JP2007258835A - Image processing apparatus, gamut correction method of image output apparatus, image processing method, program, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology of warranting color reproducibility and gradation continuity by preventing the defect of lightness inversion or the like in an image output, even when the shape in the shadow part of a gamut of an image output apparatus is complicated. <P>SOLUTION: The contour (shown in a thin line) of the gamut of the image output apparatus is corrected to a contour (outermost contour) in a thick line. In this correction, when a plurality of contour points (cross points 1, 2) whose lightness is almost the same but whose saturation only differs from each other are present in the shadow part of the gamut and the outermost contour point (cross point 2) other than the outermost contour point (cross point 1) whose saturation is the smallest is invalidated. Gamut compression is executed on the basis of the corrected gamut whose contour (outermost contour) is defined by the contour point (outermost contour point) not invalidated to prevent the lightness inversion or the like. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus and method for converting an input color image signal into a color signal suitable for an image output apparatus, and a gamut correction method for the image output apparatus.

  In general, a color gamut that can be reproduced by an image output apparatus such as an electrophotographic printer or an inkjet printer is narrower than that of a display such as a CRT display. That is, since the display reproduces the color by additive color mixing by the development of phosphors of the three primary colors of red (R), green (G), and blue (B), the gamut of the display depends on the type of phosphor used. . On the other hand, the gamut of the printer differs depending not only on the ink used but also on the type of paper and the like, and is generally smaller than the gamut of the display.

  As described above, when the output gamut is smaller than the input gamut, it is impossible to accurately reproduce the input color information depending on the image. For example, when image data displayed on the display (image data for display display) is output by a printer, the printer gamut is smaller than the display gamut, so the color of the image data outside the printer gamut is correct. Not reproduced. Therefore, in such a case, it is necessary to save the original image information as much as possible and to bring a color outside the gamut into the gamut. In this way, pushing a color that is not physically reproducible into the gamut by some processing is generally called “gamut compression”.

  Examples of prior art documents related to such gamut compression include Patent Documents 1 to 4.

  In Patent Document 1, when the gamut shapes of the input device and the output device are significantly different or the gamut shape of the output image is complicated, the color of the output image is input by performing gamut compression processing in two stages. Do not impair the color of the image. That is, a virtual gamut B that includes the gamut A of the color image output apparatus is set, and the first color conversion unit that performs color compression of the input color data with reference to the gamut B and the first color conversion unit perform color compression. Second color conversion means for compressing the color data with reference to gamut A.

  In Patent Document 2, if there is a recess in the shadow gamut, the conversion destination of gamut compression is difficult to determine uniquely, and gradation skipping is conspicuous, so that the uneven portion is approximated near the gamut boundary of the output device so as to be smooth Create a curve.

  In Patent Document 3, if the saturation of the white point is different between the input image and the output device gamut, color conversion at the time of gamut compression is unnatural. Therefore, the highest brightness point on the lightness axis in the highlight gamut of the output device. The above gamut is deleted.

  In Patent Document 4, the surface of the gamut of the output device and the input device is expressed by a polyhedron formed by a plurality of planes, and the gamut of the output device is associated with the gamut of the input device, and then L * a * b *. Perform color mapping in space.

JP 2002-252785 A JP 2000-253264 A JP 2000-253269 A JP 2004-48588 A

  FIG. 1 shows an example of a display and printer gamut in a hue on the lightness-saturation plane. Since the shaded area in the figure is a color that cannot be reproduced by the printer, gamut compression must be performed as indicated by the arrows. However, when the gamut of the printer is actually obtained, irregularities may occur on the boundary surface of the shadow. When such irregularities occur, gamut compression cannot be performed accurately, and gradation continuity is not maintained, and the impression of the input image and the output image is different. Further, if the total amount regulation value (total ink amount or total toner amount) is severe, the saturation reproducibility of the shadow portion is poor, and a gamut “blank” as shown in FIG. 2 occurs, resulting in brightness reversal and the like. .

  In order to solve such a problem, measures have been conventionally taken by a gamut compression method, color matching, or the like. For example, in Patent Document 1, the gamut compression process is performed in two stages to make the color of the output image closer to the color of the input image.

  Further, in Patent Document 2, an approximation curve is provided for the unevenness near the boundary surface in the shadow portion of the gamut of the output device to ensure gradation continuity of the output image. In addition, in order to provide an approximate curve even outside the gamut of the output device, an error in the approximation process is corrected by color conversion.

  Furthermore, recently, not only two-dimensional compression in which only the lightness / saturation direction is compressed as described above, but also three-dimensional compression in the lightness / saturation / hue direction has been proposed. For example, in Patent Document 4, the gamut surfaces of the output device and the input device are expressed by a polyhedron formed by a plurality of planes, and the gamut of the output device is associated with the gamut of the input device, and then the L * a * b * space. Perform the above color mapping.

  However, even if the gamut compression as described above is performed, if the gamut boundary surface itself of the output device is uneven as shown in FIG. As long as the surface is used, problems such as gradation discontinuity and brightness inversion occur.

  Patent Document 3 is a technique mainly related to highlight gamut correction. If the saturation of the white point is different between the input image and the output device gamut, color conversion at the time of gamut compression in the highlight area becomes unnatural. Therefore, the gamut above the maximum brightness point on the brightness axis is deleted in the highlight gamut of the output device. According to this technology, part of the gamut is deleted, so the color gamut of the output device is narrowed. However, since the characteristics of both gamuts are set to be similar, gamut compression processing is easy, and the input and output images There is an advantage that the impression is similar. However, Patent Document 3 does not refer to an example in which there are a plurality of color gamut boundaries in the shadow gamut of the output device, and there is no explanation about how to deal with the “blank” of the shadow gamut.

  The present invention has been made in view of the above, and an object of the present invention is to prevent inconveniences such as brightness reversal, color reproducibility, even if the gamut shape in the shadow portion of the image output apparatus is complicated. The purpose is to ensure gradation continuity. Another object of the present invention is to facilitate the gamut compression process even if the gamut shape in the shadow portion of the image output apparatus is complicated. Another object of the present invention is to make it possible to guarantee color reproducibility and gradation continuity while making maximum use of the gamut of the image output apparatus. Another object of the present invention is to enable color conversion including gamut compression to be performed at high speed.

