JPH0435104B2 - - 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.

For these pseudo gradation reproductions, various dither methods are widely used in which an 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: Find the total sum Sm and the sum S=Sm+Ea of the binarization correction amount Ea, and then find the distribution number N and residual error A from the sum S as follows: S=C×N+A (where C is a predetermined image signal level) distribution value calculating means and M pixels within a second scanning window corresponding to a predetermined position of the first scanning window of the ranking storage means for storing the image signal level of each pixel in the original image; , additional signal means for superimposing a signal level different from the image signal level in the original image; a first scanning window at the predetermined position of the redistribution storage means, the predetermined image signal level C and the residuals A and O of the allocation number N according to the pixel order; redistribution means for allocating M pixels among the allocated pixels; after converting the image signal level of the redistributed pixel among the allocated pixels into a binary pixel signal level, the image signal level of the redistributed pixel and the aforementioned 2 from the binarized image signal level of the reallocated pixels.
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 over the entire storage area of the correction amount storage means, according to the density of the original image. By determining the black pixel density of the reproduced image and determining the black pixel arrangement of the reproduced image according to density changes in the original image, it is possible to reproduce pseudo gradations while achieving both multi-gradation reproduction and high resolution. It is.

DESCRIPTION OF EMBODIMENTS FIG. 1 shows a block diagram of an image signal processing apparatus according to an embodiment of the present invention. In this embodiment, M numbers in configurations 1, 3, and 4 of the invention are 4.
In the explanation, it is assumed that the neighborhood ranking correction amount E _c in Configuration 6 is four. For convenience of explanation, the following symbols are given to each pixel.

The four pixels in configurations 1 and 4 are R ₀₀ , R ₀₁ , R ₁₀ ,
R ₁₁ , and the four pixels of configuration 3 are O ₀₀ , O ₀₁ , O ₁₀ ,
O ₁₁ , the storage positions of the ranked correction amounts E _c in the vicinity of configuration 6 are set to E _c1 , E _c2 , E _c3 , and E _c4 , and the storage position of the new ranked correction amount E _c is set to 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 storage means for redistribution which outputs the image signal levels of four pixels R ₀₀ , R ₀₁ , R ₁₀ , R ₁₁ of W _r ; 3 is an output signal of the storage means 2 for redistribution of the scanning window W _r ; 4
The distribution number N is calculated from the sum S obtained by adding the image signal levels of the 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 described later. and a distribution value calculating means 4 which outputs the residual A and a residual value A, and 4 stores the image signal level of the original pixel, which is the output signal of the scanning means 1, as an input and outputs the image signal level of the original pixel, which is the output signal of the scanning means 1, and calculates the output of the four pixels of the scanning window W _p .
5 is a ranking storage means 4 which outputs the image signal levels of O ₀₀ , O ₀₁ , O ₁₀ , O ₁₁ ;
The output signals of the four pixels O ₀₀ of the scanning window W _p are
Signal addition means 6 receives the image signal levels of O ₀₁ , O ₁₀ , O ₁₁ as input, and superimposes and outputs a one-dimensional (or two-dimensional) synchronous additional signal synchronized with the original image. The additional signal that is the output of
A ranking determining means takes E _b as an input, determines the pixel ranking by comparing the image signal levels of four pixels, and outputs it. 7 is the allocation number N which is the output signal of the allocation value calculation means 3, and the residual A and the pixel ranking, which is the output signal of the ranking determining means 6, are input, and the maximum value C of the N number of image signal levels and the residual error A are determined according to the pixel ranking.
A redistribution means 8 determines the allocation between and O and outputs the image signal level for redistribution, and 8 receives and fixes the image signal level of the redistributed pixel _R00 , which is the output signal of the redistribution storage means 2, as an input. binarization correction means for performing binarization processing using a threshold value and outputting it as a binarized image signal level, and outputting the difference between the input image signal level and the binarized image signal level as a binarization correction amount E _a ; is the image signal level of pixel O ₀₀ of the scanning window W _p which is the output signal of the ranking storage means 4, the binary image signal level which is the output signal of the binarization correction means 7, and the correction document storage means described later. Ranking correction means receives the ranking correction amount E _c as an output signal and outputs the neighborhood correction amount E _b and a new ranking correction amount E _c by a calculation described later; 10 is a ranking that has already been stored; Correction amount storage means outputs the assigned correction amount E _c and stores a new ranking correction amount E _c which is the output signal of the ranking correction means 9; This is an image recording/display means that inputs an image signal level and records or displays a binary 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.
0 was realized using a microcomputer. In FIG. 2, reference numeral 12 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 13 is composed of a gate, and is connected to the signal line 15 from the CPU 14.
The selection signal applied via the input terminal 12
The image signal level from is output to the CPU 14.
A program for controlling the CPU 14 is written in the ROM 16, and the CPU 14 reads necessary external data from the input port 13 or exchanges data with the RAM 17 according to this program. It performs arithmetic processing while doing so, and outputs the processed data to the output port 18 as necessary. Output port 18
is composed of a latch circuit and is applied to the output port 18 via the signal line 19.
Upon receiving the output port designation signal from the CPU 14,
Temporarily store data on that port. Reference numeral 20 denotes an output terminal for outputting the data temporarily stored in the output port 18 to the image signal recording/display means 11 as a binary image signal level.

