with the highest saturation. That is,
Min (C3, M3, Y3) = 0 ≧ K3
Max (C3, M3, Y3) = Xmax
Min (C4, M4, Y4) = 0 ≧ K4
Max (C4, M4, Y4) = Xmax
Is established.

The UCR rate can also be controlled by determining the K recording value of the developing unit from the minimum value among C, M, and Y of the developing unit, for example, as follows.
When the UCR rate is 100%: K = Min (C, M, Y)
When UCR rate is 70%: K = Min (C, M, Y) × 0.7
When dividing the color space (R, G, B) with six boundary surfaces as shown in FIG. 22, a total of eight R, G points, at least six points on each boundary surface and two points on the achromatic color axis, are used. , B and the recording values of C, M, Y, and K of the developing unit that are optimal for reproducing the color are determined in advance, and the masking coefficient of each space is obtained based on these values. As described above, the masking coefficient of each space is obtained in advance and stored in ROM, RAM, etc., and in the color correction process, an appropriate masking coefficient is selected according to the color determined in the hue determination, and color correction is performed. It can be performed.

  In (Equation 38), the case where the transparent toner T is not used (T = 0) and the case where the transparent toner T is used are Y (0) (1) to Y (0) (4), M, respectively. (0) (1) -M (0) (4), C (0) (1) -C (0) (4), K (0) (1) -K (0) (4), and Y (T) (1) to Y (T) (4), M (T) (1) to M (T) (4), C (T) (1) to C (T) (4), K (T ) (1) to K (T) (4), the masking coefficient adapted to the image area not using the transparent toner is

And The masking coefficient for the transparent toner amount T is

The masking coefficient obtained as follows is used. As a result, it is possible to reduce a difference in color reproducibility between an image area using the transparent toner and an image area not using the transparent toner.

  In order to correct the difference in the spectral characteristics of the CCD and CIS, a new linear masking coefficient is calculated based on the read value of the scanner data / calibration chart shown in FIG. The method will be described below.

  A value when a point on the boundary surface that is not on the achromatic color axis is read by, for example, a scanner CCD showing standard spectral characteristics is defined as (Ri, Gi, Bi) (i = hue 1 to 4). When the same point is read by another scanner, this point is different from (Ri, Gi, Bi) (i = hue 1 to 4) due to variations in the spectral characteristics of the scanner CCD (Ri ′, Gi ′). , Bi ′) (i = hue 1 to 4). As a result, the recording values of the developing portions C, M, Y, and K are calculated as (Ci ′, Mi ′, Yi ′, Ki ′) (i = hues 1 to 4) according to the equation (1). That is, (Equation 38) can be expressed as the following (Equation 42).

In order to obtain the linear masking coefficient aPS (hue 3′-4 ′) (P = Y, M, C, K; S = R, G, B) of the hue region 3′-4 ′ from (Equation 42), Inverse matrix on both sides

Over

The linear masking coefficient aPS (hue 3′-4 ′) (P = Y, M, C, K; S = R, G, B) of the hue region 3′-4 ′ can be obtained. Similarly, the linear masking coefficient aPS (each hue) (P = Y, M, C, K; S = R, G, B) can be obtained for each of the other hues.

  The printer vector P (i) (P = Y, M, C, K; i = each hue) is changed according to the type of the original to be copied, thereby improving the color reproducibility of the copy. Can do. Document types include, for example, a printed document using ink as a color material, a photographic paper photo document using a YMC photosensitive layer as a color material, a copy document using toner as a color material, an inkjet document using an inkjet printer output as a document, and a special color. Examples include a map document using ink, a color correction coefficient for a fluorescent pen for identifying the fluorescent pen, and the like.

  That is, the printer vector P (i) (P = Y, M, C, K; i = each hue) is a P document type (i) (P = Y, M, C, K; corresponding to each document type). i = each hue, original type = printing, photographic paper photograph, copy original, map, inkjet, highlighter pen, etc.) aPS original type (hue) corresponding to each image quality mode selected on the operation unit (P = Y, M , C, K; S = R, G, B, constants) are calculated and set in a circuit (ASIC) for use in copying.

Regarding the left side of (Equation 44), similarly to (Equation 40) and (Equation 41) described above, switching is similarly performed for an image area that does not use transparent toner and an image area that uses transparent toner.

The UCR process can be performed by calculating using the following equation.
Y ′ = Y−α · min (Y, M, C)
M ′ = M−α · min (Y, M, C)
C ′ = C−α · min (Y, M, C)
Bk = α · min (Y, M, C) (Formula 45)
In the above equation, α is a coefficient that determines the amount of UCR. When α = 1, 100% UCR processing is performed. α may be a constant value. For example, when α is close to 1 in the high density portion and close to 0 in the highlight portion (low image density portion), the image in the highlight portion can be smoothed.

  The color correction coefficient is different from the six hues of RGBYMC into 12 hues obtained by further dividing each of the six hues of RGBYMC and into every 14 hues of black and white. The hue determination circuit determines to which hue the read image data is determined. Based on the determination result, a color correction coefficient for each hue is selected.

  Generation of a printer vector for calculating the luminance L (hue) corresponding to the hue hue will be described.

Here, k [hue] [S] (S = R, G, B) is a luminance coefficient for each hue. S [hue] (S = R, G, B) indicates the respective values of the RGB components of the hue hue. cS is an offset and is usually zero. Σ represents addition for the RGB components by S = R, G, B described at the bottom of Σ.

  When expressed as a single color single printer vector P (Single) (P = Y, M, C, K), the hue hue printer vector P (hue) (hue is the hue R, G, B, C, M, Y, K). , W) is obtained by (Equation 47) by multiplying the single-color Single printer vector P (Single) by the luminance L (hue) corresponding to the hue hue obtained by (Equation 46). Note that P (Single is represented in the form of [...] on the right side of (Expression 47).

A masking coefficient for a single color is obtained by substituting the printer vector P (hue) of the hue hue obtained in (Expression 47) into (Expression 43).

