JPH057294A - Image processor - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to accurately calculate an error of a color image and faithfully reproduce the color image. According to the present invention, the color signals 1a, ... Of R, G, B of a pixel of interest in a color image to be processed are converted into complementary color signals 31a, ... Of Y, M, C, and the converted Y, M. , C
In which the complementary color signals are converted into binarized color signals 41a, ...
The reproduction color signals 51a, ... Corresponding to the original colors are calculated from a, ..., and the errors 61a between the reproduction color signals 51a, ... And the original color signal are calculated, and the calculated respective colors are calculated. .. are multiplied by a weighting coefficient 81 prepared in advance to calculate weighting errors 71a, .. The correction signals 91a ,.
Is used to correct the color signal of the pixel of interest for each color.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for subjecting a color image to gradation processing with good color reproducibility.

[0002]

2. Description of the Related Art Generally, in an image processing apparatus that handles a color image, gradation processing and color correction processing are required to output a color signal read from an original by a reading apparatus such as a color image scanner to a color printer. Will be needed.

Color correction processing is performed by using R, G, and B (R: red, G: green, B: blue) signals input from a scanner or the like as Y, M, and C drive signals for the printer.
This is a process of converting to a complementary color signal to the original color signal such as (Y: yellow, M: magenta, C: cyan). This processing is generally performed by a 3 × 3 matrix operation as shown in the equation 1.

[0004]

[Equation 1] On the other hand, for gradation processing, the systematic dither method is generally used.
Although the processing of this method is simple, there is a problem that the resolution is deteriorated. There is an “error diffusion method” as a gradation processing method that has better resolution than the systematic dither method and has sufficient gradation.

In the "error diffusion method", the color signal of the pixel of interest is added with a binarization error of the already binarized peripheral pixels multiplied by a certain weighting coefficient, and binarized with a fixed threshold value. Is the way to do it. FIG. 5 shows the configuration blocks of color image processing when the binarization processing by the "error diffusion method" is performed.

In FIG. 5, reference numerals 40a, 40b and 40c denote input color signals as R, G and B input image signals respectively, and 401 denotes each input color signal Y, by the color correction processing.
Color correction means for converting into complementary color signals 411 as M and C image signals, and 50a, 50b and 50c are color correction means 40.
Binary processing means for inputting Y, M, and C complementary color signals from 1 and binarizing the input complementary color signals.

The respective binarization processing means 50a, 50b, 5
In each of 0c, 42 is a correction unit configured by an adder, for example, for correcting the color signal of the pixel of interest by a correction signal 471 described later, and 43 is a corrected color signal 421 corrected.
Is a binarizing means for binarizing, and 44 is a binarization from a binarized color signal 431 as an output color signal binarized by the binarizing means 43 and a correction color signal 421. Binarization error calculation means for calculating an error, 45 is a weighting coefficient storage means for storing a weighting coefficient of a peripheral pixel with respect to a target pixel for calculating a weighting error, and 46 is a binarization error calculation means composed of, for example, a multiplier. Weighting error calculation means for calculating a weighting error by multiplying the binarization error signal 441 calculated in 44 by the weighting coefficient from the weighting coefficient storage means 45, and 47 stores the weighting error signal 451 calculated in the weighting error calculation means 46. ,
The error storage means outputs the correction signal 471 to the correction means 42.

The peripheral pixels whose weighting coefficients are stored in the weighting coefficient storage means 45 are the next pixel (A) on the same line as the target pixel (*) and the next pixel (B on the line next to the target pixel (*). ), The same pixel (C) on the line next to the pixel of interest (*), and the pixel (D) immediately before the line next to the pixel of interest (*). Below, 2 using the "error diffusion method"
The value conversion process will be described in detail.

For example, the R, G, B input color signals 40a, 40b, 40c read by a reading device such as a scanner are converted into Y, M, C complementary color signals by a color correcting means 401, and each of them is converted into 2 signals. Quantization processing means 50a, 50b, 50
It is output to c.

Here, the binarization processing means 50a, 50b,
Since 50c has the same configuration, the binarization processing means 50a will be described below as a representative, and the binarization processing means 50 will be described.
The description of b and 50c is omitted.

