JPH1042132A - Picture processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a in gathering fragments and a texture without increasing rough surface feeling, to solve the problem of a pseudo outline and to suppress moire by controlling the signal value of a random number generation part so that it becomes the function of a VIDEO signal value. SOLUTION: In a gradation conversion processing part, a counter 301 alternately generates the timing signals of '0' and '1' at two picture element periods. Only when the timing signal is '0', a positive random value is generated from the random number generation part 302, it is inputted to a random code control part 303 and a random code is converted into positive or negative. Then, it is inputted to an amplitude control part 304 and the amplitude of the signal from the random number code control part 303 is restricted in accordance with eight-bit signals from a color/monochrome conversion part 203. A selector 307 switches A to an A bar based on the signal of the counter 301, outputs the signal value and it is added with a VIDEO signal from the color/ monochrome conversion part 203. Then, it is inputted to an error diffusion processing part 308 and a processing by an error diffusion method to binary data and the screen processing of a dither and the like are executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus, and more particularly to an image processing apparatus for performing a gradation conversion process on a multi-valued image of one pixel m (m is an integer of 2 or more) bits into an image having a smaller number of bits than m bits. About.

[0002]

2. Description of the Related Art An error diffusion method (hereinafter referred to as ED), a screen processing method, and the like are generally known as image forming methods for performing halftone expression. These are intended to express a halftone macroscopically by expressing an area gradation using a small number of gradations. That is, it is a pseudo halftone expression method. This has the effect of reducing the load on hardware that handles image data because images can be formed with a small number of gradations.

[0003]

However, when the number of gradations of an image is reduced in consideration of simplification of hardware and a system via a network, especially when forming a 1-bit image, the rubbing and texture are reduced. Such a problem had occurred. In other words, this is a specific problem that occurs in the ED method or the screen method, and there is a problem that a dot is not formed after a character or an image in a high density portion or a pattern of a bug-like mark appears. . To solve this problem, n
(N is an integer of 2 or more) The inventor of the present invention has applied for a method of adding a random number value having the same absolute value in pixel units and only a sign regularly and positively or negatively added to input image data as Japanese Patent Application No. 7-333630. According to this method, in order to add a random value whose sign changes periodically to the image data, when the input image is a halftone image, it may interfere with a halftone image or the like and cause moire. all right.

The present invention has been made to solve the above-mentioned drawbacks of the prior art, and can solve the peculiar problems, which are caused by the ED method and the screen method, without increasing the graininess. It is an object of the present invention to provide an image processing apparatus that can solve the above problem and can also suppress moiré.

[0005]

In order to achieve the above object, an image processing apparatus according to the present invention comprises: an image input means for inputting m-bit image information; and a random number generating means for generating a positive random value every other pixel. And random number code control means for randomly or positively converting the sign of the random number value generated by the random number generation means, and the random number value of the random number code control means as a function of the signal value of the image input means, An amplitude control unit that changes the ratio and a pixel for which a random number value is not generated by the random number generation unit generates a value whose sign is inverted with the same absolute value as the value output by the amplitude control unit one pixel before. Sign inverting means, an adding means for alternately adding a signal value generated by the amplitude control means and the sign inverting means to a signal value of the image input means, and a signal value obtained by the adding means being n N to be valued And a means.

Further, the image processing apparatus of the present invention comprises: an image input means for inputting m-bit image information; a random number generating means for generating a positive random number value for every other pixel; and a random number value generated by the random number generating means. A random number code control unit that converts the sign of the random number into positive or negative at random, and a pixel whose random number value is not generated by the random number generation unit has a value output by the random number code control unit one pixel before the absolute value and an absolute value. Sign inversion means for generating a value obtained by inverting the same sign, and an amplitude for changing a signal value generated by the random number encoding means and the sign inversion means alternately as a function of a signal value of the image input means. Control means; adding means for adding the signal value generated by the amplitude control means to the signal value of the image input means; and n-value converting means for converting the signal value obtained by the adding means to n-value. .

