JP2009065559A - Image processing apparatus, image processing method, and storage medium with image processing program stored thereon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus capable of performing such color reproduction that colors are matched even if an observation light source is changed, by realizing a color reproducing system capable of approximately matching an input document and the quantity of color material to be blended. <P>SOLUTION: A color correcting section 13 is adapted to perform processing for converting multi-band data on which spatial filter processing has been performed by a filter processing section 12, into chrominance signals for a color image output device 3. In the color correcting section 13, the quantity of color material in a document is estimated from chrominance signals read in a multi-band, thereby achieving color reproduction faithful to the document. Since CMYK signals output from the color correcting section 13 have luminance linear characteristics, in an output gradation correcting section 14, gamma correction is applied in such a way as to meet characteristics of an output device, and a halftone processing section 15 converts a multi-level image signal on which gamma correction has been performed, into data of such a gradation level as to be stably output by the output device. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a color image processing technique for multiband information.

In recent years, digitalization of OA equipment has rapidly progressed, and the demand for color image output has increased, so that electrophotographic and ink jet digital color copying machines have become widespread.
There are various printing methods for input images (originals) read by an input device such as a scanner of the above digital color copying machine, and the same color appears to the human eye due to the layer structure of the image surface and the composition of color materials In some cases, however, a scanner or the like may be read as image data of different colors. This phenomenon is caused by the collapse of “metamerism (conditional color)”. “Metamerism” refers to a state in which the same color appears even though the spectral characteristics of the object are different. A state in which two originals having different spectral reflectances look the same in human eyes and a state in which they look the same with sensors having different spectral sensitivities are called “metamerism”. This phenomenon is also applied to output devices such as scanners and printers, and these output devices realize color matching by realizing metamerism.
However, colors that look the same to the human eye may be reproduced as different colors (color shift) when these colors are read by a scanner and the image data is output by an output device. In this case, metamerism is established in the human eye, but metamerism is not established in the scanner sensor.
When such a phenomenon occurs, the output image is reproduced in a color different from that of the input image, resulting in image quality degradation. Therefore, various techniques have been proposed to solve this problem.
JP 2002-9481 A JP 2005-39374 A JP 2001-86354 A Japanese Patent Laid-Open No. 7-322082

In the image processing method described in Patent Document 1, a document is read under at least two different reading conditions, and for a target pixel determined to be a predetermined color under one reading condition (first reading), It is determined whether or not the color changes to a predetermined color when reading is performed under the other reading condition (second reading). Then, for the pixels that have changed to a predetermined color during the second reading, the number of pixels is counted and compared with a certain value, and the document is determined (printing paper, generation document, inkjet document), and the document determination result is obtained. Based on this, a color correction coefficient is set. The different reading conditions in the above two readings are performed by (1) using a scanner with different CD characteristics, (2) using an infrared cut filter, (3) switching the light source, and the like. Yes.
In the image processing apparatus described in Patent Document 2, image data is corrected based on a plurality of image data read under different reading conditions. In this method, since the difference between the image data with different reading conditions is analyzed and corrected, it can be converted with high accuracy according to the metamerism characteristics.
In the image processing method described in Patent Document 3, a subject is photographed using a multiband camera that photographs through, for example, eight types of filters having different transmission wavelength ranges, and a plurality of spectral images that express color information of the subject for each wavelength. And the spectral reflectance of the subject is estimated from the spectrum image. Based on the estimated spectral reflectance, an image having the same appearance as when taken under a desired light source is acquired. If the above technique is used, a high-accuracy image can be acquired without impairing the color reproducibility of the subject even when shooting a subject using many colors such as a picture.
In the color separation device described in Patent Document 4, a method of converting a spectral reflectance into a CMYK signal using a neural network has been proposed.