That is, the C (cyan) complementary color signal 411 output by the color correction means 401 is corrected by the correction means 42 by a color correction signal 471 described later, and output as a corrected color signal 421. Correction color signal 4
The binarizing means 43 supplied with 21 supplies the corrected color signal 421.
And the binarized threshold value Th are compared to output a binarized color signal 431. That is, the binarization threshold Th
(For example, "80h", attached "h" is "hex" 16
Indicates a decimal number. However, the same threshold value is not necessarily used for each signal), and the correction color signal 421 is used.
Is greater than the binarization threshold Th, the binarization color signal 43
"1" is output as 1 and "0" is output if it is smaller.

Next, in the binarization error calculation means 44, the correction color signal 421 and the binarization color signal 431 (here, "0h" and "1" when the binarization color signal is "0"). In this case, the difference is defined as “ffh”) and this is output as a binarization error signal 441.

In the weighting error calculating means 46, the weighting coefficients A and B of the weighting coefficient storage means 45 are added to the binarization error signal 441.
C, D (however, A = 7/16, B = 1/16, C = 5
/ 16, D = 3/16) to calculate the weight error 451. Here, “*” in the weighting coefficient storage means 46
Indicates the position of the pixel of interest, and the binarization error of the pixel of interest is multiplied by the weighting factors A, B, C, D to determine the four pixels around the pixel of interest (corresponding to the positions of the weighting factors A, B, C, D). Pixel) to calculate the weighting error.

The error storage means 47 is a weight error calculation means 4
5 is for storing the weight error 451 calculated in 5, and the weight errors for the four pixels calculated by the weight error calculation means 45 are eA, eB, eC, e for the target pixel “*”, respectively.
Add to area D and store. Pixel correction signal 4 described above
Reference numeral 71 is a signal at the position of "*", which is a signal obtained by accumulating weighting errors of four pixels calculated by the above procedure.

This "error diffusion method" acts to minimize the binarization error by diffusing the binarization error generated by the binarization of the pixel of interest to the peripheral pixels and compensating the error. It is a thing. Therefore, when the input image is a photographic image, it is possible to perform binarization processing that sufficiently satisfies the gradation. However, in a color image, if this "error diffusion method" is applied independently to each of the R, G, and B input color signals (three color signals), the phases of the three binarized output signals of Y, M, and C Does not have the same phase, and even if the respective input color signals have the same phase, a binarized output signal having a different phase is output, and a color image cannot be faithfully reproduced.

[0016]

As described above, in a color image, when the error diffusion method is independently applied to a plurality of color signals, the phases of a plurality of binarized output signals do not become in-phase, and each input color does not have the same phase. Even if the signals are in phase, binary output signals of different phases are output, and there is a drawback that a color image cannot be faithfully reproduced.

Therefore, according to the present invention, even if the phases of a plurality of binarized output signals with respect to a plurality of color signals are different in a color image, the error is accurately calculated,
An object of the present invention is to provide an image processing device which can eliminate the drawbacks of the error diffusion method and can faithfully reproduce a color image.

[0018]

An image processing apparatus of the present invention comprises a conversion means for converting image data of a pixel of interest in a multicolor image to be processed into first color data corresponding to the color of the image data. , Binarizing means for converting each of the first color data converted by the converting means into binarized data, and a plurality of two pixels for each pixel in a plurality of pixels in a predetermined area including the target pixel. Generating means for generating second color data corresponding to the color of the image data from the binarized data binarized by the binarizing means using the binarized data, and the second color data generated by the generating means. Error calculating means for calculating a color error between the color data and the image data, and a weighting error calculating means for multiplying the color error calculated by the error calculating means by a predetermined weighting coefficient to calculate a weighting error.
It is composed of an error storage unit for storing the weight error calculated by the weight error calculation unit and a correction unit for correcting the image data of the pixel of interest by the weight error stored in the error storage unit.

