JP2018011129A - Image processing system, image processing method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of moire even in a case where an input image includes a binary pattern such as half-tone dot meshing.SOLUTION: A displacement quantitative acquiring section (displacement quantitative acquiring means) acquires a quantity of displacement at a coordinate point when an input image is output to a printer, and a geometrically correcting section (geometrically correcting means) makes a geometrical correction, corresponding to the quantity of displacement, to the input image. At this time, the geometrically correcting section makes the geometrical correction after fluctuation is imparted to the coordinate point of the input image; alternatively, the geometrically correcting section makes a geometrical correction to the coordinate point of the input image and then imparts fluctuation to the geometrically corrected coordinate point. Then, an interpolation arithmetic section calculates a pixel value for the geometrically corrected coordinate point through a correcting calculation. A pseudo gradation processing section (pseudo gradation processing means) performs a pseudo gradation process for the geometrically corrected input image, the pseudo gradation process showing density gradation by using pseudo gradation.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image processing apparatus, an image processing method, and a program.

  In an electrophotographic image forming apparatus, registration deviation and skew deviation occur, and in an image forming apparatus capable of printing on both sides, front and back deviations occur. In view of this, a correction technique is known in which image position correction and deformation correction are performed in advance so as to measure the shift amount and cancel the shift.

  For example, Patent Literature 1 discloses an image dividing unit that divides image information in a first direction, a random number storage unit that generates and stores a random number, or stores a pre-generated random number, and a first direction. The second direction orthogonal to the first direction is a reference position that serves as a reference when determining a pixel to be subjected to correction processing for performing pixel insertion or pixel thinning for each area of the divided image information. In each area of the image information divided in the first direction in accordance with the reference position determining means for determining different positions in the image, the random number stored in the random number storage means and the reference position determined by the reference position determining means Pixel determining means for determining a pixel to be corrected; image width changing means for performing correction processing on the pixel determined by the pixel determining means to change the image width in the first direction of the image information; , With The image processing apparatus is disclosed.

  In this image processing apparatus, a pseudo gradation process is performed on an input image, and an image width changing process involving a change in the reference position is performed on a binary image after the pseudo gradation process.

  However, according to such a conventional image processing apparatus, when an input image includes a binary pattern such as shading, neither the binary pattern period nor the pseudo gradation process screen period interferes with each other. As described above, it is difficult to determine the fluctuation cycle of the reference position, and as a result, there is a possibility that moire (interference fringes) is generated in the corrected image.

  The present invention has been made in view of the above, and an object thereof is to prevent moiré from being generated in a corrected image even when an input image includes a binary pattern such as shading.

  In order to solve the above-described problems and achieve the object, the present invention provides a shift amount acquisition unit that acquires a shift amount of an input image that occurs at the time of printer output, and the input image according to the shift amount. Geometric correction means for performing geometric correction; and pseudo gradation processing means for performing pseudo gradation processing for expressing the density gradation of the input image as a pseudo gradation on the geometrically corrected input image, The geometric correction means, after adding fluctuation to the input image or a coordinate point of the input image, calculates a pixel value of a correction position by the geometric correction by interpolation calculation.

  According to the present invention, it is possible to prevent the occurrence of moire even when the input image includes a binary pattern such as shading.

FIG. 1 is a hardware block diagram illustrating a hardware configuration of an image forming apparatus including the image processing apparatus according to the first embodiment. FIG. 2 is a functional block diagram illustrating a functional configuration of the image processing apparatus according to the first embodiment. FIG. 3 is a diagram illustrating an example of geometric correction for image distortion, and FIG. 3A is a diagram illustrating an example of an input image and an output image without geometric correction that is output from the printer without geometric correction. It is. FIG. 3B is a diagram illustrating an example of a geometrically corrected image obtained by geometrically correcting an input image and an output image obtained by outputting the geometrically corrected image to a printer. FIG. 4 is a functional block diagram illustrating a detailed configuration of the geometric correction unit. FIG. 5 is a diagram illustrating the function of the corresponding coordinate point calculation unit. FIG. 6 is a diagram illustrating the function of the interpolation calculation unit. FIG. 7 is a diagram illustrating the function of the fluctuation adding unit. FIG. 8 is a diagram illustrating an example of the fluctuation function. FIG. 9 is a diagram for explaining the effect of adding fluctuation, and FIG. 9A is a diagram illustrating an example of an input image. FIG. 9B is a diagram illustrating an example of a result of lateral magnification correction performed on the input image without adding fluctuation. FIG. 9C is a diagram illustrating an example of a result of performing pseudo gradation processing on the image of FIG. 9B. FIG. 9D is a diagram illustrating an example of a result of performing lateral magnification correction by adding fluctuation to an input image. FIG. 9E is a diagram illustrating an example of a result of performing pseudo gradation processing on the image of FIG. 9D. FIG. 10 is a flowchart illustrating a flow of processing performed by the image processing apparatus according to the first embodiment. FIG. 11 is a flowchart showing the flow of geometric correction. FIG. 12 is a functional block diagram showing a detailed configuration of the geometric correction unit in the modification of the first embodiment. FIG. 13 is a diagram illustrating the function of the fluctuation adding unit. FIG. 14 is a functional block diagram illustrating a functional configuration of the image processing apparatus according to the second embodiment. FIG. 15 is a diagram for explaining the effect of adding fluctuations. FIG. 16 is a flowchart illustrating a flow of processing performed by the image processing apparatus according to the second embodiment.

(Description of the first embodiment)
Hereinafter, a first embodiment for carrying out the present invention will be described with reference to the drawings. First, a hardware configuration of an embodiment of an image forming apparatus including the image processing apparatus of the present invention will be described with reference to the hardware block diagram of FIG.

