JP7103147B2 - Image processing equipment, color conversion methods and programs - Google Patents

Description

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

Relationship between the color value of the device-dependent color space acquired using a reader (scanner) and the color value of the device-independent color space acquired using a colorimeter, etc. for the purpose of matching the color tone of printed matter. From, a color conversion method is known in which a lookup table or a color conversion formula is created to convert a color value of a device-dependent color to a color value of a device-independent color. Here, the device-dependent color space refers to a color space formed by color values read with spectral sensitivity depending on individual characteristics of each scanning device (scanner). Hereinafter, the colors included in the color space may be referred to as device-dependent colors. Further, the device-independent color space indicates a color space formed by color values that do not depend on a reading device having different characteristics, and is formed by, for example, a color value such as an XYZ color system read by a colorimeter. It shall indicate the color space. Hereinafter, the colors included in the color space may be referred to as device-independent colors.

As a technique related to such a color conversion method, for the purpose of measuring colors with high accuracy, device non-devices are used according to the amount of K (black) contained in image data in conversion from a device-dependent color space to a device-independent color space. A technique for correcting a color value in a dependent color space is disclosed (see Patent Document 1).

However, the technique described in Patent Document 1 has a problem that color conversion cannot be performed with high accuracy depending on the recording medium or color material used for printing.

The present invention has been made in view of the above, and provides an image processing apparatus, a color conversion method, and a program capable of performing color conversion with high accuracy regardless of the type of recording medium or color material used for printing. The purpose is to do.

In order to solve the above-mentioned problems and achieve the object, the present invention has a first acquisition unit for acquiring a first color value of a device-dependent color space for a printed matter, and the first acquisition unit for the printed matter. A second acquisition unit for acquiring a second color value in a device-dependent color space based on a spectral sensitivity different from the spectral sensitivity in acquiring the color value, and the first color value and the second color value A matching unit for associating and a color conversion unit for converting into a color value in a device-independent color space based on the first color value and the second color value associated with the matching unit are provided. The color conversion unit is a device-independent color space obtained by converting each of the plurality of color conversion methods for converting the first color value and the second color value into the color values of the device-independent color space. It is characterized in that the color value of the final device-independent color space is determined based on the combination of the color values in which the difference between the two color values is the smallest among the plurality of color values .

According to the present invention, color conversion can be performed with high accuracy regardless of the type of recording medium or coloring material used for printing.

FIG. 1 is a diagram showing an example of the overall structure of the image forming apparatus according to the embodiment. FIG. 2 is a diagram for explaining an example of a difference in spectral characteristics depending on a color combination. FIG. 3 is a diagram for explaining the gray color value reproduced by K. FIG. 4 is a diagram for explaining the gray color value reproduced by CMY. FIG. 5 is a diagram showing an example of the difference in spectral characteristics between different coloring materials. FIG. 6 is a diagram showing an example of a hardware configuration of the image forming apparatus according to the embodiment. FIG. 7 is a diagram showing an example of the configuration of the functional block of the image forming apparatus according to the embodiment. FIG. 8 is a diagram illustrating the correspondence of the color values acquired by the two scanners. FIG. 9 is a diagram showing an example of the flow of the color conversion process of the image forming apparatus according to the embodiment.

Hereinafter, embodiments of an image processing apparatus, a color conversion method, and a program according to the present invention will be described in detail with reference to the drawings. Further, the present invention is not limited by the following embodiments, and the components in the following embodiments include those easily conceived by those skilled in the art, substantially the same, and so-called equivalent ranges. Is included. Furthermore, various omissions, substitutions, changes and combinations of components can be made without departing from the gist of the following embodiments.

(Overall structure of image forming apparatus)
FIG. 1 is a diagram showing an example of the overall structure of the image forming apparatus according to the embodiment. The configuration of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG. The image forming apparatus 1 according to the present embodiment will be described as being a multifunction device (MFP: Multifunction Peripheral). Here, the multifunction device is a device having at least two functions of a printing function, a copying function, a scanner function, and a fax function.

As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes an image reading apparatus 101, an automatic document feeder (ADF: Auto Document Feeder) 102, a paper feeding unit 103, and a main body 104. ing.

The image reading device 101 is a device that acquires image data by reading an image of a document fed by an automatic document feeding device 102. The image reading device 101 includes a first reading unit 101a and a second reading unit 101b.

