JPH0197066A - Image processing method - Google Patents

Abstract

PURPOSE:To prevent a stripe pattern which has occurred at the time of treatment by means of an error diffusion method by executing the error diffusion method from plural directions of a picture, majority-deciding the result and deciding a binary output. CONSTITUTION:Binarization circuits 5, 6, 7 and 8 respectively execute a binarization processing by the error diffusion method. When data for one piece of an original is stored in a picture memory 4, the binarization circuits 5, 6, 7 and 8 start processing. The processing directions with respect to one original differ in respective binarization circuits. Data binarized in respective binarization circuits are stored in binary memories 9, 10, 11 and 12 provided in respective binarization circuits. Binary data of '0' and '1' stored in the binary memories 9-12 are stored in correspondence with the addresses of the picture memory 4. A multiple decision circuit 13 multiple-decides '0' and '1' at the same address of the binary memories 9-12, decides '0' or '1' more in numbers as the binary output and outputs it to a printer 14.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an image processing method in an image forming apparatus such as a digital printer and a digital facsimile.

<Prior Art> Conventionally, there is an error diffusion method as a binarization method for reproducing halftones in digital printers, digital facsimiles, etc. This method calculates the density difference between the original image density and the output image density for each pixel, and distributes the error amount, which is the result of this calculation, after applying specific weighting to surrounding images. This error diffusion method is explained in References R and W.
, Floyd and L., Steinberg “An
Adaptive Algorithm for
5peatialGray 5cale″SID 75
It was announced in Digest (1976).

<Problems to be solved by the invention> Binarization processing using the error diffusion method described above does not cause the moiré phenomenon that is a problem with other binarization methods such as the dither method and the density pattern method, but the image processing method Since this is always fixed, a unique striped pattern occurs in uniform density portions of the image (portions other than edge portions), resulting in a deterioration in image quality.

Means and operation for solving the above-mentioned problems The present invention aims to solve the above-mentioned problems by independently performing binarization processing using an error diffusion method from a plurality of directions of an image consisting of a plurality of pixels. The results of each process are stored in a memory, and then the binary data to be output is determined by a majority vote on the results of the binarization process for the same pixel stored in the memory.

<Example> Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention.

The input sensor section 1 includes a photoelectric conversion element such as a CCD and a driving device for scanning the element, and reads and scans an original. The image data of the original read by the input cassette/slot section 1 is sent to the A/D converter 2. Here, the data of each pixel is converted into g-bit digital data and quantized into data having 256 levels of gradation.

Next, in the correction circuit 3, shading correction and the like to correct unevenness in sensitivity of the CCD sensor and unevenness in illuminance due to the illumination light source are performed by digital calculation processing.

The data corrected by the correction circuit 3 is sequentially stored in the image memory 4. The image memory 4 is a multi-level memory capable of storing data for at least one original document.

The binarization circuits 5, 6, and 7.8 each perform binarization processing using the error diffusion method described later.

These binarization circuits 5, 6, 7.8 store the original 1 in the image memory 4.
Once the data for each sheet is stored, processing begins. Each binarization circuit processes a single document in a different direction.

FIG. 2 shows the processing method in each binarization circuit.

The binarization circuit 5 performs main scanning processing in the direction of the solid line shown in FIG. 2(a) and subscanning processing in the direction of the broken line, and sequentially converts the 8-bit multi-value data into i-value processing. Similarly, the binarization circuit 6 performs binarization using the processing method shown in FIG. 2(b), the binarization circuit 7 uses the processing method shown in FIG. 2(C), and the binarization circuit 8 uses the processing method shown in FIG. 3(d). Do this.

The data binarized by each binarizing circuit is stored in binary memories 9, 10, 11 and 12 provided for each binarizing circuit. Note that 0, 1 stored in binary memories 9 to 12
The binary data is stored in correspondence with the address of the image memory 4.

Next, the majority circuit 13 takes a majority vote between 0 and 1 at the same address in the binary memories 9 to 12, and the one with more 0°1 is determined to be the binary output and output to the printer 14.

In the printer 14, dots are controlled on and off according to the 0.1 output from the majority circuit 13 to form an image.

Note that when the outputs of 0.1 from the binary memories 9 to 12 are the same, the majority circuit 13 may output a predetermined one, or it may randomly output either 0 or 1. It may also be output.

Next, the error diffusion method performed in the binarization circuits 5 to 8 will be explained with reference to FIG.

