JP2009033729A - Image copying apparatus, control method therefor, program, and method for generating 3d-lut - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for enhancing reproducibility of the colors of an original image in an output image by an image copying apparatus in which the color gamut of an output device is smaller than the color gamut of an input device, while suppressing increase in the cost of the image copying apparatus. <P>SOLUTION: In an image copying apparatus provided with a scanner and a printer, the image copying apparatus comprises: an obtaining unit which obtains image data by causing the scanner scan an image of an original; a correction unit which performs correction processing that adds, to saturation, a value corresponding to a difference between lightness before and after performing predetermined editing processing on the image data, with respect to a region where a correction is performed designated near the maximum saturation of a color gamut of the printer; and a control unit which causes the printer to print the image data corrected by the correction unit. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image copying apparatus including a scanner and a printer, a control method thereof, a program, and a method of generating a 3D-LUT.

  The image copying apparatus includes an input device such as a scanner and an output device such as a printer. For example, the image copying apparatus optically reads a document with a scanner, performs predetermined image processing on the acquired image data, and outputs (prints) the output with an output device.

  In general, an input device detects a reflected light from an original with a CCD of light emitted from a fluorescent tube or an LED. Further, the output device generally uses a recording method such as an electrophotographic method or an ink jet method.

  As the manuscript, a document having a wide color space such as a photograph or a magazine is often used. The input device generally has a relatively wide color reproduction range. On the other hand, the color reproduction range of the output device varies depending on the type of printing medium (glossy paper and photographic paper suitable for photography, plain paper that is most commonly used, and among them, environmentally friendly recycled paper). It is generally not so wide. In particular, there are many print media such as plain paper that have a very narrow output color reproduction range compared to the color reproduction range of the input device.

  In this case, a color space compression technique called gamut mapping is required. Gamut mapping defines how colors outside the color reproduction range that cannot be output as they are are expressed. It also defines how to handle color spaces within the color reproduction range. The methods are generally classified into two types, Colorimetric (colorimetric matching method) and Perceptual (perceptual importance method). The former gives priority to color reproducibility. Reproducible colors are expressed as much as possible, and unreproducible colors are mapped so as to be the closest color. In this case, colorimetric matching of reproducible colors is sufficiently achieved, but on the other hand, there are cases where a plurality of colors that cannot be reproduced are mapped to a certain same point, and gradation is impaired. There's a problem. On the other hand, the latter Perceptual realizes color reproduction that is perceptually preferable in consideration of the overall balance so as to leave gradation. However, since the color to be printed does not necessarily match the color of the image of the document colorimetrically, the color that should be reproducible may be shifted. In addition, when there is a large difference between the input and output color reproduction ranges, the print result may be dull with reduced saturation.

  Patent Document 1 discloses a technique relating to gamut mapping for compressing a display color having a wide color reproduction range into a color gamut of a printer. In this technique, when the color space within the color reproduction range is compressed, colorimetric matching is performed without compressing the portion within the predetermined range, and other portions are determined within a predetermined range with respect to a certain direction. And the maximum saturation / brightness internal ratio. According to Patent Document 1, gamut mapping that compensates for the weak points of Colorimetric and Perceptual and performs natural color reproduction is realized.

  Japanese Patent Laid-Open No. 2004-228561 performs an expansion process so that the output gamut is widely used for input data within the color reproduction range of the output device, and for input data outside the color reproduction range, Perform gamut mapping so that the area can be fully utilized. Thereby, it is realized that the color reproduction range of the output device is used as wide as possible.

Japanese Patent Application Laid-Open No. 2004-228561 holds three types of color processing of a uniform color reproduction system, color processing of a compression color reproduction system, and color processing of an enlarged color reproduction system, and selects them based on an input document. At this time, the pixel values of the input image are accumulated, and if the accumulated value of the output color reproduction pixels is equal to or less than the predetermined value of the entire pixels, the color processing of the same color reproduction system is selected. Thereby, even in the process of copying the copied image as a document (hereinafter referred to as “grandchild copy”), the color matching between the document image and the print image is enhanced.
Japanese Patent Laid-Open No. 4-196675 JP 2001-28694 A JP-A-4-217167

  However, Patent Document 1 reduces the occurrence of color dullness due to a decrease in saturation by providing a colorimetric matching region. However, when the output color reproduction range is extremely narrow with respect to the input color reproduction range, intense saturation is caused. Degradation cannot be prevented. Therefore, it is difficult to obtain a preferable image with contrast.

  Japanese Patent Laid-Open No. 2004-228688 implements suitable color reproduction by gamut mapping that effectively uses the color space of the output color reproduction range, but the color reproducibility of the original image in the output image is low. For this reason, when performing copying that requires faithful color reproduction, the image processing of Patent Document 2 is not suitable.

  These problems become more prominent when copying grandchildren. In Patent Document 1, the color existing in the compression area is further changed in the grandchild copy, and the printed image is further different from the original image. The same applies to Patent Document 2, and the fidelity cannot be obtained because the color is excessively generated by the decompression process.

  Further, although Patent Document 3 considers grandchild copy, it is necessary to determine an input document. For this reason, an operation called pre-scanning that reads a document in advance before starting copying is required, or a memory capacity that holds all the read input images is required. As a result, it takes a long time for the copy process to be completed after the copy start command is issued, which impairs usability for the user. In addition, the cost increases because a large-capacity memory for holding an input image is mounted. Furthermore, a plurality of processing contents must be stored, and when a table having a large capacity is used for processing, a large ROM capacity is required to store tables for the number of processes.

  The present invention has been made in view of such a situation. That is, the present invention suppresses an increase in the cost of an image copying apparatus, and reproduces the color of an original image in an output image for an image copying apparatus in which the color reproduction range of the output device is narrower than the color reproduction range of the input device. It aims at providing the technique which improves the property.

  In order to solve the above-described problems, a first aspect of the present invention is an image copying apparatus including a scanner and a printer, the acquisition unit acquiring the image data by causing the scanner to read the image of the document, and the printer. Correction means for performing correction processing for adding a value corresponding to the brightness difference before and after performing predetermined processing to the image data to the saturation range set in the vicinity of the maximum saturation of the color reproduction range And an image copy apparatus comprising: a control unit that causes the printer to print the image data corrected by the correction unit.

