JPH0435103B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an image signal processing device having a function of reproducing a gradation image in binary.

Conventional configurations and their problems In recent years, the use of facsimiles in daily work has been expanding more and more, and along with this, there has been a growing demand for reproduction of gradation images in addition to the conventional black and white binary. In particular, binary pseudo gradation reproduction is strongly desired because it is well suited for display devices and recording devices.

Various dither methods are widely used for these pseudo gradation reproductions, in which the image is binarized according to a matrix table of threshold values. However, these conventional methods have a contradiction in that in order to improve tone reproducibility, it is necessary to make the matrix table large, and in order to obtain high resolution, the matrix table must be made small. It was difficult to achieve both high resolution. In particular, for images in which a gradation image and a binary image coexist, one of them has to be sacrificed.

Now, as a method to achieve both resolution and gradation, A.M.R. Schleder (MR.
Schroeder)'s "minimum mean error method" (e.g. Image From Computers, IEEE Spectrum)
Spectrum 6, 1969, 66-78) and B. Floyd and L.
Steinberg) et al.'s "Error Diffusion Method" (for example, [Adaptive Algorithm
Four Special Gray Scale S.I.D. Symposium Digest of Papers] An Adaptive
Algorithm for Spatial Gray Scales.SID
Sympo Digest of Papers, 1975, 33-37).

The former "minimum average error method" calculates the binarization error from the output signal, so the quality of the output image is not very good.

On the other hand, the latter "error diffusion method" has the same basic idea of minimizing the error as the "average error minimum method," but the error is determined from the corrected original image signal and the output signal. This "error diffusion method" a) generates a specific dot pattern (texture) in a certain density level area, and b) creates a unique striped pattern (maggot-like dot pattern) due to the error filter structure, which improves visual image quality. There were issues such as lowering the

These "minimum average error method" and "error diffusion method"
Instead, there is a binarization method described in Japanese Patent Application Laid-open No. 77772/1983 as a promising technique that suppresses moiré patterns during binarization reproduction and has high resolution characteristics.
In this method, black pixels are rearranged from the sum of the image signal levels of adjacent pixels in the order of increasing original image signal levels of the adjacent pixels. This is absorbed by the image signal level, and as a result, the dot structure of the output image becomes grainy with black pixels gathered together (the ``black pixel gathering effect''), which is visually perceived as a reproduced image with high noise. There are many issues to be solved.

OBJECTS OF THE INVENTION The present invention has been made in view of the problems of the prior art described above, and by performing neighborhood correction of the pixel of interest that occurs during binarization, the arrangement order of black pixels is controlled and the order of arrangement of black pixels is controlled. The present invention provides an image signal reproducing device that suppresses the "black pixel gathering effect" and obtains a high-resolution, precise, and smooth pseudo-halftone image.

Structure of the Invention In order to achieve the above object, the present invention provides the following steps: Sum of part of Sm, part of distribution correction amount Es, and binarization correction amount Ea S = (Kmo・Sm+Kso・Es)/(Kmo+Kso)+Ea (However, Kmo and Kso are coefficients such that Kmo+Kso=1 ), and then, from the sum S, calculate the allocation number N and residual A that are S=C×N+A (where C is a predetermined image signal level), and all or part of the sum S is used for new allocation. distribution value calculation means for calculating the correction amount Es; and ranking storage means for storing the image signal level of each pixel in the original image, in a second scanning window corresponding to a predetermined position of the first scanning window. M in which the neighborhood correction amount Eb is weighted and distributed to at least two pixels
a ranking determining means for determining a pixel ranking based on the value of the image signal level of each pixel; redistributing means for allocating M pixels within the first scanning window at the predetermined position of the storage means; and after converting the image signal level of the redistributed pixel among the allocated pixels into a binary pixel signal level; , from the image signal level of the redistributed pixel and the binarized image signal level of the redistributed pixel.
Calculating a digitization correction amount Ea and supplying the calculation result to the distribution value calculation means as a new binarization correction amount Ea accompanying the movement of the first scanning window from the predetermined position; binarization correction means for outputting the converted image signal level as the image signal level of the pixel to be determined at the predetermined position of the first scanning window; and correction amount storage means for storing the ranked correction amount Ea.
Calculating the neighborhood correction amount Eb from the neighborhood correction amount Ec of the pixel in the third scanning window corresponding to the predetermined position of the first scanning window and providing it to the ranking determining means;
Further, a ranking correction amount Ec is calculated from the ranking correction amount Ec, the image signal level of a part of the pixels of the ranking storage means, and the binarized image signal level;
a ranking correction means for supplying the calculation result to the correction amount storage means as a new ranking correction amount Ec in accordance with the movement of the third scanning window from a predetermined position; the redistribution storage means; and scanning window moving means for moving the first, second, and third scanning windows by a predetermined pixel amount over the entire storage area of the correction amount storage means, and the density of the original image. By determining the black pixel density of the reproduced image according to the density change of the original image and determining the black pixel arrangement of the reproduced image according to the density change of the original image, it is possible to achieve pseudo gradation reproduction while achieving both multi-gradation reproduction and high resolution. , it is possible to realize image reproduction with noise suppressed.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 shows a block diagram of an image signal processing apparatus according to an embodiment of the present invention. In this embodiment, the number M in configurations (1), (2), and (3) of the invention is 4.
In the explanation, it is assumed that the neighboring ranking correction amount E _c in configuration (5) is four. For convenience of explanation, the following symbols are given to each pixel.