  The color correction coefficient is different from the six hues of RGBYMC into 12 hues obtained by further dividing each of the six hues of RGBYMC and into every 14 hues of black and white. The hue determination circuit determines to which hue the read image data is determined. Based on the determination result, a color correction coefficient for each hue is selected.

  A method for using the first transparent toner of the present invention will be described. In FIG. 25, transparent toner is used for the color gamut Y (0) -G (0) -C (0) -B (0) -M (0) -R (0) that does not use transparent toner. When the color gamut Y (T) -G (T) -C (T) -B (T) -M (T) -R (T) becomes narrow, the color gamut Y (0) without using transparent toner. ) (Dy) -G (0) (Dy, Dc) -C (0) (Dc) -B (0) (Dc, Dm) -M (0) (Dm) -R (0) (Dm, Dy) Is used so that the color gamut Y (T) -G (T) -C (T) -B (T) -M (T) -R (T) substantially matches the color gamut using the transparent toner. The upper limit of the amount of CMY toner used (Dc (hue) (0), Dm (hue) (0), Dy (hue) (0)) (where hue represents the hue) was used for transparent toner. CMY in case Dc (hue) (0) ≦ Dc (hue) (Dc (hue) (T), Dm (hue) (T), Dy (hue) (T)) T), Dm (hue) (0) ≦ Dm (hue) (T), Dy (hue) (0) ≦ Dy (hue) (T).

  Accordingly, it is possible to reduce a deviation between the color reproduction range in the saturation direction of the image area using the transparent toner and the color reproduction range of the image area not using the transparent toner.

  The upper limit values (Dc (hue) (0), Dm (hue) (0), Dy (hue) (0)) and Dc (hue) (T), Dm (hue) (T), Dy (hue) Since (T) differs depending on the type of transfer paper, it is switched according to the type of transfer paper.

  Accordingly, it is possible to suppress a difference in color reproducibility between an image area using the transparent toner and an image area not using the transparent toner depending on the type of paper.

  The upper limit values (Dc (hue) (0), Dm (hue) (0), Dy (hue) (0)) and Dc (hue) (T), Dm (hue) (T), Dy (hue) Since (T) differs depending on the image quality mode such as the character mode and the photo mode, it is switched according to the image quality mode.

  Thereby, regardless of the image quality mode selected by the user, it is possible to suppress the difference in color reproducibility between the image area using the transparent toner and the image area not using the transparent toner.

  The upper limit values (Dc (hue) (0), Dm (hue) (0), Dy (hue) (0)) and Dc (hue) (T), Dm (hue) (T), Dy (hue) Since (T) differs depending on the type of gradation processing (dither processing, error diffusion processing, etc.), it is switched according to the type of gradation processing.

  Color reproduction varies depending on how and how much of the color toner is covered with the transparent toner, so if the solid color of the transparent toner is placed on the color toner, the color correction amount is large and the color toner is transparent between the line patterns of the color toner. When the toner is formed in a line shape, when the color correction amount is medium, and when transparent toner is placed on the color toner in a halftone dot shape, the color toner gradation processing is performed so that the color correction amount is small. The color correction amount is switched according to the combination of gradation processing of the transparent toner. Thereby, the shift | offset | difference of the color tone of only a color toner and the color tone of a color toner + transparent toner can be made small.

  The masking coefficient used for the image area using the transparent toner can be obtained from (Equation 41), and the masking coefficient used for the image area not using the transparent toner can be obtained from (Equation 40).

  A method of using the second transparent toner of the present invention will be described. In FIG. 22, the color reproduction area W (T) -Y (0) -G (0) -C (0) -B (0) -M (0) -R (0) -K (0) is a transfer sheet. This expresses an approximate color gamut when the amount of transparent toner used is reduced when transparent toner T is used on the background of the image and the saturation is increased by increasing the amount of CMY toner attached. .

  With respect to (Equation 39), the values of R, G, B at two different points (R1, G1, B1) and (R2, G2, B2) on the achromatic color axis and the C of the developing unit optimum for the color reproduction. , M, Y, and K recorded values (C1, M1, Y1, K1), (C2, M2, Y2, K2), white portions using transparent toner for (C1, M1, Y1, K1), ( C2, M2, Y2, K2) As a black portion that does not use a transparent toner, a masking coefficient that uses a transparent toner for a white portion is:

And

  FIG. 28 is a conceptual diagram of color reproduction when coated paper is used. FIG. 28A is a conceptual diagram of the color reproduction range on the L * a * b * color system lightness L * -chromatic index a * plane, and FIG. 28B also shows L * a *. It is a conceptual diagram of the color reproduction range on the chromaticity index a * -b * plane of the b * color system.

  FIG. 29 is a conceptual diagram of color reproduction when plain paper is used. FIG. 29A is a conceptual diagram of the color reproduction range on the L * a * b * color system lightness L * -chromatic index a * plane, and FIG. 29B also shows L * a *. It is a conceptual diagram of the color reproduction range on the chromaticity index a * -b * plane of the b * color system. Compared to the color reproduction range of color toner only, the color reproduction range of color toner with transparent toner superimposed is an example of L * a * b * color system in the lightness range where the brightness index L * is close to 100. There may be a shift and a shift in the direction in which the values of the chromaticity indices a * and b * are large (the saturation is large). In this case, in the direction of increasing the saturation (the direction in which the absolute values of a * and b * are increased), a bright (close to 100) region of lightness index L * is used without using transparent toner. Adapt to

  FIG. 30 shows the relationship between the saturation of the document and the toner adhesion amount. The horizontal axis is the original chroma C * in the L * C * h * color system, and the vertical axis is the toner adhesion amount. a. (Solid line) is the amount of colored toner attached; b. (Two-dot chain line) indicates the amount of transparent toner adhered when coated paper is used as transfer paper, c. (Long broken line) is the amount of transparent toner adhered when plain paper is used as transfer paper, d. (One-dot chain line) is the sum of the adhesion amount of the colored toner and the transparent toner to the coated paper, (Short dashed line) indicates the sum of the adhesion amount of the color toner + the transparent toner to the plain paper. Since coated paper has higher surface gloss than plain paper, the amount of transparent toner may be small in order to obtain the same gloss.