  According to a second aspect of the present invention, there is provided a control method for an image copying apparatus including a scanner and a printer, the acquisition step of acquiring image data by causing the scanner to read an image of a document, and the color reproduction range of the printer. A correction step of performing a correction process for adding a value corresponding to a brightness difference before and after performing a predetermined processing process on the image data to the saturation for a range to be corrected set near the maximum saturation of And a control step of causing the printer to print the image data corrected in the correction step.

  According to a third aspect of the present invention, a computer including a scanner and a printer is set in the vicinity of the maximum saturation in the color reproduction range of the printer, an acquisition unit that causes the scanner to read an image of an original and acquires image data. Correction means for performing correction processing for adding a value corresponding to the brightness difference before and after performing predetermined processing to the image data to the saturation range, and image data corrected by the correction means. A program for causing the printer to function as a control unit is provided.

  According to a fourth aspect of the present invention, a scanner and a printer are provided. The scanner reads an image of an original to acquire image data, corrects the acquired image data, and outputs the corrected image data to the printer. In a method for generating a 3D-LUT used by the image copying apparatus to be used for the correction, a setting step for setting a correction range near the maximum saturation of the color reproduction range of the printer, and a range for performing the correction On the other hand, a correction process for performing a correction process for adding to the saturation a value corresponding to a brightness difference before and after performing a predetermined processing process on the image data, and the processing process as an output value for the value of the input image data And a registration step of registering the value of the image data corrected in the correction step in the 3D-LUT. A method for generating a 3D-LUT is provided.

  Other features of the present invention will become more apparent from the accompanying drawings and the following description of the best mode for carrying out the invention.

  With the above configuration, according to the present invention, an original in an output image for an image copying apparatus in which the color reproduction range of the output device is narrower than the color reproduction range of the input device while suppressing an increase in the cost of the image copying apparatus. It is possible to provide a technique for improving the color reproducibility of an image.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The individual embodiments described below will help to understand various concepts from the superordinate concept to the subordinate concept of the present invention.

  The technical scope of the present invention is determined by the claims, and is not limited by the following individual embodiments. In addition, not all combinations of features described in the embodiments are essential to the present invention.

[First Embodiment]
FIG. 12 is a schematic perspective view of the image copying apparatus 1 according to the first embodiment of the present invention. The image copying apparatus 1 has a function of a normal PC printer that receives data from a host computer (PC) and prints it, and a function of a scanner. In addition, as a function that operates alone in the image copying apparatus, a copy function for printing an image read by a scanner with a printer and a function for directly reading and printing image data stored in a storage medium such as a memory card are provided. Furthermore, it has a function of receiving and printing image data from a digital camera.

  In FIG. 12, the image copying apparatus 1 includes a reading device 34 such as a flatbed scanner, a printing device 33 such as an ink jet printer or an electrophotographic printer, and an operation panel 35 including a display panel 39 and various key switches. Further, a USB port (not shown) for communicating with the PC is provided on the back surface of the image copying apparatus 1, and communication with the PC is performed. In addition to the above configuration, the image copying apparatus 1 includes a card slot 42 for reading data from various memory cards and a camera port 43 for data communication with a digital camera. Further, an automatic document feeder (ADF) 31 for automatically setting a document on the document table is provided.

  FIG. 13 is a functional block diagram of the image copying apparatus 1. In FIG. 13, the CPU 11 controls various functions of the image copying apparatus 1 and executes an image processing program stored in the ROM 16 in accordance with a predetermined operation of the operation unit 15.

  The reading unit 14 having a CCD corresponds to the reading device 34 in FIG. 12, reads a document image, and outputs analog luminance data of red (R), green (G), and blue (B) colors. Note that the reading unit 14 may include a contact image sensor (CIS) instead of the CCD. If the ADF 31 as shown in FIG. 12 is provided, the order sheets can be read continuously, and the convenience is further improved.

  The card interface 22 corresponds to the card slot 42 in FIG. The card slot 42, for example, reads image data shot by a digital still camera (Digital Still Camera (DSC)) and recorded on a memory card or the like according to a predetermined operation of the operation unit 15. The color space of the image data read via the card interface 22 is changed from the DSC color space (for example, YCbCr) to the standard RGB color space (for example, NTSC-RGB or sRGB) by the image processing unit 12 if necessary. ). Further, based on the header information of the image data, the read image data is subjected to various processes necessary for the application such as resolution conversion to the effective number of pixels as necessary.

  The camera interface 23 corresponds to the camera port 43 in FIG. 12, and directly connects to the DSC to read image data.

  In the image processing unit 12, image processing such as shading correction, color conversion, processing, gamut compression, color separation, and quantization, which will be described later, is performed, and data (correction data) obtained thereby is Stored in the RAM 17. When the correction data stored in the RAM 17 reaches a predetermined amount necessary for recording by the recording unit 13 corresponding to the printing apparatus 33 of FIG. 12, the recording operation by the recording unit 13 is executed.

  The nonvolatile RAM 18 is a battery-backed SRAM or the like, and stores data unique to the image processing apparatus. The operation unit 15 corresponds to the operation panel 35 of FIG. 12, and includes a photo direct print start key for selecting image data stored in the storage medium and starting recording, and a key for printing an order sheet. . Also, a key for reading an order sheet, a copy start key for monochrome copying or color copying, and a mode key for specifying a mode such as copy resolution and image quality are provided. Furthermore, a stop key for stopping the copy operation, a numeric keypad for entering the number of copies, a registration key, and the like are provided. The CPU 11 detects the pressed state of these keys and controls each part according to the state.

  The display unit 19 corresponds to the display panel 39 of FIG. 12, and includes a dot matrix type liquid crystal display unit (LCD) and an LCD driver, and performs various displays based on the control of the CPU 11. Also, thumbnails of the image data recorded on the storage medium are displayed. The recording unit 13 corresponds to the printing device 33 of FIG. 12 and is configured by an inkjet type inkjet head, a general-purpose IC, and the like, reads out the recording data stored in the RAM 17 under the control of the CPU 11, and prints it out as a hard copy. .