By the way, in the method described in Patent Document 1, a document type is estimated based on color separation data read under different reading conditions, and color correction is performed according to the type of document such as photographic paper, generation document, inkjet document, or the like. . Therefore, it is possible to reduce color misregistration only for photographic paper, generation originals, and ink jet originals of predetermined color materials set in advance.
On the other hand, the image processing apparatus described in Patent Document 2 detects the presence or absence of color misregistration from color separation data read by a different light source, as in the technique described in Patent Document 1, and if there is color misregistration, Color correction is performed using the separation signal or its difference value. In this way, color correction is performed without limiting the document type. However, since the color signal is once converted into three signals before being converted into the color signal for the output device, the information regarding the blending amount of the color material of the document is lost.
For example, in the case of a printed document, there are two types of gray reproduction methods, CompoJet Black and Skeleton Black, but since it is not known which is reproduced with the above method, print output is performed with a different black ratio from the original Will end up doing. To deal with this problem, the area separation process is performed to separate the character area / picture area. However, a complicated process is required to perform high-precision separation, and separation errors are conspicuous. there were.

  In the method of estimating the spectral reflectance using the multi-band camera (CCD) of Patent Document 3, although the color shift hardly occurs, the calculation amount for estimating the spectral reflectance increases. For this reason, there is a demand for higher performance of the image processing apparatus, and there is a problem that the image processing apparatus becomes very expensive. Further, the blending amounts of the color materials of the input document and the output image are the same in that they are not taken into consideration at all, and there is a problem that the colors are not matched when the observation light source is changed.

Accordingly, the first object of the present invention is to realize a color reproduction method that allows the input document and the amount of color material to substantially match with a simple method, so that the colors match even when the observation light source changes. An image processing apparatus, an image processing method, and a storage medium storing an image processing program for performing such color reproduction.
The second object of the present invention is to realize a color reproduction system that allows the input document and the amount of color material to substantially match each other by a simple method in an image processing apparatus having a function of transmitting document reading data to the outside. Thus, it is an object of the present invention to provide an image processing apparatus that performs color reproduction so that colors match even when the observation light source changes.
A third object of the present invention is to provide an image processing apparatus and an image processing apparatus that perform high-quality reproduction for each area of a document by using a region separation unit for performing high-quality reproduction according to the color material color mixture degree of the document. To provide a storage medium storing a processing method and an image processing program.

According to the first aspect of the present invention, the image processing apparatus reads a document optically with four or more types of color separation characteristics to generate a color separation signal, and based on the color separation signal from the reading means, Color material amount estimating means for estimating the color material amount of the document, color correction means for performing color correction using the color material amount estimated by the color material amount estimating means and the color separation signal generated by the reading means, With the above, the first object is achieved.
In the invention according to claim 2, the image processing apparatus reads a document optically with four or more kinds of color separation characteristics to generate a color separation signal, and based on the color separation signal from the reading means, Color material amount estimating means for estimating the color material amount of the original, standard color signal generating means for generating a device independent color signal based on the color separation signal from the reading means, and the standard color signal generating means The second object is achieved by including a color correction unit that performs color correction based on the generated device-independent color signal and the color material amount estimated by the color material amount estimation unit.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the color material for which the color material amount estimation means estimates the color material amount is black ink.
According to a fourth aspect of the present invention, in the first, second, or third aspect of the invention, the reading unit includes an illumination light source having a dominant wavelength in a range of at least 500 nm ± 20 nm. To do.
In the invention according to claim 5, the image processing apparatus reads a document optically with four or more types of color separation characteristics to generate a color separation signal, and based on the color separation signal from the reading means, Color material amount estimating means for estimating the color material amount of the original, area dividing means for performing area division using the color material amount estimated by the color material amount estimating means, and color separation signals from the reading means are subjected to image processing Image processing means for generating a color signal for the output device, and the image processing means achieves the third object by performing image processing based on area division by the area division means. To do.
According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the region dividing unit includes a determining unit that determines a single color region.

