JP2009010532A - Color conversion processor and color conversion method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color conversion processor for which the number of times of referring to an LUT with the need of a lot of processing time is reduced, the entire processing time is short and a cost performance is excellent. <P>SOLUTION: When read RGB data and RGB data stored in the previous time and read from a first temporary storage means do not match, the color conversion processor replaces the RGB data stored in the first temporary storage means with the RGB data read this time, then converts the RGB data to CMYK data on the basis of a lookup table, performs linear interpolation processing on the basis of the CMYK data, temporarily stores the CMYK data, and selects whether to temporarily output the CMYK data or to output the CMYK data to which the linear interpolation processing is performed on the basis of the result of the comparison. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a color conversion technique using a lookup table.

  With the rapid progress of computers in recent years, the resolution of images displayed on a display has been improved. Along with this, the types of colors that can be expressed on the display are also increasing. Many colors displayed on the display are expressed by combining three primary colors of red (R), green (G), and blue (B) light (hereinafter referred to as “RGB” and “RGB data”). It is.

  On the other hand, when performing color printing, printing is performed with an expression color represented by so-called CMYK (CMYK data) in which black (K) is added to the three primary colors of cyan (C), magenta (M), and yellow (Y). Is done.

  Therefore, when color printing a color image expressed on a computer display, color data expressed in RGB must be converted into color data expressed in CMYK.

  One method for performing such color conversion is to use a look-up table (hereinafter referred to as LUT). The LUT stores CMYK data corresponding to each color represented by a combination of RGB. Therefore, by referring to the LUT, it is possible to convert image data represented by RGB into image data represented by CMYK.

  However, when the LUT is simply referred to in order to perform nonlinear color conversion from RGB to CMYK, when each color component of RGB data is represented by 8 bits, the color is a combination of 2 8 × 2 8 × 2 8. Exists. Moreover, if the output CMYK also has a 32-bit width with color components each consisting of 8 bits, an LUT having a capacity of 256 × 256 × 256 × 32 [bit] ÷ 8 [bit] = 64 [MB] is required.

  Therefore, normally, in the color conversion process using the LUT, the memory capacity for the LUT is reduced by using the interpolation process together. For example, in a color printing apparatus, a 3D LUT method is often used to accurately convert an RGB image from a personal computer (PC) into a CMYK image. In this method, RGB data of only representative points and the corresponding CMYK data are recorded, and the other RGB data and the corresponding CMYK data are based on neighboring data among the representative data. Calculate by interpolation calculation.

In the method using such interpolation processing together, the values stored in advance in the LUT are intermittent values at equal intervals. Therefore, when converting to a color not stored in the LUT, the original value is calculated by linear interpolation from values before and after the original value representing the color. That is, when converting RGB data into CMYK data, LUT for performing nonlinear conversion is referred to and multiplication / division for linear interpolation processing is performed.
In addition, the following are mentioned as literature relevant to this invention.

JP 2000-196903 A JP 2004-254033 A JP 2002-203225 A JP-A-6-243243

  In the linear interpolation process, the data stored in the LUT can be regarded as three-dimensional position information, and the CMYK data to be interpolated can be represented by a predetermined position in a predetermined cube on the three dimensions. Therefore, in order to obtain the CMYK data to be interpolated, it is necessary to calculate the vertex (eight lattice points) of the cube, and these eight lattice points are data registered in advance in the LUT. Therefore, when color conversion is performed with reference to the LUT, the LUT must be referenced eight times for each dot.

  In Patent Document 1, in color conversion processing performed using both LUT and interpolation calculation, parallel processing of interpolation calculation is performed to perform high-speed color conversion. In this cited document 1, the processing time is shortened by increasing the number of dots processed at one time.

  However, when this processing is performed by hardware, the circuit scale becomes the same multiple as the processing time is increased. Further, the memory used for the LUT also requires a similar multiple capacity, and particularly when the circuit for executing the processing is made ASIC (Application Specific Integrated Circuit), the influence on the cost is not small.

  In view of the above-described problems, the present invention provides a color conversion processing apparatus that reduces the number of LUT references that require a lot of processing time, has a short overall processing time, and has good cost performance.

  According to the present invention, a color conversion processing device for converting first color data output to a first medium into second color data for output to a second medium reads the first color data. Reading means, comparing means for comparing the first color data read this time with the first color data previously read, and the first color data can be temporarily stored. If the two first color data do not match as a result of comparison by the comparison means, the first color data stored previously is replaced with the first color data read this time. Temporary storage means, color conversion data storage means in which the first color data and the second color data corresponding to the first color data are intermittently stored, and the color conversion data storage means Based on the first color data, the second color A color conversion means for converting the data, an interpolation means for performing an interpolation process based on the second color data converted by the color conversion means, and the second color data subjected to the interpolation process temporarily A second temporary storage means that can store the second color data stored in the second temporary storage means based on the result of the comparison, or the interpolation process is performed. And selecting means for selecting whether to output the second color data.

