JPH0435102B2 - - 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) At least two pixels in a second scanning window corresponding to a predetermined position of the first scanning window of a distribution value calculation means and a ranking storage means for storing the image signal level of each pixel in the original image. M, which weightedly distributes the neighborhood correction amount Eb to
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. It determines the black pixel density of the reproduced image according to the density change of the original image, determines the black pixel arrangement of the reproduced image according to the density change of the original image, and distributes the neighboring correction amount with weight, achieving both multi-tone reproduction and high resolution. This allows pseudo gradation reproduction.

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), (2), and (3) of the invention are 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 ₁₁ , and the four pixels of configuration (2) are O ₀₀ , O ₀₁ , O ₁₀ ,
O ₁₁ , the storage positions of the ranking correction amount E _c in the vicinity of configuration (5) are E _c1 , E _c2 , E _c3 , E _c4 , and the storage position of the new ranking correction amount E _c 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 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
The image signal levels of O ₀₁ , O ₁₀ , O ₁₁ and the neighborhood correction amount E _b which is the output of the ranking correction means described later are input, and the pixel ranking is determined by comparing the image signal levels of the four pixels. output ranking determining means;
6 is the allocation number N which is the output signal of the allocation value calculation means 3
, the residual A, and the pixel rank which is the output signal of the rank determining means 5 are input, and the maximum value C of the N number of image signal levels and the distribution of the residuals A and O are determined according to the pixel rank. The redistribution means 7 outputs the image signal level for redistribution, and 7 receives the image signal level of the redistributed pixel _R00 , which is the output signal of the redistribution storage means 2, and performs binarization processing using a fixed threshold. Binarization correction means outputs the converted image signal level as well as the difference between the input image signal level and the binarized image signal level as the binary correction amount E _a ; 8 is the output of the ranking storage means 4; The image signal level of pixel _O00 of the scanning window _Wp which is a signal, the binarized image signal level which is an output signal of the binarization correction means 7, and the ranked correction amount E which is an output signal of the correction amount storage means to be described later. _c
As input, the neighborhood correction amount E _b is calculated by the calculation described later.
and a new ranking correction amount E _c as outputs, and 9 outputs the already stored ranking correction amount E _c and outputs a new ranking correction amount which is the output signal of the ranking correction device 8. Correction amount storage means for storing the amount E _c , 1
0 is an image recording/displaying means which inputs the binary image signal level which is the output signal of the binary correction means 7 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.
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, and the correction amount storage means 9 and the binarization correction amount _E a of the binarization correction means 7
Clear O and perform initial settings (Step 1). Next, the original image signal is transferred to the scanning window W _r of the storage means 2 for redistribution.
and the pixel _O11 of the scanning window _Wp of the ranking storage _means 4 (step 2). Next, four pixels _{R 00} , R ₀₁ ,
The sum S (=S _n + _{E a )} of the image signal level addition value S n of R ₁₀ and R ₁₁ and the binarization correction amount E _a is calculated, and S=C×
The distribution number N of the maximum value C of the image signal level that is N+A and the residual error A are calculated (step 3). Next, 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
From the average value E _ca and the coefficient K _a , the neighborhood correction amount E _b (=K _a ×
E _ca ) is calculated (step 4). Next, after weightedly distributing the neighborhood correction amount E _b to the image signal levels of pixels O ₀₀ and O ₁₀ in the scanning window W _p of the ranking storage means 4, the four pixels O ₀₀ , O ₀₁ , O ₁₀ , O _{The 11} image signal levels are compared and the pixel order is determined in ascending order (step 5). 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 , R ₀₁ ,
The image signal levels are set to 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 is
clear.

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, by setting the coefficient K _a of the ranking correction means 8 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.

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, in the ranking determining means for determining the pixel ranking,
By weighting and distributing the neighborhood correction amount Eb to at least two of the M pixels, it is possible to improve the texture that occurs in a specific density area.

[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)

[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) a calculation means; and a ranking storage means for storing the image signal level of each pixel in the original image, the pixels being arranged in the vicinity of at least two of the pixels in the second scanning window corresponding to the predetermined position of the first scanning window. M with weighted distribution of correction amount Eb
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 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. 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. 3 The ranking correction means calculates the average value Eca of the neighboring ranking correction amount 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.