In an invention according to claim 7, in an image processing apparatus comprising: a reading unit that optically reads a document with four or more types of color separation characteristics to generate a color separation signal; and a color correction unit that performs color correction. A first step in which the reading unit optically reads the document with four or more types of color separation characteristics to generate a color separation signal; and a color material of the document based on the color separation signal generated in the first step A second step of estimating the amount, and a third step in which the color correcting unit performs color correction using the color material amount estimated in the second step and the color separation signal generated in the first step. The first object is achieved by the image processing method provided.
According to an eighth aspect of the present invention, there is provided a reading means for optically reading a document with four or more types of color separation characteristics to generate a color separation signal, and image processing the color separation signal from the reading means for an output device. A first step of generating a color separation signal by optically reading a document with four or more kinds of color separation characteristics; and an image processing device comprising: an image processing unit for generating a color signal; A second step of estimating the color material amount of the document based on the color separation signal generated in the first step, and a third step of performing region division using the color material amount estimated in the second step; And a fourth step in which the image processing means performs image processing on the color separation signal generated in the first step to generate a color signal for the output device, and the color for the output device in the fourth step. When generating the signal, the third step It was based on the area division, the image processing method for performing image processing, to achieve the third object.
According to the ninth aspect of the present invention, a first function for optically reading a document with four or more types of color separation characteristics to generate a color separation signal, and a document based on the color separation signal generated by the first function A second function for estimating the amount of the color material, and a third function for performing color correction using the color material amount estimated by the second function and the color separation signal generated by the first function The first object is achieved by a storage medium storing a computer-readable image processing program for realizing the above.
According to the tenth aspect of the present invention, a first function for optically reading a document with four or more types of color separation characteristics to generate a color separation signal, and a document based on the color separation signal generated by the first function A second function for estimating the color material amount, a third function for performing region division using the color material amount estimated by the second function, and a color separation signal generated by the first function are subjected to image processing. And a fourth function for generating a color signal for the output device, and when the color signal for the output device is generated by the fourth function, image processing is performed based on the area division performed by the third function. The third object is achieved by a storage medium storing a computer-readable image processing program for causing a computer to perform the above.

According to the first, seventh and ninth aspects of the invention, color reproduction can be performed in accordance with the color mixture degree of the color material of the document.
According to the second aspect of the invention, it is possible to perform faithful color reproduction in which color misregistration is not conspicuous in accordance with the color mixture degree of the color material of the document.
According to the third aspect of the invention, since the amount of the color material of the black ink is estimated, black characters and black halftone dots can be reproduced with a single black color, and ink consumption can be reduced.
In the invention described in claim 4, since the reading means including the illumination light source having the main wavelength in the range of at least 500 nm ± 20 nm is used, the single color black and the mixed color black can be separated with high accuracy.
According to the fifth, eighth and tenth aspects of the present invention, high-quality reproduction can be performed for each area of the document by performing area division.
According to the sixth aspect of the invention, since the area dividing means includes determination means for determining a single color area, it is possible to perform filter processing, color correction processing, gradation processing, and halftone processing suitable for the single color area. it can.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS.
(First embodiment)
FIG. 1 is a block diagram showing a basic configuration of a color copying machine according to the present embodiment. As shown in FIG. 1, the digital copying machine includes a color document reading device 1, an image processing device 2, and a color image output device 3. The analog signal optically read by the color document reading device 1 is subjected to various image processing by the image processing device 2 and converted into an image output CMYK signal, which is sent to the color image output device 3. Images are printed out.

(Description of color document reader)
FIG. 3 is a schematic cross-sectional view of the color document reading apparatus 1 according to the present embodiment.
Referring to FIG. 3, the color document reading apparatus 1 is formed on a contact image sensor unit (hereinafter referred to as CIS) 301, a light guide light source 302, a document table glass (platen glass) 303, a lens array 305, and a substrate 306. The monochrome line image sensor 307, the main control board 308, the flexible cable 309, and the white reference plate 310 having a long and uniform spectral reflectance in the main scanning direction are provided.
A document 304 is placed on the document table glass 303.
In the light guide light source 302, four or more kinds of LEDs having different spectral emission characteristics are arranged at both ends of the light guide elongated in the vertical direction (main scanning direction) in the drawing, and each LED is The emitted light is guided in the main scanning direction by internal reflection, and the document 304 on the document table glass 303 is illuminated in a line shape.
The reflected light from the original 304 is imaged on a monochrome line image sensor 307 formed on the substrate 306 by the lens array 305 and converted into an analog image signal. As a result, reading in the main scanning direction is performed for one band, so that a multiband signal can be read by switching a plurality of LED light sources and repeatedly reading them.

