JPH01265670A - Color picture processing unit - Google Patents

Abstract

PURPOSE:To reproduce a picture with correct color quickly with low cost by forming an m-bit picture data subjected to color correction from a 1-bit picture data being the result of color separation picture data, binarizing it at a prescribed threshold level and applying color processing. CONSTITUTION:The picture signal subjected to color separation is converted into an 8-bit R, G, B picture data and a binarizing section 2 converts a luminance 8-bit R,G, B data into a density 1-bit Y1, M2, C1 data. Then a color processing section 3 forms an 8-bit picture data subjected to color correction from the converted 1-bit Y1, M1, C1 data through matrix calculation, the result is binarized at a prescribed threshold level to form one-bit Y2, M2, C2 data. Then the error density caused by binarization is fed to the 8-bit picture data subjected to color correction to propagate its error to the succeeding picture element. Thus, the picture with correct color is reproduced quickly with low cost without requiring product sum calculation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color image processing device, and more particularly to a color image processing device that reproduces color-separated image data in its original correct colors.

[Prior Art] This type of device requires manual color correction of image data to match the output characteristics of a printer or the like.

FIG. 6 is a block diagram of a conventional color image processing device. In the figure, the A/D converter 1 converts 8-bit R, G, and B image signals read by a COD (not shown), etc.
. Then, the color correction process of equation (1) is performed.

Here, the all-ass 7 color correction coefficient binarization unit 12 converts the color-corrected 8-bit Yl 1°Mll
, C11 data with 1 bit Y12 while preserving its density
．． M12. Convert to CI2 data.

Note that this conversion method includes the density pattern method, dither method,
Concentration-preserving binarization method ``For example, error diffusion method...R, El
oyd and L, Steinberg: “An A
adaptiveAlgorithm for 5pat
ial Gray 5cale”, 1975SI
D International Symposium
Digest of Techni-cal Pap
ers, 4.3. pp 36-37 (Apr, 1975
) There is a J.

The printer section 4 has 1 bit Y12. The original correct color image is output according to the M12°C12 data.

[Problem to be solved by the invention] However, conventionally, in order to perform the product-sum operation of the above formula (1),
Huge calculation time or lookup table (2”X3X
8 bits).

The present invention obviates the drawbacks of the prior art, and its purpose is to provide a color image processing device that can reproduce the original correct colors by simple color correction calculations or look-up tables.

[Means for Solving the Problems] In order to achieve the above object, the color image processing device of the present invention includes image conversion means for converting color-separated n-bit image data into 1-bit image data while preserving the density thereof. and a color correction means for forming m-bit image data color-corrected from the converted 1-bit image data by matrix calculation;
A binarizing means for binarizing the color-corrected m-bit image data using a predetermined threshold, and an adding means for adding error density caused by the binarization to the next color-corrected m-bit image data. The outline is as follows.

Further, in order to achieve the above object, the color image processing device of the present invention includes an image converting means for converting the color-separated n-bit image data into 1-bit image data while preserving the density, and the converted 1-bit image data. The outline of the present invention is to include a color correction means for forming m-bit image data color-corrected from data by matrix calculation, and a dither conversion means for binarizing the color-corrected m-bit image data using a dither threshold value.

[Operation] In the above configuration, the image conversion means converts the color-separated n-bit image data into 1-bit image data while preserving the density.The 0-color correction means performs color correction from the converted 1-bit image data by matrix calculation. m-bit image data is formed.

The binarization means binarizes the color-corrected m-bit image data using a predetermined threshold value. The addition means adds the error density caused by the binarization to the next color-corrected m-bit image data.

Further, in the above configuration, the image conversion means is a color-separated n
To convert bit image data into 1-bit image data while preserving its density. The color correction means forms m-bit image data which is color-corrected from the converted 1-bit image data by matrix calculation. The dither conversion means performs the color correction.
Bit image data is binarized using a dither threshold.

[Description of Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[First Embodiment] FIG. 1 is a block diagram of a color image processing apparatus according to a first embodiment of the present invention. In FIG. The R, G, and B signals are converted into, for example, 8-bit R, G, and B data. 2
is a binarization unit, which converts the 8-bit R, G, and B data of luminance into 1-bit Yl of density by, for example, a density-preserving binarization method.

Convert to Ml, Cl data. 3 is a color processing unit which processes the converted 1 bit Y1. 8-bit image data is formed from the Ml and Cl data by color correction using matrix operations, and this is binarized using a predetermined threshold value to generate 1-bit Y2. M2. C
2. Form data.