The first reading unit 101a and the second reading unit 101b are scanner devices (reading devices) that read the image of the front surface and the image of the back surface of the document. The first reading unit 101a and the second reading unit 101b usually read each of the images on both sides of the original printed on both sides, but in the present embodiment, the spectral characteristics (spectral sensitivity) of the originals are different from each other. It is explained as.

The automatic document feeder 102 is a device that automatically feeds the placed document to the image reading device 101. The automatic document feeder 102 includes a roller 102a and a paper ejection tray 102b.

The roller 102a is a roller that feeds the placed document into the inside and conveys it to the image reading device 101. The paper ejection tray 102b is a tray for ejecting a document whose image has been read by the image reading device 101.

The paper feed unit 103 is a portion that feeds printing paper (an example of a recording medium) for forming an image into the main body 104. The transport path 107 in the paper feed unit 103 is a transport path for transporting the printing paper fed from the paper feed cassette to the main body 104.

The main body 104 is a portion for forming an image on the printing paper fed from the paper feeding unit 103. The main body 104 includes a resist roller 108, an image forming unit 105, an optical writing device 109, an intermediate transfer belt 113, a fixing transport unit 110, a reading device 114, a white reference plate 115, and a double-sided tray 111. I have.

The resist roller 108 is a roller that feeds the printing paper fed from the paper feeding unit 103 so as to synchronize with the color toner image on the intermediate transfer belt 113.

The image forming unit 105 is a tandem type device that forms (images) images of each color of Y (yellow), M (magenta), C (cyan), and K (black). The image forming unit 105 includes a developing device 106 and a photoconductor drum 112 for each color.

The developer 106 is a member that supplies toner of each color to the photoconductor drum 112 on which the electrostatic image is formed to develop the electrostatic latent image and form the toner image of each color. The surface of the photoconductor drum 112 is charged, and the optical writing device 109 irradiates a laser beam modulated and polarized based on the image data of each color to form an electrostatic latent image of each color on the charged surface. It is a member.

The optical writing device 109 irradiates the surface of the photoconductor drum 112 of each color with a laser beam modulated based on the image data of each color to form an electrostatic latent image of the image of each color on the photoconductor drum 112. It is a device.

The intermediate transfer belt 113 is a belt tension-tensioned by a plurality of tension rollers, and by applying an intermediate transfer bias from a power source (not shown), toner images on each photoconductor drum 112 are sequentially superimposed in multiple layers. This is a belt on which a color toner image is transferred (primary transfer).

The fixing transport unit 110 is a member that fixes the color toner image on the printing paper by heating the printing paper on which the color toner image is secondarily transferred from the intermediate transfer belt 113, and transports the printing paper to the paper ejection unit side. be.

The double-sided tray 111 is arranged below the fixing and transporting unit 110, and the image-formed printing paper that has passed through the fixing and transporting unit 110, which has been sent by switching the transport route, is turned upside down and again put on the resist roller 108. It is a unit to carry.

(Regarding the spectral sensitivity and color matching function of the reader)
FIG. 2 is a diagram for explaining an example of a difference in spectral characteristics depending on a color combination. FIG. 3 is a diagram for explaining the gray color value reproduced by K. FIG. 4 is a diagram for explaining the gray color value reproduced by CMY.

The graph of the spectral characteristics shown in FIG. 2 shows the spectral characteristics when gray is reproduced with a color material of K (black), and gray is C (cyan), M (magenta) and Y (yellow) (hereinafter, simply CMY). The spectral characteristics (spectral reflectance) when reproduced with a color material (referred to as) are shown. Next, consider a case where the CIE XYZ value is calculated using a color matching function from the spectral characteristics that reproduce such gray.

First, among the spectral characteristics shown in FIG. 1, in order to obtain the CIE XYZ value from the spectral characteristics when gray is reproduced with a K (black) color material, first, as shown in FIG. 3, the color matching function 500 Is multiplied by the spectral characteristics (spectral reflectance) when reproduced with a K (black) color material. Then, when the graph (formula) after multiplication is integrated, the CIE XYZ value when gray is reproduced with the K (black) color material can be obtained. Here, a graph after multiplying the outer shape of the filled portion 501 shown in FIG. 3 by the color matching function 500 and the spectral characteristics (spectral reflectance) when reproduced with a K (black) color material is shown. The area of the filled portion 501 is a value obtained by integrating the graph and corresponds to the CIE XYZ value when gray is reproduced with a K (black) color material.