  FIG. 31 shows the relationship between the printed document and the read value. FIG. 31D shows a sample of a document in which printed coated paper is pasted on plain paper. The vertical axis of the graph of (c) represents the reading value of the scanner, the horizontal axis represents the reading value of the document in the main scanning direction, and the graph of (b) represents a cross-sectional view of the document. The image (a) represents a conceptual diagram in which transparent toner and colored toner are adhered to transfer paper, and the vertical axis represents the toner adhesion amount.

  An example in which the amount of transparent toner adhering to the background portion of the original document is increased because the coated paper 1 used for the original document has a high smoothness and smoothness on the surface of the coated paper 1 and a small variation in the reading value. Indicates.

  In the first method of the present invention described above, the amount of transparent toner to be used can be used at a substantially constant level, and the amount of CMY toner adhesion can be suppressed. However, the color reproduction range is particularly narrow with respect to the saturation. There is. On the other hand, in the second method of the present invention described above, the color reproduction range in the saturation direction is the same regardless of whether transparent toner is used or transparent toner is used, but the amount of transparent toner used is close to the background. It is a limited method. Thus, according to the user's preference, the latter can be selected when the color reproduction range is important, and the former can be selected when the gloss effect of the transparent toner is important.

  Returning to FIG. 3, the scaling processing circuit 408 performs scaling for main scanning and sub-scanning. The γ conversion (1) circuit 409 performs γ conversion for characters and photographs according to the image area separation signal, or the printer γ before the binarization processing is performed by the gradation processing (1) circuit 410. Perform conversion. In the gradation processing (1) circuit 410, when performing FAX transmission and scanner delivery, the character mode, photo mode, and character / photo mode are instructed from the operation unit or a PC via a LAN connected to the I / F 421. Corresponding simple binarization processing, binary dither processing, binary error diffusion processing, binary fluctuation threshold error diffusion processing, etc. are performed.

  The editing (1) circuit 411 performs editing processing such as edge mask processing and logical inversion. At the time of image data storage, compression processing is performed by the compression / decompression processing circuit 416 via the Multilayer Bus 412, and the compressed image data is stored in the HDD 419 via the HDD I / F 418. The stored image data is stored as an RGB signal, a K (Gray) signal, a CMYK signal, and an RGBX signal (X signal is an image area separation result) according to the purpose of use. Reprocessing such as RGB signal for distribution, K (Gray) signal for distribution and FAX transmission, CMYK signal for printing on paper, RGBX signal for CMYK data generation, or color space conversion to sRGB signal for distribution Store for use.

  When the image data read by the scanner 400 is used for FAX transmission or scanner transmission, the color correction / UCR processing (1) circuit 407 converts the image data into s-RGB or K (Gray) signals. The data is stored in the main memory 437 through the memory controller (2) 436. When printing on the transfer paper, the Gray / RGB conversion circuit 425 generates a Gray signal from the RGB image data via the Multilayer Bus 412. At that time, the processing of making the Green signal R = G = B and making it Gray is performed as necessary. The RGB composition circuit 426 performs overwrite composition and watermark composition on RGB image data.

  The pattern generation circuit 427 generates an ACC (automatic gradation correction) pattern, a registered color pattern, and the like which will be described later. The spatial filter (2) circuit 428 performs spatial filter processing such as edge enhancement and smoothing processing. The ADS removal circuit 429 performs document follow-type background removal processing. The functions of the hue determination processing (2) circuit 430 and the color correction / UCR processing (2) circuit 431 are the same as those of the hue determination processing circuit 406 and the color correction / UCR processing circuit 407, respectively. The scaling process (2) circuit 433 is the same as the scaling process (1) circuit 408.

  The total amount regulating circuit 434 regulates the total amount of YMCK toner on the transfer paper when converted into CMYK signals by the color correction / UCR processing (2) circuit 431. The feature amount extraction processing circuit 422 performs determination processing such as an edge of the image, a non-edge, and a weak edge between the edges, and the γ conversion (2) circuit 423 determines the edge, non-edge, weak edge, and the like. The gradation processing circuit 424 performs γ conversion processing according to the result, and the gradation processing circuit 424 performs processing such as binary or multi-value dither processing, binary or multi-value error diffusion processing, binary or multi-value variation threshold error diffusion processing, or the like. Perform key processing.

  FIG. 32 shows a configuration for explaining the gradation processing method. 32 shows the feature amount extraction unit (1) 440, the γ conversion unit (1) 409, the gradation processing unit (1) 410, the feature amount extraction unit (2) 422, the γ conversion unit (2) 423 of FIG. The processing configuration for one color of YMCK in the gradation processing unit (2) 424 is shown. The copier 101 in FIG. 1 processes four color toners and colorless toner in parallel, so the processing block shown in FIG. 32 uses four colors and five colors including colorless toner.

  As shown in FIG. 32, the feature amount extraction / low density determination processing unit 4120 includes a line memory 4121, a feature amount extraction unit 4122, and a low density determination unit 4123. The line memory 4121 stores a plurality of lines (for example, five lines) used by the feature amount extraction unit 4122. The feature amount extraction unit 4122 extracts an edge portion, a non-edge portion, and a weak edge portion (region having an intermediate edge degree between the edge portion and the non-edge portion) (1, 2) from the image data by a process described later. The low density determination unit 4123 compares the image data with a predetermined density threshold and determines whether the image data corresponds to a low density (highlight) part or is image data other than highlights.

  The printer γ conversion process (2) 4130 includes a printer γ conversion processing unit 4132 and printer γ table data 4131. The printer gamma conversion processing unit 4132 refers to the printer gamma table set in the printer gamma table data 4131 based on the 2-bit feature quantity extraction result from the feature quantity extraction unit 4122 and performs printer gamma conversion.