[0019]

According to the present invention, the image data of the pixel of interest in the multicolor image to be processed is converted into the first color data corresponding to the color of this image data, and the converted first color data is converted into 2 colors. In the conversion into the binarized data, a plurality of binarized data for each pixel in a plurality of pixels in a predetermined area including the target pixel are used to
The second color data corresponding to the color of the image data is generated from the plurality of binarized data, the color error between the second color data and the image data is calculated, and the calculated color error is calculated. , A weighting error is calculated by multiplying by a predetermined weighting factor,
The image data of the pixel of interest is corrected by this weight error.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a principle diagram showing a method of binarization processing of the present invention. That is, in FIG. 1, 1a, 1
b, 1c are input color signals of R, G, B (R: red, G: green, B: blue), and 2a, 2b, 2c are correction means for correcting the color signals 1a, 1b, 1c of the target pixel, respectively. , 21a, 21b, 21c are corrected color signals, 3a, 3b, 3c are corrected R, G, respectively.
The correction color signals 21a, 21b, and 21c of B are set to Y, M, and C.
(Y: yellow, M: magenta, C: cyan) complementary color conversion means for converting into complementary color signals 31a, 31b, 31c, 4
a, 4b and 4c are complementary color signals 31 to Y, M and C, respectively.
binarizing means for binarizing a, 31b, 31c, 41a,
41b and 41c are binarized color signals, and 5 is a binarized Y, M and C binarized color signals 41a, 41b and 41c.
Therefore, R considering the influence of peripheral pixels on the pixel of interest,
Reproduction color calculating means for calculating G and B reproduction color signals 51a, 51b, 51c, 6a, 6b, 6c are binarization error calculating means for calculating binarization error signals 61a, 61b, 61c, and 8 is a weight. Each of the weighting coefficient storage means for storing the weighting coefficient for calculating the error, 7a, 7b and 7c is 2
Weighting error calculating means 9a, 9b, 9c for multiplying the binarizing error calculated by the valued error calculating means 6a, 6b, 6c by the weighting coefficient 81 of the weighting coefficient storage means 8 to calculate the weighting errors 71a, 71b, 71c. Are weight error calculation means 7
Weighting errors 71a, 71b, 7 calculated by a, 7b, 7c
Error storage means for storing 1c, 91a, 91b, 91c
Are correction signals corresponding to the weighting errors 71a, 71b, 71c, respectively. The binarization processing method of the present invention will be described in detail below.

For example, R obtained by reading a document image with a reading device such as a color image scanner,
The G and B input color signals 1a, 1b and 1c are corrected by a correction signal 91 which will be described later in the correction means 2a, 2b and 2c, respectively.
The correction processing is performed using a, 91b, and 91c, and the corrected color signals 21a, 21b, and 21c are output. These corrected color signals 21a, 21b and 21c are respectively supplied to the complementary color conversion means 3
a, 3b, 3c are converted into Y, M, C complementary color signals 31a, 31b, 31c which are drive signals of the color printer.

These complementary color signals 31a, 31b, 31c
In the binarizing means 4, respectively.
(For example, "80h", attached "h" is "hex" 16
Indicates a decimal number. However, different thresholds are used for each color. ) Is performed and the binarized color signals 41a, 41b, 41c are output. That is, the complementary color signals 31a, 31b, 31c are
If it is larger than the binarization threshold value Th, "1" is output as the binarized color signals 41a, 41b, 41c, and if it is smaller, "0" is output.

Further, the reproduction color calculating means 5 outputs the reproduction color signals 51a, 51b and 51c of R, G and B from the Y, M and C binary color signals 41a, 41b and 41c. In the binarization error calculating means 6a, 6b, 6c, the correction color signals 21a, 21b, 21c and the reproduction color signals 51a, 51 are respectively generated.
b, 51c (however, here, when the binarized color signal is “0”, it is “0h”, and when it is “1”, it is “ffh”), and the calculated result is binarized. Error signal 61
It is output as a, 61b, 61c. The weighting error calculating means 7a, 7b, 7c have binarization error signals 61a, 61.
b and 61c, the weighting factors A and B of the weighting factor storage means 8
C, D (however, A = 7/16, B = 1/16, C = 5
/ 16, D = 3/16)
Calculate b and 71c.