The four pixels in configurations (1) and (3) are R ₀₀ , R ₀₁ , R ₁₀ ,
R _{is 11} , the four pixels of configuration (2) are O ₀₀ , O ₀₁ , O ₁₀ , O ₁₁ , and the storage location of the ranked correction amount E _c in the vicinity of configuration (5) is
E _c1 , E _c2 , E _c3 , E _c4 and new ranking correction amount E _c
The storage location of is E _c5 . The corresponding position of each pixel in the image space corresponds to the same position where R ₀₀ , O ₀₀ , and E _c5 are the same.

Each symbol group is defined as a scanning window, and R ₀₀ ,
R ₀₁ , R ₁₀ , R ₁₁ are scanning windows W _r , O ₀₀ , O ₀₁ , O ₁₀ ,
Let O ₁₁ be a scanning window W _p , and E _c1 , E _c2 , E _c3 , E _c4 , E _c5 be a scanning window W _e . In FIG. 1, it is assumed that each scanning window moves to the right on its corresponding storage means as the original image is main-scanned.

In FIG. 1, 1 is an original image scanning means that scans an original image and outputs an image signal level; 2 is an output signal of the original image scanning means 1, which is the image signal level of the original image; and an output signal of the redistribution means, which will be described later. The image signal level for redistribution is stored as input, and the scanning window
A redistribution storage means outputs the image signal levels of four pixels R ₀₀ , R ₀₁ , R ₁₀ , R ₁₁ of W _r , and 3 is a scanning window W _r which is an output signal of the redistribution storage means 2. The image signal levels of the four pixels R ₀₀ , R ₀₁ , R ₁₀ , R ₁₁ and the binarization correction amount E _a which is the output signal of the binarization correction means to be described later are input, and by the calculation described below, Distribution value calculating means outputs the distribution number N and residual A from the obtained sum S, 4 stores the image signal level of the original pixel, which is the output signal of the scanning means 1, as input, and stores the image signal level of the original pixel, which is the output signal of the scanning means 1, for the four pixels of the scanning window _Wp . ranking storage means for outputting image signal levels of O ₀₀ , O ₀₁ , O ₁₀ , O ₁₁ ;
5 is a scanning window which is an output signal of the ranking storage means 4;
The image signal levels of the four pixels O ₀₀ , O ₀₁ , O ₁₀ , O ₁₁ of W _p and the neighborhood correction amount E _b which is the output of the ranking correction means described later are input, and the image signal levels of the four pixels are calculated. A ranking determining means 6 determines the pixel ranking by comparing and outputs the pixel ranking, and 6 is an output signal of the allocation value calculation means 3, which is the allocation number N and the residual A, and the ranking determining means 5.
The maximum value C of the N number of image signal levels is determined according to the pixel order by inputting the pixel order which is the output signal of
A redistribution means determines the distribution of the residuals A and O and outputs the image signal level for redistribution, and 7 is a redistributed pixel R ₀₀ which is an output signal of the redistribution storage means 2.
inputs the image signal level, performs binarization processing using a fixed threshold value, outputs it as a binarized image signal level, and outputs the difference between the input image signal level and the binarized image signal level as the binarization correction amount E _a do 2
The digitization correction means 8 indicates the image signal level of O ₀₀ of the pixel in the scanning window W _p , which is the output signal of the ranking storage means 4, and the binary image signal level, which is the output signal of the binarization correction means 7. a ranking correction means for inputting a ranked correction amount E _c which is an output signal of a correction amount storage means to be described later, and outputting a neighborhood correction amount E _b and a new ranked correction amount E _c by a calculation to be described later; outputs the already stored ranking correction amount E _c and the ranking correction means 8
A correction amount storage means 10 stores a new ranking correction amount E _c which is an output signal of the binarization correction means 7;
It is an image recording/display means for recording or displaying a value image.