  With this configuration, it is possible to reduce the number of LUT references that require a lot of processing time, shorten the overall processing time, and improve cost performance.

  In the color conversion apparatus, the selection unit outputs the second color data stored in the second temporary storage unit when the two first color data match as a result of the comparison. It is characterized by.

  With this configuration, when converting the RGB data into CMYK, when dot information having the same content continues, the multiplication / division operation for LUT reference and linear interpolation processing can be omitted.

  In the color conversion apparatus, each of the first and second temporary storage units includes a plurality of temporary storage units.

  With this configuration, RGB data and CMYK data for a plurality of dots can be held.

  In the color conversion apparatus, the first temporary storage unit stores the first color data which is different between the temporary storage units constituting the first temporary storage unit, and the comparison unit includes: The first color data read by the reading means and the first color data stored in the first temporary storage means are sequentially compared. As a result of the comparison, the matched first colors The information indicating the location of the second color data corresponding to the data is output, and the selection unit is configured to output the information from the second temporary storage unit group based on the information indicating the location of the second color data. 2 color data is selected.

  With this configuration, a plurality of RGB data before conversion and corresponding CMYK data are stored, and whether or not the dot to be converted is the same as the stored dot is compared. Can omit multiplication and division operations for LUT reference and linear interpolation processing.

  According to the present invention, the color conversion processing method by the color conversion processing apparatus for converting the first color data output to the first medium into the second color data for output to the second medium is the first color data. And the first color data read is compared with the first color data read from the first temporary storage device in which the first color data is temporarily stored, If the two first color data do not match as a result of the comparison, the first color data stored in the first temporary storage means is replaced with the first color data read this time, And the second color data corresponding to the first color data are stored on the basis of a color conversion data storage device in which the second color data is intermittently stored. And based on the converted second color data An interpolation process is performed, the second color data subjected to the interpolation process is stored in a second temporary storage device that can be temporarily stored, and based on the result of the comparison, the second temporary storage device It is selected whether to output the second color data stored in the second color data or to output the second color data subjected to the interpolation processing.

  With this configuration, it is possible to reduce the number of LUT references that require a lot of processing time, shorten the overall processing time, and improve cost performance.

  By using the present invention, in the color conversion between RGB data and YMCK data, it is possible to reduce the number of LUT references that require a lot of processing time. Therefore, the overall processing time for color conversion can be shortened and cost performance is good.

<First Embodiment>
In this embodiment, a description will be given of a color conversion apparatus that shortens the processing time required for color conversion by omitting LUT reference and multiplication / division calculations for linear interpolation processing when dot information having the same content continues.

  The color conversion apparatus according to the present embodiment converts first color data output to a first medium into second color data for output to a second medium. The color conversion apparatus includes reading means, first temporary storage means, comparison means, color conversion data storage means, color conversion means, interpolation means, and second temporary storage means.

  The reading means reads the first color data. For example, in the present embodiment, the reading means corresponds to a read function for reading RBG data from the FIFO 1 (3) by the LUT reference control unit 8.

  The comparing means compares the first color data read this time with the first color data read before. For example, the comparison means corresponds to the comparator 6 in this embodiment.

  The first temporary storage means can temporarily store the first color data. In the first temporary storage means, if the two first color data do not match as a result of the comparison by the comparison means, the previously stored first color data is changed to the first color data read this time. Replaced. The first temporary storage means corresponds to the first temporary storage buffer 5 in the present embodiment, for example.

  The color conversion data storage means intermittently stores the first color data and the second color data corresponding to the first color data. The color conversion data storage means corresponds to, for example, a look-up table (LUT) 7 in this embodiment.

  The color conversion unit converts the first color data into the second color data based on the color conversion data storage unit. For example, in the present embodiment, the color conversion unit corresponds to the LUT reference control unit 8.

  The interpolation means performs an interpolation process based on the second color data converted by the color conversion means. For example, in the present embodiment, the interpolation means corresponds to the multiplication / division calculation unit 9.

  The second temporary storage means can temporarily store the second color data subjected to the interpolation processing. The second temporary storage means corresponds to the second temporary storage buffer 10 in this embodiment, for example.