  The driving unit 21 includes a stepping motor for driving the paper supply / discharge roller, a gear for transmitting the driving force of the stepping motor, a driver circuit for controlling the stepping motor, and the like in the operations of the reading unit 14 and the recording unit 13 described above. including.

  The sensor unit 20 includes a recording paper width sensor, a recording paper presence sensor, a document width sensor, a document presence sensor, a recording medium detection sensor, and the like. The CPU 11 detects the state of the original and the recording paper based on information obtained from these sensors.

  The PC interface 24 is an interface between the PC and the image copying apparatus 1, and the image copying apparatus 1 performs operations such as printing and scanning from the PC via the PC interface 24.

  During the copying operation, the image data read by the reading device 34 is processed in the image copying device and printed by the printing device 33.

  When a copy operation is instructed by the operation unit 15, the reading unit 14 reads a document placed on the document table. The read data is sent to the image processing unit 12, subjected to image processing to be described later, and then sent to the recording unit 13 for printing.

  Next, image processing at the time of image copying processing (copying) executed by the image processing unit 12 in FIG. 13 will be described. FIG. 1 shows a flowchart of image processing.

  In S101, the image signal values (inR, inG, inB) read by scanning are subjected to shading correction. As a result, correction for variations in the input reading element is performed and converted to (sR, sG, sB).

  In S102, an input color conversion process is performed. The purpose of this processing is to convert signal values (sR, sG, sB) depending on the input device into a color space xRGB independent of the device. Common examples of xRGB include sRGB and AdobeRGB. In addition, the color space is not limited to a general color space, and an optimum color space may be defined individually and used.

  In the present embodiment, description will be made assuming that conversion to the AdobeRGB color space is performed. As a result, the input image is converted into (AdobeR1, AdobeG1, AdobeB1). As a conversion method, matrix conversion as shown below is used.

M _{11 to} M ₃₃ in the equation are matrix coefficients prepared in advance. In the above formula, an example of a primary matrix is given, but a multi-order matrix may be used.

  Further, instead of the matrix conversion method, an interpolation method using a tetrahedron may be used. In tetrahedral interpolation, a three-dimensional lookup table (hereinafter, 3D-LUT) is prepared in advance. These are stored in the ROM 16 in the image copying apparatus 1. The 3D-LUT describes converted data (here, values of AdobeR1, AdobeG1, and AdobeB1) corresponding to 4913 points obtained by dividing the RGB values as shown in FIG. The value of (AdobeR1, AdobeG1, AdobeB1) corresponding to the value of (sR, sG, sB) is referred to, and if the (sR, sG, sB) value is between the 16 divided points, an interpolation process is performed. .

  In the interpolation processing, linear interpolation using four lattice points is performed with the division unit of the three-dimensional space as a tetrahedron. As the procedure, first, as shown in FIG. 3A, division into tetrahedrons is performed. Then, the tetrahedron to which the target point p belongs is determined. The four vertices of the tetrahedron are defined as p0, p1, p2, and p3, and the tetrahedron is further divided into smaller tetrahedrons as shown in FIG. 3B. Further, if the converted values of the vertices are f (p0), f (p1), f (p2), and f (p3), respectively, the following formula is obtained.

  Here, w0, w1, w2, and w3 are the volume ratios of the small tetrahedrons at positions opposite to the vertexes pi. As a result, conversion to AdobeR1, AdobeG1, and AdobeB1 is performed.

  Next, in S103, processing table application processing is performed. When the input data (AdobeR1, AdobeG1, AdobeB1) is outside the output color reproduction range, it is converted into values (AdobeR2, AdobeG2, AdobeB2) that have been subjected to predetermined processing using a 3D-LUT generated by a method described later. Is done. When the input data is within the output color reproduction range, no color conversion is performed, and (AdobeR1, AdobeG1, AdobeB1) = (AdobeR2, AdobeG2, AdobeB2).

  In S104, the processing table application processing (AdobeR2, AdobeG2, AdobeB2) is converted into data (outR, outG, outB) depending on the output device. This conversion process (gamut compression process) is a process (gamut mapping) for mapping image data (AdobeR2, AdobeG2, AdobeB2) within the color reproduction range of the printing apparatus. Gamut mapping is performed by tetrahedral interpolation processing by 3D-LUT, as in S102 and 103. Details of a method for generating the 3D-LUT for gamut compression will be described later.

  In S105, the RGB format data (outR, outG, outB) obtained in S104 is decomposed into ink colors used for actual recording (printing). The decomposition method uses tetrahedral interpolation processing using a 3D-LUT in the same manner as above. Taking an inkjet printer as an example, it is common to use cyan, magenta, yellow, and black inks (hereinafter, C, M, Y, and K) as inks. In recent printers with an emphasis on photographic image quality, in addition to the above inks, low density photocyan and photomagenta (hereinafter, PC, PM) inks may be used, and the 3D-LUT in that case is The table is as shown in FIG.

  In S106, the image data (C1, M1, Y1, K1, PC1, PM1) in the ink format is quantized. In this process, the number of gradations that can be output by the printing apparatus is converted. The ink jet printer according to the present embodiment is an FM screening type printer that forms an image depending on whether or not ink droplet dots are hit. Here, binarization is described as an example of quantization processing. An error diffusion method is used as the quantization method. The input signal is 8 bits from 0 to 255.

FIG. 5 is a diagram showing an error distribution method in error diffusion processing. When the signal value of the target pixel is L (0 ≦ L ≦ 255), it is compared with the threshold value TH. Depending on its size,
L> TH ・ ・ ・ ・ ・ ・ 1 (Recording)
L ≦ TH ・ ・ ・ ・ ・ ・ 0 (not recorded)
It is determined. The error E (= L−TH) generated at that time is distributed to surrounding pixels according to the distribution coefficient shown in FIG. By executing this process for all pixels and all ink colors (C, M, Y, K, PC, PM), 1-bit image data (C2, M2, Y2, K2, PC2, PM2) ) Can be obtained.

  As described above, by executing S101 to S106 as described using the flowchart, it is possible to convert the read image data into a printable format.