Further, the image processing apparatus of the present invention comprises: image input means for inputting m-bit image information; random number generation means for generating a positive or negative random number value for every other pixel; The amplitude control means for changing the ratio of the amplitude as a function of the signal value of the image input means, and the pixel for which the random number value was not generated by the random number generation means, was output by the amplitude control means one pixel before. Sign inverting means for generating a value whose sign is the same as that of the absolute value and inverting sign, and adding means for alternately adding the signal value generated by the amplitude control means and the sign inverting means to the signal value of the image input means. When,
An n-value converting means for converting the signal value obtained by the adding means into an n-value.

Further, the image processing apparatus of the present invention comprises: an image input means for inputting m-bit image information; a random number generating means for generating a positive or negative random value every other pixel; For a pixel for which a numerical value has not been generated, a sign inverting means for generating a value having the same absolute value as the value output by the random number generating means one pixel before and having a sign inverted, the random number generating means and the sign inverting means And an amplitude control means for alternately changing the ratio of amplitude as a function of the signal value of the image input means, and adding the signal value generated by the amplitude control means to the signal value of the image input means. And n-value conversion means for converting the signal value obtained by the addition means into n-value.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

<Overall Configuration> FIG. 1 is a block diagram showing the overall configuration of an image processing apparatus according to the present embodiment.

The image reading unit 109 includes the CCD sensor 1
02, an analog signal processing unit 103 and the like, and an image of the original image 100 formed on the CCD sensor 102 via the lens 101
(Red), G (Green), and B (Blue) are converted into analog electric signals. The converted image information is input to the analog signal processing unit 103, where R,
Sample and hold, dark level correction, etc. are performed for each color of G and B, and analog / digital conversion (A /
D conversion).

The full-color signal digitized by the analog signal processing unit 103 is input to an image processing unit 104.

The image processing unit 104 performs necessary correction processing such as shading correction, color correction, and r correction, smoothing processing, edge enhancement, gradation conversion processing, processing, and the like. Is done.

The printer unit 105 includes an exposure control unit (not shown) made of a laser or the like, an image forming unit (not shown), a transfer paper transfer control unit, and the like. Record the image.

The CPU circuit section 110 includes the CPU 10
6, an image reading unit 109, an image processing unit 104, a printer unit 1
05, etc., to control the overall sequence of the present apparatus.

<Configuration of Image Processing Unit> Next, the image processing unit 1
04 will be described. FIG. 2 is a configuration block diagram of the image processing unit 104.

The digital image signal output from the analog signal processing unit 103 in FIG.
1 is input. The shading correction unit 201 corrects the variation of the sensor that reads the document and the light distribution characteristics of the document illumination lamp. The corrected image signal is converted from the luminance signal into density data.
The image data is input to the tone correction unit 202 and density image data is created. The image signal converted to the density data is input to the color / monochrome conversion unit 203 and output as monochrome data. Then, the data output from the color / monochrome conversion unit 203 is input to the gradation conversion processing unit 204, and error diffusion processing is performed as pseudo halftone expression.

When outputting a color image signal,
Each of the Y, M, and C data from the tone correction unit 202 is subjected to a conversion process in a tone conversion processing unit 204.

Next, the tone conversion processing unit 204, which is the point of this embodiment, will be described with reference to FIG.

<Embodiment 1><Configuration of Gradation Conversion Processing Unit> FIG. 3 is a detailed block diagram of a gradation conversion processing unit 204 which is a point of the present embodiment.

First, the gradation conversion processing section 204 shown in FIG. 1 generates a timing signal of 0 and 1 alternately in a two-pixel cycle in the counter 301. In this configuration, a signal is transmitted in synchronization with each pixel of an image, and 0 is transmitted at an end. Next, the timing signal output from the counter 301 is input to the random number generation unit 302, and the random number generation unit 302 generates a positive random value only when the timing signal is 0. The signal output from the random number generation unit 302 is input to the random number code control unit 303, and the code is randomly converted to positive or negative and output. The signal value output from the random number code control unit 303 is input to the amplitude control unit 304, and the amplitude of the signal from the random number code control unit 303 is controlled according to the 8-bit signal from the color / monochrome conversion unit 203. It has become. In other words, the output signal value from 304 is a function of the signal from the color / monochrome conversion unit 203, and the control to reduce the amplitude of the output signal between the low density part and the high density part in the density data I am doing. This is shown in FIG. FIG. 7A shows a case without amplitude control, and FIG. 7B shows a case with amplitude control. That is, in the function (b) in which the amplitude control is performed, a function acts such that the amplitude of the random number value is reduced in the low density part and the high density part.