  The selection unit outputs the second color data stored in the second temporary storage unit based on the comparison result, or outputs the second color data subjected to the interpolation process. Select. The selection means corresponds to, for example, the selector 11 in this embodiment. The selection means outputs the second color data stored in the second temporary storage means when the two first color data match as a result of the comparison.

  Furthermore, in the color conversion apparatus according to the present embodiment, each of the first and second temporary storage units can be constituted by a plurality of temporary storage units. In this case, the first temporary storage means stores the first color data which is different between the temporary storage means constituting the first temporary storage means. The comparing means sequentially compares the first color data read by the reading means and the first color data stored in the first temporary storage means, and the result of the comparison , Information indicating the location of the second color data corresponding to the matched first color data is output. Then, the selection means can select the second color data from the second temporary storage means group based on information indicating the location of the second color data.

Example 1
In this embodiment, when converting RGB data to CMYK data, normally, LUT reference for performing nonlinear deformation and multiplication / division operation for linear interpolation processing are performed before conversion of dither processing. However, when dot data having the same content continues, dithering is continuously performed with the multiplication and division operations for LUT reference and linear interpolation processing omitted. Thereby, the whole processing time can be shortened.

  FIG. 1 is a schematic diagram showing a relationship between input color data of LUT and grid point data in color conversion. This figure is an LUT for nonlinear conversion, in which each color component of RGB data represented by 24 bits is developed in a three-dimensional direction and divided into L pieces in a lattice shape. Note that R, G, and B indicate color data, and L indicates a grid interval. The r axis represents R / L, the g axis represents G / L, and the b axis represents B / L.

First, in each 8-bit RGB data, a quotient obtained by dividing by the grid interval L and a value obtained by adding 1 to the quotient are obtained. For example, when RGB (100, 90, 70) and L = 17,
Quotient when R = 100 divided by L = 17 = 6, quotient + 1 = 7
Quotient when G = 90 divided by L = 17 = 5, quotient + 1 = 6
B = 70 divided by L = 17, quotient = 4, quotient + 1 = 5
It becomes. The following eight values are obtained by combining the respective values.
(1) rgb = (6, 5, 4), (2) rgb = (7, 5, 4)
(3) rgb = (6, 6, 4), (4) rgb = (7, 6, 4)
(5) rgb = (6, 5, 5), (6) rgb = (7, 5, 5)
(7) rgb = (6, 6, 5), (8) rgb = (7, 6, 5)

  When these eight values are applied to FIG. 1, the vertices of the cube in the center of FIG. 1 correspond to the coordinates (1) to (8) rgb. By sequentially referencing the LUT, eight values of cmyk ((1) cmyk to (8) cmyk) corresponding to each of the above eight values (1) to (8) rgb can be obtained.

  FIG. 2 shows a schematic diagram of a cube based on the eight lattice points used for the linear interpolation specified in FIG. The calculation of cmyk (32 bits) of each bit from the original RGB by linear interpolation will be described with reference to FIG.

  First, for each of the original R, G, and B, the difference when each color component is divided by L ((1) rgb) multiplied by L, that is, the original R, G, and B are divided by L. If the time remainders are x, y, and z, respectively, cmyk data corresponding to (0) RGB in the figure can be calculated by linear interpolation using the following calculation formula. In FIG. 2, (1) rgb to (8) rgb multiplied by L is expressed as (1) RGB to (8) RGB.

cmyk (32 bits) = ((1) cmyk × (L−x) × (L−y) × (L−z)
+ (2) cmyk × x × (L−y) × (L−z)
+ (3) cmyk × (L−x) × y × (L−z)
+ (4) cmyk × x × y × (L−z)
+ (5) cmyk × (L−x) × (L−y) × z
+ (6) cmyk × x × (L−y) × z
+ (7) cmyk × (L−x) × y × z
+ (8) cmyk × x × y × z)
÷ (L × L × L)
x = R− (1) r × L
y = G- (1) g * L
z = B- (1) b * L

  FIG. 3 is a block diagram of the color conversion apparatus according to the present embodiment (Example 1). In the figure, an ASIC for color conversion mounted in the printer will be described as an example. In the figure, a control system chip 20 that controls the entire printer and an ASIC 1 that performs color conversion are connected by a PCI bus 25.

  The control system chip 20 includes a CPU (Central Processing Unit) 21, a memory controller 22, and a PCI (Peripheral Component Interconnect) controller 23. The memory controller 22 controls data input / output with respect to the memory 24 outside the control system chip 20. The PCI controller is an interface to the PCI bus 25.