The CIS 301 is connected to a driving device (not shown) and is moved in the sub-scanning direction shown by the action of the driving device. As a result, scanning of the original 304 in the sub-scanning direction is performed. The main control board 308 is electrically connected to the CIS 301 via a flexible cable 309.
Further, the white reference plate 310 is read when acquiring reference data when correcting the sensitivity unevenness of each light receiving element or the uneven illumination of the original surface by the LED.
The multiband analog signal read by the color original reading apparatus 1 is converted into an image output CMYK signal by the image processing apparatus 2.

FIG. 2 is a block diagram for explaining processing in the image processing apparatus 2.
The image processing apparatus 2 includes an A / D (analog / digital) conversion unit 10, an input correction unit 11, a filter processing unit 12, a color correction unit 13, an output tone correction unit 14, a halftone processing unit 15, and the like. And connected to the color image output device 3.
The image signal output from the monochrome line image sensor 307 is subjected to gain adjustment and DC offset adjustment by an A / D conversion unit 10 including a sample / hold circuit such as a CDS (correlated double sampling circuit), and then digitally converted. The image signals DIGa1, DIGa2, DIGa3,... DIGaN (N is the number of bands) are converted and input to the input correction unit 11.
The input correction unit 11 performs shading correction, gamma correction, line delay correction, and MTF (MTF: Modulation Transfer Function) correction on the digital image signals DIGa1, DIGa2,... DIGaN sent from the A / D conversion unit 10. Perform processing.

FIG. 4 is a block diagram showing the configuration of the input correction unit 11. In order to perform the above correction, the input correction unit 11 includes a shading correction unit 11A, a gamma correction unit 11B, and an MTF correction unit 11C.
The shading correction unit 11 </ b> A is a circuit that corrects (shading correction) the sensitivity unevenness of each light receiving element of the monochrome line image sensor 307, the uneven illumination of the original surface by the LED, and the like. This shading correction is performed based on the output data of the A / D converter 10 when each LED is driven and the above-described white reference plate 310 is read.
The gamma correction unit 11B converts the signal subjected to the shading correction by the shading correction unit 11A into a luminance linear signal and corrects the read signal using a gamma curve corresponding to each band data. This gamma curve is created so that the read values of the band when the reference gray patch is read all match the brightness of the gray patch. As the reference gray patch, a printed document printed in monochrome black is used.

  The MTF correction unit 11C corrects the deteriorated MTF of the image signal output from the gamma correction unit 11B. That is, the image signal output from the monochrome line image sensor 307 includes optical components such as lenses and mirrors, aperture aperture of the light receiving surface of the monochrome line image sensor 307, transfer efficiency and afterimage, and physical scanning. Due to the integration effect and operation unevenness, the MTF is deteriorated. Therefore, since the read document image information is blurred, the MTF correction unit 11C performs an appropriate filter process (enhancement process) to repair the blur and improve the image quality. Yes.

Returning to FIG. 2, the filter processing unit 12 performs spatial filter processing using a digital filter on the image data DIGb1, DIGb2,... DIGbN input from the input correction unit 11, and outputs by correcting the spatial frequency characteristics. Processing is performed to prevent image blurring and graininess degradation.
The color correction unit 13 performs processing for converting the multiband data that has been spatially filtered by the filter processing unit 12 into a color signal for the color image output device 3. As will be described later, the color correction unit 13 estimates the color material amount of the original from the color signals read in multiband, thereby realizing color reproduction faithful to the original.
Since the CMYK signal output from the color correction unit 13 has luminance linear characteristics, the output gradation correction unit 14 performs gamma correction so as to match the characteristics of the output device.

The halftone processing unit 15 converts the gamma-corrected multi-value image signal into gradation level data that can be output stably by the output device. For this halftone correction, a dither method, an error diffusion method, or the like is generally known, and pseudo gradation reproduction can be performed with dots of 1, 2, 4 bits, and the like.
The image data subjected to each of these processes is temporarily stored in a storage unit (not shown), read out at a predetermined timing, and input to the color image output device 3. The color image output device 3 outputs image data on a recording medium (for example, paper). Examples of the color image output device 3 include a color image output device 3 using an electrophotographic method or an ink jet method. It is not limited.
The above processing is controlled by a CPU (Central Processing Unit) (not shown).

