JP4524578B2 - Image processing apparatus, image processing method, program, and recording medium - Google Patents

Description

  The present invention relates to a color correction table generation method, an image processing apparatus, an image processing method, a program, and a recording medium when an input color reproduction area and an output color reproduction area are different.

  When the monitor image signal is printed using a printer or the like, color conversion is necessary because each color system is different. In general, color matching is performed by a printer by performing color matching using a target of RGB image input data as a color reproduction region of a monitor.

  However, the range in which the RGB data can be specified in the color reproduction area of the target monitor does not include the entire color reproduction area of the printer. For example, in a color reproduction area from green to blue, there are areas where color reproduction by a printer is possible but color reproduction by a monitor is impossible.

  However, as long as color matching is performed with the color reproduction area of the monitor as a target, colors that cannot be reproduced by the monitor even if they can be reproduced by the printer are not output by the printer. In other words, even if the color of the original image can be reproduced as the capability of the printer body, since the monitor matching is performed, the printer performance cannot be fully exhibited, and printing is performed with a low-saturation color. There is a case.

  The present invention has been made to solve the above problems, and a color correction table generation method, an image processing apparatus, an image processing method, a program, and a recording medium that can more effectively use a color reproduction region of an output system such as a printer. It is an issue to provide.

  In view of the above problems, the invention described in claim 1 is an image processing apparatus that performs desired color correction on an image input signal using a color correction table, and an output gamut is more preferable than an input gamut. Using a color correction table for saturation enhancement that performs saturation enhancement processing on a desired color point of an image input signal by changing the degree of saturation enhancement processing according to the size of the input system gamut in a wide area. To perform desired color correction.

  According to a second aspect of the present invention, there is provided an image processing apparatus for performing a desired color correction on an image input signal using a color correction table, wherein the output gamut is wider than the input gamut. The desired color point of the image input signal is configured to perform desired color correction using a saturation enhancement color correction table that performs saturation enhancement processing in a direction substantially perpendicular to the input gamut surface. .

  Furthermore, the invention according to claim 3 is the image processing apparatus according to claim 1 or 2, wherein the degree of saturation enhancement processing by the color enhancement table for saturation enhancement is determined according to the type of input gamut. Configured to change.

  According to a fourth aspect of the present invention, in the image processing apparatus according to the first or second aspect, the saturation enhancement by the saturation enhancement color correction table as the size of the input gamut decreases. It is configured to increase the degree of processing.

  Further, the invention according to claim 5 is the image processing apparatus according to any one of claims 1 to 4, wherein the desired image input signal is output in a region where the output gamut is narrower than the input gamut. A desired color correction is performed using a compression processing color correction table for performing a compression process on the color point.

  The invention according to claim 6 is the image processing apparatus according to any one of claims 1 to 5, wherein the desired color point is close to an achromatic color in the color correction table for saturation enhancement. In this case, the saturation enhancement process is not performed.

  Further, the invention described in claim 7 is the image processing apparatus according to claim 1, wherein the saturation enhancement processing is performed so as to preserve the hue.

  The invention according to claim 8 is the image processing apparatus according to any one of claims 5 to 7, wherein the compression processing is performed so as to preserve the hue.

  The invention described in claim 9 is the image processing apparatus according to any one of claims 1 to 8, wherein the saturation enhancement color correction table can adjust the degree of saturation enhancement. Configured as follows.

  The invention described in claim 10 is the image processing apparatus according to any one of claims 1 to 9, wherein the saturation enhancement color correction table can set a saturation enhancement limit value. Configured to be.

  Furthermore, the invention according to claim 11 is the image processing apparatus according to any one of claims 1 to 10, wherein color correction for saturation enhancement is performed in the case of an image input signal having a large amount of green and blue components. A table is used to perform desired color correction.

  According to a twelfth aspect of the present invention, there is provided the image processing apparatus according to any one of the first to eleventh aspects, wherein a desired color correction table for saturation enhancement is used according to the type of the image input signal. Is configured to perform color correction.

  Furthermore, the invention described in claim 13 is the image processing apparatus according to any one of claims 1 to 12, wherein the saturation correction color correction table is used when the image input signal is a bit image image. To perform desired color correction.