  In order to achieve the above object, the present invention has the following features.

That is, according to the first aspect of the present invention, color conversion means for converting an input color image signal into a color signal suitable for an image output apparatus, and an image for generating outline data indicating the outline of the corrected gamut of the image output apparatus. Output device outer data generation means,
The color conversion means performs a process for compressing the color outside the gamut indicated by the outline data generated by the image output device outline data generation means on the input color image signal into the gamut. Including
The image output device outline data generation means includes:
First means for acquiring outline data indicating an outline of a gamut of the image output device;
When there are a plurality of outline points that differ only in saturation with respect to the shadow color with respect to the shadow color with respect to the outline data acquired by the first means, the least saturation among the plurality of outline points. A second means for generating outline data indicating the outline of the corrected gamut of the image output device by performing processing for invalidating outline points other than the outline points;
An image processing apparatus characterized by this.

According to a second aspect of the present invention, there is provided color conversion means for converting an input color image signal into a color signal suitable for an image output apparatus, and an image output apparatus for generating outline data indicating an outline of a corrected gamut of the image output apparatus. Outer data generation means,
The color conversion means performs a process for compressing the color outside the gamut indicated by the outline data generated by the image output device outline data generation means on the input color image signal into the gamut. Including
The image output device outline data generation means includes:
First means for acquiring outline data indicating an outline of a gamut of the image output device;
When there are a plurality of outline points that differ only in saturation with respect to the shadow color with respect to the shadow color with respect to the outline data acquired by the first means, the least saturation among the plurality of outline points. A second means for performing processing for invalidating outline points other than outline points;
Third means for generating outline data indicating the outline of the corrected gamut of the image output apparatus by performing a shaping process for adjusting the outline to a smooth shape on the outline data processed by the second means. And having
An image processing apparatus characterized by this.

  A third aspect of the present invention is the image processing apparatus according to the second aspect of the present invention, wherein the third means is a linear in which in the shaping process, the outer color of the outline is increased with increasing lightness. It is an image processing apparatus characterized by adjusting to a shape having a proper relationship.

  A fourth aspect of the present invention is the image processing apparatus according to the second aspect of the present invention, wherein the third means is similar in shape to the outline of the gamut of the input color image signal in the shaping process. The image processing apparatus is characterized in that the shape is adjusted.

  The invention according to claim 5 is the image processing device according to claim 2, 3 or 4, wherein at least one point of the outline after the shaping process is in contact with the outline before the shaping process. An image processing apparatus.

  According to a sixth aspect of the present invention, there is provided a first step of acquiring outline data indicating an outline of a gamut of an image output device, and a shadow color with respect to outline data acquired by the first step. When there are a plurality of outline points that differ only in saturation, the correction of the image output apparatus is performed by performing processing for invalidating the outline points other than the outline point with the smallest saturation among the plurality of outline points And a second step of generating outline data indicating the outline of the gamut that has been generated. A gamut correction method for an image output apparatus, comprising:

  According to a seventh aspect of the present invention, there is provided a first step of acquiring outline data indicating an outline of a gamut of an image output device, and a shadow color with respect to outline data acquired by the first step. A second step of performing a process of invalidating an outline point other than the outline point with the smallest saturation among the outline points when there are a plurality of outline points that differ only in saturation; A third step of generating outline data indicating the outline of the corrected gamut of the image output device by performing a shaping process for adjusting the outline to a smooth shape with respect to the outline data after processing in the step This is a gamut correction method for an image output apparatus.

  The invention described in claim 8 is the gamut correction method for an image output apparatus according to the invention described in claim 7, wherein in the shaping process, the outline has a linear relationship such that the higher the lightness, the higher the saturation. A gamut correction method for an image output apparatus, wherein the gamut correction method is characterized in that the shape is adjusted to a certain shape.

  A ninth aspect of the present invention is the gamut correction method of the image output apparatus according to the seventh aspect of the present invention, wherein, in the shaping process, the outer shape is changed to a gamut of a color image signal to be subjected to the gamut compression process. A gamut correction method for an image output apparatus, wherein the gamut correction method is arranged to have a shape similar to an outline.

  A tenth aspect of the invention is a gamut correction method for an image processing apparatus according to the seventh, eighth, or ninth aspect of the invention, wherein at least one point of the outline after the shaping process is in contact with the outline before the shaping process. This is a gamut correction method for an image processing apparatus.

  The invention described in claim 11 is a color conversion step for converting an input color image signal into a color signal suitable for the image output device, and a gamut of the image output device according to the invention described in claim 6, 7, 8, 9 or 10. The color conversion step is generated by the gamut correction method of the image output apparatus according to the invention of claim 6, 7, 8, 9 or 10 for the input color image signal. An image processing method comprising a gamut compression processing step of performing a process of compressing a color outside a gamut indicated by outline data into the gamut.

  The invention described in claim 12 is a program for causing a computer to execute each process according to the invention described in claim 6, 7, 8, 9, 10, or 11.

  A thirteenth aspect of the invention is a computer-readable recording medium on which a program for causing a computer to execute each step according to the sixth, seventh, eighth, ninth, tenth, or eleventh aspect is recorded.

  According to a fourteenth aspect of the present invention, there is provided color conversion means for converting an input color image signal into a color signal suitable for an image output device, and the color conversion means is described in the sixth, seventh, eighth, ninth or tenth aspect. Using the outline data indicating the outline of the gamut corrected by the gamut correction method of the image output apparatus according to the invention, the color outside the gamut indicated by the outline data is compressed into the gamut for the input color image signal. An image processing apparatus including gamut compression processing means for performing gamut compression processing.

  A fifteenth aspect of the present invention is the image processing apparatus according to the fourteenth aspect of the present invention, wherein the color conversion unit collectively executes the conversion including the gamut compression process by memory map interpolation. An image processing apparatus characterized by this.