Here, "*" in the weighting coefficient storage means 8 indicates the position of the pixel of interest, and the binarization error of the pixel of interest is multiplied by the weighting factors A, B, C and D to determine the periphery 4 of the pixel of interest.
Pixel (pixel corresponding to the position of weighting factors A, B, C, D)
Weighting errors 71a, 71b, and 71c are calculated. The error storing means 9a, 9b, 9c are for storing the weighting error 71 calculated by the weighting error calculating means 7a, 7b, 7c, respectively, and for four pixels calculated by the weighting error calculating means 7a, 7b, 7c. RGB RGB weight errors 71a, 71b,
71c shows eA, eB, and e for the target pixel “*”, respectively.
It is added and stored in the C and ED areas. Correction signals 91a, 9
Signals 1b and 91c are signals at positions of "*", which are signals obtained by accumulating weighting errors for a total of 4 pixels calculated by the above procedure.

Next, an embodiment of the image processing apparatus equipped with the binarization processing of the present invention will be described with reference to FIG. It should be noted that parts and signals having the same functions as those in the principle diagram shown in FIG.

FIG. 2 is a schematic configuration diagram showing an image processing apparatus according to an embodiment of the present invention. This image processing device
For example, a color signal read and input by a reading device such as a color image scanner is input as digital data of 24 bits (8 bits for each of R, G, and B) per pixel, and this is binarized. After processing, it is output to a color printer (not shown).

First, the correction means 2, 2b and 2c are each composed of an adder and correct each color signal of R, G and B (R: red, G: green, B: blue) of the target pixel. is there. That is, R, G, B input color signals 1a,
1b and 1c and color correction signals (Rw, Gw, Bw) 91a,
91b and 91c are added, and correction color signals (Rc, Gc,
Bc) 21a, 21b, 21c are output. Rc = R + Rw Gc = G + Gw Bc = B + Bw

Correction color signals (Rc, G) of R, G, B
c, Bc) 21a, 21b, 21c are complementary color signals 31a of Y, M, C (Y: yellow, M: magenta, C: cyan) in complementary color conversion means 3a, 3b, 3c, respectively.
31b, 31c. The conversion here does not need to be highly accurate and may be a simple complementary color conversion as shown by the following equation. C = 1-Rc M = 1-Gc Y = 1-Bc

The Y, M and C complementary color signals 31a and 31
b and 31c are binarized by being compared with a predetermined threshold value Th by the binarizing means 4a, 4b and 4c, respectively, and output as binarized color signals 41a, 41b and 41c. At this time, the complementary color signals 31a, 31b, 31c are 2
If it is larger than the threshold value Th, the binarized color signal 41a,
"1" is output as 41b and 41c, and "0" is output when it is smaller. The binarized color signals 41a, 41b,
41c is a drive signal for the color printer.

Next, the reproduction color calculating means 5 calculates the reproduction color signals of R, G and B from the Y, M and C binarized color signals 41a, 41b and 41c, and reproduce color signals 51a, 51b, 51
Output c. FIG. 3 shows the structure of the reproduced color calculation means 5.

That is, the reproduced color calculation means 5 includes delay circuits (D) 52a, 52b, 52c, 52d, 53a and 53.
b, 53c, 53d, 54a, 54b, 54c, 54
d, line buffers 55 to 57, and ROM 58. In the ROM 58, R, G, and B values of colors reproduced by a binary output signal in a (2 × 2) area including a target pixel (*) are measured and stored in advance.

FIG. 4 shows the (2 × 2) area, that is, the target pixel (*) and the four pixels of the peripheral pixels (A), (B), and (C), in bold lines. In this case, the number of colors reproduced in the (2 × 2) area is “330 colors” due to the combination of overlapping Y, M, and C, and R, G, and B of “330 colors” are set.
The values are tabulated and stored in the ROM 58. In other words, the number of colors reproduced in the (2 x 2) area is "8H4".
So, this is an overlapping combination of 8 colors x 4 pixels
"Color". The "8 colors" referred to here are Y, M, and C.
Y (yellow), M (magenta), reproduced by the value signal,
C (cyan), R (red), G (green), B (blue), Bk (black), and W (white).