  Next, the color reproduction of the image copying process, which is a feature of the present invention, will be described. As described above, color reproduction is determined by S103 (processing table application processing) and S104 (gamut compression processing) in FIG. A 3D-LUT can be used for these processes. A method for generating a 3D-LUT for each process will be described below. The 3D-LUT generated in advance is stored in, for example, the ROM 16 and used in S103 and S104 during the copy operation.

  In addition, although the following description discloses the main concept for producing | generating 3D-LUT suitable for this invention, normally 3D-LUT is produced | generated through trial and error. Therefore, in order to improve the color reproducibility during the copying operation, a part of the 3D-LUT that is finally generated may be deviated from this main concept by modifying a part of the 3D-LUT. Absent. For example, if the flowchart in FIG. 6 is followed faithfully, the input data in the output gamut is not processed (described later with reference to S605 and S606), so that contrast is not enhanced. However, in practice, in order to obtain better contrast, trial and error may be repeated to generate a 3D-LUT that performs processing on input data in the output gamut.

The 3D-LUT is obtained by dividing an input RGB value of 8 bits (0 to 255) into 16 parts every 16 steps. Each grid point gR, gG, gB is RGB value,

(0, 16, 32, 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208, 224, 240, 255)

Of 17 points. In the following description, the grid point numbers are 0 to 16 (for example, if gR = 2, the R value is 32).

  FIG. 6 is a flowchart showing details of processing for generating a 3D-LUT for the processing table application processing in S103 of FIG.

  In S601, gR = gG = gB = 0 is initialized. Eight blocks of S602 and S603 indicate that each value of the grid (gR, gG, gB) is changed from 0 to 16 to loop the process. As a result, the processing of S604 to S609 is repeated 17 grids × 3 = 4913 times.

In S604, the RGB signal value corresponding to the current grid is converted to L * a * b *. In particular,

R = (gR-1) × 16 (provided that R = 255 when R> 255)
G = (gG−1) × 16 (provided that G = 255 when G> 255)
B = (gB-1) × 16 (However, if B> 255, B = 255)

This RGB value is converted into L * a * b *. In the conversion process, first, the RGB values of the grid points gR, gG, and gB are regarded as the RGB values of AdobeRGB, and are converted into XYZ values that are tristimulus values in the assumed light source. By substituting the XYZ value into the following equation, L * a * b * is obtained.

Y / Yn> 0.008856
X / Xn> 0.008856
When Z / Zn> 0.008856,

L * = 116 (Y / Yn) ^1/3 -16
a * = 500 {(X / Xn) ¹ /3-(Y / Yn) ^1/3 }
b * = 200 {(Y / Yn) ¹ /3-(Z / Zn) ^1/3 }

Otherwise, the above formula is

(X / Xn) ^1/3 → 7.787 (X / Xn) +16/116
(Y / Yn) ¹ /3-> 7.787 (Y / Yn) +16/116
(Z / Zn) ^1/3 → 7.787 (Z / Zn) +16/116

Replace with Here, Xn, Yn, and Zn are tristimulus values of the complete reflection surface, and are normalized by Yn = 100.

  In S605, it is determined whether or not L * a * b * obtained in S604 is within the gamut of the output device (printing device 33). As a determination method, gamut data of the output device is held in advance and compared with the data. Specifically, a cross section of L * to be determined may be taken out, a hue may be obtained from a * b *, and the respective saturations in the hue direction may be compared.

  If it is determined that the RGB value of the current grid point is within the output gamut, the process proceeds to S607, and if not, the process proceeds to S606 and the processing is performed.

In the processing in S606, the brightness and saturation are processed, and L * a * b * obtained in S604 is converted into more contrasting and sharp data. Here, a table describing the machining amount is held in advance, and the signal value is changed accordingly. There are two types of tables for brightness and saturation, TABLE_L and TABLE_S, respectively.

Output L * = TABLE_L [input L *]

Is required. For saturation, a *, b *

Input saturation S = (a * × a * + b * × b *) ^1/2

Thus, the input saturation S is obtained, and the saturation correction coefficient w is

w = TABLE_S [input saturation S]

Ask for. Processing is performed by multiplying this w by a * and b *.

Output a * = input a * × w
Output b * = input b * × w

Thereby, the L * a * b * value processed so as to enhance the contrast is obtained. Next, the process proceeds to S607. Note that there are a plurality of processing processes in S606 instead of one, and each corresponds to a mode used depending on the conditions at the time of copying. For example, when the mode for performing saturation enhancement is selected by the user, or when the mode is selected automatically, or when the recording paper is plain paper, the overall brightness and saturation are increased. There are processing and processing for increasing brightness and saturation, which are part of a mode for removing the ground color of the document image.

  In S607, the L * a * b * values are converted back to RGB signals. For the conversion, the reverse conversion of S604 may be performed. When the process does not go through S606 (that is, when the processing is not performed), the original RGB values are obtained by inverse transformation.

  In S608, correction processing described later is performed on the RGB values obtained by the conversion processing in S607.

  In S609, the RGB value (output value) obtained as a result of the correction processing in S608 is set as the current grid table value.

  By applying the above processing to all grid points, a 3D-LUT for the processing table application processing in S103 is generated.

  Next, the correction process in S608 will be described in detail. FIG. 14 is a flowchart showing a detailed flow of the correction processing in S608 of FIG.

  In S1401, a correction flag for the current grid point (to be processed) is acquired. The correction flag is a value (binary data) of 0 or 1, where 0 means no correction and 1 means correction. That is, 0 or 1 data for all 4913 grid points. A method for generating the correction flag will be described later.

  In S1402, it is determined whether or not the correction flag is 1. If the correction flag is 0 (OFF), the correction is not performed and the processing of this flowchart ends. If the correction flag is 1 (ON), the process proceeds to S1403.

  In S1403, the amount of change in brightness (brightness difference) due to the processing in S606 in FIG. 6 is distributed (added) to the increase in saturation. That is, the amount of change in lightness decreases, and the saturation increases accordingly.

  The purpose of the correction processing here is to prevent image deterioration due to a significant increase in lightness or a decrease in saturation due to the processing.

The signal values before processing are R _ORG , G _ORG , and B _ORG, and the signal values after S607 after the processing and RGB conversion are R _COR , G _COR , and B _COR .