(1) According to the invention described in claim 1, when there are a plurality of outline points that differ only in saturation on the substantially same lightness with respect to the outline data indicating the outline of the gamut of the image output apparatus, Because the outline data that has been processed to invalidate the outline points other than the outline point with the least saturation among the outline points is used for the gamut compression process, the gamut shape in the shadow part of the image output device is complicated. Even if it exists, troubles, such as brightness reversal, can be prevented. According to the second, third, fourth, and fifth aspects of the present invention, the outline data indicating the outline of the gamut of the image output apparatus has a plurality of outline points that differ only in saturation on the same brightness with respect to the shadow color. In this case, the outline data other than the outline point with the least saturation among the outline points is invalidated, and the outline data subjected to the shaping process for smoothing the outline is gamut compressed. Therefore, even if the gamut shape of the shadow portion of the image output apparatus is complicated, tone continuity can be improved. Furthermore, according to the invention described in claim 4, the appearance of the input image and the output image can be brought close to each other, and according to the invention described in claim 5, the gamut of the image output apparatus can be utilized to the maximum. The effect of.
(2) According to the inventions described in claims 6 to 10, even if the shape of the shadow portion of the gamut of the image output apparatus is complicated, it is possible to generate outline data indicating the outline of the gamut corrected appropriately. Therefore, by using the corrected outline data for the gamut compression process, the effect as described in the above (1) is obtained.
(3) According to the inventions of claims 11, 14, and 15, it is apparent that the effect described in (1) can be obtained. Further, according to the fifteenth aspect of the present invention, it is possible to speed up the conversion including the gamut compression process.
(4) By using the program according to the invention of claim 12 or the program recorded on the recording medium according to the invention of claim 13, the inventions of claims 6 to 11 can be implemented on a computer. it can.

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

[1] Image Processing System [1-1] Overall Configuration of Image Processing System FIG. 3 is a block diagram showing an example of the overall configuration of the image processing system according to the present invention. In FIG. 3, 100 is a display, 101 is a digital camera, 102 is a scanner, 103 is a computer, 104 is an image output device, and 200 is an image processing device. The computer 103 can mount various applications and software such as a printer driver. The digital camera 101 and the scanner 102 are input devices for capturing image data to be processed. The display 100 is an output device for displaying image data. The image output device 104 is for printing out image data, and is, for example, a color printer, a color copier or a color facsimile machine.

[1-2] Processing Function of Image Processing System FIG. 4 is a block diagram for explaining processing functions of the computer 103 and the image processing apparatus 200 in the image processing system.

  The computer 103 outputs the read image data by the application 301 or outputs the image data created by the application 301. This output is temporarily spooled in the storage device 303 via the printer driver 302, and if the image processing device 200 is not busy, it is despooled from the storage device 303 to the image processing device 200 so as to perform output processing. Is sent out. Further, the computer 103 holds display information 304 including gamut information about the display 100 and image output device information 305 which is gamut information of the image output device 204 (in this embodiment, gamut outline calculation data). Is sent to the image output apparatus 200.

  The image processing apparatus 200 includes a rendering processing unit 201, a band buffer 202, a color conversion unit 203, a gradation processing unit 204, a page memory 205, an image output device gamut creation unit 206, and the like, and is sent from the computer 103. The drawing command is converted into data that can be processed by the image output device 104 and sent to the image output device 104.

  The image processing apparatus 200 is provided separately from the computer 103 and the image output apparatus 104. However, the image processing apparatus 200 may be configured to be mounted in the computer 103 or may be mounted in the image output apparatus 104. Alternatively, it may be mounted in a printer control device provided independently of the image output device 104. The image processing apparatus 200 can also be realized by software. For example, the function of the image processing apparatus 200 may be realized in a printer driver in the computer 103.

  Furthermore, in this image processing system, rendering processing, color conversion processing, and gradation processing are performed by the image processing apparatus 200, but some or all of them may be performed by the computer 103. Further, the image processing apparatus 200 may include other functions such as data compression processing.

[1-3] Operation of Image Processing System An operation until the computer 103 generates a drawing command in the image processing system will be described. First, an operator captures image data into a computer using an image input device such as a scanner 102. Next, the operator uses the application 301 installed in the computer 103 to edit the read image data while displaying it on the display 100, and when the editing operation is completed, the operator performs printing for output to the image output device 104. Instruct. When the computer 103 receives an instruction to print from the application 301, the computer 103 transmits document data to the printer driver 302. The printer driver 302 converts the document data into a drawing command that can be received by the image processing apparatus 200, and then transmits the drawing command to the image processing apparatus 200 via spooling.

  Next, the operation of the image processing apparatus 200 will be described. In the image processing apparatus 200, display information 304 received from the computer 103 is given to the color conversion unit 203. Also, the image output device information 305 received from the computer 103 is given to the image output device gamut creation unit 206, and image output device gamut information 505 that is outline data (described later) indicating the outline of the corrected gamut of the image output device 104. Is generated and is also given to the color conversion means 203.

  On the other hand, when the image processing apparatus 200 receives a drawing command from the computer 103, the rendering processing unit 201 converts the command format data into raster format image data (R, G, B) and stores it in the band buffer 202. The color conversion unit 203 performs color conversion processing including gamut compression on the image data (R, G, B) read from the band buffer 202, and outputs color signals (C, M, Y, and C) suitable for the image output device 104. K), and further, the gradation processing unit 204 applies dither processing or the like to convert it into gradation data that can be processed by the image output apparatus 104. The gradation data is buffered in the page memory 207 and then transmitted to the image output device 104 in synchronization with the operation of the image output device 104, whereby the image output device 104 prints an image.

[1-4] Configuration of Image Output Device Gamut Creation Unit FIG. 5 shows a functional configuration of the image output device gamut creation unit 206 as a block diagram. As illustrated, the image output device gamut creation unit 206 includes an outline data generation unit 501, a determination unit 502, a determination unit 503, and a shaping unit 504.

  The outline data generation unit 501 acquires and holds outline data representing the outline of the gamut of the image output apparatus 104 as three-dimensional data on color coordinates. In this embodiment, the outline data generation unit 501 is based on the image output apparatus information 305. The outline data is acquired and held by performing the process of generating the outline data. Here, the “outline” is a boundary between a gamut and an unreproducible color gamut. Determining means 502, determining means 502, and shaping means 504 are means for correcting the outline data and generating corrected gamut outline data.