  According to a fourteenth aspect of the present invention, there is provided an image processing method for performing a desired color correction on an image input signal using a color correction table, wherein the output gamut is wider than the input gamut. The degree of saturation enhancement processing is changed according to the size of the input gamut, and a desired color point for saturation enhancement is applied to a desired color point of the image input signal by using a saturation enhancement color correction table. It is configured to perform color correction.

  Furthermore, the invention described in claim 15 is an image processing method for performing desired color correction on an image input signal using a color correction table, and in an area where the output gamut is wider than the input gamut. The desired color point of the image input signal is configured to perform desired color correction using a saturation enhancement color correction table that performs saturation enhancement processing in a direction substantially perpendicular to the input gamut surface. .

  According to the sixteenth aspect of the present invention, in the region where the output gamut is wider than the input gamut, the degree of saturation enhancement processing is changed according to the size of the input gamut, and A program for causing a computer to execute image processing for performing desired color correction using a saturation enhancement color correction table for performing saturation enhancement processing on a desired color point.

  Furthermore, in the invention described in claim 17, in a region where the output gamut is wider than the input gamut, the desired color point of the image input signal is saturated in a direction substantially perpendicular to the input gamut surface. This is a program for causing a computer to execute image processing for performing desired color correction using a color correction table for saturation enhancement for performing enhancement processing.

  The invention according to claim 18 is a computer-readable recording medium on which the program according to claim 16 or 17 is recorded.

  Furthermore, in the invention described in claim 19, in the region where the output gamut is wider than the input gamut, the degree of saturation enhancement processing is changed according to the size of the input gamut, so that the image input signal This is a computer-readable recording medium that records a saturation enhancement color correction table for performing saturation enhancement processing on a desired color point.

  According to the twentieth aspect of the present invention, in a region where the output gamut is wider than the input gamut, the desired color point of the image input signal is saturated in a direction substantially perpendicular to the input gamut surface. It is a computer-readable recording medium on which a saturation enhancement color correction table for performing enhancement processing is recorded.

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

  FIG. 1 is a functional block diagram of a color correction table generation device according to an embodiment of the present invention, FIG. 11 is a functional block diagram of an image processing device according to an embodiment of the present invention, and FIG. A specific hardware configuration example of the color correction table generation device and the image processing device is shown by a schematic block diagram.

  In FIG. 1, the color correction table generation device 20 generates a printer gamut based on the display gamut generation unit 20 g that generates a display gamut based on the RGB image data generated by the application 12 d and the color measurement result of the colorimeter 37. A printer gamut generation unit 20e for generating a color correction table (LUT) based on the generated printer gamut and display gamut, and a color correction LUT storage for storing the generated color correction LUT Part 20h. Details of the processing of these components will be described later. On the other hand, regarding the display image data generated by the application 12d, the video driver 12b writes it in a predetermined image memory and displays it on the display 17a via the hardware circuit.

  In FIG. 11, the image processing device 20 </ b> A performs desired image processing on the color image input signal (data), and outputs the color image data subjected to the image processing to the image output device 30. Here, the color image data represents the strength of each element color while color-separating the color image for each predetermined element color, and is represented by gray when it is a chromatic color and mixed at a predetermined ratio. It consists of a neutral color and black. In the present embodiment, a case where the image output apparatus 30 such as a printer performs print processing based on CMYK data will be described.

  In the display 17a, the color image is displayed in gradation in three primary colors (R, G, B) of red, green, and blue for each pixel arranged vertically and horizontally, but in the printer of this embodiment, cyan, magenta, yellow, black The four colors (C, M, Y, K) are printed without gradation display. Therefore, for color printing, color conversion work from the display of the three primary colors (R, G, B) of red, green and blue to the display of four colors (C, M, Y, K) of cyan, magenta, yellow, and black, It is necessary to perform gradation conversion from gradation display to display without gradation.

  The image processing apparatus 20A reads the first color conversion unit 20a for converting RGB image data into image data of the Luv coordinate system, and the selected color correction table from the color correction LUT storage unit 20h, and the read A color correction unit 20b for converting the display-use Luv coordinate system image data into printer-use Luv coordinate system image data with reference to the color correction table, and the Luv coordinate system image data of CMYK (cyan, magenta, yellow, black). A second color conversion unit 20c that converts data into data and a binarization unit 20d that converts the CMYK data into binary data are provided.