(Operation of the color correction unit)
Next, the color correction unit 13 will be described in detail. The color correction unit 13 converts the input multiband data DIGc1, DIGc2,... DIGcN into CMYK signals for output devices. At this time, color correction is performed so that the color material amount of the original, particularly the K ink color material amount, is maintained.
In general, even if a printed document reproduces the same black, character objects are reproduced with K single color ink with emphasis on sharpness, but CMYK4 is emphasized with respect to gradation and dynamic range for photographic parts. Reproduced in color. Therefore, even when color reproduction is performed, the original is reproduced in black only for a black single color (monochromatic black) region, and the region reproduced in a mixed color of C, M, Y, K is mixed color. It is desirable to reproduce it.
However, in the case of a conventional system that reads in three colors of RGB, it is impossible to distinguish between a single color and a mixed color, so that the above problem is addressed by performing a region separation process and extracting a character region. However, it has been difficult to determine whether the color is monochromatic in the inside of a thick character or in a shaded area of graphics.
Therefore, in the present embodiment, the above-described problem is solved by estimating the amount of color material using multiband data and discriminating between monochromatic black and mixed color black. As a result, the color material ratios of the input document and the output material substantially match, and metamerism shift can be suppressed.

In order to predict the color material amount of black with high accuracy, it is desirable to have reading characteristics in which a difference between a mixed color and a single color is likely to occur. FIG. 5 shows the spectral reflectance of monochrome black and mixed color black of CMY in a printed document. As shown in this figure, the spectral reflectance (A) of monochromatic black has a substantially flat characteristic at 450 to 700 nm. However, with respect to 400-450 nm, the reflectance tends to be small due to the influence of the spectral characteristics of the paper.
On the other hand, in the case of mixed color black (B), unevenness is observed in the spectral reflectance. In particular, a peak is observed near 500 nm. This is because the spectral reflectances of cyan ink, yellow ink, and magenta ink of the printed document are deviated from ideal spectral characteristics, but the same tendency can be seen as long as the printing color material is used. In particular, black mixed with CMY tends to have a mountain near 500 nm, and the LED light source of the color document reading apparatus 1 preferably includes a light source having a main wavelength at least near 500 nm.

FIG. 6 is a block diagram showing the configuration of the color correction unit 13. As shown in FIG. 6, the color correction unit 13 includes an RGB signal generation unit 13A, a black amount estimation unit 13B, a CMYK signal generation unit 13C, and the like.
The RGB signal generation unit 13A generates an RGB signal from the input multiband data. Here, the RGB signal is a standard signal that does not depend on the device, and is a signal in which RGB color characteristics are defined, such as an scRGB signal or an sRGB signal. As the RGB signal generation method, a method using an interpolation table or a method using correction by matrix calculation as proposed in Japanese Patent Laid-Open No. 2005-39374 can be used.

  The black amount estimation unit 13B estimates the color material amount of the black ink from the multiband data using the black amount estimation model. As an example of the black amount estimation model, a linear function as shown in Equation 1 can be used. That is, when the reading value of the multiband data is DIGi, the following formula 1 is obtained.

Here, K_d is the color material amount of black ink, and αi is a coefficient. As a method for determining the coefficient αi, first, a large number of patches with known CMYK dot ratios are read by the color original reading device 1. Next, a black amount estimation model is constructed from the correspondence between the read multiband data and the K halftone dot rate.
In the above equation 1, a linear function is used, but other models such as a neural network may be used. In the above formula 1, the black dot ratio is obtained using all the multiband data, but the color material amount of the black ink may be estimated from only a part of the multiband data. . In that case, the color material amount of the black ink is estimated using a combination of a plurality of bands, and a band that can obtain a desired accuracy is used.