The reproduced color signals of R, G, B are calculated from the binarized color signals 41a, 41b, 41c input to the reproduced color calculation means 5, and the reproduced color signals 51a, 51b, 51c are output. Are the same, the following description will be made on behalf of the binarized color signal 41a.
The description of 41c is omitted.

That is, the binarized color signal 41a input to the reproduction color calculation means 5 is supplied to the delay circuit 52a.
The binary color signal 41a input to the delay circuit 52a is 1
The pixels are held and supplied to the ROM 58 as peripheral pixels (A), and at the same time, supplied to the delay circuit 52b. Delay circuit 5
The binarized color signal 41a input to 2b is held for one pixel and is supplied to the ROM 58 as a peripheral pixel (B) and is simultaneously supplied to the line buffer 55. Line buffer 5
The binarized color signal 41a input to 5 is held for one line and supplied to the delay circuit 52c. The binarized color signal 41a input to the delay circuit 52c is held for one pixel and supplied to the ROM 58 as a peripheral pixel (C), and at the same time, supplied to the delay circuit 52d. The binarized color signal 41a input to the delay circuit 52d is held for one pixel and is supplied to the ROM 58 as a target pixel (*). Target pixel (*)
And the surrounding pixels (A) to (C)
M58 stores "33" stored in the overlapping combination.
The reproduced color signal 51a is output from "0 color". Similarly, the binarized color signals 41b and 41c are output by the reproduction color calculation means 5 as reproduction color signals 51b and 51c, respectively.

In the above embodiment, the reproduction color signal is calculated with four pixels including the pixel of interest.
The calculation is not limited to the area of (x2), but may be calculated in the area of (n × n).

Next, the binarization errors (Re, Ge, Be) 61a, 61b, 61c generated in the binarization process are calculated. The binarization error calculation means 6a, 6b, 6c are each composed of a subtractor, and the correction color signals (Rc, Gc, Bc) 21a, 21b, 21 output by the correction means 2a, 2b, 2c are output.
c and the reproduced color signals (Rp, Gp, Bp) 51a, 51
Binarization error signals 61a, 61b, 61c are calculated by performing subtraction processing with b, 51c. That is, the binarization error (Re, Ge, Be) is obtained as Re = Rc-Rp Ge = Gc-Gp Be = Bc-Bp.

The weighting error calculating means 7a, 7b, 7c are each composed of a multiplier, and the binarization error (Re, Ge, B
e) 61a, 61b and 61c are multiplied by the weighting coefficient 81 stored in the weighting coefficient storage means 8 to output the weighting error 81. The weight coefficient storage means 8 stores the above-mentioned four weight coefficients (A = 7/16, B = 1/16, C = 5/16, D).
= 3/16) in accordance with the corresponding positions of the four pixels around the pixel of interest. The weight errors of the four pixels are: ReA = A × Rc ReB = B × Rc ReC = C × Rc ReD = D × Rc GeA = A × Gc GeB = B × Gc GeC = C × Gc GeD = D × Gc BeA = A XBc BeB = B x Bc Bec = C x Bc BeD = D x Bc. In this case, ReB, GeB and BeB may be obtained as ReB = Rp- (ReA + ReC + ReD) GeB = Gp- (GeA + GeC + GeD) BeB = Bp- (BeA + BeC + BeD), respectively.

Then, each weighting error is stored in the error storage means 9a,
9b and 9c are stored at corresponding positions. These error storage means 9a, 9b, 9c are composed of line memories for 6 lines. Color correction signals 91a, 91b, 9
1c is "*" of the error storage means 9a, 9b, 9c, respectively.
Is the signal read from the position. Error storage means 9a, 9
The weighted errors of R, G, and B for four pixels which have already been processed are stored at the positions of “*” in b and 9c. Correction means 2
a, 2b, 2c are the input color signals 1a, 1 according to the color correction signals 91a, 91b, 91c calculated by the method described above.
The correction processing of b and 1c is performed.