Further, among the spectral characteristics shown in FIG. 1, in order to obtain the CIE XYZ value from the spectral characteristics when gray is reproduced with the CMY color material, as shown in FIG. 4, the color matching function 500 and the CMY color are obtained. Multiply by the spectral characteristics (spectral reflectance) when reproduced with a material. Then, when the graph (formula) after multiplication is integrated, the CIE XYZ value when gray is reproduced with the CMY color material can be obtained. Here, the graph after multiplying the outer shape of the filled portion 502 shown in FIG. 4 by the color matching function 500 and the spectral characteristics (spectral reflectance) when reproduced with the CMY color material is shown. The area of the filled portion 502 is a value obtained by integrating the graph and corresponds to the CIE XYZ value when gray is reproduced with the CMY color material.

As shown in FIGS. 3 and 4, the gray spectral characteristics reproduced with the K (black) color material and the gray spectral characteristics reproduced with the CMY color material are different, but after multiplying by the color matching function 500. Since the areas (the areas of the filled portion 501 and the filled portion 502) are the same, the colors appear to the human eye to be the same. However, since it is difficult for an actual reader to satisfy the router condition, the spectral sensitivity of the reader and the characteristics of the color matching function are different. Therefore, the reading device reads the gray reproduced with the K (black) color material and the gray reproduced with the CMY color material as different color values. On the contrary, even if the CIE XYZ values are different colors, the color values read by the reading device may be the same.

FIG. 5 is a diagram showing an example of the difference in spectral characteristics between different coloring materials. The graph of the spectral characteristics shown in FIG. 5 shows the spectral characteristics (spectral reflectance) when reproduced using K (black) of different color materials (ink, toner). Further, although FIG. 5 shows an example of the spectral characteristics of different color materials (ink, toner), the spectral characteristics may differ depending on the type of pigment even if the same color material is used. As described above, depending on the type of coloring material, the relationship between the CIE XYZ value and the color value of the reading device may not match, as in the case of K (black) and CMY described above. Similarly, since the spectral characteristics differ depending on the type of recording medium, the relationship between the CIE XYZ value and the color value of the reader does not match depending on the type of recording medium, as in the case of K (black) and CMY described above. Sometimes.

In general, the spectral sensitivity of the reader is in error with the color matching function (ie, does not meet the router conditions). Therefore, when converting the color value of the device-dependent color space acquired by the reader to the color value of the device-independent color space, it is highly accurate depending on the spectral characteristics of the color material or recording medium used for the color to be read. Color conversion cannot be performed. In order to avoid this problem, for example, a plurality of color conversion formulas are prepared in advance according to the type of color material or recording medium used for the color to be read, and the color conversion corresponding to the color material or recording medium is prepared. A method of switching the expression is also conceivable. However, in this case, it is necessary to specify the color conversion formula one by one during the color conversion process, which causes a problem of inconvenience.

Even if the color values in the device-dependent color space are the same in a certain reader, if a reader having a spectral sensitivity different from that of the reader is used, the color values in the device-dependent color space will differ, and the spectral characteristics of the printed matter will be different. It will be recognized that there is a difference in. In the present embodiment, the device is not obtained from the color values of two or more types of device-dependent color spaces acquired by the reading device (the first reading unit 101a and the second reading unit 101b described above) by utilizing the spectral characteristics different depending on the reading device. The process of converting to the color value of the dependent color space will be described.

(Hardware configuration of image forming apparatus)
FIG. 6 is a diagram showing an example of a hardware configuration of the image forming apparatus according to the embodiment. The hardware configuration of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG.

As shown in FIG. 6, the image forming apparatus 1 according to the present embodiment includes a controller 200, an operation display unit 210, an FCU (Facsimile Control Unit) 220, a plotter 231 and a first scanner 232, and a second scanner. The 233 is connected to the PCI (Peripheral Component Interface) bus. Of these, the first scanner 232 corresponds to the first reading unit 101a shown in FIG. 1 described above, and the second scanner 233 corresponds to the second reading unit 101b.

The controller 200 is a device that controls the entire image forming apparatus 1, drawing, communicating, controlling various engines, and controlling the input from the operation display unit 210.