  In the present embodiment, a computer system is employed as an example of hardware that realizes such a color correction table generation device 20 and the image processing device 20A. FIG. 2 is a block diagram showing the computer system. The computer system includes a scanner 11a, a digital still camera 11b, and a video camera 11c as image input devices, and is connected to a computer main body 12. Each input device can generate image data in which an image is expressed by a dot matrix pixel and output the image data to the computer main body 12. Here, the image data is displayed in 256 gradations for each of the three primary colors of RGB. About 16.7 million colors can be expressed.

  A floppy disk drive 13a, a hard disk 13b, and a CD-ROM drive 13c as external auxiliary storage devices are connected to the computer main body 12, and main programs related to the system are recorded on the hard disk 13b. Necessary programs and the like can be read from a CD-ROM or the like as appropriate. In addition, a modem 14a is connected as a communication device for connecting the computer main body 12 to an external network or the like, and it can be connected to an external network via the public communication line, and can be installed by downloading software and data. It has become. In this example, the modem 14a accesses the outside via a telephone line, but it is also possible to adopt a configuration where the network is accessed via a LAN adapter. In addition, a keyboard 15a and a mouse 15b are also connected for operating the computer main body 12.

  Furthermore, a display 17a and a color printer 17b are provided as image output devices. The display 17a has a display area of 800 pixels in the horizontal direction and 600 pixels in the vertical direction, and the above-described display of 16.7 million colors can be performed for each pixel. This resolution is merely an example, and can be appropriately changed such as 640 × 480 pixels or 1024 × 768 pixels.

The color printer 17b is an ink jet printer, and can print an image by adding dots on a printing paper as a medium using four color inks of CMYK. The image density can be printed at a high density of 360 × 360 dpi or 720 × 720 dpi, but the gradation expression is a two-gradation expression such as whether or not color ink is applied. On the other hand, in order to display or output to the image output device while inputting an image using such an image input device, a predetermined program is executed in the computer main body 12. Among them, an operating system (OS) 12a is operating as a basic program, and the operating system 12a displays a display driver (DSP) that displays on the display 17a.
DRV) 12b and a printer driver (PRT DRV) 12c for causing the color printer 17b to perform print output are incorporated. These drivers 12b and 12c depend on the models of the display 17a and the color printer 17b, and can be additionally changed to the operating system 12a according to the respective models. In addition, depending on the model, additional functions beyond standard processing can be realized. That is, various additional processes within an allowable range can be realized while maintaining a common processing system on the standard system called the operating system 12a.

  As a premise for executing such a program, the computer main body 12 includes a CPU 12e, a RAM 12f, a ROM 12g, an I / O 12h, etc., and the CPU 12e that executes arithmetic processing uses the RAM 12f as a temporary work area or a setting storage area. While using it as a program area, a basic program written in the ROM 12g is executed as appropriate to control external devices and internal devices connected via the I / O 12h.

  Here, the application 12d is executed on the operating system 12a as a basic program. The processing contents of the application 12d are various. The operation of the keyboard 15a and the mouse 15b as operation devices is monitored, and when operated, various external devices are appropriately controlled to execute corresponding arithmetic processing, Furthermore, the processing result is displayed on the display 17a or output to the color printer 17b.

  In such a computer system, it is possible to acquire image data with the scanner 11a as an image input device, execute predetermined image processing by the application 12d, and then display and output the image data on a display 17a or a color printer 17b as an image output device. It is.

  The display driver 12b and the printer driver 12c are stored in the hard disk 13b, and are read and operated by the computer main body 12 at startup. At the time of introduction, it is recorded on a medium such as a CD-ROM or floppy disk and installed. Therefore, these media constitute a medium on which an image processing program is recorded. The image processing program itself is also included within the scope of the present invention. In this embodiment, the image processing apparatus is realized as a computer system. However, such a computer system is not necessarily required, and any system that requires image processing according to the present invention for similar image data may be used. Good. For example, a system in which an image processing apparatus for performing image processing according to the present invention is incorporated in a digital still camera and a color printer is printed using the image processed image data may be used. In a color printer that inputs and prints image data without going through a computer system, the image processing according to the present invention is automatically performed on image data inputted through a scanner, a digital still camera, a modem, or the like. It is also possible to configure to perform printing processing.

