JPH01108868A - Color conversion method - Google Patents

Abstract

PURPOSE:To attain color conversion with excellent color reproducibility with less memory capacity by dividing separated color components by a bit plane, applying local color conversion into plural data by a memory means, combining them again to apply partial color conversion of color components. CONSTITUTION:Respective picture signals R, G, B are separated into achromatic and chromatic components, and the color conversion to a partial print ink signal is executed by the table conversion of the memory for each separated component and the final result is obtained by the synthesis of the partial data. Then the separated color component signal is split into the bit plane. Thus, the color conversion in the unit of picture elements is attained and the color conversion with very excellent color reproduction is attained and the memory capacity is reduced remarkably, one chip LSI incorporating ROMs 21, 22 is realized easily technologically and cost reduction in device is attained.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is a method for printing image signals consisting of red (hereinafter referred to as R), green (hereinafter referred to as G), and blue (hereinafter referred to as B). Yellow (hereinafter referred to as Y), magenta (hereinafter referred to as M), and cyan (hereinafter referred to as C) necessary for
3 colors or 3 colors plus black (hereinafter referred to as K)
The present invention relates to a color conversion method for converting into a printing ink signal consisting of four colors with the addition of .

[Prior art] Conventionally known color conversion methods include, for example,
The adaptive matrix calculation method disclosed in Publication No. 0-220660 and the patent application No. 62-60520 in the earlier application by the present applicant et al.
There is a pixel separation type color conversion method shown in the issue.

FIG. 4 is a block diagram showing the configuration of the color conversion method disclosed in the former publication. In the same figure, (11G) is a matrix multiplier, and (120) is a color conversion method provided with a plurality of color conversion coefficient matrices. Conversion coefficient matrix table, (130
) is a color conversion coefficient matrix switch.

The operation shown in FIG. 4 will be explained.

First, the image signals (R), (G), and (B) are input to the color conversion coefficient matrix switch (130). This color conversion coefficient matrix switch (130) is (R), (G),
Each image signal in (B) increases the intensity of each color signal component by 3
In the color signal space defined as an axis, each pixel is identified to which of a plurality of predetermined regions it belongs, and the identification signal is stored in a color conversion coefficient matrix table (1
20). In this color conversion coefficient matrix table (120), a plurality of color conversion coefficient matrices are prepared in advance, corresponding to each area defined in the color signal space, and color conversion coefficients corresponding to input identification signals are prepared in advance. Output the matrix to a matrix multiplier (110). This matrix multiplier (110) has (R), (G
), CB) and the above color conversion coefficient matrix are input at the same time, and multiplication is performed here (Y),
Printing ink signals (M) and (C) are output.

Figure 5 shows the patent application filed in 1986-605, which is based on the applicant's earlier application.
This is a block diagram showing the configuration of the color conversion method proposed in No. 20, in which (1), (2), and (3) represent the image signals of (R), (G), and (B), respectively. Input terminal.

(4) is a minimum value calculator, which includes address signals for conversion of achromatic color components (α=MIN (R, G, B)) and (R) and (
Code (a) indicating which of G) and (B) is the minimum value
Compute and generate. (5) is a subtractor, (R), (G)
, then subtract (α) from (B). (6) is an address synthesizer, which is the output signal of the subtracter (5) (R
−α).

An address signal (b) is generated from two signals excluding the zero term in (G-α) and (B-α).

(7) is a memory consisting of, for example, a ROM, (8) is a latch that temporarily holds 1 byte of data, (9) is a memory consisting of, for example, a ROM, and (lO) is an output processor. 9), combine and add or select each partial data and output. (11) is an input terminal for a control signal (hereinafter referred to as C0NT) necessary to execute the operation, and (12) are (Y) and (M).

This is the output terminal for the color conversion data in (C).

Next, the operation of the configuration shown in FIG. 5 will be explained.

Each of the 6-bit (N=6) image signals (R), (G), and (B) given to the input terminals (1), (2), and (3) is calculated by calculating the minimum value, respectively. Container (4) and subtractor (
5). The minimum value calculator (4) is composed of, for example, a digital comparator and a selector, and α=MIN(R
, G, B) and outputs (R), (G)
, (B), a predetermined 2-bit code (a) indicating which signal is the minimum is output. The subtractor (5) is the above (α)
As input, from each signal of (R), (G), and (B)
Subtract (α), (R-α), (G-α), (B-α)
Output. At least one of these three outputs is 0. The address synthesizer (6) outputs the above output (R-α), (
G-α).

From (B-α), an address signal (b) necessary for changing the color component is generated according to the instruction of the 2-bit code (a). For example, when α=B, (R-α) and (G-α
), when α=G, (R-α) and (B-α), α=R
When (R-α) and (B-α) are respectively used, the former is placed in the upper 6 bits of each signal pair, and the latter is placed in the lower 6 bits, resulting in a total of 12 bits of address signal (b). .