The CMYK signal generation unit 13C calculates a CMY output value based on the RGB signal estimated by the RGB signal generation unit 13A and the black ink color material amount estimated by the black amount estimation unit 13B. The calculation of the output value of CMY can be realized by, for example, four-dimensional interpolation calculation as proposed in Japanese Patent Application Laid-Open No. 2003-698414.
As the K output value for the output device, the color material amount of black ink is used to store the black amount.
Here, the lookup table (= 4D-LUT) used for the four-dimensional interpolation calculation is created by calculating the output CMY value for each lattice point. For example, when the 4D-LUT divides each color component of R, G, B, and K into 16 parts, the RGBK color signal at the grid point has a value of 16 steps for each color.

Specifically, a prediction formula for calculating the Lab value from the CMYK output value of the output device is used. The prediction formula measures the color of a patch output by shaking CMYK, and predicts the color measurement result from the CMYK output value using a neural network or a multi-order polynomial. Then, LabK → CMY can be calculated by applying the CMYK → Lab prediction formula to convergence calculation processing such as Newton-Raphson method. Further, instead of the Lab value, an XYZ tristimulus value or CIECAM02 may be used.
When the above is prepared, the Lab value is obtained from the RGB value of the grid point, and the CMY value can be calculated from the Lab value and the color material amount of the black ink.
In the above description, an example of 6 bands is shown as multiband data. However, the present embodiment is not limited to this, and may be 4 bands or more.

(Second Embodiment)
In the first embodiment, the method of performing color correction on the output signal using the estimated color material amount has been described. In the present embodiment, an example will be described in which region separation processing is performed using the estimation result of the color material amount to perform more faithful reproduction.
FIG. 7 is a block diagram showing the configuration of the image processing apparatus 2 in the present embodiment. The image processing apparatus 2 includes an A / D (analog / digital) conversion unit 30, an input correction unit 31, a filter processing unit 32, a color correction unit 33, a gradation correction unit 34, a halftone processing unit 35, and a color material amount estimation unit. 36 and an area separation unit 40, and is connected to the color image output device 3. Among these, the A / D conversion unit 30 and the input correction unit 31 are the same as those in the above-described embodiment, and thus description thereof is omitted.

The color material amount estimation unit 36 uses the color material amount estimation model to estimate the C, M, Y, and K color material amounts of the document for each pixel based on the multiband data. The color material amount estimation model uses a linear operation, a neural network, or the like from DIGc1, DIGc2,... DIGcN as in the black amount estimation model of the first embodiment.
The region separation unit 40 determines the attribute of each pixel of the input image data from the C, M, Y, and K color material amount data estimated by the color material amount estimation unit 36. The region separation unit 40 outputs, to the filter processing unit 32, the color correction unit 33, the gradation correction unit 34, and the halftone processing unit 35, a region identification signal indicating which region the pixel belongs to based on the separation result. To do.

FIG. 8 is a block diagram showing the configuration of the region separation unit 40. The region separation unit 40 includes a color determination unit 41, a halftone dot region determination unit 42, an edge determination unit 43, and an overall determination unit 44.
After determining whether or not the target pixel is a single color, the color determination unit 41 finally determines the attribute of the target pixel based on the determination result of the adjacent pixels. In the pixel unit determination, since three types of color materials among C, M, Y, and K are not used, C <Th, M <Th, Y <Th: K single color M <Th, Y <Th, K < Th: C single color C <Th, Y <Th, K <Th: M single color C <Th, M <Th, K <Th: A case where any of the conditions of Y <mono is determined as a single color. Here, Th is a predetermined threshold value. Also, a blank area where no color material is used is also determined as a single color pixel.