  The ASIC 1 includes a PCI controller 2, a first temporary storage buffer 5, a comparator 6, a LUT 7, an LUT reference control unit 8, a multiplication / division operation unit 9, a second temporary storage buffer 10, a selector 11, and a dither processing unit 12. The

  The PCI controller 2 includes a FIFO 1 (3) and a FIFO 2 (4). FIFO1 (3) and FIFO2 (4) are used to fill a gap between the speed at which the 32-bit 64-bit PCI bus 25 is accessed in burst mode and the speed at which RGB data is periodically converted to CMYK one dot at a time. This is a first-in first-out (FIFO) type storage circuit.

  The first temporary storage buffer 5 is a buffer circuit that temporarily stores RGB data (8 bits × 3 colors). The second temporary storage buffer 10 is a buffer circuit that temporarily stores CMYK data (8 bits × 4 colors).

  The LUT 7 is a memory for performing non-linear conversion shown in FIG. 1, and CMYK data is obtained when RGB data is input. However, as described with reference to FIG. 1, since the quotient of the value obtained by dividing the RGB data (24 bits) by the grid interval L in bit units of each color is used, there is only accuracy in units of grid intervals.

  The comparator 6 determines whether or not the RGB data (24 bits) stored in the first temporary storage buffer 5 matches the RGB data (24 bits) acquired this time, and the determination result is used as the LUT reference control unit 8. It is a circuit to notify to.

  The LUT reference control unit 8 reads out eight types of cmyk obtained from the combination of the quotient obtained by dividing RGB (24 bits) by L and the quotient obtained by dividing L from the LUT and transfers them to the multiplication / division calculation unit 9. The LUT reference control unit 8 transfers xyz representing the difference between the eight types of cmyk ((1) to (8) cmyk) and the original RGB to the multiplication / division calculation unit 9.

  The multiplication / division calculation unit 9 performs multiplication / division calculation from xyz representing the difference between the eight types of cmyk ((1) to (8) cmyk) transferred from the LUT reference control unit 8 and the original RGB, and will be described with reference to FIG. As described above, CMYK (32 bit) data is obtained.

  The selector 11 selects which of the result calculated by the multiplication / division calculation unit 9 or the content previously stored in the second temporary storage buffer 10 is output to the dither processing unit 12.

  The dither processing unit 12 is a circuit that performs dither processing on the CMYK data output from the selector 11. After the dither processing, for example, CMYK data of 2 bits × 4 colors suitable for the printer engine is obtained. The CMYK data of 2 bits × 4 colors is output to FIFO 2 (4).

  If this CMYK data is video transferred, color printing can be performed. Here, it is assumed that a video transfer controller (not shown) once transfers data in the memory to the printer engine.

  FIG. 4 shows an example of the LUT 7 in the present embodiment (Example 1). On the input color side, quotients r, g, and b obtained by dividing the RGB color data by the grid interval L are stored. On the output color side, a numerical value of cmyk corresponding to the combination of rgb on the input side is stored. In the figure, as an example, R, G, and B are 00h to FFh, respectively. Therefore, when L = 17, the value when divided by L is set to 0 to 15 (0h to Fh). Has been. Therefore, since R ÷ 17, G ÷ 17, and B ÷ 17 can take 16 values of 0 to 15, respectively, the table corresponds to the input and the output in 16 × 16 × 16 = 4096 combinations.

  FIG. 5 shows an operation sequence of the LUT reference control unit 8 in the present embodiment (Example 1). Here, it is assumed that the output bit width of FIFO1 (3) is the same as the number of bits per dot. That is, in the case where the bit width of PCI does not match the number of RGB bits, a circuit for converting the bit width is provided in the middle, and the output of the conversion circuit is described as the output of FIFO1.

  The LUT reference control unit 8 is in the state ST0 in the initial state, and waits if there is no data in the FIFO1 (3) (goes to “N” in the state ST0-1). If there is data in FIFO1 (3) (goes to “Y” in state ST0-1), the LUT reference control unit 8 reads the data for one word, that is, data for one RGB dot.

  At this time, the data for one RGB dot is simultaneously input to the comparator 6. The comparator 6 determines whether or not the RGB data (24 bits) stored in the first temporary storage buffer 5 matches the RGB data (24 bits) acquired this time (state ST0-2), and the determination result Is notified to the LUT reference control unit 8.

  Based on the notification signal from the comparator 6, the LUT reference control unit 8 does not match the read RGB 1 dot data with the previous RGB 1 dot data (goes to “N” in state ST0-2). ), Transition to the state ST1. At this time, the LUT reference control unit 8 overwrites and saves the read RGB 1 dot data in the first temporary storage buffer 5 as the previous dot information (RGB 24 bits).