  An image forming apparatus 100a illustrated in FIG. 1 includes a controller 101, an engine control unit 110, an image reading unit 111, an electrophotographic plotter unit 112, an image processing unit 113, and an operation unit 108. . The image forming apparatus 100a is configured as, for example, a copying machine, a printer, a facsimile apparatus, a digital multifunction peripheral (MFP) or the like.

  The controller 101 includes a CPU 102, a RAM 103, a ROM 104, an HDD (Hard Disk Drive) 105, a communication I / F (interface) 106, and an operation I / F 107, and the operation I / F 107 is connected to the operation unit 108. These components are connected to each other by a system bus 109. The controller 101 has a general microcomputer configuration.

  The CPU 102 controls the entire image forming apparatus 100a by executing a program stored in the ROM 104 or the HDD 105 using the RAM 103 as a work area. The program is provided by being incorporated in advance in the ROM 104 or the HDD 105. The program is recorded in a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, and a DVD (Digital Versatile Disc) as a file in an installable or executable format. It may be configured to be provided. Furthermore, the program may be provided by being stored on a computer connected to a network such as the Internet and downloaded via the network. The program may be provided or distributed via a network such as the Internet.

  The ROM 104 and the HDD 105 are nonvolatile storage media (storage means) and store various programs executed by the CPU 102 and various fixed data.

  The communication I / F 106 is an interface for connecting the image forming apparatus 100a to a network such as a LAN (not shown in FIG. 1).

  The operation I / F 107 is an interface for connecting the operation unit 108 to the system bus 109 so that the CPU 102 can control it.

  The operation unit 108 is a user interface including an operation unit such as a key, a button, and a touch sensor for receiving an operation from a user, and a display unit such as a display for presenting information to the user.

  The image reading unit 111 is an image reading unit having a function of reading an image of a document and acquiring the image data.

  The plotter unit 112 has a function of forming an image on output paper (paper) and outputting it to a printer based on image data read by the image reading unit 111 or image data input from the outside via the communication I / F 106. An electrophotographic image forming unit provided.

  The image processing unit 113 is an image processing unit that performs various image processing to be described later on image data read by the image reading unit 111 and image data input from the outside. The image processing unit 113, the CPU 102, the RAM 103, the ROM 104, the HDD 105, the engine control unit 110, and the plotter unit 112 constitute an image processing apparatus 115a according to the present invention.

  The engine control unit 110 is a control unit that controls the image reading unit 111, the plotter unit 112, and the image processing unit 113 in accordance with commands received from the CPU 102 via the system bus 109.

(Description of functional configuration of image processing apparatus)
Next, the functional configuration of the image processing apparatus 115a according to the first embodiment of the present invention will be described with reference to FIG. FIG. 2 is a functional block diagram illustrating a functional configuration of the image processing apparatus 115a according to the first embodiment.

  The image processing apparatus 115a includes a drawing instruction acquisition unit 1, a rendering unit 2, a deviation amount acquisition unit 3, a geometric correction parameter setting unit 4, a geometric correction unit 5a, a pseudo gradation processing unit 6, and a printer output unit 7a.

  Of the image processing apparatus 115a, the printer output unit 7a corresponds to the plotter unit 112 shown in FIG. In the image processing apparatus 115a, each unit other than the printer output unit 7a is realized by the controller 101, the engine control unit 110, and the image processing unit 113 illustrated in FIG.

  The drawing instruction acquisition unit 1 acquires an input image I1 (see FIG. 3) described in a page description language. In addition, an instruction reflecting the results selected by the user, such as an instruction for single-sided printing or double-sided printing, an instruction on whether or not to draw a register mark for cutting on the corner of the output paper, is also acquired. A registration mark, also called a registration mark, is a mark that is printed on the left and right corners of the bottom of a block for creating printed material, for cutting the printed material into finished sizes, or for registering multicolored prints. It is.

  The rendering unit 2 interprets the page description language acquired by the drawing instruction acquisition unit 1, and converts the input image I1 into a bitmap image having, for example, a gradation value of 8 bits for each color. At that time, object information such as characters, lines, graphics, and images included in the input image I1 is also interpreted and given to each pixel of the bitmap image.

  The deviation amount acquisition unit 3 is a deviation amount acquisition unit that measures and acquires how the coordinate points of the four corners change (or how much) when output from the printer without performing geometric correction processing described later. Therefore, register marks for measuring the deviation amount are printed at the four corners of the front and back surfaces of the output paper, and the respective coordinate points are measured. As the measurement, there are a method of automatically measuring with a sensor built in the apparatus, and a method of manually measuring what is printed on a recording medium with a ruler and inputting the result.

  The geometric correction parameter setting unit 4 is a geometric correction parameter setting unit that calculates a geometric correction parameter from the coordinate data acquired by the deviation amount acquisition unit 3. The geometric correction parameter is a parameter for the geometric correction unit 5a to perform geometric correction according to the shift amount on the input image I1. The amount of deviation is the amount of deviation of the four coordinate points on the front and back surfaces of the output paper.

  The geometric correction unit 5a is a geometric correction unit that performs geometric correction on the image (for example, a bitmap image) output from the rendering unit 2 in accordance with the shift amount by image processing. In other words, the geometric correction unit 5a applies the geometric correction parameter calculated by the geometric correction parameter setting unit 4 and performs geometric correction by projective transformation in anticipation of displacement and distortion that occur during output. Details will be described later. Further, the geometric correction unit 5a performs fluctuation addition described later.

  The pseudo gradation processing unit 6 performs screen processing on the geometrically corrected bitmap image, and binarizes white pixels and black pixels. The pseudo gradation processing unit 6 switches the screen to be applied according to the object information. That is, when the object is a character or a line, for example, a screen of about 300 lines is applied. Further, when the object is a graphic or an image, for example, a screen of about 200 lines is applied.