  When the outline data of the image output apparatus 104 is given as the image output apparatus information 305, the outline data generation unit 501 simply acquires and holds the outline data by capturing the outline data. Included in the embodiment.

  With respect to the outline data obtained by the outline data acquisition means 501, the determination means 502 determines whether or not there are a plurality of outline points that are substantially the same brightness and differ only in saturation for any color of the shadow portion. If it is determined that there is a point, the determining unit 503 determines the least saturated one of the plurality of outline points as an effective outline point (outermost outline point), and determines the other outline points. To disable. All the outline points other than the outline points invalidated in this way are set as valid outline points (outermost outline points). It is also possible to use outline data representing the outline (outermost outline) at this stage as the corrected image output device gamut information 505, and such an aspect is also included in this embodiment. In this embodiment, the shaping unit 504 performs necessary shaping on the outermost contour, and the contour data after the shaping processing is sent to the gamut compression processing unit 402 as final image output device gamut information 505.

[1-5] Configuration of Color Conversion Unit FIG. 5 shows a functional configuration of the color conversion unit 203 as a block diagram. As illustrated, the color conversion unit 203 includes a color coordinate conversion unit 401, a gamut compression processing unit 402, a device signal conversion unit 403, and a black generation unit 404.

  The color coordinate conversion unit 401 converts the color image data (R, G, B) input from the band buffer 202 according to the display color temperature, chromaticity coordinates, and photoelectric conversion characteristic information included in the display information 304. Color conversion is performed to an independent color space (L * a * b * space). The gamut compression processing unit 402 applies the display information 304 and the corrected image output device gamut information 505 received from the image output device gamut creation unit 206 to the L * a * b * data converted by the color coordinate conversion unit 401. Apply the necessary gamut compression. The device signal conversion unit 403 converts the L * a * b * values compressed and mapped by the gamut compression processing unit 402 into control signals (C, M, Y) for the image output device 104. If the image output device 104 uses only C, M, and Y color materials, the conversion data (C, M, Y) by the device signal conversion unit 403 can be output to the gradation processing unit 204. It is. In this embodiment, the image output device 104 uses color materials of C, M, Y, and K (black), passes the CMY data through the black generation unit 404, generates black, and includes data (C ', M', Y ', K') and output to the gradation processing unit 204.

  The number of gradations of each color component of the input color image data (R, G, B) is generally 256 gradations (8 bits), but the number of gradations such as 64 gradations, 512 gradations may be used.

[1-6] Operation of Image Output Device Gamut Creation Unit The outline of the operation of the image output device gamut creation unit 206 will be described. FIG. 6 is a flowchart for explanation.

  First, the outline data generation unit 501 generates outline data based on the image output device information 305 (outline calculation data) (S511). When outline data is given as the image output device information 305, the outline data generation unit 501 only needs to capture and hold the outline data. In any case, the outline data generation unit 501 acquires outline data.

  Here, a boundary between a reproducible color gamut (gamut) and a non-reproducible color gamut of the image output apparatus 104 is defined as an outline.

  The subsequent processing relates to the determination unit 502, the determination unit 503, and the shaping unit 504.

  Chromaticity and lightness are set (S512, S513), and an outline with the set chromaticity and lightness is obtained (S514). Here, the outline is described by a polygon (polyhedron). Next, it is determined whether or not there are a plurality of outlines having substantially the same hue and the same brightness (S515). If there are a plurality of outlines, the outline having the lowest saturation is selected from the outlines. The outermost contour is designated and other contours are invalidated (S516). If there is only one outline, the outline is set as the outermost outline (S517).

  With respect to the set chromaticity, when the brightness is changed and the processes of S514 to S517 are repeated for all brightness (S518, Yes), a necessary shaping process is applied to the obtained outermost contour (S519).

  The same processing is repeated while changing the chromaticity, and if the processing of S513 to S519 is completed for all the chromaticities (S520, Yes), the processing ends.

  Hereinafter, the processing of the image output device gamut creation unit 206 and the image output device information 305 will be described in more detail.

[1-6-1] Image output device information 305 (outline calculation data)
FIG. 7 is a flowchart for explaining a method for obtaining the image output device information 305 (outline calculation data).

First, complementary color conversion is performed on sample data (R, G, B: 0 to 255, 16 samples for each color, a total of 4096 data) in the RGB space prepared in advance, and the values of (C, M, Y) are obtained. Obtained (S601). Next, for example, black processing shown in the following formula (1) is performed to obtain (C ′, M ′, Y ′, K ′) signals (S602).
K ′ = α × min (C, M, Y)
C ′ = C−β × K
M ′ = M−β × K
Y ′ = Y−β × K (1).

  Next, total amount restriction is performed if necessary, and control signals (C ″, M ″, Y ″, K ″) after the total amount restriction are obtained (S603). In this example, an actual input / output relationship (CMYK → L * a * b *) is measured, and L * a * b * for C, M, Y, and K calculated by the least square method or the like using this data. Is previously set as a printer model. Using this printer model, outline calculation data (L * a * b *) is calculated (S604) and output (S605).

  The outline calculation data (L * a * b *) is given as the image output device information 305. However, as the image output device information 305, an actual input / output (CMYK → L * a * b *) relationship and a control signal (C ″, M ″, Y ″, K ″) after the total amount regulation are given, The outline data generation means 501 may be used to calculate outline calculation data (L * a * b *). In any case, the outline calculation data is obtained as (L * a * b *).

[1-6-2] Generation of Polygon Outline Data FIG. 8 is a flowchart for explaining processing for generating polygon outline data from the outline calculation data (L * a * b *) in the outline data generation means 501. It is. 9 and 10 are explanatory diagrams.

  The polyhedral model will be described. FIG. 8 shows an algorithm for generating a polyhedron model based on a sample data group. FIG. 9 is a diagram showing an example of the generated polyhedron model, and FIG. 10 is a plan view thereof.

  In the algorithm shown here, an octahedron connecting the maximum point and the minimum point of each coordinate axis of (L * a * b *) is formed with respect to the contour calculation data, and each triangular surface is regarded as the base of triangulation, and a triangular shape is formed. A polygon is formed by recursively performing a process of searching for the apex of the cone.