  In addition, the present invention can naturally be applied to various apparatuses that handle image data such as a color facsimile apparatus and a color copying apparatus.

  The color correction table generation / storage processing program executed by the color correction table generation apparatus 20 shown in FIG. 1 will be described below with reference to FIGS.

  FIG. 3 shows a flowchart for explaining a color correction table generation / storage processing program executed by the color correction table generation apparatus 20 of the embodiment.

  As shown in FIG. 3, first, a 256 gradation pattern 36 of CMYK ink is printed (step 42). The printed pattern is colorimetrically measured by the colorimeter 37, and the colorimetric data for each colorimetric pattern is supplied to the printer gamut generation unit 20e (step 44). The printer gamut generation unit 20e generates a printer gamut (output system gamut) in the L * a * b * space based on the color measurement data (step 46), and supplies the printer gamut generation unit 20e to the color correction LUT generation unit 20f.

  On the other hand, the display gamut generation unit 20g generates a display gamut (input gamut) in the L * a * b * space based on the RGB data generated by the application 12d (step 56), and the color correction LUT generation unit 20f. To supply.

  Next, the color correction LUT generation unit 20f generates a color correction table by a color correction table generation method described later with reference to FIGS. 4 to 6 (step 58). The color correction LUT generated by the color correction LUT generation unit 20f is stored in the color correction LUT storage unit 20h (step 60).

  Next, the color correction LUT generation processing in step 58 will be described with reference to FIGS.

First Embodiment FIG. 4 is a flowchart for explaining a first embodiment of the color correction LUT generation process.

  First, the color correction LUT generator 20f obtains a variable S indicating the size of the display gamut generated by the display gamut generator 20g (step 62). S is a distance between the chromaticity coordinate system value of RGB = (0,1,1) in the input RGB space and the chromaticity coordinate point (0.33, 0.33) of the white point in the xy chromaticity coordinate system.

  In the case of the SRGB space, the chromaticity coordinate value of RGB = (0,1,1) is (0.225, 0.329), so the distance S from the white point is 0.105.

  In the case of NTSC space, the chromaticity coordinate value of RGB = (0,1,1) in the case of SRGB space is (0.225, 0.329), so the distance S from the white point is 0.165.

Then, the color correction LUT generation unit 20f obtains the saturation enhancement rate limit value limit from the S value obtained in Step 62 (Step 64). This restriction prevents the shape of the display gamut after the display gamut is stretched from being greatly collapsed due to the influence of the printer gamut shape. From the graph shown in FIG.
limit = f (S)
It is obtained by. As shown in FIG. 12, the saturation emphasis rate limit value limit is changed according to the size (size) of the input system gamut to change the degree of saturation emphasis. Specifically, the limit value limit of the saturation enhancement rate is increased as the size (size) of the input system gamut is decreased. That is, the degree of saturation enhancement is increased as the size (size) of the input system gamut is reduced.

  In this way, when the specified input system gamut is sRGB, saturation enhancement processing is performed, but when the specified color space is sufficiently wide with respect to the output system gamut like NTSC (S> 0.15). When), do not perform saturation enhancement processing. If the specified input gamut is sufficiently wider than the output gamut, high-saturation color reproduction in the natural world is possible without performing saturation enhancement processing. This is because an unnatural color reproduction will occur. FIG. 13 is a diagram for explaining the relationship between the sizes of the sRGB color space and the NTSC color space.

  Next, the color correction LUT generation unit 20f obtains a correspondence relationship between the printer gamut generated by the printer gamut 20e and the display gamut generated by the display gamut generation unit 20g in the CIELAB space (step 70).

  FIG. 5 is a diagram for explaining color conversion processing in the color correction LUT generation processing. Here, a desired color point of the input data is a point A. Then, a straight line passing through the point A is drawn from the point O (L * = 50) of the achromatic color axis. The intersection of the straight line OA and the display gamut boundary surface is M, and the intersection of the straight line OA and the printer gamut boundary surface is P.