Next, the signal output from the amplitude control 304 is input to the memory 305 and the selector 307. This memory 305 is for temporarily storing the signal value output from the amplitude control 304. Selector 3
07 is configured to switch between A and A bar based on the signal of the counter 301 and output a signal value. That is, when the signal of the counter 301 is 0, the amplitude control 30
4 is output as it is, and when the signal of the counter 301 is 1, the signal from the sign inversion unit 306 is output. The sign inverting unit 306 is configured to invert the sign of the signal from the memory 305 and output the inverted signal. That is, when the data in the memory 305 is negative, the sign is inverted to a positive value and output, and when the data in the memory 305 is positive, the sign is inverted to a negative value and output. With such a configuration, it is possible to output a random number value that has the same absolute value for two consecutive pixels and has only a positive or negative sign or a different negative / positive set.

The signal value output from the selector 307 in this way is
It is added to the IDEO signal at 309 and the error diffusion processing unit 30
8 is input. Here, although not shown, 309
When the signal value exceeds 255 (8 bits) or becomes 0 or less when the addition is performed, the signal value is increased by 25, respectively.
The processing of clipping to 5 or 0 is performed. Although the details of the error diffusion processing unit 308 are not shown, the error diffusion processing unit 308 performs processing such as normal error data diffusion processing to binary data and screen processing such as dithering to binary data.

The VIDE which has performed the processing as described above
The O signal is output from the image processing unit 104 and output from the printer unit 105.

As described above, according to the present embodiment, in order to solve the problem that the granularity is deteriorated if a random number is added to the normal image density data, a random number generation unit as shown in FIG. Is controlled so as to be a function of the VIDEO signal value.

Further, if a random number whose absolute value is equal in two pixel units and whose sign regularly changes to plus or minus is added to the VIDEO signal, it interferes with the read halftone image and moire is generated. In this configuration, a signal whose absolute value is equal in units of two pixels and whose sign changes randomly between positive and negative or negative and positive is added to the VIDEO signal.

As described above, according to the present embodiment, it is possible to solve the problem of the unique problem caused by the n-bit ED method or the screen method without increasing the roughness, and to reduce the pseudo contour. The problem described above can be solved and moire can be controlled.

In the present embodiment, the sign of the random value is switched between positive and negative, negative and positive at random in units of two pixels, but this is not limited to the unit of two pixels and may be, for example, three pixels. In this case, (positive, 0, negative) or (negative, 0, positive)
And the random number code may be randomly switched.

<Embodiment 2> An image processing apparatus according to a second embodiment of the present invention will be described below. The second
In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 4 is a detailed block diagram of the gradation conversion processing unit 204 according to the second embodiment.

In the figure, the signal value output from the random number code control unit 303 is input to the memory 305 and the selector 307. This memory 305 is for temporarily storing the signal value output from the random number code control unit 303 as in the first embodiment. The selector 307 is
Based on the signal of the counter 301, A and A bars are switched to output a signal value. That is, when the signal of the counter 301 is 0, the signal from the random number code control unit 303 is output as it is, and the signal of the counter 301 is 1
In the case of, the signal is output from the sign inversion unit 306. The sign inverting unit 306 is configured to invert the sign of the signal from the memory 305 and output the inverted signal, as in the first embodiment. That is, when the data in the memory 305 is negative, the sign is inverted to a positive value and output, and when the data in the memory 305 is positive, the sign is inverted to a negative value and output. With this configuration, 2
It is possible to output a random value having the same absolute value but a different sign only for successive pixels.