  The gradation processing unit 4140 includes a quantization threshold value generation unit 4150 and an error diffusion processing unit 4151. The quantization threshold value generation unit 4150 obtains a 2-bit feature value extraction result Chr (x0, y0) (≡C = {0, 1, 2, 2) at the target pixel (x0, y0) from the feature value extraction / low density determination process 4120. 3}, hereinafter referred to as C), and a 2-bit low density determination result Dns (x0, y0) (≡D = {0, 1, 2, 3}, hereinafter referred to as D) to generate a quantization threshold . Here, x0 is a value that designates a pixel in the main scanning direction, and y0 is a value that designates the position of the pixel in the sub-scanning direction. In the case of 600 dpi, for example, a blank portion is added to the number of pixels read from an A3-size document, and x0 = {0, 1, 2,..., X0max}; y = {0, 1, 2,. X0max = 7,100, y0max = 10,000 or so. When it corresponds to the document size such as A1 size, x0max and y0max are larger values.

  The quantization threshold value table unit 4142 includes a quantization threshold value Thr [C, corresponding to the feature value extraction result C = {0, 1, 2, 3} and the low density determination result D = {0, 1, 2, 3}. D] [x, y, i] are set in advance. Also, the blue noise addition selection table unit 4144 has a blue noise addition table Fbn [C, corresponding to each of the quantization thresholds Thr [C, D] [x, y, i] set in the quantization threshold table unit 4142. D] [x, y, i] are set.

Here, x and y of [x, y, i] are respectively used as the matrix size xmax in the main scanning direction and the matrix size ymax in the sub-scanning direction of the quantization threshold matrix.
x = {0, 1, 2,..., xmax-1}
y = {0, 1, 2,..., ymax-1}
I is the number of output gradations of the image data, M,
i = {0, 1, 2,..., M-2}
Move the value of. In the following, for simplicity of explanation, let Z be a set of integers, and the above formulas are expressed as Z {xmax} = {x∈Z; 0 ≦ x <xmax}, respectively.
Z {ymax} = {y∈Z; 0 ≦ y <ymax}
Z {M−1} = {i∈Z; 0 ≦ i <M−1}
Represents the same meaning. That is, x∈Z represents “x is an integer” and represents movement within the range of 0 ≦ x <xmax. Therefore, the value of x = {0, 1, 2,..., Xmax−1} is set. Possible. Similarly, a value range Z {x0max} that can be taken by the position x0 in the main scanning direction, a value range Z {y0max} that can be taken by the position y0 in the sub-scanning direction, and a value range Z {that can be taken by the feature amount extraction result C. Cmax}, a range of values Z {Dmax} that the low density determination result D can take, a range of values Z {N} that the quantization threshold Thr [C, D] [x, y, i] can take, and blue noise Bn [ k] can take a range of values Z {Bn}, a range of values Z {Bnmax} that an index k of Bn [k] can take, and a blue noise addition selection Fbn [C, D] [x, y, i]. Define the range of values to be obtained Z {Fbn},
Z {x0max} = {x0∈Z; 0 ≦ x0 <x0max}
Z {y0max} = {y0εZ; 0 ≦ y0 <y0max}
Z {Cmax} = {CεZ; 0 ≦ C <Cmax}
Z {Dmax} = {DεZ; 0 ≦ D <Dmax}
Z {N} = {DinεZ; 0 ≦ Din <N−1}
Z {Bn} = {± 1}
Z {Bnmax} = {kεZ; 0 ≦ k <bnmax}
Z {Fbn} = {0, 1}
And so on. In this embodiment, Cmax = Dmax = 4. However, the value is not limited to this value, and may be changed as necessary.

  FIG. 33 shows the configuration of the quantization threshold Thr [C, D] [x, y, i]. Quantization threshold values Thr [C, D] [x, y, i] of the main scanning direction size xmax and the sub-scanning direction size ymax are prepared for M−1 levels, which is the feature amount extraction result Chr (x0, y0). ) (= C) εZ {Cmax}, and four types corresponding to the low density determination result Dns (x0, y0) (= D) εZ {Dmax}, the quantization threshold value table unit 4142 Set to Since this is a quantization threshold for one color, actually four colors are set.

  Quantization threshold Thr [C, D] [x, y, i] εZ {N} (CεZ {Cmax}, DεZ {Dmax} xεZ {xmax}, yεZ {ymax}, i Corresponding to each threshold value of εZ {M−1}), blue noise addition selection Fbn [C, D] [x, y, i] εZ {Fbn} (CεZ {Cmax}, DεZ { Dmax} xεZ {xmax}, yεZ {ymax}, iεZ {M−1}) are set in the blue noise addition selection table unit 4144.

  The quantization threshold selection unit 4141 and the blue noise addition selection unit 4143 are respectively applied to the pixel of interest (x0, y0) based on the feature amount extraction result C and the low density determination result D, and the quantization threshold Thr [C, D]. [X, y, i] is selected from the quantization threshold table 4142, and the blue noise addition selection flag Fbn [C, D] [x, y, i] is selected from the blue noise addition selection table 4144.

  FIG. 34A shows the configuration of the feature quantity extraction unit 4122 (FIG. 32). The feature amount extraction unit 4122 performs edge detection of the image data Din (x0, y0). In this embodiment, the feature amount extraction unit 4122 outputs a level as an output of the feature amount extraction result Chr (x0, y0) for the target pixel (x0, y0). 2 bits of edge data representing an edge level from 3 (edge degree maximum) to level 0 (non-edge) are output.

  For example, the feature amount is extracted by using four types of first-order differential 5 × 5 differential filters 1 to 4 shown in FIG. 34B and four types of second-order differential filters shown in FIG. Edge amount is detected in 4 directions, which are ± 45 ° tilted from the direction, sub-scanning direction, and main scanning direction, the edge amount having the maximum absolute value is selected, and the absolute value of the edge amount is changed from level 0 to level. Quantize to 4 edge levels up to 3 and output.