(Description of geometric correction for image distortion)
Next, geometric correction for image distortion in the present embodiment will be described with reference to FIG. FIG. 3A shows an example of the input image I1 with a broken line. As an example of image distortion that occurs when the input image I1 is output to the printer without geometric correction, an example of the output image I2 without geometric correction is shown. It is shown with a solid line. That is, according to the present embodiment, when the input image I1 is printed out without geometric correction, the input image I1 is deformed wider toward the bottom and narrower toward the top.

  Further, FIG. 3B shows a geometrically corrected image I3 that has been reversely corrected in advance in anticipation of the occurrence of image distortion by a solid line, and an output image I4 when the geometrically corrected image I3 is subjected to geometric correction. Is indicated by a broken line. In other words, the post-geometric correction image I3 is an image in which distortion is applied in advance so that the output image I4 has the same shape as the input image I1.

  For example, in the case of front / back displacement, the input image I1 is the front surface, the output image I2 without geometric correction is the back surface output image when the geometric correction is not performed, the geometrically corrected image I3 that has been reversely corrected in advance is the geometrically corrected image for the back surface, and the output The image I4 is an image obtained by outputting the geometrically corrected image I3 obtained by reverse correction. Here, it is assumed that distortion does not occur on the front surface even when output from a printer.

  The deviation amount acquisition unit 3 acquires the coordinate data of the four corners of the input image I1 and the coordinate data of the four corners of the output image I2 when there is no geometric correction. Then, the geometric correction parameter setting unit 4 calculates and sets a geometric correction parameter for generating the geometrically corrected image I3 by performing reverse correction in anticipation of image distortion occurring at the time of printer output.

(Description of detailed configuration of geometric correction unit)
Next, a detailed configuration of the geometric correction unit 5a will be described. FIG. 4 is a functional block diagram showing a detailed configuration of the geometric correction unit 5a included in the image processing apparatus 115a.

  As shown in FIG. 4, the geometric correction unit 5a includes a corresponding coordinate point calculation unit 51, a four-point extraction unit 52a, an interpolation calculation unit 53, and a fluctuation addition unit 54a.

  The corresponding coordinate point calculation unit 51 is an example of a corresponding coordinate point calculation unit. The corresponding coordinate point calculation unit 51 converts the coordinate points (X, Y) on the input image I1 corresponding to the coordinate points (x, y) on the geometrically corrected image I3 to geometric correction parameters h1, h2,. Calculate using h8. The coordinate point (X, Y) is calculated as a real value having a value after the decimal point.

  The four-point extraction unit 52a extracts four neighboring points surrounding the coordinate point (X, Y) based on the values of the integer parts of X and Y.

  The interpolation calculation unit 53 is an example of an interpolation calculation unit. The interpolation calculation unit 53 performs interpolation calculation on the pixel values of the four neighboring points surrounding the coordinate point (X, Y), and calculates the result of the interpolation calculation as the pixel value of the coordinate point (x, y).

  The fluctuation adding unit 54a performs a process of adding fluctuation to, for example, an 8-bit image input to the geometric correction unit 5a before performing the interpolation calculation.

(Description of the corresponding coordinate point calculation process)
Next, the corresponding coordinate point calculation process performed by the corresponding coordinate point calculation unit 51 will be described with reference to FIG. The corresponding coordinate point calculation unit 51 uses the two-dimensional projective transformation expressions shown in Expressions 1 and 2 to express the coordinate point (X, Y) on the input image I1 corresponding to the coordinate point (x, y) on the geometrically corrected image I3. , Y).

  In equations 1 and 2, h1, h2,..., H8 described as coefficients represent geometric correction parameters. The values of the geometric correction parameters h1, h2,..., H8 are determined by extracting at least four pairs of corresponding points between the image before geometric correction and the image after geometric correction. Specifically, at least four pairs of corresponding points extracted (the coordinate point (X, Y) on the input image I1 and the coordinate point (x, y) on the geometrically corrected image I3) are respectively ( Equations 1) and (Equation 2) are generated. Then, the values of the geometric correction parameters h1, h2,..., H8 are determined by solving simultaneous equations relating to the geometric correction parameters h1, h2,.

  Thereafter, the pixel value and object information of the coordinate point (X, Y) in the input image I1 are obtained by interpolation, and the pixel value and object information of the coordinate point (x, y) of the geometrically corrected image I3 are obtained. The geometric correction of the input image I1 is performed.

(Explanation of operation of interpolation calculation unit)
Next, the operation of the interpolation calculation unit 53 will be described with reference to FIG. First, in the four-point extraction unit 52a (FIG. 4), the coordinate point (X0, Y0) corresponding to the integer part of the coordinate point (X, Y) and the coordinate point (X0 + 1) adjacent to the coordinate point (X0, Y0) are displayed. , Y0), (X0, Y0 + 1), (X0 + 1, Y0 + 1), a total of four coordinate points, respectively.

