JPS6148275A - Picture signal processor - Google Patents

Abstract

PURPOSE:To decrease a storage capacity of an error data storage means by L- bit per picture element without losing the gradation reproducibility in comparison with a conventional mean error least method by correcting the data for L- bit's share at the next picture element. CONSTITUTION:A weight means operating means 11 operates a weight mean value EW from the content of an error matrix 2 and gives the result as an output. An operating circuit 6 adds an original picture data IXY at an input terminal 5 and a mean error Ea taking a mean value EW as a high-order bit and a low- order L-bit data EX-1,YL in a binary error before one picture element being an output of a delay means 12 as a low order bit to output the result IXY'. A binary means 9 compares the value IXY' with a prescribed value R/2' and a binary output PXY is outputted to an output terminal 7. On the other hand, an operation means 10 operates a difference EXY between the value IXY' and the binary output PXY, the high-order U bit EXYU is outputted to a storage means 1 as a new error on a coordinate XY of an original picture and the low order L- bit EXYL is outputted to the means 12.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention 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 an increasing demand for reproduction of gradation images in addition to the conventional black and white binary. In particular, pseudo gradation reproduction based on binary values is strongly desired since it is well suited for display devices and recording devices.

For these pseudo gradation reproductions, various dithering methods are widely used in which an image is binarized according to a matrix table of threshold values. However, in these conventional methods, it is necessary to increase the size of the matrix staple in order to improve gradation reproducibility, and in order to obtain high resolution, it is necessary to reduce the size of the IJ table. There is a contradiction between gradation reproducibility and high resolution.

It was difficult to balance Noh. In particular, this method has the disadvantage that, for images in which a gradation image and a binary image are mixed, one of them must be sacrificed.

The minimum average error method is a method that achieves both the above-mentioned gradation reproducibility and high resolution, and has been given a relatively good evaluation for reproduced image quality among various conventional methods.

FIG. 1 is a block diagram of the main parts of a device that implements the above-described minimum average error method.

In FIG. 1, 1 is an error data storage means, 2 is an error matrix, 3 is a storage position of the error Exa at the coordinates xy of the original image, and 4 is an input device for inputting the error data of the error matrix 2 and outputting the average error Ea. average error calculation means; 5 is an input terminal for original image data Ixa at coordinates xy of the original image;
6 is a calculation means for the air (-Ixa + Exa), and 7 is O
or the output terminal of the binary signal Pxy of R, 8 is a constant threshold value R
/2 is applied to the signal terminal, 9 compares the input signal 1/, A with a constant threshold value R/2, and when I', > R/2, Pxy
=R, and in other cases p=Q, and 10y is a calculation means for Exy (-I'xy-Pxa).

Now, the calculation of the above average error Ea will be explained as follows.

Ea″ <14.ij): Σ, aij Ex+i
, y+j (1)1] 11 (However, l+1 is 0 indicating the coordinate in error matrix 2)
In addition, the coefficient Ma) IJ coefficient αij weights the error with respect to the distance from the coordinates explain. First, the average error calculation means 4 calculates and outputs the average error Ea from the contents of the error matrix 2, and then the calculation means 6 adds the original image data ``Air'' of the input terminal 5 and the average error Ea to obtain the value ■ ′□A is output. Then, the binarization means 9 compares the value ■'Y with a constant threshold value R/2, and outputs a binary output P to the output terminal 7. On the other hand, in the calculation means 10, the value 1'
The difference Exy between the air and the 2' value output PXy is calculated and output to the storage means 1 as a new error in the coordinates xy of the original image. The IJ box 2 stores the storage means 1 for each pixel input of the original image data IxA in the main scanning direction of the original image.
It moves along the top to the right in the figure, and returns to the left end for each sub-scan, moving down one line.

Now, the above-mentioned minimum average error method There were few. The reason for this is that the amount of calculation required for image data processing is large and that a line buffer for storing error data is required, resulting in higher manufacturing costs than the simple dither method. In particular, when a line buffer is used to process a color image, the buffer capacity increases and the h load becomes heavier6,-2. In view of the conventional problems with the minimum method, an object of the present invention is to provide an image processing device that does not impair the gradation reproducibility of a binary image even when the storage capacity of a line buffer is reduced.

Structure of the Invention The present invention provides (1) the pixel of interest x stored in the error data storage means;
(2) a weighted average calculating means for calculating a weighted average value E7 of binarization errors in the y neighborhood;
Lower L bit data of value conversion error Ex, -1, A (L)
The average error Ea and the original image data I, where is the lower bit
The first operation xy that calculates the added value ■'
xy calculation means; (3) binarization means for thresholding the added values 1/, a to obtain a binary output P air; (4) 2 from the added values 1/, a and the binary output Pxy.
(5) storing the upper U via) data of the binarization error Exy in the error data storage means; This image signal processing device is equipped with means for holding the lower L bit data of until the next pixel calculation, and reduces the storage capacity of the error data storage means compared to the conventional minimum average error method, and therefore reduces the storage capacity of the error data storage means, thereby reducing the weighted average calculation. This also makes it possible to reduce the number of bits.