  Describing in detail with reference to FIG. 8, first, the maximum value and the highest value of each coordinate axis of (L * a * b *) are obtained for the contour calculation data to form an octahedron (S901).

  Next, the first division (i = 1) is performed. Each face of the octahedron created in S901 is regarded as the bottom face of triangulation, and it is determined whether there is data outside (S904). If there is data outside, the farthest point is the triangular pyramid. A triangular pyramid is formed as a vertex (S905), and if there is no data outside, a triangular pyramid is formed with the nearest point as the vertex of the triangular pyramid inside the bottom surface (S906). Here, to search for the farthest point or the nearest point, the distance from the center of gravity of the triangle that is the bottom surface may be calculated.

That is, each vertex vector of the triangle is
P _k1 = (L * _k1 , a * _k1 , b * _k1 )
P _k2 = (L * _k2 , a * _k2 , b * _k2 )
P _k3 = (L * _k3 , a * _k3 , b * _k3 ) Equation (2)
, The center of gravity P _kp is P _kp = ((L * _k1 + L * _k2 + L * _k3 ) / 3, (a * _k1 + a * _k2 + a * _k3 ) / 3,
(B * _k1 + b * _k2 + b * _k3 ) / 3) ≡ (L * _kp , a * _kp , b * _kp ) (3)
It can be expressed as

Distance with an arbitrary point P _r = (L * _r , a * _r , b * _r ): R is
R = srqt {(L * _kp- L * _r ) ^ 2 + (a * _kp- a * _r ) ^ 2 + (b * _kp- b * _r ) ^ 2}
... Formula (4)
It is. In S905, the point with the longest distance represented by Equation (4) may be selected, and in S906, the shortest point may be selected.

  A process of searching for the farthest point or the nearest point is performed for all eight faces (S907), and when the process is finished for all the faces, the first division process is terminated.

  One division process is a step from S903 to S908, and this is performed recursively. In the i-th division, the number of bottom surfaces is 8 × (3 ^ i).

  In S908, it is determined whether or not the polygon shape is sufficient as compared with the actual gamut as a result of the division. If the division is sufficient, the outline of the polygon is formed (S909). If insufficient, i is incremented. Then, a new division is performed (S903). As the number of divisions increases, the outer shape of the gamut approaches the actual shape.

FIG. 9 shows an octahedron composed of six points: a maximum point WP and a minimum point BP of the L * coordinate, a maximum point a _max and a minimum point a _{min of the} a * coordinate, and a maximum point b _max and a minimum point b _min of the b * coordinate. It is a figure which shows a mode that is formed. According to the figure, it can be seen that by connecting these points, eight triangular closed regions are formed, that is, an octahedron is formed.

FIG. 10 shows the number of divisions on the (L *, b *) plane and how the outer surface (side in the figure) is formed. The left view in FIG. 10 shows a state in which an octahedron (WP-b _max -BP in the figure) is formed. The central view in FIG. 10 shows the shape after the first division, and an outside point: P ₁ is added to the highlight, and an inside point: P ₂ is added to the shadow. The right side view in FIG. 10 shows the shape after the second division. In the highlight, an outer point: P ₃ is added, and in the shadow, inner points: P ₄ , P ₅ , P ₆ are added.

By repeating such division, a final polygon is formed, and the coordinates of each vertex: (P ₁ , P ₂ ..., P _n : n = 8 × (3 ^ i) +1 (i: number of divisions)) _Pv = ( _Lv , _av , _bv ): v = 1, 2, ... n
Get.

[1-6-3] Generation of Polygon Outermost Outline Data FIG. 11 shows the polygon outermost outline data (before the shaping process) from the polygon outline data (indicating the outline of the gamut before correction) by the determining means 502 and the determining means 503. It is a flowchart of a more specific process for generating a contour of a corrected gamut). 12 to 15 are diagrams for explaining the above.

The polygon outermost contour will be described with reference to FIG. FIG. 15 is a diagram in which a gamut in a certain hue C is observed on the (L *, C) plane. Any lightness L * _∀ above searches on the same hue to obtain the intersection of the outer surface (boundary point). When there are a plurality of intersections, the intersection with the smallest saturation is selected as the outermost point, and the other intersections are invalid. That is, in the example of FIG. 15, the intersection 1 and the intersection 2 are found, but the intersection 1 with a small saturation is the outermost outline (effective outline), and the intersection 2 is invalidated. When there is only one intersection (outline point), that intersection is the outermost point (effective outline point). When the intersections are selected for all the lightness in this way, the outermost contour of the polygon is obtained. In FIG. 15, the bold line is the outermost outline of the gamut.

  Next, a process for obtaining polygon outermost contour data will be described with reference to FIG. First, plane equations are obtained for all planes obtained by the processing of FIG. 8, that is, all planes of polygon outline data (S801, S802).

  Next, a plane that intersects the set hue and lightness is searched (S806), and an intersection point is obtained (S808). When there are a plurality of intersecting planes, intersections are obtained for all the planes (S809), and the plane with the lowest saturation is selected from them, and the intersection is set as the outermost contour (S810). The outermost contour is calculated for all brightness and hue (S811, S812), and the process is terminated. Hereinafter, each step will be described in detail.

<Calculation of plane equation>
FIG. 13 is a diagram for explaining a plane equation. As shown in the figure, in order to obtain a plane including vectors P _k1 , P _k2 , and P _k3 representing the three vertices represented by the expression (2), two edge vectors e ₁ obtained from the respective vertex vectors are used. , E ₂ , it is known that this outer product becomes a plane equation including the triangular plane. That is, taking each vertex vector as in equation (2), the plane equation is
α _k · L * + β _k · a * + γ _k · b * + ξ _k = 0 Equation (5)
And

When the triangle plane is viewed from a certain point, the edge vector is set to e ₁ = (L * ₂ −L * ₁ , a * ₂ −a * ₁ , b * ₂ −b * ₁ ) ≡ (e _{1x, e} 1y, _{e 1z)}
... Formula (6)
e ₂ = (L * ₃ −L * ₂ , a * ₃ −a * ₂ , b * ₃ −b * ₂ ) ≡ (e _2x , e _2y , e _2z )
... Formula (7)
Further, these outer products are obtained as follows.
_{n = e 1 × e 2 =} (e 1y · e 2z -e 1z · e 2y, e 1z · e 2x -e 1x · e 2z, e 1x · e 2y -e 1y · e 2x,) = (α k , Β _k , γ _k ) (8)
As a result, n is a normal vector of a triangular plane and represents a coefficient of a plane equation. The remaining constant terms use arbitrary vertices,
ξ _k = − (α _k · L * + β _k · a * + γ _k · b *)
=-((Alpha) _k * L * _k1 + (beta) _k * a * _k1 + (gamma) _k * b * _k1 ) ... Formula (9)
It can be obtained more.