The operation display unit 210 is, for example, a touch panel or the like, which is a device that receives input to the controller 200 (input function) and displays the state of the image forming apparatus 1 (display function), and is an ASIC (Application Specific Integrated) described later. It is directly connected to the Circuit) 206.

The FCU 220 is a device that realizes a fax function, and is connected to the ASIC 206 by, for example, a PCI bus.

The plotter 231 is a device that realizes a printing function, and is connected to the ASIC 206 by, for example, a PCI bus. The first scanner 232 and the second scanner 233 are functions that realize a scanner function, and are connected to the ASIC 206 by, for example, a PCI bus.

The controller 200 includes a CPU 201, a system memory (MEM-P) 202, a north bridge (NB) 203, a south bridge (SB) 204a, a network I / F204b, a USB (Universal Social Bus) I / F204c, and the like. It has a centronics I / F 204d, an ASIC 206, a local memory (MEM-C) 207, and an auxiliary storage device 208.

The CPU 201 controls the entire image forming apparatus 1, is connected to a chipset including a system memory 202, a north bridge 203, and a south bridge 204a, and is connected to other devices via this chipset.

The system memory 202 is a memory used as a memory for storing programs and data, a memory for expanding programs and data, a memory for drawing a printer, and the like, and has a ROM (Read Only Memory) and a RAM (Random Access Memory). is doing. Of these, the ROM is a read-only memory used as a memory for storing programs and data, and the RAM is a memory for expanding programs and data, and a writable and readable memory used as a drawing memory for a printer and the like. ..

The north bridge 203 is a bridge for connecting the CPU 201, the system memory 202, the south bridge 204a, and the AGP (Accelerated Graphics Port) bus 205, and is a memory controller that controls reading and writing to the system memory 202, a PCI master, and a PCI master. It has an AGP target.

The south bridge 204a is a bridge for connecting the north bridge 203 to PCI devices and peripheral devices. The south bridge 204a is connected to the north bridge 203 via a PCI bus, and networks I / F204b, USB I / F204c, Centronics I / F204d, and the like are connected to the PCI bus.

The AGP bus 205 is a bus interface for a graphics accelerator card proposed for speeding up graphics processing. The AGP bus 205 is a bus that speeds up the graphics accelerator card by directly accessing the system memory 202 with a high throughput.

The ASIC 206 is an IC (Integrated Circuit) for image processing applications having hardware elements for image processing, and has a role of a bridge connecting the AGP bus 205, the PCI bus, the auxiliary storage device 208, and the local memory 207, respectively. The ASIC 206 includes a PCI target and an AGP master, an arbiter (ARB) that forms the core of the ASIC 206, a memory controller that controls the local memory 207, and a plurality of DMACs (Direct Memory Access) that rotate image data by hardware logic or the like. It is composed of a controller) and a PCI unit that transfers data between the plotter 231 and the first scanner 232 and the second scanner 233 via the PCI bus. For example, the FCU 220, the plotter 231 and the first scanner 232 and the second scanner 233 are connected to the ASIC 206 via the PCI bus. The ASIC 206 is also connected to a host PC (Personal Computer), a network, and the like (not shown).

The local memory 207 is a memory used as a copy image buffer and a code buffer.

The auxiliary storage device 208 is a storage device such as an HDD (Hard Disk Drive), SSD (Solid State Drive), SD (Secure Digital) card or flash memory, and stores image data, programs, font data, etc. And storage for accumulating forms.

The program of the image forming apparatus 1 described above may be recorded and distributed on a computer-readable recording medium in an installable format or an executable format file.

Further, the hardware configuration of the image forming apparatus 1 shown in FIG. 6 is an example, and it is not necessary to include all the constituent devices, or it may be provided with other constituent devices.

(Configuration and operation of functional blocks of the image forming apparatus)
FIG. 7 is a diagram showing an example of the configuration of the functional block of the image forming apparatus according to the embodiment. FIG. 8 is a diagram illustrating the correspondence of the color values acquired by the two scanners. The configuration and operation of the functional block of the image forming apparatus 1 according to the present embodiment will be described with reference to FIGS. 7 and 8.

As shown in FIG. 7, the image forming apparatus 1 according to the present embodiment includes a first scanned image acquisition unit 301 (first acquisition unit), a second scanned image acquisition unit 302 (second acquisition unit), and It has a color value processing unit 303 (correspondence unit), a color conversion unit 304, and a storage unit 305.