  Then, the color correction LUT generation unit 20f determines whether or not OM <OP (step 72). That is, it is determined whether the printer gamut boundary surface (point P) in the predetermined area is outside the display gamut boundary surface (point M).

When OM <OP (step 72, Yes), that is, when the printer gamut boundary surface of the predetermined area is outside the display gamut boundary surface, the input is performed in order to use the printer gamut region wider than the display gamut more effectively. Enlargement (saturation enhancement) processing is performed on a desired color point A of the data. Assuming that the point A after enlargement (saturation enhancement) of point A is A ′, point A ′ is
OA '= OA × β
γ = (OM + α (OP−OM)) / OM
β = limit (γ> limit)
β = γ (γ ≦ limit)
(Step 74).

  In this way, by performing the enlargement process toward the point A ′ on the straight line OA, the enlargement process can be performed while keeping the hue constant. That is, the enlargement process can be performed so as to preserve the hue.

  Here, the gamut expansion rate is α. α takes a value of 0 ≦ α ≦ 1.0 and is a parameter for setting how much the gamut is enlarged with respect to the target display gamut. When α = 1.0, the image is expanded to the full printer gamut.

  Instead of performing the saturation enhancement process so as to preserve the hue as described above, the saturation enhancement process can be performed in a direction substantially perpendicular to the input gamut surface. In the RGB color space as shown in FIG. 14, when the color point before saturation enhancement processing is C, the R value of this color point C is R <0. Since the RGB color values that are normally processed by a computer are positive values, generally, the R value of this color point P is set to R = 0 and converted to M chromaticity. As shown in FIG. 14, this color conversion moves substantially perpendicularly to the boundary of the RGB color space (input system gamut surface). As shown in FIG. 14, the enlargement process may be performed in the direction perpendicular to the BG straight line for the patina area, but the direction perpendicular to the straight lines RG and RB in the other color areas. It is necessary to perform enlargement processing.

  According to the saturation enhancement process, the hue changes. In this way, when the hue is changed from the original color by the saturation enhancement process, in order to bring the changed color closer to the original color during the saturation enhancement process, as shown in FIG. It is preferable to perform the saturation enhancement process in the decreasing direction (P → M direction) and in the opposite direction (M → P direction).

  Although the above description has been made with respect to the xy coordinate space, the same applies to other spaces such as the L * a * b * space.

  As shown in FIG. 15, when the saturation enhancement process is performed with the processing space as the L * a * b * space, MP is perpendicular to the input color space.

  On the other hand, when OM> OP (step 72, No), that is, when the printer gamut boundary surface of the predetermined area is inside the display gamut boundary surface, the color point outside the printer gamut and existing in the display gamut The compression process is performed (step 73). The compression process is performed so as to preserve the hue.

  Then, the processing in steps 70 to 76 is performed on all the pixels (step 76, Yes), a color correction table is generated (step 78), and the processing in step 58 is terminated.

  By performing color conversion using the color correction table generated in this way, even a color that cannot be reproduced by the display can be reproduced by the printer, and a printer gamut area wider than the display gamut can be obtained. It can be used more effectively.

Second Embodiment FIG. 6 is a flowchart for explaining a second embodiment of the color correction LUT generation process.

  According to the first embodiment of the color correction LUT generation process, the saturation is emphasized even for a color close to an achromatic color. However, according to the second embodiment described below, a color close to an achromatic color is saturated. The degree can be prevented from being emphasized.

First, as in the first embodiment, the color correction LUT generation unit 20f obtains a variable S indicating the size of the display gamut generated by the display gamut generation unit 20g (step 79). A limit value limit of the saturation enhancement rate is obtained from the value (step 80). The definitions of S and limit are the same as in the first embodiment. That is, the value of the saturation emphasis rate limit value limit is calculated from the graph shown in FIG.
limit = f (S)
As shown in FIG. 12, the saturation emphasis rate limit value limit is changed according to the size (size) of the input system gamut to change the degree of chroma emphasis. Specifically, the limit value limit of the saturation enhancement rate is increased as the size (size) of the input gamut is decreased. That is, the degree of saturation enhancement is increased as the size (size) of the input gamut is reduced.

  In this way, when the specified input system gamut is sRGB, saturation enhancement processing is performed. However, when the specified color space is sufficiently wide with respect to the output system gamut such as NTSC, saturation enhancement is performed. Do not perform processing.