Here, the brightness components before and after processing are I _ORG and I _COR , respectively, and the saturation components are C _ORG and C _COR , respectively. I _ORG and I _COR are respectively

I _ORG = min (R _ORG , min (G _ORG , B _ORG ))
I _COR = min (R _COR , min (G _COR , B _COR ))

C _ORG and C _COR are respectively calculated by

C _ORG = max (R _ORG −I _ORG , max (G _ORG −I _ORG , B _ORG −I _ORG ))
C _COR = max (R _COR -I _COR , max (G _COR -I _COR , B _COR -I _COR ))

It is calculated by. Here, min (a, b) and max (a, b) are functions for obtaining the minimum value and the maximum value of (a, b), respectively.

Then, if the difference between the brightness component and the saturation component before and after processing is ΔI and ΔC, respectively,

ΔI = I _COR -I _ORG
ΔC = C _COR -C _ORG

It is calculated by.

Here, when the flag is 1, the increase in the brightness component is corrected by the following equation. In addition, in order to simplify the description here, the target is a color between Red and Yellow, that is,

R _ORG > G _ORG > B _ORG

Signal value. In this case, the corrected signal values R _NEW , G _NEW , and B _NEW to be obtained are represented by the following equations, respectively.

R _NEW = R _ORG + ΔI + ΔC
G _NEW = (R _NEW −I _ORG ) / rate + I _ORG
B _NEW = B _ORG

Here, rate represents the ratio between the maximum signal value excluding the brightness component and the next largest signal value. Here, it means the ratio of the G signal to the R signal excluding the brightness component.

rate = (R _ORG -I _ORG ) / (G _ORG -I _ORG )

  A similar calculation may be performed for regions other than Yellow to Red, that is, Yellow to Green, Green to Cyan, Cyan to Blue, Blue to Magenta, and Magenta to Red.

If it is determined in the determination process of S605 that the output is within the output gamut and the process of S606 is not performed, at this time,

R _ORG = R _COR
G _ORG = G _COR
B _ORG = B _COR

Because

ΔI = ΔC = 0

As a result, no correction processing is applied as a result.

R _NEW = R _ORG
G _NEW = G _ORG
B _NEW = B _ORG

  Next, a flag for determining whether or not correction is performed will be described. In this embodiment, a case where the correction flag is set to 1 (ON) in the vicinity of the maximum saturation of the output device will be described. Copying using plain paper by an image copying apparatus equipped with an ink jet printer has low color reproduction capability and poor color development. For this reason, the gamut mapping of the color outside the color reproduction range is converted so as to be mapped to a color having a high saturation and a good appearance in the processing of S606.

  FIG. 15 is a diagram showing color reproduction of a copy by an image copying apparatus provided with an ink jet printer. As an example, White-Red-Black is taken up. In this graph, the vertical axis represents lightness L *, and the horizontal axis represents saturation S. The start point of the arrow indicates a point obtained by dividing Adobe RGB on 17 grid points, and the end point indicates a mapping destination of the color within the color reproduction range. From this figure, many colors outside the color reproduction range of plain paper are mapped to the portion corresponding to the triangle side of the reproducible color space. In particular, the maximum saturation portion is particularly dense in color, and in normal copying, it can be said that colors are often reproduced in the vicinity. In other words, in the grandchild copy that becomes the original document next time, by suppressing the color deterioration of this portion, it greatly contributes to the improvement of the image quality.

  Taking this into consideration, FIG. 16 shows the flow of processing for obtaining the correction flags for the 4913 lattice points. Before executing this flowchart, it is necessary to obtain what color is to be output when RGB signal values are input to the output device in advance. For this purpose, a color patch or the like having RGB signal values may be printed on a recording sheet and measured by a measuring device or may be obtained by simulation. In the former case, if all the RGB signal values are recorded and measured, the number of patches becomes enormous, which is not realistic. Therefore, a method may be used in which thinned patches, for example, 729 patches divided into 8 channels are measured, and color prediction is performed by interpolation processing during the measurement.

  In S1600, flag data of all grid points (4913 points) is initialized with zero. In S1601, the grid number is initialized to gR = gG = gB = 0.

  Eight blocks of S1602 and S1603 indicate that each value of the grid (gR, gG, gB) is changed from 0 to 16, and the process is looped. As a result, the processing from S1604 to S1608 is repeated 17 grids × 3 = 4913 times.

In S1604, it is determined whether the minimum and maximum values of gR, gG, and gB are 0 and 16, respectively. That is, it is determined whether at least one of gR, gG, and gB is 0 and at least one is 16. If the condition is not satisfied, the processing proceeds to S1603 without executing the processing of S1604 to S1608. If the condition is satisfied, the RGB signal value corresponding to the current grid point represents the maximum saturation point of any hue of the output device. In other words, it can be said that the colors are easy to gather in the first copy. If the condition is satisfied, the process proceeds to S1605, and the recording color of the output device when the signal value is input is obtained. First, the grid point is converted into an 8-bit signal value by the following equation.

R = (gR-1) × 16 (provided that R = 255 when R> 255)
G = (gG−1) × 16 (provided that G = 255 when G> 255)
B = (gB-1) × 16 (However, if B> 255, B = 255)

  A color prediction value is obtained from the obtained RGB signal value and the color data of the output device prepared in advance. As an interpolation method, the interpolation process using the tetrahedron described with reference to FIG. 3 may be used. As a result, a color predicted value when a predetermined RGB signal value is recorded, in this case, an L * a * b * value is obtained.

  In S1606, the obtained L * a * b * value is converted into AdobeRGB, and at this time, the AdobeRGB value (Rtgt, Gtgt, Btgt) of the maximum saturation point in a certain hue of the output device is acquired.

In step S1607, Adobe RGB grid points surrounding the point are obtained. Here, since the flag data has 17 grids 4913 points, that is, an interval of 16 signal values with 8 bits, the obtained grid points R_0, G_0, and B_0 (0 to 16) are respectively

R_0 = Rtgt / 16
G_0 = Gtgt / 16
B — 0 = Btgt / 16

It is obtained by rounding down the decimal part. Furthermore, based on R_0, G_0, and B_0, the remaining eight points surrounding the maximum saturation point from the following formula,

(R_1, G_1, B_1), (R_2, G_2, B_2),
(R_3, G_3, B_3), (R_4, G_4, B_4),
(R_5, G_5, B_5), (R_6, G_6, B_6),
(R_7, G_7, B_7)

Is calculated.