The first scanned image acquisition unit 301 is a functional unit that acquires the color value (first color value) of the device-dependent color space read by the first scanner 232 (first scanning device) for the printed matter to be color-converted. Is.

The second scanned image acquisition unit 302 reads the color value of the device-dependent color space (the second scanning device) of the printed matter to be color-converted by the second scanner 233 (second scanning device) having a spectral sensitivity different from that of the first scanner 232. This is a functional unit that acquires the second color value).

That is, the first scanner 232 and the second scanner 233 each read the image of the same printed matter, and the first scanned image acquisition unit 301 and the second scanned image acquisition unit 302 each read the image of the same printed matter. Get color values for different device-dependent color spaces. As described above, the first scanner 232 and the second scanner 233 are the first scanning unit 101a and the second scanning unit 101b, and are assumed to be the double-sided document reading device in the image forming apparatus 1 which is the MFP. As described above, if the first reading unit 101a and the second reading unit 101b are used as the first scanner 232 and the second scanner 233 in the present embodiment, high-precision color can be obtained without preparing a special device. The conversion can be realized.

Although the first scanner 232 and the second scanner 233 have been described as separate devices in FIG. 6, the present invention is not limited to this, and for example, a plurality of reading sensors or a plurality of light sources for irradiating printed matter with light. It may be configured as one device capable of switching between.

The color value processing unit 303 is a functional unit that associates the color value acquired by the first scanned image acquisition unit 301 with the color value acquired by the second scanned image acquisition unit 302. Further, even if the resolutions of the images read by the first scanner 232 and the second scanner 233 are different, the color value processing unit 303 is acquired by the first scanned image acquisition unit 301 and the second scanned image acquisition unit 302, respectively. Color values can be associated.

The color conversion unit 304 acquires a color conversion parameter from the storage unit 305, and uses the color conversion parameter from the color value (device-dependent color) associated with the color value processing unit 303 to change the color to a device-independent color. It is a functional part that performs conversion.

Here, a specific method for converting a color value in a device-dependent color space into a color value in a device-independent space will be described. As a method of converting a color value in a device-dependent color space to a color value in a device-independent space, a method using a look-up table, a method of creating a color conversion formula, and the like are known. Color conversion can be performed in the same manner in the present embodiment, but here, from the RGB values as the color values of the device-dependent color space acquired by the two scanner devices (first scanner 232 and second scanner 233). , A method of creating a color conversion formula for converting to a CIE XYZ value (hereinafter, may be simply referred to as an XYZ value) which is a color value of a device-independent color space will be described.

First, a chart in which a plurality of color patches are arranged is read by a first scanner 232 and a second scanner 233 in order to create a color conversion formula. The first scanned image acquisition unit 301 acquires the RGB values of each color patch read by the first scanner 232, and the second scanned image acquisition unit 302 acquires the RGB values of each color patch read by the second scanner 233. To get.

Next, as shown in FIG. 8, the color value processing unit 303 acquires the RGB values (RGB_R, RGB_G, RGB_B) acquired by the first scanned image acquisition unit 301 and the second scanned image acquisition unit 302. It is associated with the RGB values (RGB_R', RGB_G', RGB_B'). Further, as shown in FIG. 8, the color value processing unit 303 measures the RGB values of the associated patches with respect to the regular XYZ values assigned to the patches (for example, in advance with a colorimeter. (Colored XYZ values, etc.) are associated. Further, as shown in FIG. 8, the color value processing unit 303 uses the coefficients ax to gx of the following equation (1) so as to minimize the conversion error from the two RGB values to the XYZ values for each patch. Calculate ay to gy and az to gz. By calculating the coefficients ax to gx, ay to gy, and az to gz in this way, a color conversion formula from an RGB value to an XYZ value can be created. Here, the conversion error is the difference between the regular XYZ values (for example, the XYZ values measured in advance by the colorimeter) and the XYZ values after the color conversion, which are assigned to each patch of the chart in advance. (Error). Further, the color value processing unit 303 stores the calculated coefficients ax to gx, ay to gy, and az to gz in the storage unit 305 as color conversion parameters.