The above three means generate an achromatic color component conversion address signal (α), a color component conversion address signal (b), and a 2-bit code (a).

Next, partial data of the two components is obtained by converting the ROM table.゛First, the color component conversion ROM that stores partial data divides 4 data for each l address: (Y), (Ill), (C), and the secondary achromatic color component (K) generated by the color component. The entire set of 12 bits is divided into three pieces and stored in memory (
7). Therefore, 4 data x 8 bits x 2
The number of addresses x 32393 kilobits.

In addition, the ROM for achromatic color component conversion is (Y) for every l address.
, (M), (C), totaling 2
number of addresses. However, as mentioned above, since there is a secondary achromatic color component (K), (K) and (α)
When a composite address is used, the number of addresses is increased by the value of (K) to form memory (9).

The memory (7) contains the address signal (b) for conversion of the color component obtained previously, and the 2-bit code (a) indicating the minimum value signal.
) and (Y
1), (Ml), (C1), and (K) are input, first, (K) is obtained and stored in the latch (8). Next, control is executed to obtain desired conversion data among the three colors (Yl), (Ml), and (CI).

The memory (9) stores the output of the latch (8) and the achromatic color components (α) and (Y2), (M2), (C2
) to obtain the desired conversion data. By inputting these two partial conversion data to the output processor (lO), Ytou Yl + Y2. M=M1,
M2. Execute the operation C=CI+C2 to obtain predetermined (Y), (M), ((:).

[Problems to be Solved by the Invention] Since the conventional color conversion method is configured as described above, in the case of the former adaptive matrix calculation method, it is difficult to solve the problem in the boundary area due to discontinuity of the matrix coefficients. Poor color reproducibility,
In other words, it has the disadvantage of increasing color difference, and although the latter pixel separation color conversion method is superior to the former in terms of color reproducibility, it requires a very large memory capacity and requires a built-in ROM. This was a technical issue in realizing LSI implementation, and had the drawback of being inferior in terms of manufacturing costs.

This invention was made to solve the above-mentioned problems, and its purpose is to provide a color conversion method that can perform color conversion with good color reproducibility using a very small memory capacity. do.

[Means for solving the problem] The color conversion method according to the present invention includes (R), (G), CB)
Each image signal is separated into an achromatic color component and a color component on a pixel basis, and the color component of both of these separated components is divided into bits.
The method is characterized in that the planes are divided into a plurality of planes, and the memory means performs partial color conversion into a plurality of planes, and the color components are combined and added again to perform partial color conversion of the color components.

[Operation] According to the present invention, each image signal of (R), (G), and (B) is separated into two, an achromatic color component and a color component, and the separated color components are converted into a bit plane. By dividing and performing multiple partial color conversions, and then combining and adding them again, the memory capacity of the memory means is reduced, and at the same time, the final result is obtained by combining and adding multiple color-converted parts. As a result, color conversion with good color reproducibility is realized.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing the configuration of a color conversion method according to an embodiment of the present invention.
) are ROMI and ROM II which serve as memory means for storing partial conversion data of color components, (23) is a subtractor for adjusting the achromatic color portion, and (24) is a memory means for storing conversion data of the achromatic color portion. ROMI[I serves as a memory means. (25) is the color composition amount, and the above ROMI (21)
and the partial data of ROM II (22) are combined and added. Other components that are the same as those of the conventional example shown in FIG. 5 are given the same reference numerals, and their explanations will be omitted.

Next, the operation of the above configuration will be explained.

(R) given to input terminals (1), (2), (3),
(G).

Each image signal (8) is input to a minimum value calculator (4) and a subtracter (5), respectively. In the minimum value calculator (4), α
Calculation of = MIN (R, G, B) and the above (α) or (R)
.

A 2-bit code (a) indicating whether the signal is (G) or (B) is output. On the other hand, the subtractor (5) is the above (α)
As input, from each signal (R), (G), and (B), (
α) is subtracted, (R-α), (G-α), and (B-α) are calculated, and the results are output. One of these three outputs is 0. Therefore, the address synthesizer (
6) outputs two calculation results (β) designated as non-zero in accordance with the code (a) designating the color of the minimum value from the three calculation results.

In other words, the output signal (β) is (R-α) and (G-α) when α=B, (R-α) and (B-α) when α=G, and (B-α) when α=R. G-α) and (B-α). At this time,
All signals are 6 bits.

Here, (R-Q) is (β5. β4 , β3. β2 , r
l, rO) (G-α) (β5, β4, β3
, β2 , gl , go ) (B-α) (β5 ,
β4, β3, β2, bl, bO).