The interpolation calculation unit 53 applies weighting factors wx (0 ≦ wx ≦ 1) and wy (0 ≦ wy ≦ 1) to the pixel values of the four coordinate points described above, and performs linear interpolation represented by Expression 3. The pixel value of the coordinate point (x, y) is calculated. Note that the pixel value of the coordinate point (α, β) is represented by I (α, β).
I (x, y)
= I (X, Y)
= I (X0, Y0) * (1-wx) * (1-wy) +
I (X0 + 1, Y0) * wx * (1-wy) +
I (X0, Y0 + 1) * (1-wx) * wy +
I (X0 + 1, Y0 + 1) * wx * wy (Formula 3)

(Explanation of fluctuation addition)
Next, the operation of the fluctuation adding unit 54a will be described. The fluctuation adding unit 54a calculates the coordinate point (X ′, Y ′) to which the fluctuation is added with respect to the coordinate point (X, Y) by the following expressions 4 and 5.
X ′ = X + F (Y% P) (Formula 4)
Y ′ = Y + F (X% P) (Formula 5)
Here, F () represents a fluctuation function of a period P pixel and an amplitude Q pixel. Y% P represents a remainder obtained by dividing Y by P, and X% P represents a remainder obtained by dividing X by P. The fluctuation function F () will be described later in detail.

  FIG. 7 is a diagram for explaining the function of the fluctuation adding unit 54a. As shown in FIG. 7, for example, the point R1 (X, Y) is converted into a point R1 ′ (X ′, Y) in the printing direction of the plotter unit 112 (FIG. 1), that is, the main scanning direction. Thus, vertical line fluctuation is added to the vertical line. This has the effect of shaking the vertical line. Further, the horizontal line fluctuation is added to the horizontal line by converting the point R2 (X, Y) to the point R2 ′ (X, Y ′), for example, with respect to the paper transport direction, that is, the sub-scanning direction. The This has the effect of shaking the horizontal line.

  The pixel value I (X ′, Y ′) of the coordinate point (X ′, Y ′) to which the fluctuation is added can be obtained by the interpolation calculation shown in Equation 3.

Next, a specific example of the fluctuation function F (n) will be described with reference to FIG. The fluctuation function F (n) can be generated using a trigonometric function of sin or cos, for example. FIG. 8 shows an example in which the fluctuation function F (n) is generated from the cos function. The fluctuation function F (n) generated at this time is expressed by Expression 6.
F (n) = Q cos (2πn / P) (n = 1, 2, 3,...) (Formula 6)

  In FIG. 8, the horizontal axis represents n, and the vertical axis represents the fluctuation function F (n). The value of the fluctuation function F (n) may be calculated each time and added to the coordinate point (X, Y). The value of the fluctuation function F (n) calculated in advance is used as a table, for example, the HDD 105 (FIG. 1). ) And the value read from the table may be added to the coordinate point (X, Y).

(Explanation of the effect of adding fluctuation)
Next, the effect of the above-described fluctuation addition will be described with reference to FIG. FIG. 9 is a diagram illustrating the effect of adding fluctuation based on an example.

  When the input image I1 includes a binary pattern, the addition of fluctuation has the effect of suppressing the occurrence of moire. Hereinafter, a case where a halftone dot pattern is used as a binary pattern will be described as an example.

  When the magnification correction is performed on the halftone dot pattern of the input image I1, the pixel value of the white dot and the pixel value of the black dot are averaged by the interpolation calculation. A gray pixel area is generated in which the pixel values of white dots are averaged. Further, in the case where fluctuation is not added to the input image I1 shown in FIG. 9A, as shown in FIG. 9B, an area where the amount of gray pixels is large and an area where the amount of gray pixels is small are , Appear alternately. As shown in FIG. 9C, an area where the gray pixel generation amount is large and an area where the gray pixel amount is small, as shown in FIG. 9C, are an area where the dot shape is largely broken and an area where the dot shape is little broken. , Is replaced. Due to the writing characteristics of the plotter unit 112 (FIG. 1), it is difficult to output an area where the dot shape collapse is large and an area where the dot shape collapse is small so that the same density appears on the output paper. Therefore, moire occurs.

  By adding the fluctuation, gray pixels are scattered and generated throughout the halftone dot pattern, so that the deviation in the appearance frequency of gray pixels due to the area is reduced as shown in FIG. Therefore, as shown in FIG. 9 (e), even after the pseudo gradation processing, the area deviation of the dot shape collapse is reduced, and moire is less likely to occur.

  As can be seen from FIG. 9, it is effective to add vertical line fluctuation in order to suppress the occurrence of moire by correcting the magnification in the horizontal direction (X direction, main scanning direction). On the other hand, it is effective to add horizontal line fluctuation in order to suppress moire by magnification correction in the vertical direction (Y direction, sub-scanning direction).

  Even if fluctuations are added to the solid area (flat part) included in the input image I1, the density distribution inside the solid area does not change at all. That is, it is the same as the state where no fluctuation is added. Therefore, moire does not occur due to the interference between the fluctuation period and the pseudo gradation processing screen period in the solid area.

  The fluctuation period P and the amplitude Q shown in FIG. 8 may be determined in consideration of the point that interference with the binary pattern included in the input image I1 is not noticeable. However, if it can be visually recognized on the output image (particularly, a character part other than the binary pattern part), it becomes a side effect.

(Description of processing flow of the first embodiment)
Hereinafter, the flow of processing performed by the image processing apparatus 115a will be described with reference to FIG. FIG. 10 is a flowchart showing the flow of processing performed by the image processing apparatus 115a.

  The drawing instruction acquisition unit 1 acquires the input image I1 and the drawing instruction (step S10).

  The rendering unit 2 converts the input image I1 into, for example, a bitmap image having a gradation value of 8 bits for each color (step S12).

  The deviation amount acquisition unit 3 measures and acquires the deviation amount generated by the printer output (step S14).

  The geometric correction parameter setting unit 4 calculates the values of the geometric correction parameters h1, h2,..., H8 (Formula 1 and Formula 2) based on the coordinate data acquired by the deviation amount acquisition unit 3 (Step S16).

  The geometric correction unit 5a performs geometric correction on the image (bitmap image) output from the rendering unit 2 according to the shift amount by image processing (step S18). The detailed flow of processing performed by the geometric correction unit 5a is shown in FIG.