  The low density determination unit 4123 compares a predetermined threshold value with the input image data Din, and outputs the low density determination result Dns (x0, y0) for the target pixel (x0, y0) with the lowest density being 0 and the highest. A value with a density of 3 or the like is output.

  The error integrating unit 4149 calculates a diffusion error to be added to the next target pixel from the quantization error data stored in the error buffer 4148. In this embodiment, the error integrating unit 4149 calculates diffusion error data using an error diffusion matrix having a size of 3 pixels in the sub-scanning direction and 5 pixels in the main scanning direction as shown in FIG. In FIG. 35A, the * mark corresponds to the position of the next pixel of interest, and a, b,. . . , K, l are coefficients corresponding to the positions of the 12 processed pixels in the vicinity (the sum is 32). In the error integrating unit 4149, a value obtained by dividing the product sum of the quantization errors for the 12 processed pixels and the corresponding coefficients a to l by 32 is given to the adding unit as a diffusion error for the next pixel of interest.

  As an example, the quantization threshold selection unit 4141 is arranged so as to grow the lines in order of increasing thresholds from 1 to 6 as shown in FIG. 35B (1 is the minimum, 6 is the maximum). Using a dither threshold matrix of 4, a dither threshold that oscillates periodically from 1 to 6 on the image plane is output. Here, the same threshold value is used for pixels having the same value. The dither threshold period corresponds to 192 Lpi in the case of 600 dpi image formation. Such a quantization threshold selection unit 4141 is easily realized by a ROM that stores the dither threshold matrix and a counter that counts main and sub-scan timing signals of image data and generates a read address of the ROM. it can.

  Here, in FIG. 35B, the pixels set to 1 represent that dots arranged in the main scanning direction are first formed by arranging them in the main scanning direction. In this way, for the purpose of stable dot formation, two pixels of one value, which is a writing level with less energy, are arranged. The screen angle and line growth direction in this case are shown in FIG. The growth direction of the line is indicated by “direction 1 in which the line grows” in the drawing.

  Further, as shown in FIG. 35D, when the edge level indicated by the edge data from the feature amount extraction unit 4122 is level 0 (non-edge), the coefficient 3 is set, and when the edge level is level 1, the coefficient 2 is set. The output value of the quantization threshold selection unit 4141 is multiplied by a coefficient 1 when 2 and a coefficient 0 when level 3 (maximum edge degree).

  If the quantized data of the image processing apparatus configured as described above is given to, for example, an electrophotographic printer or the like, the resolution of characters, image change points, and relatively low number of halftone dot image portions is good. A photograph, a portion with little change in the image, a halftone dot image with a high number of lines, and the like are smooth and stable, and a high-quality image in which these regions are aligned without a sense of incongruity can be formed. This will be described below.

  In a portion where the change is steep and the edge level is level 3 (edge degree is the highest) such as the edge of a character or line drawing in the image, the quantization threshold generated by the quantization threshold selection unit 4141 is fixed, and the quantization is performed. Since the processing unit 4147 performs a quantization process by a pure error diffusion method using a fixed threshold value, an image with high resolution can be formed.

  In a portion where the degree of edge is low, such as a flat portion of a photograph or an image, the vibration width of the quantization threshold generated by the quantization threshold selection unit 4141 becomes large. Therefore, the quantization processing of the quantization processing unit 4147 is dithered. Processing is performed, and the image data is converted to halftone dots with a dither threshold period. Since the dither threshold value matrix having the threshold value arrangement as shown in FIG. 35B is used to generate the quantization threshold value, the center of the line grown along the screen angle within the dither threshold period as the density level of the image data increases. The output dots grow in a spiral shape from the part.

  FIG. 35 (c) shows the order of line growth and the magnitude relationship between the quantization thresholds as another example of FIG. 35 (b). Although the order of the pixels formed when the line grows is different from the case of FIG. 35B, even if such a value is set, a line along the screen angle is formed in the same manner, and a smooth image is formed. Can be obtained.

  FIG. 37 is a diagram for explaining feature amount extraction. As shown in FIG. 37, the character region is determined by the values of the high density threshold value, the primary differential feature value extraction threshold value 1, the primary differential feature value extraction threshold value 2, the secondary differential feature value extraction threshold value 1, and the secondary differential feature value extraction threshold value 2. It is possible to adjust the region (hatched portion in the figure) determined as. For example, by setting any threshold value low, the area determined as a character is expanded.

  An operation screen for selecting a function of automatic gradation correction (ACC: Auto Color Calibration) of image density (gradation property) will be described.

  When the automatic gradation correction ACC menu is called on the liquid crystal screen of the operation unit (FIG. 38), the screen of FIG. 39 (a) is displayed. FIG. 38B shows the liquid crystal screen of FIG. 38A, and particularly shows a screen for selecting settings in the copy application. The surface is a touch panel, and when the user touches the surface with a finger or a touch pen, paper size selection, density adjustment, image quality mode selection, selection of whether to store documents, stack sorting selection, scaling size, etc. A screen (not shown) for selecting is displayed and can be selected.

  When [Execute] of automatic gradation correction for copy use or printer use is selected, the screen shown in FIG. 39B is displayed. When the copy use is selected, the gradation correction table used when using the copy is changed. When the printer is used, the gradation correction table when the printer is used is changed based on the reference data. If the result of image formation with the changed YMCK tone correction table is not desirable, the [Undo] key is shown in FIG. 39 (a) so that the YMCK tone correction table before processing can be selected. ) Is displayed on the screen.

  Other items in the screen of FIG. 39A will be described. When “automatic gradation correction setting” is selected, “execution” or “non-execution” of “background correction”, “high density portion correction”, and “RGB ratio correction”, which will be described later, can be selected. In the “Auto gradation correction setting” menu, “Auto gradation correction setting” and “Light intensity unevenness detection setting” can be selected. Note that these selections are not always necessary, and may be always “execution”.