In the case of a printed matter, halftones are reproduced with halftone dots, so even a mixed color region may be determined as a single color when viewed in pixel units. Therefore, next, the determination result is corrected using the determination result of the adjacent pixel. That is, when the target pixel is a single color pixel and m% or more of the surrounding s × t pixels is a single color pixel, the target pixel is regarded as a single color region. Although the value of m is determined experimentally, it is approximately 90% or more.
The halftone dot region determination unit 42 determines whether or not the pixel is in the halftone dot region based on the color material amount data around the target pixel. In the halftone dot region, since the change in shading is large, it is regarded as a halftone dot region when the change in the color material amount data is large around the pixel of interest.
The edge determination unit 43 detects a character edge in order for the filter processing unit 32 to perform edge enhancement. For edge detection, a pattern matching method or the like can be used. The edge extraction does not need to be particularly determined by the amount of color material, and may be extracted using specific band information of the read multiband data, for example.
The overall determination unit 44 comprehensively determines the results of the color determination unit 41, the dot area determination unit 42, and the edge determination unit 43, and determines the attribute of the target pixel. The attributes are classified into, for example, character area / monochromatic solid area / mixed color solid area / monochromatic halftone dot area / mixed color halftone dot area.

The filter processing unit 32 performs a spatial filter process using a digital filter on the multiband data based on the region identification signal, and corrects the spatial frequency characteristics to prevent blurring of the output image and deterioration of graininess. To do. The filter processing may use different filter masks for each band or the same filter.
Similar to the filter processing unit 32, the gradation correction unit 34 and the halftone processing unit 35 also perform predetermined processing on the image data of the color-corrected CMYK signal based on the region identification signal. For example, the region separated into the character region by the region separation unit 40 has a high frequency enhancement amount increased by sharp enhancement processing in the spatial filter processing by the filter processing unit 32 in order to improve reproducibility of black characters or color characters. The Similarly, in the halftone processing unit 35, a binarization process or a multi-value process on a high-resolution screen suitable for reproducing a high frequency is selected.

Further, with respect to the region separated into halftone dot regions by the region separation unit 40, the filter processing unit 32 performs low-pass filter processing for removing the input halftone dot component. The tone correction unit 34 performs an output tone correction process for converting a signal such as a density signal into a halftone dot area ratio that is a characteristic value of the color image output device 3, and then the halftone processing unit 35 Binarization or multilevel processing is performed on the screen with an emphasis on reproducibility.
The color correcting unit 33 converts the output device into CMYK signals for the output device based on the multiband data and the color material data that have been filtered in the same manner as in the first embodiment. However, if the area separation unit 40 determines that the area is a single color area, it is reproduced in a single color.
For example, when the CMYK value after color correction is [5, 10, 0, 240], it is set to [0, 0, 0, 240]. As a result, the single color area of the original can be reproduced with a single color in the same manner, and an output with no color turbidity can be obtained.
The standard RGB signal or the color material estimation amount described above is temporarily stored in a storage unit (not shown), and can be transmitted to the outside through the network I / F.

(Third embodiment)
The present invention can also be provided as a program for causing a computer to execute the above-described image processing function, or as a computer-readable storage medium storing such a program. The program code stored in the storage medium is read by the program reader and stored in DlSK or the like, and the program code stored in DlSK or the like is executed by the CPU, thereby realizing the above-described image processing function or the like. Will be able to.
The program reading apparatus is a storage medium storing various program codes, that is, a flexible disk, a hard disk, an optical disk (CD-ROM, CD-R, CD-R / W, DVD-ROM, DVD-RAM, etc.), magneto-optical A device that reads a program code stored in a disk, a memory card, or the like, such as a flexible disk drive, an optical disk drive, or a magneto-optical disk drive.
Further, by executing the program code read by the computer, an OS (operating system) or the like running on the computer performs part or all of the actual processing based on the instruction of the program code. The case where the above-described function is achieved is also included.

1 is a block diagram showing a basic configuration of a color copying machine according to a first embodiment. It is a block diagram explaining the process in an image processing apparatus. 1 is a schematic cross-sectional view of a color document reading apparatus according to a first embodiment. It is the block diagram which showed the structure of the input correction part. It is the figure which showed the spectral reflectance of the mixed color black by monochrome black and CMY in a printing original. It is the block diagram which showed the structure of the color correction part. It is the block diagram which showed the structural example of the image processing apparatus in 2nd Example. It is the block diagram which showed the structure of the area | region separation part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color document reading apparatus 2 Image processing apparatus 3 Color image output apparatus 10 A / D conversion part 11 Input correction part 11A Shading correction part 11B Gamma correction part 11C MTF correction part 12 Filter processing part 13 Color correction part 14 Output gradation correction part 15 halftone processing unit 30 A / D conversion unit 31 input correction unit 32 filter processing unit 33 color correction unit 34 tone correction unit 35 halftone processing unit 36 color material amount estimation unit 40 area separation unit 41 color determination unit 42 halftone dot Area determination unit 43 Edge determination unit 44 General determination unit 301 Contact image sensor unit (CIS)
302 Light guide light source 303 Platen glass (platen glass)
304 Document 305 Lens array 306 Substrate 307 Monochrome line image sensor 308 Main control substrate 309 Flexible cable 310 White reference plate