  The pseudo gradation processing unit 6 performs pseudo gradation processing on the geometrically corrected bitmap image, and binarizes white pixels and black pixels (step S20).

  The printer output unit 7a forms an image on a sheet and outputs it to the printer (step S22).

(Description of the flow of processing performed by the geometric correction unit)
Next, the flow of geometric correction performed by the geometric correction unit 5a will be described with reference to FIG. FIG. 11 is a flowchart showing a flow of processing performed by the geometric correction unit 5a.

  The fluctuation adding unit 54a adds fluctuation to the bitmap image (step S30).

  The corresponding coordinate point calculation unit 51 calculates the coordinate point (X, Y) on the input image I1 corresponding to the coordinate point (x, y) on the geometrically corrected image I3 (step S32).

  The four-point extraction unit 52a calculates four neighboring points surrounding the coordinate point (X, Y) (step S34).

  The interpolation calculation unit 53 performs the interpolation calculation on the pixel values of the four neighboring points surrounding the coordinate point (X, Y), and the result of the interpolation calculation is the pixel value I (x, y) of the coordinate point (x, y). (Step S36). Thereafter, the process returns to the main routine (FIG. 10).

(Description of Modification of First Embodiment)
Next, an image forming apparatus 100b, which is a modification of the first embodiment of the image processing apparatus of the present invention, will be described. The image forming apparatus 100b has substantially the same configuration as the image forming apparatus 100a described in the first embodiment, and includes an image processing apparatus 115b instead of the image processing apparatus 115a provided in the first embodiment. . The configuration of the image processing device 115b is substantially the same as the configuration of the image processing device 115a (FIG. 2), but only the configuration of the geometric correction unit 5a is different.

  FIG. 12 is a functional block diagram illustrating a detailed configuration of the geometric correction unit 5b included in the image processing apparatus 115b included in the image forming apparatus 100b which is a modified example of the first embodiment. The geometric correction unit 5b includes a corresponding coordinate point calculation unit 51, a four-point extraction unit 52b, an interpolation calculation unit 53, and a fluctuation addition unit 54b.

  Unlike the first embodiment, the fluctuation adding unit 54b adds fluctuation to the coordinate point data instead of the bitmap image. The addition of fluctuation is performed using Expressions 4 and 5 as in the first embodiment. Here, the fluctuation adding method performed by the fluctuation adding unit 54b will be described with reference to FIG. As shown in FIG. 13, the fluctuation adding unit 54b calculates coordinate points (X ′, Y ′) obtained by adding fluctuations to the coordinate points (X, Y). Then, the four-point extraction unit 52b extracts the coordinates of the four neighboring points P1, P2, P3, and P4 surrounding the coordinate point (X ′, Y ′) to which the fluctuation is added from the input image I1. Thereafter, the interpolation calculation unit 53 obtains the pixel value I (X ′, Y ′) of the coordinate point (X ′, Y ′) by interpolation calculation of the pixel values of the four points P1, P2, P3, and P4.

  Since the geometric correction unit 5b adds fluctuation to the coordinate point data, not the coordinate point on the input image I1, but the coordinate position for obtaining the pixel value by the interpolation calculation is shaken. However, from a relative viewpoint, it can be considered that the coordinate point on the input image I1 is fluctuating with respect to the coordinate position for which the pixel value is obtained by the interpolation calculation. Therefore, as an output value from the geometric correction unit 5b, Other than the quantization error described later, there is no difference from the first embodiment.

  In other words, the geometric correction unit 5a according to the first embodiment adds the fluctuation to the bitmap image output from the rendering unit 2, so that the interpolation calculation is performed in both the fluctuation addition unit 54a and the interpolation calculation unit 53. Accordingly, the quantization error is inevitably increased. On the other hand, since the geometric correction unit 5b in the modification of the first embodiment adds fluctuation to the coordinate point data, the interpolation calculation is performed only once in the interpolation calculation unit 53, and the quantization error does not increase. It is different in the configuration.

(Description of Second Embodiment)
Next, an image forming apparatus 100c according to a second embodiment of the image processing apparatus of the present invention will be described. The image forming apparatus 100c according to the second embodiment includes an image processing apparatus 115c instead of the image processing apparatus 115a with respect to the image forming apparatus 100a described in the first embodiment. FIG. 14 is a functional block diagram illustrating a functional configuration of the image processing apparatus 115c according to the second embodiment. Hereinafter, the configuration of the image processing apparatus 115c will be described with reference to FIG.

  As shown in FIG. 14, the image processing apparatus 115c includes a drawing instruction acquisition unit 1, a rendering unit 2, a deviation amount acquisition unit 3, a geometric correction parameter setting unit 4, a geometric correction unit 5a, and pseudo gradation processing. Section 6 and a printer output section 7b. The printer output unit 7b corresponds to the plotter unit 112 in FIG. 1 and includes a write timing control unit 8 serving as a write timing control unit.

  The image processing apparatus 115 c further includes a correction mode determination unit 9, a correction amount distribution unit 10, and a write control parameter setting unit 11. Each unit other than the printer output unit 7b of the image processing apparatus 115c is realized by the controller 101, the engine control unit 110, and the image processing unit 113 shown in FIG.

  In addition to acquiring the input image I1 described in the page description language, the drawing instruction acquisition unit 1 includes an instruction for single-sided printing or double-sided printing, an instruction for drawing a registration mark for cutting on the corner of the output paper, etc. Instructions reflecting the results of various selections made by the user are also acquired. A registration mark is a mark that is attached to the left and right corners of the bottom of a printing plate for the purpose of registering a multicolored printing position and the position for cutting the printed material into a finished size. Also say.