  As described above, a scanner γ conversion table is created for each RGB read component used during copying from an achromatic color patch. On the other hand, the reading value of each YMCK gradation pattern obtained by reading an adjustment pattern output during execution of ACC (automatic gradation correction) described later from the chromatic color patch and the achromatic color patch is corrected. Therefore, in the former process, three RGB conversion tables are used, and in the latter process, four YMCK conversion tables are used.

  FIG. 40 shows a process flowchart of ACC execution. When [Execute] of automatic gradation correction for copy use or printer use is selected on the screen of FIG. 39A, the screen of FIG. 39B is displayed.

  When the print start key in the screen of FIG. 39B is depressed, a plurality of density gradation patterns corresponding to each color mode of YMCK, character, and photograph as shown in FIG. 39C are transferred. It is formed on top (step S1101).

  This density gradation pattern is stored and set in the IPU ROM in advance. The written values of the pattern are 16 patterns of 00h, 11h, 22h, ..., EEh, FFh in hexadecimal notation. In the figure, patches for five gradations are displayed excluding the background portion, but any value can be selected from the 8-bit signals of 00h-FFh. In the character mode, a dither process such as a pattern process is not performed, and a pattern is formed with 1 dot 256 gradations. In the photo mode, a dither process described later is performed.

  After the pattern is output on the transfer material, the screen of FIG. 41A is displayed on the operation screen so that the transfer material is placed on the document table. In accordance with the instructions on the screen, the transfer material on which the pattern is formed is placed on the document table (step S1102), and “read start” is selected on the screen of FIG. 39B, or “cancel” is selected (step S1103).

  If “Cancel” is selected, the process ends. If “Reading start” is selected, the scanner runs and reads the RGB data of the YMCK density pattern (step S1104). At this time, the data of the pattern portion and the data of the background portion of the transfer material are read.

  It is determined whether or not the data in the pattern portion has been read normally (step S1105). If it is not read normally, the screen of FIG. 39B is displayed again. If it is not read normally twice, the process is terminated (step S1106).

  Each read value of the ACC pattern is corrected for each YMCK color in the above-described ACC pattern read value correction table D [ii] (ii = 0, 1, 2,..., 255) (step S1107). “Execution” or “non-execution” of the process using the background data is determined based on the result selected on the screen of FIG. 39A (step S1108). If “execution” of the process using the background data is selected, the background data is processed for the read data (step S1109).

  Further, “execution” and “non-execution” of the correction of the high image density portion of the reference data are determined based on the result selected on the screen of FIG. 39A (step S1110). If “execution” of the correction of the high image density portion of the reference data has been selected (Yes in step S1110), the processing of the high image density portion is performed on the reference data (step S1111). A YMCK gradation correction table is created and selected (step S1112).

  The above processing is performed for each color of YMCK (step S1113). The above processing is performed for each picture and character image quality mode (step S1114). During the process, the screen of FIG. 41B is displayed on the operation screen.

  If the result of image formation using the YMCK tone correction table after the end of processing is not desirable, the [Undo] key is shown in FIG. 39 so that the YMCK tone correction table before processing can be selected. It is displayed on the screen of (a).

  The background correction will be described. There are two purposes for the background correction process. One is to correct the whiteness of the transfer material used during ACC. This is because even if an image is formed on the same machine at the same time, the value read by the scanner differs depending on the whiteness of the transfer material used. As a disadvantage of not performing correction, for example, when recycled paper or the like having low whiteness is used for this ACC, the recycled paper generally has a lot of yellow components, and therefore, when a gradation correction table for yellow is created. The correction is made so that the yellow component is reduced. In this state, when copying is next performed on art paper or the like having high whiteness, an image with a small amount of yellow components may be obtained and a desired color reproduction may not be obtained.

  As another reason, when the thickness of the transfer paper (paper thickness) used at the time of ACC is thin, a color such as a pressure plate for pressing the transfer material is seen through and read by the scanner. For example, when an automatic document feeder called ADF (Auto Document Feeder) is installed instead of the pressure plate, a belt is used for conveying the original, but depending on the rubber material used, The whiteness is low and there is a slight gray taste. For this reason, the read image signal is also read as an image signal that is apparently high as a whole. Therefore, when the YMCK tone correction table is created, the image signal is created so as to be thinner. In this state, when a transfer sheet having a thick paper thickness and poor transparency is used, an image having a low overall density is reproduced, so that a desirable image is not necessarily obtained.

  In order to prevent the above problems, the read image signal of the pattern portion is corrected from the read image signal of the paper background portion based on the image signal of the paper background portion. However, there is an advantage even when the above correction is not performed. When a transfer sheet having a large amount of yellow components is always used, such as recycled paper, color reproduction is not performed for a color containing a yellow component without correction. May be better. In addition, when only the transfer paper having a thin paper thickness is always used, there is an advantage that the gradation correction table is created in a state matched to the thin paper. As described above, the correction of the background portion can be turned ON / OFF according to the user's situation and preference.

  LD [i] (i = 0, 1,..., 9) is the written value of the gradation pattern (FIG. 39C) formed on the transfer paper, and the read value of the formed pattern by the scanner is v in vector format. [T] [i] ≡ (r [t] [i], g [t] [i], b [t] [i]) (t = Y, M, C, orK, i = 0, 1,. , 9). Instead of (r, g, b), it is expressed by lightness, saturation, hue angle (L *, c *, h *), lightness, redness, blueness (L *, a *, b *), etc. Also good.

  A reference white reading value stored in advance in the ROM 132 or RAM 131 is assumed to be (r [W], g [W], b [W]). A method of generating a gradation conversion table (LUT) performed by the γ conversion processing unit 409 when ACC is executed will be described.

  In the pattern read value v [t] [i] ≡ (r [t] [i], g [t] [i], b [t] [i]), the image signal of each complementary color of YMC toner is b. Since [t] [i], g [t] [i], and r [t] [i], only the complementary color image signals are used. Here, in order to simplify the subsequent description, a [t] [i] (i = 0, 1, 2,..., 9; t = C, M, Y, orK) is used. Processing is simple if a gradation conversion table is created. For black toner, sufficient accuracy can be obtained by using any of RGB image signals, but here, a G (green) component is used.