  Next, the color correction LUT generation unit 20f obtains a correspondence relationship between the printer gamut generated by the printer gamut 20e and the display gamut generated by the display gamut generation unit 20g in the CIELAB space (step 81).

  FIG. 5 is a diagram for explaining color conversion processing in the color correction LUT generation processing. Here, a desired color point of the input data is a point A. Then, a straight line passing through the point A is drawn from the point O (L * = 50) of the achromatic color axis. The intersection of the straight line OA and the display gamut boundary surface is M, and the intersection of the straight line OA and the printer gamut boundary surface is P.

  As in the first embodiment, the color correction LUT generation unit 20f determines whether or not OM <OP (step 82). That is, it is determined whether the printer gamut boundary surface (point P) in the predetermined area is outside the display gamut boundary surface (point M).

When OM <OP (step 82, Yes), that is, when the printer gamut boundary surface of the predetermined area is outside the display gamut boundary surface, the input is performed in order to use the printer gamut region wider than the display gamut more effectively. Enlargement (saturation enhancement) processing is performed on a desired color point A of the data. Assuming that the point after the point A is enlarged (saturation enhancement) is A ′, the point A ′ is
When OA <εOM (step 84, Yes), OA ′ = OA is set (step 86).
When OA ≧ εOM (step 84, No),
OA '= εOM + β (OA−εOM)
γ = ((1−ε) OM + α (OP−OM)) / ((1−ε) OM)
β = (limit−1) / (1−ε) (γ> (limit−1) / (1−ε))
β = γ (γ ≦ (limit−1) / (1−ε))
(Step 88).

  In this way, by performing the enlargement process toward the point A ′ on the straight line OA, the enlargement process can be performed while keeping the hue constant. That is, the enlargement process can be performed so as to preserve the hue.

  Here, the non-extension area ratio is assumed to be ε (for example, the value of ε is about 0.5). When OA is smaller than εOM, it is possible to prevent the saturation from being emphasized for a color close to an achromatic color without performing the expansion process.

  Similarly to the first embodiment, the gamut expansion rate is α. α takes a value of 0 ≦ α ≦ 1.0 and is a parameter for setting how much the gamut is enlarged with respect to the target display gamut. When α = 1.0, the image is expanded to the full printer gamut.

  Instead of performing the enlargement process so as to preserve the hue in this way, the enlargement process can be performed in a direction substantially perpendicular to the BG line in the xy chromaticity coordinate system.

  On the other hand, when OM> OP (step 82, No), that is, when the printer gamut boundary surface of the predetermined area is inside the display gamut boundary surface, the color point outside the printer gamut and existing in the display gamut The compression process is performed (step 83). The compression process is performed so as to preserve the hue.

  Then, the processing in steps 80 to 86 is performed on all the pixels (step 90, Yes), a color correction table is generated (step 92), and the processing in step 58 is terminated.

  By performing color conversion using the color correction table generated in this way, even a color that cannot be reproduced by the display can be reproduced by the printer, and a printer gamut area wider than the display gamut can be obtained. It can be used more effectively.

  Next, the operation of the printer driver 12c will be described with reference to FIGS.

First Embodiment FIG. 7 is a flowchart for explaining a first embodiment of the operation of the printer driver 12c. In the first embodiment, image analysis is performed on the input image data, and when there are many highly saturated colors from green to blue, the color of the original scene is brighter than the input gamut. Consider saturation saturation. On the other hand, it is possible to prevent saturation enhancement for an image that does not require saturation enhancement. In this embodiment, a color correction table for performing saturation enhancement generated by the color correction LUT generation method and a normal color correction table for which saturation saturation is not performed are stored in advance in the color correction LUT storage unit 20h. It shall be.

As shown in FIG. 7, when the start of printing is instructed by the user, image analysis is performed on the input image data (step S80). The color correction unit 20b refers to the RGB values of the input image data, and satisfies the conditions R <5 and G> 40 and B> 40.
It is determined whether or not there are 3% or more pixels satisfying the condition (step S82). Then, when the number of pixels satisfying the above condition is 3% or more of the entire image (step S82, Yes), the color correction unit 20b regards the color of the original scene as a brighter color than the input gamut, and enhances the saturation. I do. That is, the color correction table for saturation enhancement is read from the color correction LUT 20h and read into the RAM (step S84). Then, the color correction table is incorporated into the color correction unit 20b (step S86), and printing processing is performed (step S90).