(R_1, G_1, B_1) = (R_0 + 1, G_0, B_0)
(R_2, G_2, B_2) = (R_0, G_0 + 1, B_0)
(R_3, G_3, B_3) = (R_0, G_0, B_0 + 1)
(R_4, G_4, B_4) = (R_0 + 1, G_0 + 1, B_0)
(R_5, G_5, B_5) = (R_0, G_0 + 1, B_0 + 1)
(R_6, G_6, B_6) = (R_0 + 1, G_0, B_0 + 1)
(R_7, G_7, B_7) = (R_0 + 1, G_0 + 1, B_0 + 1)

  In S1608, the grid flag obtained in S1607 is set to 1.

Here, the flags 0 and 1 are taken as an example. However, when the processing is strongly applied, depending on the value of the flag, the change is too intense, the switching portion becomes extreme, and an image such as a pseudo contour is displayed. A phenomenon that causes deterioration may occur. Therefore, an intermediate portion between 0 and 1 may be generated. In this middle region, with the signal value _R NEW in the case of performing correction described _above, G _NEW, and _{B NEW,} unprocessed signal values _{R ORG,} G _ORG, the _{B ORG, R NEW ', G} NEW', Change to B _{NEW '} .

R _{NEW ′} = (R _NEW −R _ORG ) /2.0+R _{ORG
G NEW '= (G NEW -G} ORG) /2.0+G ORG
B _{NEW ′} = (B _NEW −B _ORG ) /2.0+B _ORG

  That is, the correction ratio is halved, this is used as a buffer area, and the switching portion is smoothed.

  In addition, the flag for the buffer area is obtained by re-searching the flag obtained once with 0 and 1, the current flag is 0, and the flag value 1 is included in any of the surrounding 8 grids. In such a case, the buffer area may be set. In this case, the correction flag is, for example, 2-bit data of 0 (no correction), 1 (with correction), and 2 (buffer area).

  FIG. 17 shows the case where the correction process of S608 in FIG. 6 is not performed (upper) (after execution of S607, the process proceeds to S609 without executing the correction process of S608) and the lower case (after execution of S607). FIG. 6 is a diagram showing an outline of a processing table application process of S103 of FIG. 1 when the correction process of S608 is executed and the process proceeds to S609. As shown in the upper part of FIG. 17, the value of the image data is converted so that the contrast is enhanced by the processing in S606 of FIG. On the other hand, saturation is decreasing in many areas.

  On the other hand, as shown in the lower part of FIG. 17, correction processing is applied to the part surrounded by a circle. As a result of the correction process, the amount of change in brightness decreases, and the saturation increases accordingly.

  In addition, a 3D-LUT with a buffer area introduces a balance between increase in saturation and contrast enhancement in the vicinity of the boundary between the medium lightness and high saturation range and the other range. In the meantime, image correction processing is applied to the image data.

  As described above, by performing correction on the once-determined processing, processing that suppresses image degradation of the grandchild copy is performed. In the correction process of this table, only portions that have a great influence on the grandchild copy are corrected, so that there is no significant influence on normal copying.

  Next, the 3D-LUT for gamut compression executed in S104 of FIG. 1 will be described. FIG. 11 is a diagram illustrating an outline of gamut mapping using a 3D-LUT. In FIG. 11, “+” indicates a grid point of the 3D-LUT, and a mountain-shaped graph indicates the color reproduction range of the output device. The 3D-LUT is set so that colors outside the color reproduction range of the output device are mapped within the color reproduction range, as shown in the lower part of FIG. 11.

  First, gamut mapping according to the first embodiment will be described with reference to FIG. FIG. 7 is a cross-sectional view of a color space in a certain hue. In the figure, 701 indicates the color reproduction range of AdobeRGB, and 702 indicates the color reproduction range of the output device. Reference numeral 703 indicated by a dotted line represents a preset colorimetric matching region. In gamut compression processing (gamut mapping), a color space having the color reproduction range 701 is mapped to the color reproduction range 702.

  Colors in the colorimetric match region 703 are mapped to the color matching points without being compressed, and colors in the range between the colorimetric match region 703 and the color reproduction range 701 are colorimetric match regions 703. And the color reproduction range 702 are compressed and mapped. The compression at this time is advanced in a direction toward a certain lightness point, for example, L * = 50, and is mapped to any location between the colorimetric matching region 703 and the color reproduction range 702. If the mapping is linear, the color before compression is determined by how far from the outermost point of the colorimetric matching region 703 in the colorimetric matching region 703 and the color reproduction range 701. .

S _org : Distance between L * = 50 and color before compression S _col : Distance between L * = 50 and colorimetric matching region 703 (L * = 50 and color direction before compression)
S _gam : Distance between L * = 50 and color reproduction range 702 (L * = 50 and color direction before compression)
S _max : Distance between L * = 50 and the color reproduction range 701 (L * = 50 and the color direction before compression)
In this case, the mapping point M is determined by the following formula.

M = S _col + (S _gam −S _col ) × (S _org −S _col ) / (S _max −S _col )

In addition, although linear mapping was described in the above formula, there is another method of performing mapping nonlinearly. In this case, it is effective to weight the mapping closer to the color reproduction range 702 in order to suppress saturation reduction. In that case, the coefficient g (<1) is used and is expressed by the following formula.

M = S _col + (S _gam −S _col ) × {(S _org −S _col ) / (S _max −S _col )} ^g

  In other words, in the color reproduction range of the printer, in the range excluding the vicinity of the boundary line excluding the portion where the saturation is 0, the color of the original image and the color of the image printed by the printer match. Data is mapped. In other ranges, the image data is mapped so as to be compressed by a predetermined scale.

  Further, a method of referring to a table prepared in advance without obtaining M by calculation may be used.

  FIG. 8 is a flowchart showing the flow of processing for generating a 3D-LUT for gamut mapping. Similar to the 3D-LUT for S103 (processing table application processing) in FIG. 1, the generated 3D-LUT is stored in, for example, the ROM 16 and used in the copying operation.