  The reference data includes the scanner reading v0 [t] [i] ≡ (r0 [t] [i], g0 [t] [i], b0 [t] [i]) and the corresponding laser writing value LD [ i] (i = 1, 2,..., m). Similarly, in order to simplify the subsequent description using only YMC complementary color image signals, A [t] [n [i]] (0 ≦ n [i] ≦ 255; i = 1, 2,... , M; t = Y, M, C, or K). m is the number of reference data.

  The YMCK gradation conversion table is obtained by comparing a [LD] described above with reference data A [n] stored in the ROM 132. Here, n is an input value to the YMCK gradation conversion table, and the reference data A [n] is a YMC toner pattern output with the laser writing value LD [i] after the input value n is YMCK gradation converted. Is the target value of the read image signal read by the scanner. Here, the reference data includes two types of values: a reference value A [n] that is corrected according to the image density that can be output by the printer, and a reference value A [n] that is not corrected. The determination as to whether or not to perform the correction is made based on determination data, which will be described later, stored in advance in the ROM or RAM. This correction will be described later.

  The laser output value LD [n] corresponding to the input value n to the YMCK gradation conversion table is obtained by obtaining the LD corresponding to A [n] from the a [LD] described above. By obtaining this with respect to the input values i = 0, 1,..., 255 (in the case of an 8-bit signal), a gradation conversion table can be obtained. At that time, instead of performing the above processing on all values for the input values n = 00h, 01h..., FFh (hexadecimal number) for the YMCK gradation conversion table, ni = 0, 11h, 22h,. The above processing is performed for the jump value such as the above, and other points are interpolated by a spline function or the like, or obtained by the above processing in the YMCKγ correction table stored in the ROM 132 in advance. The nearest table passing through the set of (0, LD [0]), (11h, LD [11h]), (22h, LD [22h]),..., (FFh, LD [FFh]) is selected.

  The above processing will be described with reference to FIG. 42. The horizontal axis of the first quadrant (a) in the figure is the input value n to the YMCK gradation conversion table, and the vertical axis is the reading value of the scanner (after processing). Represents the reference data A [i] described above. The scanner reading value (after processing) is the RGB γ conversion (no conversion is performed here) to the value read by the scanner, and the average processing and addition processing of the read data in several places in the gradation pattern This is a later value, and is processed here as a 12-bit data signal in order to improve calculation accuracy.

  The horizontal axis of the second quadrant (b) in the figure represents the reading value (after processing) of the scanner, like the vertical axis. The vertical axis of the third quadrant (c) represents the written value of the laser beam (LD). This data a [LD] represents the characteristics of the printer unit. In addition, the LD writing values of the pattern to be actually formed are 16 points of 00h (background), 11h, 22h,... EEh, FFh, which indicate skipping values. And treated as a continuous graph. The graph (d) of the fourth quadrant is a YMCK gradation conversion table LD [i], and the purpose is to obtain this table.

  The vertical axis and horizontal axis of the graph (f) are the same as the vertical axis and horizontal axis of the graph (d). When forming a gradation pattern for detection, the YMCK gradation conversion table (g) shown in the graph (f) is used. The horizontal axis of the graph (e) is the same as that of the third quadrant (c), and represents the relationship between the LD writing value at the time of gradation pattern creation and the reading value (after processing) of the gradation pattern scanner. Represents a linear transformation for convenience. Reference data A [n] is obtained for a certain input value n, and an LD output LD [n] for obtaining A [n] is used as an arrow in the figure using a gradation pattern read value a [LD]. Obtain along (l).

  FIG. 43 shows a flowchart of an ACC calculation procedure. In step S1201, an input value necessary for obtaining the YMCKγ correction table is determined. Here, n [i] = 11 (h) × i (i = 0, 1,..., Imax = 15). In step S1202, the reference data A [n] is corrected according to the image density that can be output by the printer.

  The writing value of the laser that can obtain the maximum image density that can be created by the printer unit is FFh (hexadecimal number display), and the reading value m [FFh] of the pattern at this time is mmax. Reference data A [i] (i = 0, 1,..., I1) that is not corrected from the low image density side to the intermediate image density side, and reference data A [i] (i = , imax−1) (i1 ≦ i2, i2 ≦ imax−1), and reference data A [i] (i = i1 + 1,..., i2) to be corrected.

In the following, a specific calculation method will be described on the assumption that the image signal is proportional to the document reflectance without RGB-γ conversion. Among the reference data that is not corrected, the difference between the reference data A [i2 + 1] having the lowest image density in the high image density portion and the reference data A [i1] having the lowest image density in the low image density portion. Δref is obtained. That is,
Δref = A [i1] −A [i2 + 1]
Here, Δref> 0 in the case of reflectance linearity or lightness linearity that does not perform RGBγ conversion, which is inversion processing.

On the other hand, the difference Δdet is similarly obtained from the read value mmax of the pattern that can obtain the maximum image density that can be created by the printer unit. That is,
Δdet = A [i1] −mmax
And Thereby, the reference data A [i] (i = i1 + 1,..., I2) obtained by correcting the high density portion is
A [i] = A [i1] + (A [i] −A [i1]) × (Δdet / Δref) (i = i1 + 1, i1 + 2,..., I2-1, i2)
And

  In step S1203, the read image signal m [i] of the scanner corresponding to n [i] is obtained from the reference data A [n]. Actually, the reference data A [n [j]] (0 ≦ n [j] ≦ 255, j = 0, 1,... Jmax, n [j] ≦ n [k] corresponding to the skipped n [j] forj ≦ k) is as follows.

  Find j (0 ≦ j ≦ jmax) such that n [j] ≦ n [i] <n [j + 1]. In the case of an 8-bit image signal, calculation is performed when reference data is obtained as n [0] = 0, n [jmax] = 255, n [jmax + 1] = n [jmax] 1, and A [jmax + 1] = A [jmax]. It will be easy. Further, the accuracy of the γ correction table finally obtained is higher when the interval of the reference data is such that n [j] is as small as possible.