20 is an error calculation circuit, 28 is a comparator that binarizes input data with a threshold value T (for example, 127) and outputs an output Z (Q or 1), and 36 to 42 are image data and error E output from the error calculation circuit. A D flip-flop (hereinafter referred to as DFF) that stores the sum of the image data and the diffusion error (diffusion error), 21 to 27 are addition paths that calculate the sum of the image data and the diffusion error, and 28 to 35 are error calculation circuits 20. A multiplier that calculates the product of the error E output from the above-mentioned weighting coefficient, 43 and 44 a line memory that stores image data for pixels excluding 3 dots from one line of image data, and 4 a line memory that stores image data for pixels excluding 3 dots from one line of image data. This is the image memory of FIG. Here, the weighting coefficients are such that pixels closer to the pixel of interest are weighted more heavily, and the total weighting coefficients are 1.

Next, the circuit operation in FIG. 3 will be explained.

Image data is sequentially output from the image memory 4. Here, the line buffer 43 stores image data of pixels on the same line as the pixel of interest to be binarized by the comparator,
The line buffer 44 stores image data of pixels one line later to be processed thereafter.

First, image data to which error data from pixels for which the binarization process has already been completed is output from the DFF 35 and binarized by the comparator 28 using a threshold value 127.

At this time, for example, if the output from the DFF 36 is 200, 1 (black) is output as the binary output Z.

In the error calculation circuit 20, this 1 is expanded to 8 bits, 255, and the error with the output 200 from the DFF 36 is -5.
5 is output as error data E. In reality, image data with a density of 200 is printed on a binary printer with a density of 200.
Since it is output as a density of 55, the data of -55 is diffused to unprocessed surrounding pixels in order to subtract the extra 55. FIG. 3 shows an example of error data diffusion. Here, as described above, the weighting coefficients are determined so that more weighting is applied depending on the pixel of interest. FIG. 5 shows an example of weighting coefficients.

The error data E outputted from the error calculation circuit 20 is multiplied by a weighting coefficient in multipliers 28 to 35, and added to the image data in adders 21 to 27, respectively. The added image data is added to the DFFs 36 to 42 and shifted by one pixel.

Binarization processing using the error diffusion method is performed by repeating the above processing. Note that the error diffusion state or weighting coefficients are not limited to those shown in FIGS. 4 and 5.

In the binarization circuits 5 to 8, processing using this error diffusion method is performed as a second process.
The processing is carried out from the four directions shown in the figure, and the processing results for the same pixel are judged by a majority vote to determine the binary output.

In this way, according to the embodiment described above, since the error diffusion method is performed from multiple directions, it is possible to prevent the occurrence of a unique striped pattern in the output image, which was a problem when processing from one direction in the past. .

In the above-mentioned embodiment, processing from four directions was explained, but the striped pattern can be reduced by processing from two directions as shown in FIG. 2(a) and (d).

Furthermore, since striped patterns often occur in uniform density areas other than literary areas of an image, processing may be performed only on those areas (blocks) from a plurality of directions. In this case, the presence or absence of an edge is detected from the output from the image memory 4 in FIG. 1 using a well-known Laplacian method, etc., and a binary output is determined by binarization processing from one direction at the edge portion, and a binary output is determined from the output from the image memory 4 in FIG. Binary output is determined by majority decision in binarization processing from a plurality of directions.

<Effects of the Invention> As explained above, according to the present invention, the error diffusion method is performed from multiple directions of the image, and υ
Since the binary output is determined, it is possible to prevent the striped pattern that occurs during processing using the error diffusion method, and it is possible to reproduce images of any original with high quality and high definition.

[Brief Description of the Drawings] Figure 1 is a block diagram showing an embodiment of the present invention, Figure 2 is a diagram showing an image processing method using the error diffusion method, and Figure 3 is a diagram showing an image processing method using the error diffusion method. FIG. 4 is a diagram showing the process of diffusing errors to surrounding pixels, and FIG. 5 is a diagram showing an example of coefficients for weighting errors to surrounding pixels. 1... Input sensor section 2... A/D converter 3... Correction circuit 4... Image memory 5-8... Binarization circuit 9-12... Binary memory 13...・Majority circuit 14...Printer (n) <b) (C) <d) Fig. 2

Claims (1)

[Claims] Performing binarization processing independently from a plurality of directions of an image consisting of a plurality of pixels using an error diffusion method, storing the results of the binarization processing from the plurality of directions in a memory, and 1. An image processing method, characterized in that binarization of one pixel is determined by majority voting on the results of binarization processing for the same pixel stored in a memory.