Further, at this time, the error density caused by the binarization is added to the next color-corrected 8-bit image data, and the error is propagated to the next pixel. 4 is a printer section, and 1 bit Y2. M
2. Output an image with the correct color according to C2 data.

FIG. 2 is a block diagram showing the details of the color processing section 3 of the first embodiment. In FIG.
8-bit Y3.I, Ml, Cl data output. M3. C
Convert to 3 data.

Margin below where: a++-ass: Color correction coefficient (positive or negative decimal number less than or equal to 1) In this case, the input Yl, Ml, and Cl data are each 1 bit, and their contents can be “1” or “0”. Therefore, the output Y3. M3. C3 data is color correction coefficient all~as
This can be done by simply calculating the sum of s.

In addition, the color correction coefficient a I I"' a 33 is multiplied by 100 to make it an integer, for example, so that floating point calculation is not required. Therefore, the output Y3.M3.C3 data has the most significant 1 bit. consists of the sign bit and the lower 7 bits of data.

Reference numeral 3-2 is a threshold value determination section, which has an 8-bit Y3°M3. C3
The data is compared with a predetermined threshold value Ty and binarized. Above (2
), for example, if we focus on the calculation of the n-th output Y3n data, the term (Dyn-+) on the right side is the error density caused by the immediately preceding (n-1st) binarization. . This error is determined as follows.

Now, the previous output Y3. ．． Looking at the data, YB4-
When +≧Ty, Y2n-, = 1, and D yn-1
= Y 3 n-1-1 (where 1 means the maximum value that the output Y3 can take). Also, Y 3 n-1 Ty
When , Y2rl-, =O, and D y n-+ =
It becomes Y3n-1. Error D carried forward in this way:
Jn-r is the n-th color correction term (a-th Y 1 n
+a+zM 1 n+a+sc 1 n),
It is compared with a threshold value Ty.

FIG. 3 is a diagram showing the scanning direction of output pixels, and as the pixels are scanned in the six directions of arrows, the number of pixels is n-1, n.

Proceed to n+1.

[Second example] The second embodiment relates to an apparatus that performs dither conversion after color correction.

FIG. 4 is a block diagram showing details of the color processing section 3' of the second embodiment. Incidentally, the same components as those in FIG. 2 are given the same reference numerals and their explanations will be omitted.

In the figure, numeral 3-3 denotes a threshold determination section, which includes a dither threshold matrix (FIG. 5(B)).

FIG. 5(A) is a conceptual diagram of a normal dither threshold matrix, and FIG. 5(B) is a diagram showing a specific example of the dither threshold matrix of the second embodiment.

In FIG. 5A, considering a 4×4 dither threshold matrix, each threshold is divided into 16 levels from 1 to 16. On the other hand, in FIG. 5(B), in this embodiment, input Y3. M3. Since C3 data is 8 and cut data,
Its level will range from -127 to +127. Therefore, in this embodiment, the range from O to 255 is divided into 16 threshold values, with 256/16=16 being the unit, for example.

As a result, the threshold determination unit 3-3 receives the input 8-bit Y3. M3. C
3. Dither convert the data. Note that since the dither conversion is a conversion that preserves density by itself, the error density is not propagated as in the first embodiment.

[Effects of the Invention] As described above, according to the present invention, since color processing is performed using binary data, there is no need for conventional sum-of-products calculations, and a quick and inexpensive color image processing device can be provided.

Also, since the density is preserved within a reasonable range, correct colors can be reproduced.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram of a color image processing device according to a first embodiment of the present invention. FIG. 2 is a block diagram showing details of the color processing section 3 of the first embodiment. FIG. 3 is a scanning of output pixels. 4 is a block configuration diagram showing details of the color processing unit 3' of the second embodiment, FIG. 5(A) is a conceptual diagram of a normal dither threshold matrix, and FIG. 5(B) is a diagram showing the direction. A diagram showing a specific example of the dither threshold matrix of the second embodiment. FIG. 6 is a block diagram of a conventional color image processing device. Patent applicant Canon Co., Ltd. ・”Par-7゜Figure 2

Claims (2)

[Claims] (1) Image conversion means for converting color-separated n-bit image data into 1-bit image data while preserving the density, and forming m-bit image data color-corrected by matrix operations from the converted 1-bit image data. a binarizing unit that binarizes the color-corrected m-bit image data using a predetermined threshold;
A color image processing device comprising an addition means for adding bit image data. (2) image conversion means for converting the color-separated n-bit image data into 1-bit image data while preserving the density; and forming m-bit image data color-corrected by matrix operations from the converted 1-bit image data. a color correction means to perform the color correction;
A color image processing device comprising a dither conversion means for converting into values.