  FIG. 8 is a diagram for explaining the relationship between the color gamut of the original scene and the RGB color space (display gamut) when performing saturation enhancement processing. As shown in FIG. 8, when the colors in the color conversion area are digitized by the input device, R = 0. Color conversion as indicated by an arrow is performed.

  On the other hand, when 3% or more of the pixels satisfying the above conditions do not exist (No in step S82), normal color correction processing is performed with reference to the normal color correction table (step S88), and printing processing is performed (step S82). S90).

  FIG. 9 is a diagram for explaining the relationship between the color gamut of the original scene and the RGB color space (display gamut) when saturation enhancement processing is not performed. As shown in FIG. 9, if the color gamut of the original scene is sufficiently included in the RGB space, data of R <0 is not generated. In such a case, it is preferable not to perform saturation enhancement processing.

  As described above, according to this embodiment, it is possible to prevent saturation enhancement from being performed on an image that does not require saturation enhancement.

Second Embodiment FIG. 10 is a flowchart for explaining a second embodiment of the operation of the printer driver 12c. In the second embodiment, saturation enhancement is performed only when the target object is a bit image image, and saturation enhancement processing is not performed when the target object is a text or graphics image. Text images usually do not need to enhance saturation, and graphics images are originally computer-generated colors, so the display color is the color of the original scene, so the display image is not enhanced without saturation enhancement. This is because it is more preferable to reproduce the color. In this way, it is possible to prevent saturation enhancement for an image that does not require saturation enhancement. Also in the second embodiment, the color correction table for performing saturation enhancement generated by the color correction LUT generation method and the normal color correction table for which saturation enhancement is not performed are previously stored in the color correction LUT storage unit 20h. Is stored.

  As shown in FIG. 10, when the user instructs to start printing, the color correction unit 20b determines whether or not the target object is a bit image image (step S92).

  Then, when the target object is a bit image (Yes in step S92), the color correction unit 20b performs saturation enhancement. That is, the color correction table for saturation enhancement is read from the color correction LUT 20h and read into the RAM (step S94). Then, the color correction table is incorporated into the color correction unit 20b (step S96), and printing processing is performed (step S100).

  On the other hand, when the target object is not a bit image image (No in step S92), normal color correction processing is performed with reference to a normal color correction table (step S98), and printing processing is performed (step S100).

  As described above, according to this embodiment, it is possible to prevent saturation enhancement from being performed on an image that does not require saturation enhancement.

1 is a functional block diagram of an image processing apparatus according to an embodiment of the present invention.

It is a schematic block diagram which shows the specific hardware structural example of the image processing apparatus concerning one Embodiment of this invention.

It is a flowchart for demonstrating the color correction table production | generation / storage process by the image processing apparatus 20 by this invention.

6 is a flowchart for explaining a first embodiment of color correction LUT generation processing;

It is a figure for demonstrating the color conversion process in a color correction LUT production | generation process.

12 is a flowchart for explaining a second embodiment of the color correction LUT generation process.

4 is a flowchart for explaining a first embodiment of an operation of the printer driver 12c.

It is a figure for demonstrating the relationship between the color gamut of an original scene and RGB color space (display gamut) in the case of performing saturation emphasis processing.

It is a figure for demonstrating the relationship between the color gamut of an original scene and RGB color space (display gamut) when not performing saturation emphasis processing.

6 is a flowchart for explaining a second embodiment of the operation of the printer driver 12c.

It is a functional block diagram of the color correction table production | generation apparatus concerning one Embodiment of this invention.

It is a graph which shows the relationship between the size of an input type gamut, and the limit value limit of a saturation emphasis rate.

The figure for demonstrating the relationship of the magnitude | size of sRGB color space and NTSC color space is shown.

It is a figure for demonstrating the saturation emphasis process performed in a substantially perpendicular | vertical direction with respect to the input gamut surface.