  In the state ST1, the LUT reference control unit 8 calculates RGB ÷ L and sets the value to (1) rgb. Further, xyz is calculated from RGB-((1) rgb × L).

  In the next state ST2, the LUT reference control unit 8 outputs (1) rgb to the input of the LUT 7, that is, to the address of the memory where the LUT 7 is expanded.

  In the next state ST3, the LUT reference control unit 8 acquires cmyk from the output of the LUT 7. For example, if the LUT input is (1) rgb, (1) cmyk is acquired.

  Since up to (8) cmyk has not been acquired in the next condition determination, the LUT reference control unit 8 moves to the state ST4, and (1) rgb is changed to (2) as described in the lower part of FIG. ) Convert to rgb. That is, the value of r is r + 1. Similarly to the above, the LUT reference control unit 8 outputs (2) rgb to the LUT 7 in the state ST2, and obtains (2) cmyk in ST3. The LUT reference control unit 8 acquires all values from (1) cmyk to (8) cmyk, and repeats until it is determined in the determination of state ST3 that (8) cmyk has been acquired. The LUT reference control unit 8 transfers the acquired (1) cmyk to (8) cmyk and xyz to the multiplication / division calculation unit 9.

  In the next state ST5, the multiplication / division calculation unit 9 performs multiplication / division calculation using the values of (1) to (8) cmyk and xyz, calculates CMYK (32 bits), and passes the result to the dither processing unit 12. . Also, CMYK (32 bits) is stored in the second temporary storage buffer 10 as the previous dot information (CMYK (32 bits)).

  Next, a flow when the RGB data is read from the FIFO1 (3) and is the same as the previous RGB data for one dot (goes to “Y” in the state ST0-2) will be described. If it is the same as the previous dot information (RGB (24 bits)), the LUT reference control unit 8 causes the selector 11 to select the previous dot information ((CMYK32 bits)) by shifting to the state ST7. Then, the selector 11 passes the data to the dither processing unit 12 (state ST6). After processing up to the state ST6, the LUT reference control unit 8 returns to the state ST0 and starts conversion of the next dot.

  According to the present embodiment, when converting RGB data into CMYK, when dot information of the same content is consecutive when performing LUT reference for nonlinear conversion and multiplication / division calculation for linear interpolation processing, Dithering can be performed continuously by omitting multiplication and division operations for LUT reference and linear interpolation processing. Thereby, the whole processing time can be shortened. Furthermore, cost performance can be improved.

(Example 2)
In the first embodiment, RGB data for one dot and CMYK data corresponding thereto are temporarily stored, but in this embodiment, RGB data for a plurality of dots and corresponding CMYK data can be temporarily stored. A color conversion apparatus will be described.

  FIG. 6 is a block diagram of a color conversion apparatus according to the present embodiment (Example 2). The ASIC 1 in FIG. 6 is obtained by replacing the first temporary storage buffer 5 and the second temporary storage buffer 10 of the ASIC 1 in FIG. 3 with a first temporary storage buffer group 31 and a second temporary storage buffer group 32, respectively. It is.

  The first temporary storage buffer group 31 includes a plurality of first temporary storage buffers 5. The second temporary storage buffer group 32 includes a plurality of second temporary storage buffers 10.

  FIG. 7 shows an operation sequence of the LUT reference control unit 8 in the present embodiment (Example 2). In the flow of FIG. 7, the portions different from the flow of FIG. 5 are a state ST0-3 corresponding to the state ST0-2, a state ST5-1 corresponding to the state ST5, and a state ST7-1 corresponding to the state ST7. is there. ST0-3 will be described with reference to FIGS. The states S5-1 and ST7-1 will be described with reference to FIGS.

  FIG. 8 shows the configuration of the first temporary storage buffer group 31 in the present embodiment (Example 2). In the present embodiment, four types of data (RGB) and four types of data (CMYK) can be temporarily stored in the first temporary storage buffer group 31 and the second temporary storage buffer group 32, respectively.

  This figure corresponds to the processing in the state ST0-3. The first temporary storage buffer group 31 includes buffers 31-0 to 31-3. The addresses of the buffers 31-0 to 31-3 are 0 to 3, respectively. The RGB data output from the FIFO1 is assumed to be F0. Let RGB data stored in the buffers 31-0 to 31-3 be A0 to A3, respectively.