This calculation is performed for all the planes, and the plane equation is calculated. Or
(Α _k , β _k , γ _k , ξ _k ) (1 ≦ k ≦ S, S: number of planes) is obtained.

<Hue setting>
FIG. 12 is a diagram for explaining setting of the hue. In the example of FIG. 12, the hue is divided into twelve, and each hue is numbered with i = 1, 2,... N-1, N: number of divisions. Initially, i = 1 is set, and the chromaticity vector at this time is set as a unit vector (ea * _i , eb * _i ).

<Lightness setting>
Set the brightness as well as the hue. In this example, the lightness is divided into M, and each lightness is numbered with j = 1, 2,... M-1, M: the number of divisions. Initially, j = 1 is set, and the lightness at this time is L * _j .

<Plane search>
A search is made for a plane that intersects the extension lines of the brightness and hue vectors (L * _j , ea * _i , eb * _i ) set in S802 to S805. For an arbitrary plane represented by Expression (2), a surface that satisfies the following expression is searched with reference to FIG.
Min (L * _k1 , L * _k2 , L * _k3 ) ≦ L * _j ≦ Max (L * _k1 , L * _k2 , L * _k3 )
Min (θ _k1 , θ _k2 , θ _k3 ) ≦ θ _j ≦ Max (θ _k1 , θ _k2 , θ _k3 )
However, θ _x = arc (tan (b * _x / a * _x )), x = k1, k2, k3
θ _i = arc (tan (eb * _i / ea * _i )) (10)
It is.

The extracted surface is defined as Q _t (t = 1, 2... T, T: number of extracted surfaces).
Further, the plane equation of this surface is already known because it has been calculated in S801. The plane equation of Q _t is
α _t · L * + β _t · a * + γ _t · b * + ξ _t = 0 Equation (11)
far.

<Intersection calculation>
The intersection point qt existing on the extension line of the brightness and hue vectors (L * _j , ea * _i , eb * _i ) set with the surface Qt is calculated. First, in this hue direction,
η _i = eb * _i / ea * _i (12)
Therefore, ηi is known.

Next, an intersection is calculated using Expression (12), brightness: L * _j , and Expression (11).
If the intersection point is q _t = (L * _t , a * _t , b * _t ),
a * _t =-([gamma _] t.L * j + [xi] _t ) / ([alpha] _t + [eta _] i. [beta] _t )
b * _t = η _i * a * _t
L * _t = L * _j Expression (13)
It is.

<Outermost calculation>
When there are a plurality of surfaces extracted in S806, that is, when T ≠ 1, saturation: _St is calculated for each intersection.
S _t = sqrt (a * _t ^ 2 + b * _t ^ 2) ... Formula (14)
The outermost point is the intersection of the surface with the least saturation with the set brightness and hue.
The coordinates of the outermost contour point when the lightness is L * _j and the hue vector is (ea * _i , eb * _i ) are (L * _j , a * _i , b * _i ).

[1-6-4] Shaping Outermost Data FIG. 16 and FIG. 17 are diagrams for explaining the shaping process by the shaping unit 504, both of which represent gamut in terms of lightness / saturation coordinates.

In the example shown in FIG. 16, in order to improve tone continuity during gamut compression processing, the outermost points are connected to the outermost data with a smooth curve so that the relationship between lightness and saturation is linear. To shape. In order to secure the largest possible area with respect to the outermost outline of the gamut (that is, in order to make maximum use of the original gamut), one point of the curve is made to contact the outermost outline of the gamut before shaping.
In the example shown in FIG. 17, the gamut of the input image (here, the display gamut) is assigned to the outermost data in order to bring the appearance impression of the input image and the output image closer to the same in the gamut compression process. And shaping the outermost points with smooth curves so that the gamut shapes of the output image device after shaping are similar. Also in this case, in order to secure a region as large as possible with respect to the outermost outline of the gamut, one point of the curve is made to contact the outermost outline of the gamut before shaping.

[1-7] Operation of Color Conversion Unit FIG. 18 is a flowchart for explaining the operation of the color conversion unit 203. First, image data is read from the band buffer 202 and input to the color coordinate conversion unit 401 (S700). The color coordinate conversion unit 401 converts the image data into CIELab, which is a representative uniform color space, according to the display color temperature, chromaticity coordinates, and photoelectric conversion characteristic information included in the display information 304 (S701).

  Next, in the gamut compression processing unit 402, for the L * a * b * data converted by the color coordinate conversion unit 401, first, the outermost data generated by the image output device gamut creation unit 206 (the image image output device It is determined whether the color is in the gamut indicated by the gamut information 505) (S702). If the color is in the gamut, no processing is performed. If the color is out of gamut, the display gamut information included in the display information 304 is displayed. Referring to FIG. 4, a gamut compression process for compressing the gamut is performed (S703).

  Next, the device signal conversion unit 403 converts the L * a * b * data into a (C, M, Y) signal (S704). This color conversion is performed using memory map interpolation. In this memory map interpolation, as shown in FIG. 19, when the L * a * b * space is an input color space, the L * a * b * space is divided into solids of the same type (here, cubes) and input. In order to obtain the output value P at the coordinates (L * a * b *), a cube including the input coordinates is selected, the output values preset at the eight vertices of the selected cube, and the input coordinates The output value P is calculated by linear interpolation on the basis of the position (distance from each vertex) in the cube including.