FIG. 2 is a specific circuit diagram of this embodiment, which is the main part of the block diagram of the image signal processing device shown in FIG.
was realized using a microcomputer.
In FIG. 2, reference numeral 11 denotes an input terminal to which the image signal level of the original image, which is the output signal of the original image scanning means 1, is input. The input port 12 is composed of a gate, and outputs the image signal level from the input terminal 11 to the CPU 13 in response to a selection signal applied from the CPU 13 via a signal line 14. ROM
A program for controlling the CPU 13 is written in 15, and the CPU 13 reads necessary external data from the input port 12 or exchanges data with the RAM 16 according to this program. Process the calculations while
The processed data is output to the output port 17 as necessary. The output port 17 is composed of a latch circuit, and the CPU 1 is applied to the output port 17 via the signal line 18.
3, data is temporarily stored in that port. Reference numeral 19 denotes an output terminal for outputting the data temporarily stored in the output port 17 to the image signal recording/display means 10 as a binary image signal level.

Note that the CPU 13, ROM 15, and RAM 16 can be configured by a well-known microcomputer.

A flowchart of the program written in the ROM 15 is shown in FIG. The operation of the image signal processing apparatus shown in FIG. 1 will be explained below with reference to FIG.

When the program starts, first, the contents of the redistribution storage means 2, the ranking storage means 4, the correction amount storage means 9, the binarization correction amount E _a of the binarization correction means 7,
Then, the distribution correction amount E _s of the distribution value calculation means 3 is cleared to O and initial setting is performed (step 1). Next, the original image signal is transferred to the pixel R ₁₁ of the scanning window W _r of the storage means 2 for redistribution.
is read into the pixel _O11 of the scanning window _Wp of the ranking storage means 4 (step 2). _{Next , the weighted average} ( _{Kmo ・}Sm＋Kso・E _s )／(Kmo＋Kso)
(However, Kmo and Kso are coefficients such that Kmo + Kso = 1), and the sum S (=Kmo・Kso) with the binarization correction amount E _a
Sm+Kso·E _s )/(Kmo+Kso)+E _a ) is calculated, and the distribution number N of the maximum value C of the image signal level and the residual A are calculated so that S=C×N+A (step 3). Next, the average value E ca and coefficient _{K a} of the four ranked correction amounts E _c at the ranked correction amount storage positions E _c1 , E _c2 , E _c3 , and E _c4 within the scanning window _{W e} of the correction amount storage means ₉ are calculated. The neighborhood correction amount E _b (=K _a ×E _ca ) is calculated from , and the sum S is updated as a new distribution correction amount E _s . (Step 4). Next, the pixels of the scanning window W _p of the ranking storage means 4
After adding the neighborhood correction amount E _b to the image signal level of O ₀₀ , the image signal levels of the four pixels O ₀₀ , O ₀₁ , O ₁₀ , and O ₁₁ are compared, and the pixel ranking is determined in descending order (step 5). ). Next, according to the pixel order obtained in step 5, the maximum value C of the N image signal levels obtained in step 3 and the residuals A and O are stored in the scanning window _Wr of the redistribution storage means 2. 4 pixels R ₀₀ ,
The image signal levels are set to R ₀₁ , R ₁₀ , and R ₁₁ (step 6). Next, the redistributed pixels of the redistribution storage means 2
The difference between the image signal level of R ₀₀ and the binarized image signal level of the reallocated pixel R ₀₀ is set as the binarization correction amount E _a in the next step 3 (step 7). Next, the average value E _ca and coefficient in step 4
The image signal level of pixel O ₀₀ within the scanning window W _p is added to the value multiplied by K _b , and the difference between that value and the binarized image signal level in step 7 is used as a new ranking correction amount E _c and scanning is performed. It is stored in the pixel _Ec5 within the window _We (step 8). Next, the image signal level binarized in step 7 is output to the image recording/display means 10 (step 9). Next, the completion of processing in the main scanning direction and the sub-scanning direction is determined for all original image signal levels (step 10), and if the processing has not been completed, the scanning window is moved (step 11), and the process is repeated from step 2. If the processing is completed, the processing is completed for all original image signals. However, each time the processing in the main scanning direction is completed, the binarization correction amount E _a and the distribution correction amount E _s are cleared to O in step 11.