Note that the CPU 14, ROM 16, and RAM 17 can be configured by a well-known microcomputer.

A flowchart of the program written in the ROM 16 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, and the correction amount storage means 10 and the binarization correction amount of the binarization correction means 8 are stored.
Clear E _a to O and perform initial settings (Step 1).
Next, the original image signal is transferred to the scanning window of the storage means 2 for redistribution.
Pixel R ₁₁ of W _r and scanning window W _p of ranking storage means 4
(step ₂ ). Next, four pixels R ₀₀ within the scanning window W _r of the redistribution storage means 2,
The sum S ( ₌ S n +E _a ) of the image signal level addition value S _n of R ₀₁ , R ₁₀ , R ₁₁ and the binarization correction amount E _a is calculated, and S=
The distribution number N of the maximum value C of the image signal level, which is C×N+A, and the residual error A are calculated (step 3). Next, the average value E ca and coefficient _{K a} of the four ranked correction amounts E _c of 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 ₁₀ are calculated. Neighborhood correction amount E _b
(=K _a ×E _ca ) is calculated (Step 4). Next, a one-dimensional (or two-dimensional) periodic additional signal synchronized with the four pixels of the scanning window W _p of the ranking storage means 4 is superimposed on the pixel signal level of the four pixels, and each of them is set to O′. Image signal levels of ₀₀ , _O'01 , _O'10 , and _O'11 are obtained (step 5). Next, after adding the neighborhood correction amount E _b in step 4 to the image signal level of the pixel O' ₀₁ on which the additional signal was superimposed, the values of the four pixels O' ₀₀ , O' _{01 , O' 10 , O' 10} , O' ₁₀ , The image signal levels of _O'11 are compared and the pixel order is determined in descending order (step 6). Next, according to the pixel order obtained in step 5, the maximum value C of the N number of 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 7). 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 8). 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 8 is set as a new ranking correction amount E _c and scanned. It is stored in the pixel _Ec5 within the window _We (step 9). Next, the image signal level binarized in step 8 is output to the image recording/display means 11 (step 10). Next, the completion of processing in the main scanning direction and the sub-scanning direction is determined for all original image signal levels (step 11), and if the processing has not been completed, the scanning window is moved (step 12), 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 is
clear.

In the above description, the redistribution storage means 2 to the correction amount storage means 10 are realized by a microcomputer, but each of these means can also be realized by a logic circuit, an external memory, etc.

Furthermore, by setting the coefficient K _a of the ranking correction means 9 to 1/2 ⁿ (however, n is a positive integer),
By setting K _b to 1-1/2 ^m (where m is a positive integer), calculations can be made easier when realized using a microcomputer, and hardware can be reduced when realized using a logic circuit. can do.

Furthermore, in the above explanation, the visual characteristics of the reproduced image are improved by superimposing periodic signals, but it is also possible to improve the image or obtain a reproduced image with special effects by superimposing random signals or other images. I can do it.

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, by superimposing a signal level different from the image signal level of the original image on the M pixels of the ranking storage means by the signal addition means, it is possible to improve the visual characteristics of the reproduced image and to create special effects. A certain reproduced image can be obtained.

[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... Signal addition means, 6... Ranking determining means, 7... ...Redistribution means, 8...Binarization correction means,
9... Ranking correction means, 10... Correction amount storage means, 11... Image recording/display means, 12... Input terminal, 13... Input port, 14...
CPU, 15, 19...signal line, 16...ROM,
17...RAM, 18...Output port,
20...Output terminal.

Claims (1)

[Scope of Claims] 1. A sum 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.
Calculate the sum S=Sm+Ea of Sm and the binarization correction amount Ea, and then calculate the distribution value N and residual A from the sum S as follows: S=C×N+A (where C is a predetermined image signal level) arithmetic means; and a ranking storage means for storing the image signal level of each pixel in the original image; Additional signal means for superimposing a signal level different from the image signal level in the original image, and a pixel ranking based on an image signal level value obtained by adding a neighborhood correction amount Eb to some of the M pixels outputted by the additional signal means. a ranking determining means for determining the predetermined image signal level C of the allocation number N and the residual errors A and O according to the pixel ranking within a first scanning window at the predetermined position of the redistribution storage means; reallocation means for allocating M pixels; after converting the image signal level of the reallocated pixel among the allocated pixels into a binary pixel signal level, the image signal level of the reallocated pixel and the reallocation; 2 above from the binary image signal level of the completed 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. 2. Image signal processing according to claim 1, wherein the signal adding means repeatedly superimposes a finite number of superimposed signals on the image signal level of each pixel of the original image in synchronization with the pixels of the original image. Device. 3. A patent characterized in that the ranking correction means calculates the average value Eca of the neighboring ranking correction amounts Ec, and multiplies it by a coefficient 1/2 ⁿ (where n is a positive integer) to obtain the neighborhood correction amount Eb. An image signal processing device according to claim 1. 4 The ranking correction means calculates the average value Eca of the neighboring ranking correction amounts Ec, multiplies it by a coefficient of 1-1/2 ^m (where m is a positive integer), and calculates a part of the pixels in the ranking storage means. By adding the image signal levels of and further subtracting the binarized image signal level, a new ranking correction amount Ec is obtained.
An image signal processing device according to claim 1, characterized in that the image signal processing device calculates the following.