  Here, the output value P is a (C, M, Y) value. For the coordinates (L * a * b *) on the input space used for the interpolation calculation, the actual input / output (L * a * b * → CMY) relationship is measured, and this data is used to determine the minimum (C, M, Y) values corresponding to (L * a * b *) values calculated by the square method or the like are preset.

  Next, the black generation unit 404 converts the CMY signal into a CMYK signal, for example, by a calculation such as the above-described equation (1) (S705).

  It is determined whether or not conversion has been completed for all data (S706). If conversion has not been completed, the process returns to S701.

  As is apparent from the above description, according to the present image processing system, even if the image output device 104 is a color image output device having a complicated gamut shape in the shadow portion, brightness inversion is performed while maximizing the gamut. In addition, color reproducibility and gradation continuity can be ensured.

[1-8] Modifications Note that outline data indicating the outline of the corrected gamut generated in advance by the image output device gamut creation unit 206 (generated in advance by the same gamut correction method) is held on the computer 103 side. You may make it give this to the color conversion means 203. FIG. In this case, the image processing apparatus 200 does not need to include the image output apparatus gamut creation unit 206. Such forms are also encompassed by the present invention.

[1-9] Acceleration of processing As can be understood from the above description, if the gamut information 505 of the image output apparatus is generated, that is, the corrected gamut of the image output apparatus 104 is determined. Then, the signals (R, G, B) input from the band buffer 202 to the color conversion unit 203 and the black-generated signals (C ′, M ′, Y ′, K ′) output from the color conversion unit 203. The relationship is established. Therefore, the color conversion unit 203 prepares a table for converting the input signal (R, G, B) into the signal (C ′, M ′, Y ′, K ′) after the black generation, in advance. It is possible to adopt a configuration in which conversions including gamut compression processing are collectively executed by memory map interpolation, thereby speeding up the conversion. In this case, since it is not necessary to perform processing for generating the gamut information 505 of the image output apparatus when outputting the image data, the image output apparatus gamut generation unit 206 can be omitted.

  FIG. 20 is an explanatory diagram of the color conversion unit 203 based on the above idea, and includes an address generation unit 410 and a C′M′Y′K ′ data conversion table 411.

  Conversion including gamut compression processing is performed at once by memory map interpolation. In this memory map interpolation, as shown in FIG. 21, the RGB space is set as an input color space, the RGB space is divided into the same type of solid (here, a cube), and input / output (RGB → C The value of the signal (C′M′Y′K) after black generation corresponding to the signal (RGB) from the band buffer 203 in FIG. 5 is set in advance. When obtaining the signal value P after black generation at the input coordinates (RGB), a cube including the input coordinates (RGB) is selected, and preset to the eight vertices of the selected cube (C′M ′). Y′K) and linear interpolation is performed based on the input coordinate position in the cube (distance from each vertex). At this time, the address generation unit 301 receives an input color signal (R, G, B) as an input and generates an address for accessing the C′M′Y′K ′ data conversion table 410. The C′M′Y′K ′ data conversion table 411 outputs a signal (C′M′Y′K ′) after the black generation using the address output from the address generation unit 410.

[2] Image Processing Method and Gamut Correction Method The processing contents of the image processing system according to the present invention described in [1-1] to [1-7] are the image processing method and the image output device gamut correction according to the present invention. It is also an embodiment of the method, and the procedure can be illustrated as in FIG.

  Referring to FIG. 22, in step S110, an image signal (R, G, B) to be printed and output image device information 305, that is, outline calculation data described in [1-6-1] are input. In the next step S111, the polygon outline data described in [1-6-2] is generated. In the next step S112, the polygon outermost contour data described in [1-6-3] is generated. In the next step S113, the outermost data shaping process described in [1-6-4] is performed. However, step S113 can be omitted. In the next step S114, the color conversion process including the gamut compression process described in [1-7] is performed, and the signal (C ′, M ′, Y ′, K ′) that is the conversion result is output in step S115. .

  Note that the configuration described in [1-8] or [1-9] can be used. In this case, only the image signal (R, G, B) is input in Step 110, and Steps 111 to 111 are performed. 113 is omitted, and the conversion is executed in step 114.

  Steps S111 to S113 correspond to a processing procedure for the image output apparatus gamut correction method according to the present invention.

[3] Program and Storage Medium As mentioned in [1-2] above, all or part of the functions of the image processing apparatus 200 can be implemented as software in the computer 103, for example, as the printer driver 302. . The image processing apparatus 200 can be realized by software using a general-purpose computer such as a personal computer other than the computer 103, a microcomputer, or the like.

  Also, the image output device gamut creation unit 206 shown in FIG. 5 can be realized by software using a computer. A program for that purpose, that is, a program that causes a computer to function as each of the means 501, 502, 503, and 504 is also included in the present invention. In addition, various recording (storage) media that can be read by a computer, such as a magnetic disk, an optical disk, a magneto-optical disk, and a semiconductor storage device in which such a program is recorded, are also included in the present invention. The functions described above can be realized on a computer by reading the program from such a recording medium, installing the program on a hard disk of a computer, and executing the program on the computer.

  Further, the procedure of the image processing method or the gamut correction method described in [2] can be performed by software using a computer. A program for this purpose and various recording (storage) media that can be read by a computer on which the program is recorded are also included in the present invention.

  Note that it is easy for a person skilled in the art to which the present invention belongs to embody the program as described above, so that further explanation is omitted. The computer that runs the program may have a general configuration including a CPU, a memory, and the like, and the description thereof is omitted.