Next, the output signal (β) is divided into two signals (bl) and (β2)
divided into ROMI (21) and ROMn (2
2) Input to the address terminal. At this time, (β1) is α=B (β5. β41 β3. gs eg4 +
g3 ), and with a=a (β5. β4 , β3. β
5, β4, β3).

α=R (β5, β4, β3, β5, β4
, β3).

Also, (β2) is α=B and (β2. rl , rO
, β2.

gl , gO) and with α=G (β2. rl ,
re, β2, bl.

bo ), and with α=R (β2, gl, gO, β
2 , bl , bO), this (bl) and (β2
) divides the bits of the same order of magnitude of the two signals into the same address set, and this is generally called bit-brain division.

The above-mentioned ROMI (21) and ROMn (22) require bank switching in three ways: Q=R, α=G, and α=B, and this is performed according to the instruction indicated by symbol (a). Also, each ROM (21), (22) is (
(Xl) data consisting of yl), (ml) and (cl), (xl) data consisting of (y2), (■2) and (C2), and achromatic color generated by the combination of (xl) and (Xl) It consists of data on component amount (kl) and (kl).

FIG. 2 shows an example of the BANK configuration of the ROMI (21) and the address arrangement of print ink data (yl, ml, cl, kl), and the ROM n (22) is also formed in the same way, although not shown. There is.

ROM I (21) and ROM II (
22) address terminal with a 5-divided signal (β1) and (β2
), the instruction code (a) of the minimum value signal and the color designation signal to be converted (Y, M, C ink classification) are connected to the terminal (11
), partial data (xi), (xl) $5, (kl), and (kl) corresponding to the address signal can be obtained by table conversion. At this time, the capacity of each ROM is 2 (number of addresses) β3 (BANK
number) β4 (data) x 8 (bit) = 6,1
It becomes 44 kbit.

Partial data (β1) and (β2) obtained in this way
is input to the color synthesizer (25) and (yl" y2), (
ml + m2).

The other (kl) and (kl) data that performs the addition operation of (cl◆c2) are input to the subtractor (23) and αl=α−
Perform the calculation kl - kl.

This (C1) is input to the address terminal of ROM m (24). ROM m (24) stores partial data of (y3), (m3), and (C3) for printing achromatic color components, and partial data (β3) corresponding to the address signal is immediately determined by table conversion. However, terminal (11
) A color designation signal for printing ink is input by the C0NT signal.

The output processor (lO) includes the color synthesizer (25) and ROMm.
Adding the partial data of (24), Y = yl◆y2◆3
13°M=sl + m2 + m3. Cxcl
+C2+ Outputs the calculation result of c.

In the manner described above, the image signals (R), (G), and (B) are converted into printing ink signals (Y), (M), and (C).

Note that the ROM capacity of this example is 6.144 kbi.
tx2+2x3 (color) β8 (btt) =13.8
It becomes 24 kbit. This is the conventional R shown in Figure 5.
Compared to the OM capacity of approximately 394 kbits, this is approximately 1728, achieving a significant compression of the ROM capacity.

FIG. 3 is a block diagram showing the configuration of a color conversion method according to another embodiment of the present invention.
) is three color component data (R-α).

The two data in (G-α) and (B-α) are set as one set, and each set of data is further divided into two into an upper bit group and a lower bit group, and six pieces of data are used as each address signal. This is a ROM. Each of these ROMs (31) to (3
6) is (yl), (at) for each address.

(cl), (kl) or (y2), (m2
), (C2), and (kl) are stored in predetermined locations. (37) is the (xl) signal (y
l, sl, cl), (xl) signal (y2.m2.C2)
and (β3) signal (y3.■3.c3) for each ink color. (38) is the addition result (Y),
These are the output terminals of (M) and (C). Other configurations are the first
Since it is the same as the figure, the same reference numerals are given and the explanation is omitted.

Next, the operation of the configuration shown in FIG. 3 will be explained.

(R) given to input terminals (1), (2), (:l)
, (G).

As in the case of FIG. 1, each image signal in (B) is processed by a minimum value calculator (4) and a subtracter (5) into achromatic color component data (α) and three data representing color components ( R-α)
, (G-α), (B-α) and (R), (G), (B
) is decomposed into code (a) indicating the minimum signal of

The upper 3 bits of each of (R-α) and (G-α) are stored in ROM (31), and (R-α) is stored in ROM (32).
) and (B-α), the upper three bits of each are stored in the ROM (
33) is input from the upper 3 bits of each of (G-α) and (B-α) or from the address terminal. Also, R.O.
M (34), ROM (35) and ROM (36).