  The processing from S801 to S804 is the same as S601 to 604 in FIG. Thereby, initialization, processing loop, and conversion of RGB values into L * a * b * values are executed.

  In S805, it is determined whether or not the L * a * b * value obtained in S804 is within a preset colorimetric matching region. The determination method may be the same as the method described for the processing table application process. If it is determined that it is within the colorimetric matching region, no processing is performed, and the process proceeds to S806. If it is determined that it is outside the colorimetric matching region, the process proceeds to S808, and compression mapping is executed. Is done.

  In S808, the above-described mapping is executed, and after obtaining a new L * a * b * value, the process proceeds to S806.

  In S806, RGB format data (outR, outG, outB) when the target L * a * b * value is printed by the output device is obtained. As a calculation method, it is derived from the relationship between the output device RGB value and the output L * a * b * value that are held in advance. At that time, as described above, if it is impossible to hold the L * a * b * values corresponding to the RGB values (outRGB) of all the output devices, the data of only the determined sample points is held. , By interpolating between them.

  The outRGB obtained in S806 is set as grid point data of the 3D-LUT in S807. In this way, a 3D-LUT for gamut compression is generated.

  If the 3D-LUT generated by the processing of this flowchart is used, the compression processing shown in FIG. 9 is performed. 9, the same elements as those in FIG. 7 are denoted by the same reference numerals as those in FIG. In the figure, data within the color reproduction range at the point L does not move even after mapping, whereas data outside the color reproduction range at the point N corresponds to the colorimetric matching region 703 and the color reproduction range. 702 and 702 are mapped. In addition, the point originally located between the colorimetric matching region 703 and the color reproduction range 702, such as point M, is slightly in the direction of the colorimetric matching region 703. Note that the direction of movement is a direction toward a predetermined brightness (L * = 50 in FIG. 9).

  As described above, when the color reproduction of the input document is performed according to the color conversion process described in FIG. 1 of the present embodiment, the color reproduction characteristics as shown in FIG. 10 are obtained. The white circles in the figure represent the color of the document, and the black circles are colors realized by copying based on the present embodiment. A hatched circle indicates a case where the input and the output are colorimetrically matched. The color of point C in the figure is colorimetrically matched, and the input document color is maintained colorimetrically. Point A in the figure is a color that cannot be reproduced by the recording apparatus, and is compressed within the color reproduction range of the printer. At this time, processing is added to the saturation and lightness so that the contrast of the image is enhanced. It is mapped. Point B in the figure is a color that can be reproduced by the recording apparatus, but is slightly compressed toward a certain lightness point. Point B 'is an area that is slightly compressed, as is point B, but is located near the maximum saturation of the printer, so no reduction in saturation has occurred.

In this specification, it is often described as “colorimetric match”. However, in actuality, due to measurement errors, calculation errors such as interpolation, and processing bit accuracy, etc. It does not always match. Also in FIG. 17, it can be seen from the fact that it has a slight arrow length despite the colorimetric matching region. Therefore, in the color difference ΔE value shown below, colors below a certain value are regarded as colorimetric matches.

ΔE = (ΔL * ² + Δa * ² + Δb * ² ) ^1/2

  In the present specification, it is considered that those having ΔE of 5 or less that can be regarded as actually the same color are colorimetrically matched.

  Further, among the target colors, those close to yellow or close to blue have extremely high or low brightness values. Furthermore, due to the characteristics of the recording apparatus, there are colors with an extremely wide color reproduction range during recording and narrow colors. In consideration of such a case, the color reproduction method of this specification may not be used uniformly for all colors, but may be applied only to specific colors. Even in this case, the effect of the present invention can be sufficiently obtained for the specific color.

  As described above, according to this embodiment, the image copying apparatus 1 corrects the image data acquired from the reading device 34 as shown in the lower part of FIG. 17 and then executes gamut mapping. .

  As a result, the color reproducibility of the original image in the output image is improved for the image copying apparatus for which the color reproduction range of the output device is narrower than the color reproduction range of the input device while suppressing an increase in the cost of the image copying apparatus. It is possible to provide the technology to be performed. In addition, color change during grandchild copy is suppressed.

[Second Embodiment]
In the first embodiment, focusing on the maximum saturation point of the recording apparatus, correction is performed in consideration of grandchild copy. At that time, the presence or absence of correction was determined using correction flags of 0 and 1. This is effective when the color reproduction range of the recording device is extremely small, since it is often effective to collect colors at the maximum saturation point in the first copy process, but this is not always appropriate when the color reproduction range is large. Not exclusively.

  Therefore, in the second embodiment, an example is given in which the distribution after color reproduction is taken into account and correction is performed based on the distribution. Note that the correction portion in S608 of FIG. 6 is a feature, and other processing, compression, and the like are the same as those in the first embodiment, and thus the description of that portion is omitted.

  FIG. 18 shows the flow of the correction process. Before starting this process, distribution data is generated in advance. In this case, when a color in a certain target color space is input, the correction in S608 in FIG. 6 is not performed, and only the processing in S606 is performed, and the distribution is generated as data. For simplicity, a two-dimensional diagram will be used.

FIG. 15 is a mapping diagram in a certain hue. This end point, that is, the L * a * b * value of the reproduced color is acquired and converted into AdobeRGB. This is assigned to an area that has been divided into small areas in advance. For example, if the color reproduced and converted to AdobeRGB is (R1, G1, B1), and the small area is an area obtained by dividing AdobeRGB into 16 areas, the target area (R _BOX , G _BOX , B _BOX ) of this color is used. Is

(R _BOX , G _BOX , B _BOX ) = (R 1/16, G 1/16, B 1/16)

It is obtained by rounding down the decimal point. Each area has a counter indicating how many colors are mapped, and the counter of the target area is incremented. By performing this for all space data and dividing the counter by the total number of data, the distribution probability in the color space by processing / compression processing can be obtained. Outside the color reproduction range of the printing apparatus, it cannot be mapped, so it is zero.

  Using these data, in S1801, a corresponding small region is extracted from AdobeRGB as the target grid, and a correction coefficient γ (0 to 1) is obtained from the distribution probability. FIG. 19 is an example of a graph for obtaining γ. If the distribution probability is greater than or equal to a certain value A, γ is 1, and below that, it becomes linearly smaller. That is, the intensity of the correction process varies depending on the value of γ.

