JP2606846B2 - Image signal processing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a multi-gradation (multi-density) digital pixel signal in a copier, facsimile, printer, or the like using digital image data. The present invention relates to an image signal processing device that converts a pixel signal into a pixel signal.

(Prior Art) As a method of processing this kind of image signal, a method of feeding back a conversion error generated by a dither method to an image signal before dither processing of a next block or image binarization in which error correction is performed using a weight matrix are conventionally used. There is a processing method.

However, when the dither method is used, the resolution is degraded due to the size of the dither matrix, and the binarization process has a problem that the reproducibility of gradation is poor.

(Purpose) As described above, in the conventional image signal processing technology, there is a dither method as a method of outputting a multi-tone image signal to an output device that can express only a few gradations. There are drawbacks such as degradation and complicated hardware.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image signal processing apparatus which compensates for the above-mentioned drawbacks and suppresses the occurrence of moire from a document including a dot document and performs gradation processing without lowering the resolution.

(Structure) In order to achieve the above object, the present invention separates an image signal represented by multiple gradations into even-numbered pixels and odd-numbered pixels, and adds them.
An error caused by the gradation processing of the signal after the addition is held for one block in the main scanning direction and one line in the sub-scanning direction, and the error is field-backed to the next block and the pixel signal of the next line. It is characterized in that the correction is performed by performing the following.

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

 First, the principle of the present invention will be described with reference to FIG.

FIG. 4 is a conceptual diagram of the image signal processing.
.. Indicate one block of two pixels, A and B indicate the pixels constituting each block, and n indicates a line.

In the figure, processing of an image signal is basically performed in a block in units of two pixels which are in the main scanning direction. Here, the process of block processing will be specifically described.

Each block is composed of a left pixel A and a right pixel B. To process the block, an error Em generated by the block processing and an error Es generated by the block processing are required. Each pixel of the block after processing is represented by A 'and B', and the processing error generated here is represented by E
Assuming m 'and Es', an example of the operation of the present invention is represented by the following equation.

A '= INT [max {A + B + Em + Es) × N / M, N-1}] B' = INT [max {(A + B + Em + Es)] × N / M-A ', N-1} Em' = INT [｛(A + B + Em + Es) ) − (A ′ + B ′) × M / N｝ × Cm] Es ′ = INT [｛(A + B + Em + Es) − (A ′ + B ′) × M / N｝ × Cs] where M is the number of input gradations and N Is the number of output (processing) gradations,
Cm is a constant which is an error correction rate in the main scanning direction, Cs is a constant which is an error correction rate in the sub-scanning direction, max (a, b) is a function which outputs the larger of a and b, and INT (a) is a Function to extract the integer part of.

Next, an image signal processing device based on the above processing principle will be described.

FIG. 1 is a block diagram showing an embodiment of an image signal processing apparatus according to the present invention, in which 1 is a pixel distribution section, 2, 3, and 4 are adders, 5 and 6 are gradation processing sections, and 7 is a pixel. A coupling unit, 8 and 9 are multipliers, and 10 is a line memory for error in the sub-scanning direction.

In the figure, an input multi-tone image signal is divided into the above-mentioned two pixels A and B by a pixel distribution unit 1 and the above-mentioned Em, Es by adders 2, 3, and 4.
Is added. The gradation processing section 5 converts the input signal into an N gradation output A '. The conversion error generated at that time is determined by the gradation processing unit 6.
Where B 'is created. Further, the conversion error generated here is input to multipliers 8 and 9 for error correction to the next block. The error correction ratios are respectively multiplied by the two multipliers to obtain the above-mentioned Em 'and Es', which are used for correcting the next block. However, in the sub-scanning direction, the next line is used instead of the next block, so that the data is input to the line memory 10 for one line.

FIG. 2 is a block diagram showing another embodiment of the present invention, wherein 11, 18, 19, 28 are latches, 12, 23 are adders, 13, 24, 26, 2
7 is a multiplier, 14 and 25 are dividers, 15 is an overflow corrector, 16 is a subtractor, 17 is an overflow corrector, 20 is a data selector, 21 is a division counter, 22 is an address counter, and 29 is a line memory. is there.

 FIG. 3 is an operation waveform diagram of a main part of FIG.

 Hereinafter, the operation of FIG. 2 will be described with reference to FIG.

The input multi-tone image signal is distributed to an even-numbered pixel A and an odd-numbered pixel B in the latch 11, and is added by an adder 12 together with a main scanning direction error Em and a sub-scanning direction error Es. The output of the adder 12 passes through the multiplier 13, the divider 14, and the overflow correction 15, and becomes the processing result A 'of the even-numbered pixel. Further, the signal passing through the subtractor 16 and the overflow correction 17 is the processing result B 'of the odd-numbered pixel. Here, it is assumed that the overflow compensator outputs a maximum value signal when the input pixel signal exceeds a maximum value signal input in advance. The latches 18 and 19 and the data selector 20 constitute a pixel coupling unit, and combine even-numbered pixel signals and odd-numbered pixel signals into one and output them as N gradation pixel signals. The adder 23, the multiplier 24, the divider 25, and the multipliers 26 and 27 constitute a feedback error correction unit for each of the main and sub scanning directions, and correct an error generated by the gradation processing unit. Here, the multipliers 26 and 27 are transmission rate variable means having a function of changing the transmission rate of the error to the next block. The error correction in the sub-scanning direction is stored in the line memory 29 until the block signal of the target correction position comes because the input image signal is continuous in the main scanning direction.

The waveforms of the main parts in the above operation are as shown in FIG.

(Effects) As described above, according to the present invention, i) since the even-numbered pixels and the odd-numbered pixels are separated and added, the resolution of the reproduced image is good and no moire occurs.

ii) Since the gradation processing error is feedback-corrected, multi-gradation expression can be performed for the entire image.

iii) Since the correction is performed in both the main scanning direction and the sub-scanning direction, density unevenness due to the correction is eliminated and uniformity can be maintained.

iv) By making the error correction rate (next block transmission rate) variable, it is possible to set parameters corresponding to the characteristics of the image output device. Thus, it is possible to provide an excellent image signal processing apparatus by eliminating the disadvantages of the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the present invention, and FIG. 3 explains the operation of FIG. FIG. 4 is a conceptual diagram for explaining the principle of the present invention. 1 ... Pixel distribution unit, 2,3,4 ... Adder, 5,6 ... Grayscale processing unit, 7 ... Pixel combination unit, 8,9 ... Multiplier, 10 ... For sub-scanning direction error Line memory.

Claims (2)

(57) [Claims] An image signal processing apparatus for processing a subsequent two pixels of an image signal from a multi-gradation-expressed image signal as one block to obtain a reproduced image, wherein the image signal is divided into even-numbered pixels and odd-numbered pixels. Separating means for separating the pixels, adding means for adding the even-numbered pixels and odd-numbered pixels, and holding for holding a processing error resulting from gradation processing of the added signal for one block in the main scanning direction. Means for holding the error for one line, and feedback means for feeding back the processing error to the pixel signal of the next block and the next line. 2. The image signal processing apparatus according to claim 1, wherein said feedback means has a transmission rate varying means for changing a transmission rate of said processing error.