The lower 3 bits of (R-α) and (G-α), (R-α
) and (B-α), and the lower three bits of (G-α) and (B-α) are sequentially input from the address terminals. Note that symbol (a) is input to the chip enable terminals of the ROMs (31) to (36). This code (a) is, for example, ROM (31) and R when α=B.
When OM (34) is α;G, ROM (32) and RO
When M (35) and α=R, ROM (33) and R
OM (36) or each is controlled to operate selectively.

By such address distribution method and control of the chip enable terminal, it is possible to
(xl) data of (cl) and achromatic color component data (kl) generated secondarily and (=2) of (y2.=2.c2)
data and incidentally generated achromatic color component data (k2
) can be found by converting the ROM table. (kl) and (k2) data in this data and (α) de,
- input evening into the subtractor (23), α1-kl -
Perform S calculation of k2. However, at this time, αl≧0.

This calculation result (α1) is input to the address terminal of ROM m (24), and (=3) data of (y3.=3.c3) corresponding to the address value is obtained by table conversion.

These (xi), (=2), and (=3) data are input to the adder (37), and Y=yl + y2 + y
3. M=ml+m2+=3. C=cl+
Execute the addition operation of c2 + c3 and connect the terminal (3
8) Output the results. As described above, (R), (
The image signals of G) and (B) are converted into (Y), (M), and (C
) can be converted to printing ink signals. At this time, the ROM (
The capacity of each ROM of 31) to (36) is 2 (number of addresses) = 4 (number of data) x 8 (number of bits/data) = 2.
048 bits, and the capacity of ROM III (24) is 26 (number of addresses) x 3 (number of data) = 8 (number of bits/data) = 1,536 bits. Therefore, the total capacity is 13.824 kbit, which is also about 1728 compared to the conventional example shown in FIG.

However, experimental results have shown that even if the number of bits for one color component is reduced by one bit compared to the number of bits for an achromatic color component, there is no noticeable deterioration in print image quality. Therefore, (R-α
), (G-α), and (B-α) can be rounded to 5 bits, and separated into, for example, the upper 3 bits and the lower 2 bits for partial color conversion. RO in this case
The M capacity is 9.216 bits and the compression ratio is z42.

In the above embodiment, each of the image signals (R), (G), and (B) was explained using 6 bits, but it can be similarly realized using 7 bits or 8 bits. At this time, the color components may be rounded to 6 bits, and only the achromatic color components may be reduced to 7 or 8 bits, thereby achieving both compression of the ROM capacity and higher image quality by increasing the number of gradations.

In addition, the method of separating the achromatic color component and the color component is different from the one described in this embodiment, for example, in Japanese Patent Application No. 62-6, which is an earlier application filed by the present applicant.
The decomposition method of the embodiment shown in FIG. 2 described in No. 0520 may be adopted.

[Effect of the invention] As described above, according to the present invention, (R) and (G).

Separate each image signal in (B) into achromatic color components and color components, perform color conversion into partial printing ink signals using memory table conversion for each separated component, and combine and add these partial data. This is a color conversion method that obtains the final result with a configuration in which the separated color component signals are further divided into bit planes, making it possible to perform color conversion on a pixel-by-pixel basis, resulting in color conversion with very good single-color reproducibility. Furthermore, it is possible to significantly reduce the memory capacity, and it is technically easy to implement an L-chip LSI with a built-in ROM, which has the effect of reducing equipment costs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a color conversion method according to one embodiment of the present invention, FIG. 2 is a diagram showing an example of address arrangement of the ROM in FIG. 1, and FIG. 3 is another embodiment of the present invention. FIGS. 4 and 5 are block diagrams showing the configuration of a conventional color conversion method, respectively. (1), (2), (3)...R, G, B image signal input terminal, (4)...Minimum value calculator, (5)...Subtractor, (6)...・Address synthesizer, (10)... Output processor, (11)... C0NT signal input terminal, (1
2)... Output terminals for color conversion signals Y, M, C, (21
), (22), (24)...ROM storing partial color conversion data, (23)...subtractor, (25)...
Color synthesizer, (31) to (3B)...ROM storing partial color conversion data, (37)...Adder, (38)
...Y. Parallel output terminals for M and C. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (2)

[Claims] (1) In the color conversion method of converting an image signal consisting of multiple bits of red, green, and blue, respectively, into a printing ink signal consisting of three colors, yellow, magenta, and cyan, or four colors, yellow, magenta, cyan, and black, the above-mentioned means for separating red, green, and blue image signals into two components, an achromatic color component and a color component, for each pixel; a memory means for converting the separated achromatic color components into partial printing ink signals; A color conversion device comprising: memory means for dividing a color component into bit planes and converting it into a plurality of partial printing ink signals; and means for synthesizing and adding the plurality of partial printing ink signals. Law. (2) An achromatic color component that occurs secondarily depending on the color component,
The color conversion method according to claim 1, further comprising means for reducing the value of the achromatic color component separated from the color component.