Claims (10)

Reading means for optically reading a document with four or more color separation characteristics to generate a color separation signal;
Color material amount estimating means for estimating the color material amount of the document based on the color separation signal from the reading means;
An image processing apparatus comprising: a color correction unit that performs color correction using the color material amount estimated by the color material amount estimation unit and the color separation signal generated by the reading unit. Reading means for optically reading a document with four or more color separation characteristics to generate a color separation signal;
Color material amount estimating means for estimating the color material amount of the document based on the color separation signal from the reading means;
Standard color signal generation means for generating a device independent color signal based on the color separation signal from the reading means;
Image processing comprising: a device independent color signal generated by the standard color signal generation unit and a color correction unit that performs color correction based on the color material amount estimated by the color material amount estimation unit apparatus. The image processing apparatus according to claim 1, wherein the color material for which the color material amount estimation unit estimates the color material amount is black ink. 4. The image processing apparatus according to claim 1, wherein the reading unit includes an illumination light source having a dominant wavelength in a range of at least 500 nm ± 20 nm. Reading means for optically reading a document with four or more color separation characteristics to generate a color separation signal;
Color material amount estimating means for estimating the color material amount of the document based on the color separation signal from the reading means;
Area dividing means for performing area division using the color material amount estimated by the color material amount estimating means;
Image processing means for image-processing the color separation signal from the reading means to generate a color signal for an output device,
The image processing apparatus, wherein the image processing means performs image processing based on area division by the area division means. The image processing apparatus according to claim 5, wherein the area dividing unit includes a determination unit that determines a single color area. An image processing apparatus comprising: a reading unit that optically reads a document with four or more color separation characteristics to generate a color separation signal; and a color correction unit that performs color correction.
A first step in which the reading means optically reads a document with four or more types of color separation characteristics to generate a color separation signal;
A second step of estimating the color material amount of the document based on the color separation signal generated in the first step;
An image processing method, wherein the color correction means includes a third step of performing color correction using the color material amount estimated in the second step and the color separation signal generated in the first step. . Reading means for optically reading a document with four or more types of color separation characteristics to generate a color separation signal, and image processing means for processing a color separation signal from the reading means to generate a color signal for an output device In an image processing apparatus comprising:
A first step in which the reading means optically reads a document with four or more types of color separation characteristics to generate a color separation signal;
A second step of estimating the color material amount of the document based on the color separation signal generated in the first step;
A third step of performing region division using the color material amount estimated in the second step;
The image processing means includes a fourth step of performing image processing on the color separation signal generated in the first step to generate a color signal for an output device;
An image processing method comprising: performing image processing based on the region division performed in the third step when generating the color signal for the output device in the fourth step. A first function for optically reading a document with four or more color separation characteristics to generate a color separation signal;
A second function for estimating the color material amount of the document based on the color separation signal generated by the first function;
A computer-readable image processing program for causing a computer to realize a third function for performing color correction using the color material amount estimated by the second function and the color separation signal generated by the first function. Stored storage medium. A first function for optically reading a document with four or more color separation characteristics to generate a color separation signal;
A second function for estimating the color material amount of the document based on the color separation signal generated by the first function;
A third function for performing region division using the color material amount estimated by the second function;
And a fourth function for generating a color signal for an output device by performing image processing on the color separation signal generated by the first function,
A computer-readable image processing program for causing a computer to perform image processing based on the area division performed by the third function when generating the color signal for the output device by the fourth function is stored. Storage media.

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