  The geometric correction parameter setting unit 4 is a geometric correction parameter setting unit that calculates a geometric correction parameter from the coordinate data acquired by the deviation amount acquisition unit 3 and distributed by the correction amount distribution unit 10.

  The correction mode determination unit 9 is a correction mode determination unit that selects and determines a correction mode according to at least the shift amount acquired by the shift amount acquisition unit 3.

  The correction mode determination unit 9 selects and determines one of the first correction mode and the second correction mode when the input image is output to the printer according to the shift amount acquired by the shift amount acquisition unit 3. . The first correction mode is a correction mode in which geometric correction by the geometric correction unit 5a is performed in the main scanning direction and the sub-scanning direction. On the other hand, the second correction mode is a correction mode in which geometric correction by the geometric correction unit 5a is performed in the main scanning direction and geometric correction by the writing timing control unit 8 is performed in the sub-scanning direction.

  The correction mode determination unit 9 further selects the correction mode based on the instruction information from the drawing instruction acquisition unit 1, such as single-sided printing or double-sided printing, and instruction information such as whether to draw a register mark for cutting on the corner of the output paper. You may decide.

  For example, when the correction function required for the deviation correction is geometric correction other than registration correction, magnification correction, and skew correction (for example, trapezoid correction), the first correction mode is selected with emphasis on the function. Even when the user gives an instruction to draw a register mark for cutting at the corner of the sheet, the first correction mode is selected with an emphasis on positional accuracy. Even when double-sided printing is selected by the user, it is desirable to select the first correction mode with emphasis on positional accuracy.

  On the other hand, the correction function required for the correction of misalignment is one of registration correction, magnification correction, skew correction, or a geometric correction based on a combination thereof, and there is no instruction for drawing a register mark for cutting, and single-sided printing. Selects the second correction mode. Even in the second correction mode, it can be handled as a correction function, and in a case where the position accuracy is relatively unimportant, it is desirable to select the second correction mode in which there is no fear of occurrence of moire.

  The write control parameter setting unit 11 calculates a write control parameter for the write timing control unit 8 to perform geometric correction corresponding to the shift amount on the input image based on the shift amount acquired by the shift amount acquisition unit 3. Write control parameter setting means.

  The correction amount distribution unit 10 is correction amount distribution means for transferring the front and back coordinates obtained by the deviation amount acquisition unit 3 to the geometric correction parameter setting unit 4 and the writing control parameter setting unit 11.

  When the first correction mode is selected by the correction mode determination unit 9, geometric correction by the geometric correction unit 5a is performed in both the main scanning direction (the left-right direction of the input image) and the sub-scanning direction (the vertical direction of the input image). Process. That is, the correction amount distribution unit 10 performs the geometric correction parameter setting unit 4 and the write control parameter setting unit 11 so that the coordinate data acquired by the deviation amount acquisition unit 3 is corrected by the geometric correction unit 5a in any direction. Hand over to each of the.

  On the other hand, when the second correction mode is selected by the correction mode determination unit 9, the geometric correction processing by the writing timing control unit 8 is performed in the main scanning direction, and the geometric correction unit 5a is performed in the sub scanning direction. The geometric correction process is performed. That is, the correction amount distribution unit 10 applies the coordinate data acquired by the deviation amount acquisition unit 3 to each of the geometric correction parameter setting unit 4 and the write control parameter setting unit 11 so that the geometric correction process is performed. Deliver.

  The writing timing control unit 8 of the printer output unit 7b applies the writing start position in the main scanning direction and the coordinate data distributed from the correction amount distribution unit 10 according to the parameters calculated by the writing control parameter setting unit 11. Adjust the write clock cycle. This corresponds to geometric correction by electric control. Note that registration correction and magnification correction by adjusting the writing start position and writing clock cycle in the main scanning direction are existing image correction techniques.

  When the first correction mode is selected by the correction mode determination unit 9, both the vertical line fluctuation and the horizontal line fluctuation shown in FIG. 7 are added, as in the first embodiment.

  On the other hand, when the second correction mode is selected by the correction mode determination unit 9, only vertical line fluctuation is added as shown in FIG. It is geometric correction by the geometric correction unit 5a that is involved in moire, not geometric correction by the write timing control unit 8. Since geometric correction by the geometric correction unit 5a in the second correction mode is performed only in the main scanning direction, only vertical line fluctuation that has a moire suppressing effect with respect to magnification correction in the main scanning direction is given by Expression 4. Good.

  In the second correction mode, contrary to the above, geometric correction may be performed in the main scanning direction, and geometric correction by writing timing control may be performed in the sub scanning direction. In that case, when the second correction mode is selected by the correction mode determination unit 9, only the horizontal line fluctuation may be given by Equation 5.

(Explanation of the processing flow of the second embodiment)
Hereinafter, with reference to FIG. 16, regarding the flow of processing performed by the image processing apparatus 115 c, when the correction mode determination unit 9 selects the second correction mode, the geometry by the write timing control unit 8 in the main scanning direction. A case where correction processing is performed and geometric correction processing by the geometric correction unit 5a is performed in the sub-scanning direction will be described as an example. FIG. 16 is a flowchart showing the flow of processing performed by the image processing apparatus 115c.

  The drawing instruction acquisition unit 1 acquires the input image I1 and the drawing instruction (step S40).

  The rendering unit 2 converts the input image I1 into, for example, a bitmap image having a gradation value of 8 bits for each color (step S42).

  The deviation amount acquisition unit 3 measures and acquires the deviation amount generated by the printer output (step S44).

  The geometric correction parameter setting unit 4 calculates a geometric correction parameter based on the coordinate data acquired by the deviation amount acquisition unit 3 (step S46).