In addition, in the weighted average calculation means, each binarized error data in the vicinity of the pixel xy of interest is set to -L bits, and after adding L bits of 0 to each lower bit, the weighted average value Ew is calculated.
It is also possible to improve the calculation accuracy by calculating the value obtained by adding the data Ex-1,y(L) to the Ew in the first calculation means and setting the value obtained by adding the data Ex-1, y(L) to the Ew as the average error Ea.

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

FIG. 2 shows a block diagram of an image signal processing device according to an embodiment of the present invention.

In the figure, numbers 1 to 3 are the same as the explanation in FIG. 1, but the number of data bits handled is reduced to U bits. 5-1
o is the same as in FIG. The weighted average calculation means 11 performs the same calculation as the average error calculation shown in FIG. 1 on U-bit data. The difference from the configuration shown in FIG. 1 is that a delay means 12 is provided, which delays the lower bit data of the binarization error by one pixel.

The operation of the configuration shown in FIG. 2 will be explained step by step below.

First, the weighted average calculation means 11 calculates and outputs the weighted average value Ew from the contents of the error matrix 2, and the calculation circuit 6 uses the weighted average value II as the upper bit and calculates the weighted average value Ew from the content of the error matrix 2. Average error E with lower L bit data Ex-1,y(L) as lower bit in binarization error
Add a and the original image data of input terminal 5 ■゛, and the value is 1
′ is output.

The xy xy binarization means 9 compares the value 1'air with the constant amount value R/2 and outputs a binary output P to the output terminal 7.

y On the other hand, in the calculation means 1o, the value ′ air and the binary output P
xy difference E! A is calculated, and its upper U bit Exa9
. The delay means 12 is one pixel before Ex-1.
, y(L) are updated to new input data Exy(L) and held. The IJ block 2 is main-scanned on the storage means 1 to the right in the figure and sub-scanned downward.

Note that when calculating the average error Ea, the error matrix)
By adding 0 of L pinot to the lower order of the error data of each U bit of IJx, performing a weighted average calculation, and adding it with the output data of the delay circuit to obtain the average error Ea,
The calculation accuracy of weighted average can be improved. Furthermore, the timing of data input/output in each program is set at the time when the calculation means 6 takes in the input data Ea.
By adjusting the state in which the previous calculation result is held, the delay means 12 becomes unnecessary.

In the experimental results, no deterioration in image quality was observed even if the lower 5 bits of the 8-via data were reduced, and on the contrary, the visually unpleasant part of the striped texture characteristic of conventional minimum average error was eliminated. I've had good results with 10 and 17 results.

Effects of the Invention As described above, in the present invention, by correcting data for L bits by the next pixel calculation, the gradation reproducibility is not impaired compared to the conventional minimum average error method, and the storage capacity of the error data storage means is reduced to 1. L bits per pixel can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a main part of an apparatus for realizing the conventional minimum average error method, and FIG. 2 is a block diagram of an image signal processing apparatus according to an embodiment of the present invention. 1... Error data storage means, 2... Error matrix, 3... Error data storage position of the target pixel xy. 4: Average error calculation means, 6: Original image data input terminal, 6,1o: Addition/subtraction calculation means, 7: Output of binary signal Terminal, 11...
- Weighted average calculation means, 12... Delay means.

Claims (2)

[Claims] (1) Pixel of interest x stored in error data storage means
A weighted average calculating means for calculating a weighted average value E_w of the binarization error in the y neighborhood, and a lower bit data E_x_ of the binarization error one pixel before, with the previous weighted average value E_w as the upper bit.
−_1_, average error E_ with _y(L) as the lower bit
a and the original image data I_x_y; a binarization means for thresholding the added value I'_x_y to obtain a binary output P_x_y; and the binarization error E_x_y from the binary output P_x_y (however, E_x_y=I′_x_y−
P_x_y), and a holding means for storing the upper U bit data of the binarization error E_x_y in the error data storage means and holding the remaining lower L bit data until the next pixel operation. Equipped with an image signal processing device. (2) Pixel of interest x stored in error data storage means
After setting each binarized error data in the y neighborhood as the upper bits and adding L bits of O data to the lower bits of each binarized error data, a weighted average value E_w is calculated, and the value of the previous pixel is added to the E_w. Lower bit data of binarization error E_x_-_
1. The image signal processing device according to claim 1, wherein the average error E_a is a value obtained by adding 1_,_y(L).