In step S1204, the ACC pattern read value a [LD] with respect to the write value LD is corrected using the correction table D [ii] (ii = 0, 1, 2,..., 255) described above. a1 [LD] = D [a [LD]]
This a1 [LD] is expressed as a [LD] below.

In step S1205, m [i] is obtained from the following equation from j obtained as described above. m [i] = A [j] + (A [j + 1] -A [i]). (n [i] -n [j]) / (n [j + 1] -n [j])
Here, interpolation is performed using a linear expression, but interpolation may be performed using a higher-order function or a spline function. In that case, m [i] = f (n [i])
And In the case of a k-th order function, f (x) = Σbixi or the like (Σ is the sum from i = 0 to k).

In step S1206, an LD write value LD [i] for obtaining m [i] is obtained by the same procedure. When image signal data that has not undergone RGBγ conversion is processed, a [LD] decreases as the value of LD increases. That is,
For LD [k] <LD [k + 1], a [LD [k]] ≧ a [LD [k + 1]]. Here, the values at the time of pattern formation are 10 values of LD [k] = 00h, 11h, 22h,..., 66h, 88h, AAh, FFh, (k = 0, 1,..., 9). This is because the change in the reading value of the scanner with respect to the toner adhesion amount is large at an image density with a small amount of toner adhesion, so that the interval between the pattern writing values LD [k] is narrowed. Since the change in the reading value of the scanner with respect to the adhesion amount is small, reading is performed with a wider interval.

  Advantages of this include that toner consumption can be suppressed compared to the case where the number of patterns is increased to LD [k] = 00h, 11h, 22h,..., EEh, FFh (16 points in total), etc. In the density area, the reading value is likely to be reversed due to the small change in the LD writing value, the potential unevenness on the photoconductor, the toner adhesion unevenness, the fixing unevenness, and the potential unevenness. Narrowing the width is not necessarily effective in improving the accuracy, and thus the pattern was formed with the LD writing value as described above.

  For LD [k] where a [LD [k]] ≧ m [i]> a [LD [k + 1]], LD [i] = LD [k] + (LD [k + 1] −LD [k] ) · (M [i] −a [LD [k]]) / (a [LD [k + 1]] − a [LD [k]]).

  When 0 ≦ k ≦ kmax (kmax> 0), when a [LD [kmax]]> m [i] (when the image density of the target value obtained from the reference data is high), LD [i] = LD [k] + (LD [kmax] -LD [kmax-1]). (M [i] -a [LD [kmax-1]]) / (a [LD [kmax]]-a [LD [ kmax-1]]), and is predicted by extrapolating with a linear equation.

  Thus, a set (n [i], LD [i]) (i = 0, 1,..., 15) of the input value n [i] and the output value LD [i] to the YMCKγ correction table is obtained. Based on the obtained (n [i], LD [i]) (i = 0, 1,..., 15), interpolation is performed with a spline function or the like, or γ correction possessed in the ROM Select a table.

  According to the present invention, a storage medium storing software program codes for realizing the functions of the above-described embodiments is supplied to a system or apparatus, and the computer (CPU or MPU) of the system or apparatus is stored in the storage medium. It is also achieved by reading and executing the program code. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment. As a storage medium for supplying the program code, for example, a hard disk, an optical disk, a magneto-optical disk, a nonvolatile memory card, a ROM, or the like can be used. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) operating on the computer based on an instruction of the program code. A case where part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing is also included. Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. A case where the CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing is included. Further, the program for realizing the functions and the like of the embodiments of the present invention may be provided from a server by communication via a network.

501 Input image I / F (interface)
502 Delay adjustment memory unit 503a Image area separation unit 504a Gloss addition unit 505 ACS (automatic color selection) unit 506 Output image I / F

JP 2007-057111 A

Claims (10)

  An image forming apparatus that forms an output image using colored toner and transparent toner on a predetermined medium based on image data obtained by reading an original, and determines whether or not to add gloss to each pixel of the image data And an deciding means for deciding a gloss addition amount by a transparent toner and a color toner adhesion amount according to the gloss addition amount for the pixel determined to add gloss. Forming equipment.   Color correction means for applying a first color correction coefficient to the pixel to which the gloss is added and applying a second color correction coefficient to the pixel to which the gloss is not added to perform color correction; The image forming apparatus according to claim 1, wherein:   The colored toner is composed of chromatic color toner and achromatic color toner, and the color correction unit uses the transparent toner when a color reproduction range using the transparent toner is narrower than a color reproduction range not using the transparent toner. The upper limit of the amount of chromatic color toner used for the pixels to which no gloss is added is set so that the color gamut to be used does not coincide with the color gamut using the transparent toner. The image forming apparatus according to claim 2, wherein the image forming apparatus is set to be equal to or less than an upper limit value of the amount.   4. The image forming apparatus according to claim 3, wherein the upper limit values are switched according to the type of the predetermined medium.   4. The image forming apparatus according to claim 3, wherein the upper limit values are switched according to an image quality mode of the output image.   The image forming apparatus according to claim 3, wherein the upper limit values are switched according to a type of gradation processing of the output image.   The determination unit determines whether each pixel of the image data is a background pixel having a predetermined density or less, and the determination unit determines a gloss addition amount by the transparent toner according to a variation in the background pixel. The image forming apparatus according to claim 1.   An image forming method for forming an output image using color toner and transparent toner on a predetermined medium based on image data obtained by reading a document, and determining whether or not to add gloss to each pixel of the image data And a determination step of determining a gloss addition amount by a transparent toner and a color toner adhesion amount according to the gloss addition amount for the pixel determined to add gloss. Forming method.   A program for causing a computer to realize the image forming method according to claim 8.   A computer-readable recording medium on which a program for causing a computer to implement the image forming method according to claim 8 is recorded.