  The correction mode determination unit 9 selects a correction mode (step S48).

  The controller 101 (FIG. 1) determines whether the selected correction mode is the first correction mode (step S50). When the first correction mode is selected (step S50; Yes), the process proceeds to step S52, and otherwise (step S50; No), the process proceeds to step S56.

  The geometric correction unit 5a performs geometric correction on the image (bitmap image) output from the rendering unit 2 in accordance with the shift amount by image processing in both the main scanning direction and the sub-scanning direction (step S52). The detailed flow of processing performed by the geometric correction unit 5a is as described in the first embodiment (FIG. 11).

  The pseudo gradation processing unit 6 performs pseudo gradation processing on the geometrically corrected bitmap image, and binarizes white pixels and black pixels (step S53).

  The printer output unit 7b forms an image on the paper and outputs it to the printer (step S54). Thereafter, the process of FIG. 16 is terminated.

  When the second correction mode is selected in step S50 (step S50; No), the geometric correction unit 5a performs image processing only in the sub-scanning direction on the image (bitmap image) output from the rendering unit 2. Geometric correction corresponding to the amount of deviation is performed by the processing (step S56). The flow of processing performed by the geometric correction unit 5a is as described in the first embodiment (FIG. 11).

  The pseudo gradation processing unit 6 performs pseudo gradation processing on the geometrically corrected bitmap image, and binarizes white pixels and black pixels (step S57).

  While the writing timing control unit 8 performs geometric correction by writing timing control in the main scanning direction, the printer output unit 7b forms an image on paper and performs printer output (step S58). Thereafter, the process of FIG. 16 is terminated.

  As described above, according to the image processing apparatus 115a (115b) according to the first embodiment, the deviation of the coordinate point when the deviation amount acquisition unit 3 (deviation amount acquisition unit) outputs the input image I1 to the printer. The amount is acquired, and either the geometric correction unit 5a or the geometric correction unit 5b (geometric correction unit) performs geometric correction according to the shift amount on the input image I1. At this time, the geometric correction unit 5a performs geometric correction after the fluctuation adding unit 54a adds fluctuations to the coordinate points of the input image I1. Further, the geometric correction unit 5b adds the fluctuation to the geometrically corrected coordinate point by the fluctuation addition unit 54b after geometrically correcting the coordinate point of the input image I1. Then, the interpolation calculation unit 53 calculates the pixel value of the coordinate point after geometric correction by correction calculation, and the pseudo gradation processing unit 6 (pseudo gradation processing means) applies the geometrically corrected input image I1. Thus, pseudo gradation processing is performed in which the density gradation is represented by pseudo gradation. Therefore, since the pseudo gradation processing is performed on the image after the image deformation accompanied by the addition of fluctuations, even if the input image I1 includes a binary pattern such as shading, the printer Generation of moire in the output can be prevented.

  In particular, according to the image processing apparatus 115a according to the first embodiment, the deviation amount acquisition unit 3 (deviation amount acquisition unit) acquires the deviation amount of the coordinate point when the input image I1 is output to the printer, The geometric correction unit 5a (geometric correction means) performs geometric correction corresponding to the shift amount on the input image I1. At this time, the geometric correction unit 5a adds the fluctuation to the coordinate value of the coordinate point after the geometric correction by the fluctuation addition unit 54a (fluctuation addition means) with respect to the coordinate point of the input image I1, and then the interpolation calculation unit 53. (Interpolation calculation means) calculates by interpolating the pixel value of the coordinate point after geometric correction. Therefore, by a simple process of adding fluctuation, even when the input image I1 includes a binary pattern such as shading, occurrence of moire in the printer output can be prevented.

  Further, according to the image processing apparatus 115a according to the first embodiment, the fluctuation adding unit 54a (fluctuation adding means) uses a trigonometric function to calculate a fluctuation function F (n) representing the magnitude of fluctuation to be added. Generate. Alternatively, the magnitude of fluctuation to be added is calculated using the stored value of the table storing the data of the generated fluctuation function F (n). Therefore, it is possible to easily calculate the magnitude of fluctuation with an existing function.

  In particular, according to the image processing apparatus 115b according to the modification of the first embodiment, the deviation amount of the coordinate point when the deviation amount acquisition unit 3 (deviation amount acquisition unit) outputs the input image I1 to the printer. And the geometric correction unit 5b (geometric correction means) performs geometric correction according to the shift amount on the input image I1. At this time, the geometric correction unit 5b adds the fluctuation to the coordinate point after the geometric correction by the fluctuation addition unit 54b (fluctuation addition means), and then calculates the pixel value of the coordinate point after the geometric correction to which the fluctuation is added. The interpolation calculation unit 53 (interpolation calculation means) calculates the pixel value of the corresponding coordinate point of the input image I1 by performing interpolation calculation. Therefore, since the interpolation calculation only needs to be performed once in the interpolation calculation unit 53, the quantization error caused by the calculation is compared with a case where fluctuation is added to, for example, a bitmap image generated from the input image I1. Can be kept small. That is, geometric correction can be performed with higher accuracy.

  According to the image processing apparatus 115c according to the second embodiment, when the second correction mode is selected by the correction mode determination unit 9 (correction mode determination unit), the fluctuation addition unit 54a (fluctuation addition unit) ) Adds vertical line fluctuations that are fluctuations in the main scanning direction, and does not add horizontal line fluctuations that are fluctuations in the sub-scanning direction. Therefore, it has a moire suppression effect for magnification correction in the main scanning direction. Furthermore, by suppressing the addition of fluctuations to the minimum necessary, occurrence of unnecessary side effects such as an increase in fluctuations in the character part can be suppressed.