The signal output from the selector 307 is input to the amplitude control 304, and the signal is output to each pixel as shown in FIG.
After the control of the ratio of the random number amplitude is performed as shown in FIG.

The signal value output from the amplitude control 304 in this way is added to the VIDEO signal from the color / monochrome conversion unit 203 at 309 as in the first embodiment, and input to the error diffusion processing unit 308. , Normal nbi
Processing such as an error diffusion method for t and screen processing is performed.

The VIDEO signal on which the above-described processing has been performed is output from the image processing unit 104 and is output from the printer unit 105.

In the second embodiment, as compared with the first embodiment, since the amplitude control 304 is performed for each pixel, the absolute value is equal between the odd-numbered pixel and the even-numbered pixel, and only the sign is used. Does not add a different random value, so that accurate density is not preserved. However, it is possible to control not to add more data than necessary at the edge of the character part or image part, and the reproducibility of the edge part improves. There is such a feature.

<Embodiment 3> An image processing apparatus according to a third embodiment of the present invention will be described below. The third
In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 5 is a detailed block diagram of the gradation conversion processing unit 204 according to the third embodiment.

In the same figure, the counter 301 alternately generates timing signals 0 and 1 every two pixels, as in the first embodiment. In this configuration, a signal is transmitted in synchronization with each pixel of an image, and 0 is transmitted at an end. The timing signal output from the counter 301 is input to the random number generation unit 501, and the random number generation unit 501 generates a random value only when the timing signal is 0. The signal output from the random number generation unit 501 is a random number value that is positive or negative. The signal output from the random number generation unit 501 is input to the memory 305 and the selector 307, and based on the signal of the counter 301, the signal value from the random number generation unit 501 and the sign inversion unit 306
And the signal from A and A are switched and output between A and A bar. The sign inverting unit 306 is configured to invert the sign of the signal from the memory 305 and output the inverted signal, as in the first embodiment.

The signal value output from the selector 307 in this way is added to the VIDEO signal from the color / monochrome conversion unit 203 at 309 as in the first embodiment, and input to the error diffusion processing unit 308. Normal nbi
Processing such as an error diffusion method for t and screen processing is performed.

The VIDEO signal having undergone the above-described processing is output from the image processing unit 104 and output from the printer unit 105.

As described above, in the third embodiment, as compared with the first embodiment, since the random number output from the random number generation unit 501 generates a random number with a positive / negative intersection, the sign inversion unit 306 is used.
Can be omitted, and the hardware can be simplified.

Embodiment 4 Hereinafter, an image processing apparatus according to Embodiment 4 of the present invention will be described. In the fourth embodiment, the same configuration as in the first embodiment will be described.
The same reference numerals are given and the detailed description is omitted.

FIG. 6 shows a gradation conversion processing unit 2 according to the fourth embodiment.
04 is a detailed block diagram of FIG.

In the same drawing, in the counter 301, timing signals of 0 and 1 are alternately generated in a two-pixel cycle as in the first embodiment. The timing signal output from the counter 301 is input to the random number generation unit 501, and the random number generation unit 501 generates a random value only when the timing signal is 0. This random number generation unit 501
Is a random number value that is positive or negative as in the third embodiment.

The signal value output from random number generation section 501 is input to memory 305 and selector 307. This memory 305 is for temporarily storing the signal value output from the random number generation unit 501. The selector 307 switches between A and A based on the signal of the counter 301 and outputs a signal value. That is, when the signal of the counter 301 is 0, the signal from the random number generation unit 501 is output as it is, and when the signal of the counter 301 is 1, the signal from the sign inversion unit 306 is output. The sign inverting unit 306 is configured to invert the sign of the signal from the memory 305 and output the inverted signal, as in the first embodiment. With such a configuration, it is possible to output a random value having the same absolute value but different sign only for two consecutive pixels.

The signal output from the selector 307 is input to the amplitude controller 304, and the signal is output to each pixel as shown in FIG.
After the control of the ratio of the amplitude of the random numbers as shown in FIG.