  As a result of the comparison by the comparator 6, when the output data F0 of the FIFO1 (3) does not coincide with any of the four types of data A0 to A3 of the addresses 0 to 3, the contents of the address 3 are discarded and the address 2 Is overwritten at address 3. Similarly, the contents of the address 1 are overwritten to the address 2, the contents of the address 0 are overwritten to the address 1, and the output data F0 of the FIFO1 (3) is stored in the address 0.

  If the output data F0 of the FIFO1 matches even one of the four types of data (RGB) from address 0 to address 3, data is not stored redundantly in the temporary storage buffer group 31. In this case, the comparator 6 sequentially compares the RGB data F0 output from the FIFO 1 and the RGB data A0 to A3 output from the buffers 31-0 to 31-3. After the comparison, the comparator 6 outputs to the LUT reference control unit 8 a signal indicating the coincidence / non-coincidence and the address information in which the matched RGB data is stored when they match.

  FIG. 9 shows the contents of the comparator 6 in the present embodiment (Example 2). In the figure, S indicates 1: match, 0: mismatch. N indicates address information. 9 will be described with reference to FIG.

  First, the comparator 6 compares the RGB data F0 output from the FIFO 1 with the RGB data A0 output from the buffer 31-0. If F0 and A0 match as a result of the comparison, the comparator 6 outputs a signal (S = 1) and address information (N = 0) indicating that they match.

  When the comparison with the RGB data A0 does not match, the comparator 6 compares the RGB data F0 with the RGB data A1 output from the buffer 31-1. If F0 and A1 match as a result of the comparison, the comparator 6 outputs a signal (S = 1) and address information (N = 1) indicating that they match.

  When the comparison with the RGB data A1 does not match, the comparator 6 compares the RGB data F0 with the RGB data A2 output from the buffer 31-2. If F0 and A2 match as a result of the comparison, the comparator 6 outputs a signal (S = 1) and address information (N = 2) indicating that they match.

  When the comparison with the RGB data A0 does not match, the comparator 6 compares the RGB data F0 with the RGB data A3 output from the buffer 31-3. If F0 and A3 match as a result of the comparison, the comparator 6 outputs a signal (S = 1) and address information (N = 3) indicating that they match.

  If the RGB data F0 does not match any of the RGB data A0 to A3, the comparator 6 outputs a signal (S = 0) indicating that they do not match.

  FIG. 10 shows the configuration of the second temporary storage buffer group 32 in the present embodiment (Example 2). In the figure, the second temporary storage buffer group 32 includes buffers 32-0 to 32-3. Addresses of the buffers 32-0 to 32-3 are set to addresses 0 to 3, respectively. The CMYK data output from the multiplication / division calculator 9 is assumed to be M0. Let CMYK data stored in the buffers 32-0 to 32-3 be B0 to B3, respectively.

  The selector 11 uses the CMYK data M0 output from the multiplication / division calculation unit 9 or the buffers 32-0 to 32- based on the signal S indicating the match / mismatch output from the LUT reference control unit 8 and the address information N. 3 selects one of B0 to B3 stored in 3 and outputs the selected data Y to the dither processing unit 12.

  FIG. 11 shows the contents of the selector 11 in the present embodiment (Example 2). In the figure, S = 1 corresponds to state ST7-1, and S = 0 corresponds to state ST5-1.

  The selector 11 outputs the CMYK data B0 stored in the buffer 32-0 as the selected output data Y when the output information from the LUT reference control unit 8 is S = 1 and N = 0.

  The selector 11 outputs the CMYK data B1 stored in the buffer 32-1 as the selected output data Y when the output information from the LUT reference control unit 8 is S = 1 and N = 1.

  The selector 11 outputs the CMYK data B2 stored in the buffer 32-2 as the selected output data Y when the output information from the LUT reference control unit 8 is S = 1 and N = 2.

  The selector 11 outputs the CMYK data B3 stored in the buffer 32-3 as the selected output data Y when the output information from the LUT reference control unit 8 is S = 1 and N = 3.

  Thus, when the output information from the LUT reference control unit 8 is S = 1, data is not stored redundantly in the second temporary storage buffer group 32 in any case.

  On the other hand, when the output information from the LUT reference control unit 8 is S = 0, the selector 11 outputs the CMYK data M0 output from the multiplication / division calculation unit 9 as the selection output data Y. At this time, with respect to the buffers 32-0 to 32-3, the contents of address 3 are discarded, and the contents of address 2 are overwritten to address 3. Similarly, the contents of address 1 are overwritten with address 2, the contents of address 0 are overwritten with address 1, and CMYK data M0 is stored at address 0.