XYZ_X = ax × RGB_R + bx × RGB_G + cx × RGB_B + dx × RGB_R'+ ex × RGB_G'+ gx
XYZ_Y = ay x RGB_R + by x RGB_G + cy x RGB_B + dy x RGB_R'+ ey x RGB_G'+ gy
XYZ_Z = az x RGB_R + bz x RGB_G + cz x RGB_B + dz x RGB_R'+ ez x RGB_G'+ gz
... (1)

Although only the first-order term is used in the equation (1), for example, a second-order or higher term such as RGB_R2 may be used, and the coefficient of the color conversion equation may be switched depending on the hue or lightness. good. Further, it is not always necessary to create a color conversion formula using all the color values read by the two scanners (first scanner 232 and second scanner 233). For example, the R (R) of the two readers When the difference in reading characteristics of red) is small, only the R value of the first scanner 232 may be used. Further, the image forming apparatus 1 according to the present embodiment can perform highly accurate color conversion regardless of the recording medium or color material of the printed matter, but the spectral characteristics change depending on the color combination even with the same color material. , It is not always necessary to use a chart using a plurality of recording media or color materials to create a color conversion formula.

Here, returning to FIG. 7, the description of the functional block will be continued.

The storage unit 305 is a functional unit that stores image data storage, programs, font data, color conversion parameter information for color conversion processing, and the like. The storage unit 305 is realized by the auxiliary storage device 208 or the system memory 202 shown in FIG.

The first scanned image acquisition unit 301, the second scanned image acquisition unit 302, the color value processing unit 303, and the color conversion unit 304 described above are realized by, for example, a program executed by the CPU 201 shown in FIG. A part or all of the first scanned image acquisition unit 301, the second scanned image acquisition unit 302, the color value processing unit 303, and the color conversion unit 304 may be realized by a hardware circuit such as ASIC206. Further, the hardware circuit here may be an FPGA (Field-Programmable Gate Array) or the like.

It should be noted that each functional unit of the image forming apparatus 1 shown in FIG. 7 conceptually shows a function, and is not limited to such a configuration. For example, a plurality of functional units illustrated as independent functional units in the image forming apparatus 1 shown in FIG. 7 may be configured as one functional unit. On the other hand, in the image forming apparatus 1 shown in FIG. 7, the functions of one functional unit may be divided into a plurality of functions and configured as a plurality of functional units.

Further, the image forming apparatus 1 according to the present embodiment can be regarded as an example of the "image processing apparatus" according to the present invention. Alternatively, a component including at least one of the functional units shown in FIG. 7 (for example, a first scanned image acquisition unit 301, a second scanned image acquisition unit 302, a color value processing unit 303, and a color conversion unit 304). Can be taken as an example of the "image processing apparatus" according to the present invention.

(Flow of color conversion process)
FIG. 9 is a diagram showing an example of the flow of the color conversion process of the image forming apparatus according to the embodiment. The flow of the color conversion process of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG.

<Steps S11, S12>
The first scanned image acquisition unit 301 acquires the color value (for example, RGB value) of the device-dependent color space read by the first scanner 232 for the printed matter to be color-converted. The second scanned image acquisition unit 302 receives the color values in the device-dependent color space read by the second scanner 233 for the printed matter to be color-converted in parallel with the color value acquisition process by the first scanned image acquisition unit 301. For example, RGB value) is acquired. The acquisition process by the first scanned image acquisition unit 301 and the second scanned image acquisition unit 302 is not limited to the acquisition in parallel, and one acquisition process may be followed by the other acquisition process. Then, the process proceeds to step S13.

<Step S13>
The color value processing unit 303 associates the color value acquired by the first scanned image acquisition unit 301 with the color value acquired by the second scanned image acquisition unit 302. The color value processing unit 303 sends the two associated color values to the color conversion unit 304. Then, the process proceeds to step S14.

<Step S14>
The color conversion unit 304 receives the associated color value from the color value processing unit 303, and reads and acquires the color conversion parameter from the storage unit 305. Then, the process proceeds to step S15.

<Step S15>
The color conversion unit 304 performs color conversion from the color value (device-dependent color) associated with the color value processing unit 303 to a device-independent color using the acquired color conversion parameter.

In the flow of the above steps S11 to S15, the color conversion from the device-dependent color to the device-independent color is performed.

As described above, the image forming apparatus 1 according to the present embodiment depends on two devices acquired from an image of a printed matter to be color-converted by using two scanner devices (reading devices) having different spectral characteristics (spectral sensitivity). The color conversion parameters are calculated using the color values in the color space, that is, the color conversion formula is created. Then, the image forming apparatus 1 converts the color values of the two device-dependent color spaces acquired from the two scanner devices into the color values of the device-independent color space by using the color conversion parameters. As a result, color conversion can be performed with high accuracy regardless of the type of recording medium or color material used for printing.