It is a figure for demonstrating the relationship of the points O, M, and P when preserve | saving a hue and performing saturation emphasis processing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image input device, 11a Scanner, 11b Digital still camera 11c Video camera, 12 Computer main body, 12a Operating system 12b Display driver, 12c Printer driver, 12d Application 13a Floppy disk drive, 13b Hard disk 13c CD-ROM drive, 14a Modem, 15a Keyboard, 15b Mouse 17a Display, 17b Color printer, 20 Image processing device 20a First color conversion unit, 20b Color correction unit, 20c Second color conversion unit, 20d Binarization unit 20e Printer gamut generation unit, 20f Color correction LUT generation 20g Display gamut generation unit, 20h Color correction LUT storage unit 30 Image output device, 37 Colorimeter

Claims (12)

An image processing apparatus that performs desired color correction on an image input signal using a color correction table,
In a region where the output gamut is wider than the input gamut, the saturation enhancement processing is performed on the desired color point of the image input signal by changing the degree of the saturation enhancement processing according to S rows that have the desired color correction by using the emphasis color correction table,
S is the chromaticity coordinate system value of RGB = (0,1,1) in the input RGB space and the chromaticity coordinate point (0.33, 0.33) of the white point in the xy chromaticity coordinate system of the input gamut. Is the distance of
The saturation enhancement process emphasizes at least saturation among lightness, hue, and saturation.
Image processing device. The image processing apparatus according to claim 1,
The degree of saturation enhancement processing by the saturation enhancement for color correction table, the image processing apparatus is changed according to the type of the input system gamut. The image processing apparatus according to claim 1, wherein:
An image processing apparatus that increases the degree of saturation enhancement processing by the saturation enhancement color correction table as the size of the input gamut decreases. The image processing apparatus according to any one of claims 1 to 3 , wherein
In the narrow region towards said output system gamut than the input system gamut, image processing for desired color correction with the desired color correction table for compression processing for performing compression processing on the color point of the image input signal apparatus. An image processing apparatus according to any one of claims 1 to 4 , wherein
The saturation enhancement color correction table is an image processing apparatus that does not perform saturation enhancement processing when the desired color point is close to an achromatic color. The image processing apparatus according to claim 1,
An image processing apparatus, wherein the saturation enhancement process is performed so as to preserve a hue. The image processing apparatus according to claim 4 or 5 , wherein
An image processing apparatus in which the compression processing is performed so as to preserve a hue. The image processing apparatus according to any one of claims 1 to 7 ,
The color correction table for saturation enhancement is an image processing apparatus capable of adjusting the degree of saturation enhancement. An image processing apparatus according to any one of claims 1 to 8 ,
The saturation enhancement color correction table is an image processing apparatus in which a saturation enhancement limit value can be set. An image processing apparatus according to any one of claims 1 to 9 ,
Color correction for saturation enhancement when the red component is less than the predetermined red threshold, the green component exceeds the predetermined green threshold, and the number of pixels whose blue component exceeds the predetermined blue threshold is greater than or equal to a predetermined ratio in the entire pixel An image processing apparatus that performs desired color correction using a table. An image processing method for performing desired color correction on an image input signal using a color correction table,
In a region where the output gamut is wider than the input gamut, the saturation enhancement processing is performed on the desired color point of the image input signal by changing the degree of the saturation enhancement processing according to S rows that have the desired color correction by using the emphasis color correction table,
S is the chromaticity coordinate system value of RGB = (0,1,1) in the input RGB space and the chromaticity coordinate point (0.33, 0.33) of the white point in the xy chromaticity coordinate system of the input gamut. Is the distance of
The saturation enhancement process emphasizes at least saturation among lightness, hue, and saturation.
Image processing method. In a region where the output gamut is wider than the input gamut, the saturation enhancement processing is performed on the desired color point of the image input signal by changing the degree of the saturation enhancement processing according to S A program for causing a computer to execute image processing for performing desired color correction using a color correction table for emphasis ,
S is the chromaticity coordinate system value of RGB = (0,1,1) in the input RGB space and the chromaticity coordinate point (0.33, 0.33) of the white point in the xy chromaticity coordinate system of the input gamut. Is the distance of
The saturation enhancement process emphasizes at least saturation among lightness, hue, and saturation.
program.

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