  According to the present embodiment, RGB data and CMYK data for a plurality of dots can be held. As a result, a plurality of RGB data before conversion and CMYK data corresponding thereto are stored, and it is compared whether or not the dot to be converted is the same as the stored dot. The multiplication / division calculation for the interpolation processing is omitted, and the dither processing is performed continuously. As a result, since the detection rate of the same data can be increased, the overall processing time can be further shortened.

  In the second embodiment, the address to be written to the temporary storage buffer group is fixed to address 0, but the address of the stored data may be changed without changing the address of the stored data. In the second embodiment, the addresses of the temporary storage buffer group are four types from address 0 to address 3, but the address range may be expanded as much as possible.

  Also, white and black RGB data and CMYK data may be fixedly held in advance in the first and second temporary buffer groups, respectively.

<Second Embodiment>
In the embodiment, a case will be described in which a lookup table storing CMYK data to be converted is prepared in a memory for all RGB inputs.

Example 1
FIG. 12 shows an overview of the overall configuration of the color conversion apparatus according to this embodiment (Example 1). In the figure, the ASIC includes at least an LUT reference control unit (not shown) and a ROM (Read Only Memory) 42. A ROM (Read Only Memory) 42 stores an LUT in which CMYK data corresponding to all input RGB data is stored.

  First, the LUT reference control unit inputs RGB input data (each 8 bits) 41 to the address of the ROM 42. For example, R input data R0, R1,... Are input to addresses A0, A1,.

  Then, CMYK data (each 8 bits) 43 corresponding to the input RGB data 41 is output from the ROM 42. For example, C0, C1,... Are output as dot data D0, D1,.

  Thus, since the RGB data is converted into CMYK data only by referring to the conversion table (LUT) on the memory (ROM 42), the color conversion process can be performed at a very high speed.

  The color conversion can also be performed by software operating on a personal computer (PC). In this case, for example, the table size of the LUT can be 16M × 4 bytes = 64M bytes.

  Also, conversion from CMYK data to RGB data can be performed in the same manner. This will be described with reference to FIG.

  FIG. 13 shows an outline of the overall configuration of the color conversion apparatus according to the present embodiment (modified example of Example 1). First, the LUT reference control unit inputs CMYK input data (each 8 bits) 43 to the address of the ROM 42. Then, RGB data (8 bits each) 41 corresponding to the input CMYK data 43 is output from the ROM 42.

  In this embodiment, the LUT is stored in the ROM. However, the present invention is not limited to this. For example, the LUT may be stored in a flash memory, DRAM (Dynamic RAM), or HDD (hard disk drive).

(Example 2)
In the present embodiment, a color conversion device that reduces the size by using a plurality of LUTs stored in the ROM and also serving as a part of the table will be described.

FIG. 14 shows an overview of the overall configuration of the color conversion apparatus according to the present embodiment (Example 2). The ROM 52 is a table capable of storing 2 ⁴ × 2 ⁴ × 2 ⁴ = 4096 data. The contents of each data stored in this table are the addresses (addresses 0 to 255) of the ROM 53 for specifying any one of the 256 ROM 53 groups. Therefore, when the upper 4 bits of each color of the input data (8 bits each) of the RGB data 51 is input to the ROM 52 as an address by the LUT reference control unit, a predetermined number of the ROM 53 group is determined from the data in the table specified by the address. An address for specifying the ROM 53 can be obtained.

  Next, the LUT reference control unit inputs the lower 4 bits of each color to the address of the ROM 53 selected above. As a result, the data stored at the input address is output as CMYK data 54. In this way, color conversion can be performed using the two-stage ROM table.

  Here, each ROM 53 is a small range RGB → CMYK conversion table. Therefore, one of the two or more tables can be used as a representative table within a range in which colors can be approximated, and the other tables can be omitted. That is, the representative table also serves as the omitted table.

  FIG. 15 is a diagram for explaining the downsizing of the ROM table in the present embodiment (Example 2). In the figure, if the ROM 53-0 and the ROM 53-1 are tables within a range in which colors can be approximated, one can be used as a representative table, and the other can be omitted. Therefore, the table that is not omitted is also used as the table that is omitted. At this time, if the ROM 52 stores an address for specifying the ROM 53-1, it is rewritten to the address of the ROM 53-0.

  According to this embodiment, the LUT for color conversion from the RGB data in the ROM to the CMYK data can be omitted, so the LUT can be reduced in size.

  As in the first embodiment, this color conversion can also be performed by software operating on a personal computer (PC). Similarly to the first embodiment, conversion from CMYK data to RGB data can be performed in the same manner.