It is explanatory drawing of gamut compression. It is a figure which shows the "gutting" of gamut. 1 is a block diagram of an image processing system according to the present invention. It is a block diagram for demonstrating the processing function of the computer and image processing apparatus in an image processing system. It is a block diagram which shows the functional structure of an image output device gamut preparation part and a color conversion means. It is a flowchart for operation | movement description of an image output device gamut preparation part. It is a flowchart for demonstrating the production | generation of the data for outline calculation. It is a flowchart of the process which produces | generates polygon outline data from outline calculation data. It is explanatory drawing of an octahedral model. It is a figure which shows the change of the frequency | count of a division | segmentation, and the shape of an outer surface. It is a flowchart of the process which produces | generates the polygon outermost contour data which consists only of an effective outer contour point (outermost contour point) from the polygon outer contour data before correction | amendment. It is a figure which shows the division | segmentation of a hue. It is explanatory drawing of a plane equation. It is explanatory drawing of the search conditions of a plane. It is a figure which shows the example which selects 1 effective outline point (outermost outline point) from several outline points. It is explanatory drawing of a shaping process. It is explanatory drawing of a shaping process. It is a flowchart for demonstrating operation | movement of a color conversion means. It is explanatory drawing of the memory map interpolation for the conversion from the L * a * b * signal after a gamut compression to a CMY signal. It is a block diagram for demonstrating the structure of the color conversion means which performs collectively conversion including gamut compression by memory map interpolation. It is explanatory drawing of the memory map interpolation for the conversion from the input signal (RGB) to the signal (C'M'Y'K ') after black generation. It is a flowchart for demonstrating the procedure of the gamut correction method of an image output device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Display 101 Digital camera 102 Scanner 103 Computer 104 Image output device 200 Image processing device 202 Band buffer 203 Color conversion means 204 Tone processing unit 205 Image output device gamut creation unit 304 Display information 305 Image output device information (outline calculation data)
401 Color coordinate conversion unit 402 Gamut compression processing unit 403 Device signal conversion unit 404 Black generation unit 501 Outline data generation unit 502 Determination unit 503 Determination unit 504 Shaping unit 505 Image output device gamut information after correction (polygon outermost frame data)

Claims (15)

Color conversion means for converting an input color image signal into a color signal suitable for an image output device;
Image output device outline data generation means for generating outline data indicating the outline of the corrected gamut of the image output device,
The color conversion means performs a process for compressing the color outside the gamut indicated by the outline data generated by the image output device outline data generation means on the input color image signal into the gamut. Including
The image output device outline data generation means includes:
First means for acquiring outline data indicating an outline of a gamut of the image output device;
When there are a plurality of outline points that differ only in saturation with respect to the shadow color with respect to the shadow color with respect to the outline data acquired by the first means, the least saturation among the plurality of outline points. A second means for generating outline data indicating the outline of the corrected gamut of the image output device by performing processing for invalidating outline points other than the outline points;
An image processing apparatus. Color conversion means for converting an input color image signal into a color signal suitable for an image output device;
Image output device outline data generation means for generating outline data indicating the outline of the corrected gamut of the image output device,
The color conversion means performs a process for compressing the color outside the gamut indicated by the outline data generated by the image output device outline data generation means on the input color image signal into the gamut. Including
The image output device outline data generation means includes:
First means for acquiring outline data indicating an outline of a gamut of the image output device;
When there are a plurality of outline points that differ only in saturation with respect to the shadow color with respect to the shadow color with respect to the outline data acquired by the first means, the least saturation among the plurality of outline points. A second means for performing processing for invalidating outline points other than outline points;
Third means for generating outline data indicating the outline of the corrected gamut of the image output apparatus by performing a shaping process for adjusting the outline to a smooth shape on the outline data processed by the second means. And having
An image processing apparatus.   3. The image processing apparatus according to claim 2, wherein the third means arranges the outline in the shaping process so as to have a linear relationship such that the higher the lightness, the higher the saturation.   3. The image processing apparatus according to claim 2, wherein the third means adjusts the shape of the outline to a shape similar to the outline of the gamut of the input color image signal in the shaping process.   The image processing apparatus according to claim 2, wherein at least one point of the outline after the shaping process is in contact with the outline before the shaping process. A first step of acquiring outline data indicating an outline of the gamut of the image output device;
For the outline data acquired in the first step, when there are a plurality of outline points that differ only in saturation with respect to the shadow color, only the saturation is the smallest among the plurality of outline points. A second step of generating outline data indicating the outline of the corrected gamut of the image output device by performing processing for invalidating outline points other than the outline points;
A gamut correction method for an image output apparatus, comprising: A first step of acquiring outline data indicating an outline of the gamut of the image output device;
For the outline data acquired in the first step, when there are a plurality of outline points that differ only in saturation with respect to the shadow color, only the saturation is the smallest among the plurality of outline points. A second step of performing processing for invalidating outline points other than outline points;
A third step of generating outline data indicating the outline of the corrected gamut of the image output device by performing a shaping process for adjusting the outline to a smooth shape on the outline data processed in the second step. When,
A gamut correction method for an image output apparatus, comprising:   8. The gamut correction method for an image output apparatus according to claim 7, wherein in the shaping process, the outline is adjusted to a shape having a linear relationship such that the higher the lightness, the higher the saturation.   8. The gamut correction method for an image output apparatus according to claim 7, wherein in the shaping process, the outer shape is adjusted to a shape similar to the outer shape of the gamut of the color image signal to be subjected to the gamut compression process.   The gamut correction method for an image processing apparatus according to claim 7, wherein at least one point of the outline after the shaping process is in contact with the outline before the shaping process. A color conversion step of converting an input color image signal into a color signal suitable for an image output device;
Each step of the gamut correction method of the image output device according to claim 6, 7, 8, 9 or 10,
In the color conversion step, a color outside the gamut indicated by the outline data generated by the gamut correction method of the image output device according to claim 6, 7, 8, 9, or 10 is applied to the input color image signal. Including a gamut compression process for applying compression into the gamut,
An image processing method.   A program for causing a computer to execute each step according to claim 6, 7, 8, 9, 10 or 11.   A computer-readable recording medium in which a program for causing a computer to execute each step according to claim 6, 7, 8, 9, 10, or 11 is recorded. Color conversion means for converting an input color image signal into a color signal suitable for an image output device;
The color conversion means uses the outline data indicating the outline of the gamut corrected by the gamut correction method of the image output apparatus according to claim 6, 7, 8, 9, or 10 to the input color image signal. An image processing apparatus comprising gamut compression processing means for performing gamut compression processing for compressing a color outside a gamut indicated by data into the gamut.   The image processing apparatus according to claim 14, wherein the color conversion unit is configured to collectively execute the conversion including the gamut compression processing by memory map interpolation.

Images