  Further, according to the image processing apparatus 115c according to the second embodiment, when the second correction mode is selected by the correction mode determination unit 9 (correction mode determination unit), the fluctuation addition unit 54a (fluctuation addition unit) ) Adds a horizontal line fluctuation that is a fluctuation in the sub-scanning direction, and does not add a vertical line fluctuation that is a fluctuation in the main scanning direction. Therefore, it has a moire suppressing effect in the sub-scanning direction. Furthermore, by suppressing the addition of fluctuations to the minimum necessary, occurrence of unnecessary side effects such as an increase in fluctuations in the character part can be suppressed.

  Although the embodiment has been described above, the specific configuration of each part, the content of processing, and the like are not limited to those described in each embodiment.

  For example, instead of causing the CPU 102 to operate according to a program, the image processing apparatuses 115a, 115b, and 115c implement a dedicated ASIC (Application Specific Integrated Circuit) having the same calculation function and control function that the program executes, It may be operated in hardware.

3. Deviation amount acquisition unit (deviation amount acquisition means)
5a, 5b Geometric correction unit (geometric correction means)
6 Pseudo gradation processing unit (pseudo gradation processing means)
8 Write timing controller (write timing control means)
9 Correction mode determination unit (correction mode determination means)
51 Corresponding coordinate point calculation unit (corresponding coordinate point calculation means)
53 Interpolation calculation unit (interpolation calculation means)
54a, 54b Fluctuation addition part (fluctuation addition means)
100a, 100b, 100c Image forming apparatus 115a, 115b, 115c Image processing apparatus

Japanese Patent No. 4003803

Claims (8)

A deviation amount acquisition means for acquiring a deviation amount of an input image generated at the time of printer output;
Geometric correction means for performing geometric correction according to the shift amount on the input image;
Pseudo gradation processing means for performing pseudo gradation processing for expressing the density gradation of the input image in a pseudo gradation with respect to the geometrically corrected input image,
The geometric correction means, after adding fluctuation to the coordinate point of the input image or the coordinate point after the geometric correction, calculates the pixel value of the coordinate point after the geometric correction by interpolation calculation,
An image processing apparatus. The geometric correction means includes
Corresponding coordinate point calculating means for calculating a corresponding coordinate point of the input image corresponding to a coordinate point after geometric correction corresponding to the shift amount in the input image
Fluctuation adding means for adding fluctuation to the coordinate points of the input image;
Interpolation calculation means for calculating the pixel value of the coordinate point after the geometric correction by interpolating the pixel value of the corresponding coordinate point of the input image to which the fluctuation is added. The image processing apparatus according to 1. The geometric correction means includes
Corresponding coordinate point calculating means for calculating a corresponding coordinate point of the input image corresponding to a coordinate point after geometric correction corresponding to the shift amount in the input image
Fluctuation adding means for adding fluctuation to the coordinate point after the geometric correction;
Interpolation calculation means for calculating a pixel value of the coordinate point after the geometric correction to which the fluctuation is added by calculating a pixel value of a corresponding coordinate point of the input image. The image processing apparatus according to 1. The fluctuation adding means generates the fluctuation using a trigonometric function.
Alternatively, the fluctuation is generated using a stored value of a table storing data representing the magnitude of the generated fluctuation.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. Write timing control means for performing geometric correction according to the shift amount by controlling the write timing for the input image;
In accordance with the deviation amount acquired by the deviation amount acquisition means, when the input image is output to the printer, a geometric correction is performed by the geometric correction means in the main scanning direction of the input image and the sub-scanning direction of the input image. And a second correction mode in which geometric correction by the geometric correction unit is performed for the main scanning direction and geometric correction by the writing timing control unit is performed for the sub-scanning direction. Correction mode determining means for selecting one of them, and
When the second correction mode is selected, the fluctuation adding means adds a vertical line fluctuation that is a fluctuation with respect to the main scanning direction, and does not add a horizontal line fluctuation that is a fluctuation with respect to the sub-scanning direction.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. Write timing control means for performing geometric correction according to the shift amount by controlling the write timing for the input image;
In accordance with the deviation amount acquired by the deviation amount acquisition means, when the input image is output to the printer, a geometric correction is performed by the geometric correction means in the main scanning direction of the input image and the sub-scanning direction of the input image. And a second correction mode in which geometric correction by the geometric correction unit is performed for the sub-scanning direction and geometric correction by the writing timing control unit is performed for the main scanning direction. Correction mode determining means for selecting one of them, and
When the second correction mode is selected, the fluctuation adding means adds horizontal line fluctuation that is fluctuation in the sub-scanning direction, and does not add vertical line fluctuation that is fluctuation in the main scanning direction.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. A deviation amount acquisition step for acquiring a deviation amount of the input image generated at the time of printer output;
A geometric correction step for performing geometric correction according to the shift amount on the input image;
A pseudo gradation processing step for performing a pseudo gradation process for expressing the density gradation of the input image as a pseudo gradation for the geometrically corrected input image, and
In the geometric correction step, after adding fluctuation to the coordinate point of the input image or the coordinate point geometrically corrected by the geometric correction step, the pixel value of the geometrically corrected coordinate point is calculated by interpolation calculation. ,
An image processing method. Computer
A deviation amount acquisition means for acquiring a deviation amount of an input image generated at the time of printer output;
Geometric correction means for performing geometric correction according to the shift amount on the input image;
The geometrically corrected input image functions as pseudo gradation processing means for performing pseudo gradation processing for expressing the density gradation of the input image as a pseudo gradation,
The geometric correction unit adds fluctuations to the coordinate point of the input image or the coordinate point geometrically corrected by the geometric correction unit, and then calculates the pixel value of the geometrically corrected coordinate point by interpolation calculation. ,
A program characterized by that.

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