In S1802, using γ obtained in S1801, corrected signal values (R _{NEW ′} , G _{NEW ′} , B _{NEW ′} ) are obtained by the following equations.

R _{NEW ′} = (R _NEW −R _ORG ) × (1−γ) + γR _ORG
G _{NEW ′} = (G _NEW −G _ORG ) × (1−γ) + γG _ORG
B _{NEW ′} = (B _NEW −B _ORG ) × (1−γ) + γB _ORG

R _NEW , G _NEW , and B _NEW mean the same values as in the first embodiment, and when complete correction is performed, a signal value corresponding to the flag value 1 in the first embodiment is used. To express.

  In this way, by considering the distribution probability, it is possible to realize a more optimal correction process when there is a certain color reproduction capability and the first copy does not necessarily gather near the maximum saturation. As a result, with respect to colors that are likely to be color-mapped in the first copy, it is possible to more accurately realize deterioration in image quality that lightness and saturation decrease in grandchild copy.

[Other Embodiments]
In order to realize the functions of the above-described embodiments, a recording medium in which a program code of software embodying each function is recorded may be provided to the system or apparatus. The functions of the above-described embodiments are realized by the computer (or CPU or MPU) of the system or apparatus reading and executing the program code stored in the recording medium. In this case, the program code itself read from the recording medium realizes the functions of the above-described embodiments, and the recording medium on which the program code is recorded constitutes the present invention. As a recording medium for supplying such a program code, for example, a floppy (registered trademark) disk, a hard disk, an optical disk, a magneto-optical disk, or the like can be used. Alternatively, a CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM, or the like can be used.

  The configuration for realizing the functions of the above-described embodiments is not limited to executing the program code read by the computer. Including the case where the OS (operating system) running on the computer performs part or all of the actual processing based on the instruction of the program code, and the functions of the above-described embodiments are realized by the processing. It is.

  Further, the program code read from the recording medium may be written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Thereafter, the CPU of the function expansion board or function expansion unit performs part or all of the actual processing based on the instruction of the program code, and the functions of the above-described embodiments may be realized by the processing. Is included.

3 is a flowchart showing a flow of image processing during a copying operation by the image copying apparatus according to the first embodiment. It is a figure which shows an example of the three-dimensional look-up table (3D-LUT) for the process in S102 of FIG. It is explanatory drawing of the interpolation process using 3D-LUT. It is explanatory drawing of the interpolation process using 3D-LUT. It is a figure which shows an example of 3D-LUT for a color separation process. It is a figure which shows the error distribution method in an error diffusion process. It is a flowchart which shows the detail of the process which produces | generates 3D-LUT for the process table application process in S103 of FIG. It is a figure which shows the outline | summary of a gamut mapping. It is a flowchart which shows the flow of the production | generation process of 3D-LUT for gamut mapping. It is a figure which shows the gamut mapping which concerns on 1st Embodiment. FIG. 3 is a diagram illustrating color reproduction characteristics of the image copying apparatus according to the first embodiment. It is a figure which shows the outline | summary of the gamut mapping using 3D-LUT. 1 is an overview perspective view of an image copying apparatus according to a first embodiment. 1 is a functional block diagram of an image copying apparatus according to a first embodiment. 7 is a flowchart showing a detailed flow of a correction process in S608 of FIG. It is a figure which shows the color reproduction of the copy by an image copying apparatus provided with an inkjet printer. It is a flowchart which shows the flow of a process which calculates | requires the correction flag of the lattice point of 4913 points. FIG. 7 is a diagram illustrating an outline of a processing table application process of S103 of FIG. 1 when the correction process of S608 of FIG. 6 is not performed (upper) and when performed (lower). It is a flowchart which shows the flow of the correction process which concerns on 2nd Embodiment. It is a figure which shows the graph which calculates | requires correction coefficient (gamma) in 2nd Embodiment.

Explanation of symbols

1 Image Copying Device 31 Auto Document Feeder (ADF) 31
33 Printing device 34 Reading device 34
35 Operation panel 39 Display panel 43 Camera port

Claims (6)

An image copying apparatus comprising a scanner and a printer,
Acquisition means for causing the scanner to read an image of a document and acquiring image data;
A correction process for adding a value corresponding to a brightness difference before and after performing a predetermined processing process to the image data to the saturation for a correction range set near the maximum saturation of the color reproduction range of the printer. Correction means to perform,
Control means for causing the printer to print the image data corrected by the correction means;
An image copying apparatus comprising:   The image copying apparatus according to claim 1, wherein the correction unit performs the correction process using a pre-generated 3D-LUT that stores the result of the correction process.   The image copying apparatus according to claim 1, wherein the correction unit sets a range in which the intensity of the correction process is different. An image copying apparatus control method comprising a scanner and a printer,
An acquisition step of causing the scanner to read an image of a document and acquiring image data;
A correction process for adding a value corresponding to a brightness difference before and after performing a predetermined processing process to the image data to the saturation for a correction range set near the maximum saturation of the color reproduction range of the printer. A correction process to be performed;
A control step for causing the printer to print the image data corrected in the correction step;
A control method comprising: A computer with a scanner and a printer,
Acquisition means for causing the scanner to read an image of a document and acquiring image data;
A correction process for adding a value corresponding to a brightness difference before and after performing a predetermined processing process to the image data to the saturation for a correction range set near the maximum saturation of the color reproduction range of the printer. Correction means to perform,
Control means for causing the printer to print the image data corrected by the correction means;
Program to function as. An image copying apparatus that includes a scanner and a printer, acquires image data by causing the scanner to read an image of a document, corrects the acquired image data, and outputs the corrected image data to the printer. In a method of generating a 3D-LUT for use in
A setting step for setting a correction range near the maximum saturation of the color reproduction range of the printer;
A correction step of performing a correction process for adding a value according to a brightness difference before and after performing a predetermined processing process on the image data to the saturation for the range to be corrected;
A registration step of registering in the 3D-LUT the value of the image data corrected by the processing and the correction step, as an output value for the value of the input image data;
A method for generating a 3D-LUT, comprising:

Images