As described above, according to the above embodiment,
Since the error of the error diffusion method is calculated by the binarized color signal as the output result of Y, M, C, the input 3
Even if the phase of the output signal of the error diffusion method cannot be synchronized with one color signal, the error can be accurately calculated, and faithful color reproduction is possible. In this case, Y, M, which are out of phase,
Since the C output signal is converted to R, G, B signals and fed back to the input side, that is, the phase state is fed back to the input side by the R, G, B signals, color reproducibility is improved. To do.

Further, by the reproduction color calculation means, Y, M, C
Since the R, G, and B reproduced color signals are calculated from the output signal of, the error diffusion processing is performed on the R, G, and B reproduced color signals. Therefore, the error diffusion process is performed by inputting R,
The color correction process for converting the G and B signals into the Y, M and C signals is unnecessary, and the process can be simplified.

In addition, the error of the "error diffusion method" is set to Y, M, C
Since it is calculated from the output signal of, the accuracy is high and the color reproducibility can be improved. In addition, it is possible to prevent the color reproducibility from being deteriorated because the phases of the outputs of the three colors do not become in-phase by the processing of independent of the three colors found in the conventional "error diffusion method".

In the above embodiment, the reproduction color signal is calculated in the area of 4 pixels, that is, in the area of (2 × 2). However, in the case of 1 pixel, for example, there is an influence of surrounding pixels and the color image of the color image is This is because faithful color reproduction cannot be realized and the color reproducibility is improved by calculating in the area. The present invention is
The area is not limited to (2 × 2), but (n × n)
It is also possible to calculate in the area of.

In the above embodiment, the case where the binary output is performed has been described, but the present invention is not limited to this. For example, by setting a plurality of threshold values Th, a multi-value output is also possible. It is possible, and it becomes possible to perform optimum color reproduction for a multi-value color silver salt photographic printer, a sublimation type thermal transfer printer, and the like.

[0045]

As described above in detail, according to the present invention, in a color image, even if the phases of a plurality of binarized output signals with respect to a plurality of color signals are different, the error is accurately calculated, It is possible to eliminate the drawbacks of the error diffusion method and provide an image processing apparatus that can faithfully reproduce a color image.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the principle of binarization processing of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of an image processing apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a reproduction color calculation circuit.

FIG. 4 is a diagram showing an example of an output image area referred to by a reproduction color calculation circuit.

FIG. 5 is a diagram for explaining the principle of a conventional “error diffusion method”.

[Explanation of symbols]

1a, 1b, 1c ... Input color signals, 2a, 2b, 2c ... Correction means, 3a, 3b, 3c ... Complementary color conversion means, 4a, 4
b, 4c ... Binarizing means, 5 ... Reproduction color calculating means, 6a, 6
b, 6c ... Binary error calculation means, 7a, 7b, 7c ... Weight error calculation means, 8 ... Weight coefficient storage means, 9a, 9b,
9c ... Error storage means, 21a, 21b, 21c ... Correction color signal, 41a, 41b, 41c ... Binary color signal, 51
a, 51b, 51c ... Reproduction color signal, 61a, 61b, 6
1c ... Binarization error signal, 71a, 71b, 71c ... Weighting error, 81 ... Weighting coefficient, 91a, 91b, 91c ... Correction signal.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04N 1/40 103 C 8943-5C

Claims (1)

Claim: What is claimed is: 1. A conversion unit for converting image data of a pixel of interest in a multicolor image to be processed into first color data corresponding to the color of the image data, and conversion by the conversion unit. The converted first color data into binary data respectively 2
An image is obtained from the binarized data binarized by the binarization unit using the binarization unit and a plurality of binarized data for each pixel in a plurality of pixels in a predetermined area including the target pixel. Generation means for generating the second color data corresponding to the color of the data, error calculation means for calculating the color error between the second color data generated by this generation means and the image data, and calculation by this error calculation means A weighting error calculating means for calculating a weighting error by multiplying the obtained color error by a predetermined weighting factor, an error storing means for storing the weighting error calculated by the weighting error calculating means, and an error storing means An image processing apparatus, comprising: a correction unit that corrects image data of a pixel of interest based on the stored weight error.