  In this embodiment, the LUT is stored in the ROM. However, the present invention is not limited to this, and the LUT may be stored in a flash memory, a DRAM (Dynamic RAM), or an HDD (Hard Disk Drive). The present invention is not limited to the above-described embodiment, and various configurations or embodiments can be taken without departing from the gist of the present invention.

It is a schematic diagram which shows the relationship between the input color data of LUT and grid point data in color conversion. The schematic diagram of the cube based on eight lattice points used for the linear interpolation specified in FIG. 1 is shown. 1 is a block diagram of a color conversion apparatus in a first mode for embodying the present invention (embodiment 1); FIG. An example of LUT7 in 1st Embodiment (Example 1) is shown. The operation | movement sequence of the LUT reference control part 8 in 1st Embodiment (Example 1) is shown. It is a block diagram of the color conversion apparatus in 1st Embodiment (Example 2). The operation | movement sequence of the LUT reference control part 8 in 1st Embodiment (Example 2) is shown. The structure of the 1st temporary storage buffer group 31 in 1st Embodiment (Example 2) is shown. The contents of the comparator 6 in the first embodiment (Example 2) are shown. The structure of the 2nd temporary storage buffer group 32 in 1st Embodiment (Example 2) is shown. The content of the selector 11 in 1st Embodiment (Example 2) is shown. An overview of the overall configuration of the color conversion apparatus according to the second embodiment (Example 1) will be described. An outline of the overall configuration of a color conversion apparatus according to a second embodiment (a modification of Example 1) will be described. An overview of the overall configuration of a color conversion apparatus according to a second mode for embodying the present invention (embodiment 2) is shown. It is a figure for demonstrating size reduction of the ROM table in 2nd Embodiment (Example 2).

Explanation of symbols

1 ASIC
2 PCI controller 3 FIFO1
4 FIFO2
5 First temporary storage buffer 6 Comparator 7 LUT
8 LUT reference control unit 9 Multiplication / division calculation unit 10 Second temporary storage buffer 11 Selector 12 Dither processing unit 20 Control system chip 21 CPU
22 memory controller 23 PCI controller 24 memory 25 bus 31 first temporary storage buffer group 32 second temporary storage buffer group 42, 52, 53 ROM

Claims (5)

A color conversion processing device for converting first color data output to a first medium into second color data for output to a second medium,
Reading means for reading the first color data;
Comparing means for comparing the first color data read this time with the first color data read previously;
When the first color data can be temporarily stored and the two first color data do not match as a result of comparison by the comparison means, the previously stored first color data Is temporarily replaced with the first color data read this time;
Color conversion data storage means in which the first color data and the second color data corresponding to the first color data are intermittently stored;
Color conversion means for converting the first color data into the second color data based on the color conversion data storage means;
Interpolation means for performing interpolation processing based on the second color data converted by the color conversion means;
Second temporary storage means capable of temporarily storing the second color data subjected to the interpolation processing;
Based on the result of the comparison, it is selected whether to output the second color data stored in the second temporary storage means or to output the second color data subjected to the interpolation processing. A selection means;
A color conversion processing apparatus comprising: The selection means outputs the second color data stored in the second temporary storage means when the two first color data match as a result of the comparison. The color conversion processing apparatus according to 1. The color conversion processing apparatus according to claim 1, wherein each of the first and second temporary storage units includes a plurality of temporary storage units. The first temporary storage means stores the first color data that is different between the temporary storage means constituting the first temporary storage means,
The comparison means sequentially compares the first color data read by the reading means and the first color data stored in the first temporary storage means, and as a result of the comparison, matches Outputting information indicating the location of the second color data corresponding to the first color data,
4. The color according to claim 3, wherein the selection unit selects the second color data from the second temporary storage unit group based on information indicating a location of the second color data. 5. Conversion processing device. A color conversion processing method by a color conversion processing device for converting first color data output to a first medium into second color data for output to a second medium,
Reading the first color data;
Comparing the read first color data with the first color data read from the first temporary storage device in which the first color data is temporarily stored;
If the two first color data do not match as a result of the comparison, the first color data stored in the first temporary storage means is replaced with the first color data read this time,
Based on a color conversion data storage device in which the first color data and the second color data corresponding to the first color data are intermittently stored, the first color data is converted into the second color data. Converted to color data,
An interpolation process is performed based on the converted second color data,
Storing the second color data subjected to the interpolation processing in a second temporary storage device capable of temporarily storing;
Based on the comparison result, it is selected whether to output the second color data stored in the second temporary storage device or to output the second color data subjected to the interpolation processing. And a color conversion processing method.