In the above description, the color values of the two types of device-dependent color spaces are converted into the color values of the device-independent color space, but the present invention is not limited to this, and three or more types of device-dependent color spaces are used. The color values of three or more types of device-dependent color spaces may be converted into the color values of the device-independent color space by using the color conversion parameters calculated from the color values of.

(Modification example)
Next, as a method of color conversion processing in the above-mentioned image forming apparatus 1, a method capable of performing more accurate color conversion will be described.

In the above-described embodiment, the color conversion parameters calculated by a specific method (in the above-mentioned example, a method of reading a printed matter printed with a plurality of patches by two scanning devices (first scanner 232, second scanner 233)) are used. Explained how to convert device-dependent colors to device-independent colors. In this modification, a method of finally determining the device-independent color will be described using the device-independent colors calculated based on the plurality of color conversion methods.

First, it is the same method according to the above-described embodiment, and color conversion can be performed by a plurality of methods. For example, the color conversion parameters obtained by using a printed matter in which a plurality of patches are printed on a recording medium of a specific material are obtained, and further, a printed matter in which a plurality of patches are printed on a recording medium of a material different from the material is used. When different color conversion parameters are obtained, two color conversion methods are prepared. Furthermore, instead of the method of creating a color conversion formula (method using color conversion parameters), as described above, the method of creating a look-up table and performing color conversion should be used so that color conversion can be performed. You may.

Next, the color conversion unit 304 uses a plurality of color conversion methods obtained in advance for the color values of the two device-dependent color spaces acquired by the first scanned image acquisition unit 301 and the second scanned image acquisition unit 302. Then, each of them calculates the color value of the device non-color space. The color conversion unit 304 searches for a combination of color values having the smallest difference from the calculated color values of the plurality of device non-color spaces. Then, the color conversion unit 304 determines the final color value of the device-independent color space based on the color value of the device-independent color space related to the combination. For example, the color conversion unit 304 sets one of the color values (small value or large value) of the device-independent color space related to the combination, or the average value thereof, into the final device-independent color space. Determined as a color value.

As a result, the color conversion method suitable for the printed matter is automatically selected without preparing a dedicated color conversion formula for converting the color values of the two device-dependent color spaces to the color values of the device-independent color space. It is possible to realize highly accurate color conversion.

In the above-described embodiments and modifications, when at least one of the functional units of the image forming apparatus 1 is realized by executing a program, the program is provided by being incorporated in a ROM or the like in advance. Further, in the above-described embodiment and modification, the program executed by the image forming apparatus 1 is a file in an installable format or an executable format, which is a CD-ROM (Compact Disk Read Only Memory) or a flexible disk (FD). , CD-R (Compact Disk-Recordable), or DVD (Digital Versaille Disc) may be configured to be recorded and provided on a computer-readable recording medium. Further, in the above-described embodiment and modification, the program executed by the image forming apparatus 1 is stored on a computer connected to a network such as the Internet, and is provided by being downloaded via the network. May be good. Further, in the above-described embodiment and modification, the program executed by the image forming apparatus 1 may be configured to be provided or distributed via a network such as the Internet. Further, in the above-described embodiment and modification, the program executed by the image forming apparatus 1 has a module configuration including at least one of the above-mentioned functional units, and the CPU 201 is described above as the actual hardware. By reading a program from the storage device (for example, system memory 202 or auxiliary storage device 208, etc.) and executing the program, each of the above-mentioned functional units is loaded on the main storage device and generated.