In the above description, the redistribution storage means 2 to the correction amount storage means 9 are realized by a microcomputer, but each of these means can also be realized by a logic circuit, an external memory, etc.

Furthermore, the distribution value calculation means 3 calculates the sum S _n and the distribution correction amount.
By setting the weighted average of E _s to (1-1/2 ^p )・S _n +E _s /2 ^p (where p is a positive integer), calculations can be made easier when realized on a microcomputer. , if implemented using logic circuits, the hardware can be reduced. In addition, such weighted average calculation does not require mathematical rigor, but is an approximate weighted average K _n · S _n + K _s · E _s (however,
An image of sufficient quality can be reproduced even if the coefficients K _n and K _s are values whose sum is close to 1. Further, the distribution correction amount E _s may be updated by either the sum S or a weighted average of the sum S _n and the distribution correction amount E _s .

Effects of the Invention As described above, the present invention determines the black pixel density of a reproduced image according to the density of the original image, and also prioritizes the placement of black pixels by the neighborhood correction amount of the pixel of interest according to the density change of the original image. By controlling this, it is possible to improve the graininess of the reproduced image caused by the "black pixel gathering effect" and obtain a high-resolution, dense, and smooth pseudo-gradation image. Further, in the present invention, the distribution value calculation means calculates the sum S of a part of the sum Sm of M image signal levels within the first scanning window, a part of the distribution correction amount Es, and the binarization correction amount Ea. ,
All or part of that sum S is converted into a new distribution correction amount.
Since Es is used, noise components in the output image can be suppressed.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an image signal processing device according to an embodiment of the present invention, Fig. 2 is a specific circuit diagram of the same device realized by a microcomputer, and Fig. 3 is a flowchart explaining the operation of this embodiment. It's a chat. DESCRIPTION OF SYMBOLS 1... Original image scanning means, 2... Storage means for redistribution, 3... Distribution value calculation means, 4... Storage means for ranking, 5... Ranking determining means, 6... Redistribution means,
7... Binarization correction means, 8... Ranking correction means,
9... Correction amount storage means, 10... Image recording/display means, 11... Input terminal, 12... Input port, 13... CPU, 14, 18... Signal line,
15...ROM, 16...RAM, 17...output port, 19...output terminal.

Claims (1)

[Claims] 1. A part of the sum Sm of M image signal levels within a first scanning window at a predetermined position of a redistribution storage means for storing redistributed image signal levels of each pixel in the original image. Find the sum of a part of the distribution correction amount Es and the binarization correction amount Ea, S=(Kmo・Sm+Kso・Es)/(Kmo+Kso)+Ea (however, Kmo and Kso are coefficients such that Kmo+Kso=1), and then From the sum S, calculate the distribution number N and the residual A that are S=C×N+A (where C is a predetermined image signal level), and calculate the distribution value by using all or part of the sum S as the new distribution correction amount Es. a calculation means, and a ranking storage means for storing the image signal level of each pixel in the original image, performing neighborhood correction on some of the pixels within a second scanning window corresponding to a predetermined position of the first scanning window. a ranking determining means for determining a pixel ranking based on the value of the image signal level of M pixels to which an amount Eb has been added; and a redistribution means that allocates the image signal level of the redistributed pixels among the allocated pixels to the M pixels within the first scanning window at the predetermined position of the redistribution storage means; After converting into a signal level, the above-mentioned 2 is calculated from the image signal level of the reallocated pixel and the binary image signal level of the reallocated pixel
Calculating a digitization correction amount Ea and supplying the calculation result to the distribution value calculation means as a new binarization correction amount Ea accompanying the movement of the first scanning window from the predetermined position; binarization correction means for outputting the converted image signal level as the image signal level of the pixel to be determined at the predetermined position of the first scanning window; and correction amount storage means for storing the ranked correction amount Ec.
Calculating the neighborhood correction amount Eb from the neighborhood correction amount Ec of the pixel in the third scanning window corresponding to the predetermined position of the first scanning window and providing it to the ranking determining means;
Further, a ranking correction amount Ec is calculated from the ranking correction amount Ec, the image signal level of a part of the pixels of the ranking storage means, and the binarized image signal level;
a ranking correction means for supplying the calculation result to the correction amount storage means as a new ranking correction amount Ec in accordance with the movement of the third scanning window from a predetermined position; the redistribution storage means; and scanning window moving means for moving the first, second, and third scanning windows by a predetermined number of pixels with respect to the entire storage area of the correction amount storage means.