1 Image forming device 101 Image reading device 101a First reading unit 101b Second reading unit 102 Automatic document feeder 102a Roller 102b Paper ejection tray 103 Feeding unit 104 Main body 105 Image drawing unit 106 Developer 107 Transport path 108 Resist roller 109 Light Writing device 110 Fixing carrier 111 Double-sided tray 112 Photoreceptor drum 113 Intermediate transfer belt 200 Controller 201 CPU
202 system memory (MEM-P)
203 Northbridge (NB)
204a Southbridge (SB)
204b Network I / F
204c USB I / F
204d Centronics I / F
205 AGP
206 ASIC
207 Local memory (MEM-C)
208 Auxiliary storage 210 Operation display 220 FCU
231 Plotter 232 1st scanner 233 2nd scanner 301 1st scanned image acquisition unit 302 2nd scanned image acquisition unit 303 Color value processing unit 304 Color conversion unit 305 Storage unit 500 Color matching function 501, 502 Filling unit

Japanese Patent No. 60779704

Claims (9)

A first acquisition unit that acquires the first color value of the device-dependent color space for printed matter, and
A second acquisition unit that acquires a second color value in a device-dependent color space based on a spectral sensitivity different from the spectral sensitivity in the acquisition of the first color value for the printed matter.
An associating unit that associates the first color value with the second color value,
A color conversion unit that converts a color value in a device-independent color space based on the first color value and the second color value associated with the matching unit, and a color conversion unit.
With
The color conversion unit is a device-independent color space obtained by converting each of the plurality of color conversion methods for converting the first color value and the second color value into the color values of the device-independent color space. An image processing device that determines the color value of the final device-independent color space based on the combination of color values that minimizes the difference between two color values among a plurality of color values . The first acquisition unit acquires the first color value of the device-dependent color space read by the first reading device, and obtains the first color value.
The image according to claim 1, wherein the second acquisition unit acquires the second color value of the device-dependent color space read by the second reader having a spectral sensitivity different from that of the first reader. Processing equipment. The first acquisition unit acquires the first color value of the device-dependent color space read by a specific reading sensor, and obtains the first color value.
The image processing apparatus according to claim 1, wherein the second acquisition unit acquires the second color value of the device-dependent color space read by a reading sensor different from the specific reading sensor. The first acquisition unit is a reading device capable of switching a plurality of light sources to irradiate light by the reading device by irradiating the printed matter with light from a specific light source among the plurality of light sources . The first color value of the read device-dependent color space is acquired, and
The second acquisition unit is the second color value of the device-dependent color space read by the reader by irradiating the printed matter with light from a light source different from the specific light source among the plurality of light sources. The image processing apparatus according to claim 1. The color conversion unit, as one of the plurality of color conversion methods, has the first color value and the first color value based on the color conversion formula created based on the first color value and the second color value. The image processing apparatus according to any one of claims 1 to 4, which converts the second color value into a color value in a device-independent color space. The color conversion unit, as one of the plurality of color conversion methods, has the first color value and the first color value based on a lookup table created based on the first color value and the second color value. The image processing apparatus according to any one of claims 1 to 4, which converts the second color value into a color value in a device-independent color space. The association unit further obtains color values of one or more types of device-dependent color spaces based on spectral sensitivities different from the respective spectral sensitivities in the acquisition of the first color value and the second color value. Corresponding to the first color value and the second color value,
The color conversion unit is a device-independent color based on the first color value, the second color value, and the color value of one or more types of device-dependent color spaces associated with the matching unit. The image processing apparatus according to any one of claims 1 to 6, which converts a color value into a space. The first acquisition step of acquiring the first color value of the device-dependent color space for the printed matter, and
A second acquisition step of acquiring a second color value in a device-dependent color space based on a spectral sensitivity different from the spectral sensitivity in the acquisition of the first color value for the printed matter, and a second acquisition step.
An association step of associating the first color value with the second color value, and
A color conversion step of converting to a color value in a device-independent color space based on the associated first color value and the second color value, and
Have,
In the color conversion step, the device-independent color space obtained by converting each of the plurality of color conversion methods for converting the first color value and the second color value into the color values of the device-independent color space. A color conversion method that determines the color value of the final device-independent color space based on the combination of color values that minimizes the difference between two color values among a plurality of color values . On the computer
The first acquisition step of acquiring the first color value of the device-dependent color space for the printed matter, and
A second acquisition step of acquiring a second color value in a device-dependent color space based on a spectral sensitivity different from the spectral sensitivity in the acquisition of the first color value for the printed matter, and a second acquisition step.
An association step of associating the first color value with the second color value,
A color conversion step of converting to a color value in a device-independent color space based on the associated first color value and the second color value, and
To run ,
In the color conversion step, the device-independent color space obtained by converting each of the plurality of color conversion methods for converting the first color value and the second color value into the color values of the device-independent color space. A program for determining the final device-independent color space color value based on the combination of color values that minimizes the difference between two color values among multiple color values .

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