The signal value output from the amplitude control 304 in this way is added to the VIDEO signal from the color / monochrome conversion unit 203 at 309 as in the first embodiment, and input to the error diffusion processing unit 308. , Normal nbi
Processing such as an error diffusion method for t and screen processing is performed.

The VIDEO signal having undergone the above-described processing is output from the image processing unit 104 and output from the printer unit 105.

The fourth embodiment is different from the first embodiment in that the amplitude control 3 is applied to each pixel as in the second embodiment.
Although the density is not accurately preserved due to performing step 04, the control that does not add more data than necessary at the edge of the character portion or the image portion becomes possible, and the reproducibility of the edge portion is improved.

Further, as in the third embodiment, since the random number output from the random number generator 501 generates a random number with a positive / negative intersection, the sign inverting unit can be omitted and the hardware can be simplified. .

As described above, the image processing apparatus according to the present embodiment
Random number generation means for generating a positive random number value for every other pixel, random number code control means for randomly or positively converting the sign of the random number value generated by the random number generation means, and random number value of the random number code control means The amplitude control means for changing the ratio of the amplitude as a function of the signal value of the input image data, and the pixel whose random number value has not been generated by the random number generation means, the value output by the amplitude control means one pixel before. Sign inverting means for generating a value in which only the sign is inverted with the same absolute value, and adding means for alternately adding the signal value generated by the amplitude control means and the sign inverting means to the signal value of the input image data And

As a result, when input image information of 8 bits is binarized by the ED method or the screen method, problems such as gathering and texture have occurred. However, every other pixel is changed according to the input image data value. Each pixel of the input image data is controlled while controlling the ratio of the amplitude value of the generated random number and changing the code pattern of the random value having the same absolute value to be added to each pixel in units of two pixels at random in a positive / negative or negative / positive set. Adding these values solved these problems.

Further, it is characterized in that moire can be controlled while solving the problem that graininess is deteriorated when a random number is added to normal image density data.
Further, the present invention is not limited to image formation in which gradation conversion from 8 bits to 1 bit is performed, and is not limited to 2 bits.
Switching noise generated by gradation conversion to another gradation (n bit) such as 3 bits or 3 bits, that is, a problem that a pseudo contour occurs can be simultaneously solved while suppressing moire.

[0054]

As described above, according to the present invention, there are specific problems caused by the ED method and the screen method.
It is possible to solve the intrusion and the texture without increasing the roughness, to solve the problem of the false contour, and to suppress the moire.

[Brief description of the drawings]

FIG. 1 is a block diagram of an image forming apparatus.

FIG. 2 is a block diagram of an image processing unit.

FIG. 3 is a block diagram of a gradation conversion processing unit according to the first embodiment.

FIG. 4 is a block diagram of a gradation conversion processing unit according to the second embodiment.

FIG. 5 is a block diagram of a gradation conversion processing unit according to the third embodiment.

FIG. 6 is a block diagram of a gradation conversion processing unit according to a fourth embodiment.

FIG. 7 is an explanatory diagram of amplitude control in the embodiment.

[Explanation of symbols]

 301 counter 302 random number generation unit 303 random number code control unit 304 amplitude control unit 305 memory 306 sign inversion unit 307 selector 308 error diffusion processing unit 309 adder 1

Claims (4)

[Claims] An image input unit for inputting m-bit image information; a random number generation unit for generating a positive random number value for every other pixel; and a positive or negative random number sign generated by the random number generation unit. Random number code control means for converting the random number value of the random number code control means into a function of the signal value of the image input means; and a random number value generated by the random number generation means. For a pixel that did not exist, a sign inverting unit that generates a value whose sign is inverted with the same absolute value as the value output by the amplitude control unit one pixel before, generated by the amplitude control unit and the sign inverting unit An image processing apparatus comprising: an adding unit that alternately adds a signal value to a signal value of the image input unit; and an n-value converting unit that converts the signal value obtained by the adding unit into an n-value. 2. An image input means for inputting m-bit image information; a random number generation means for generating a positive random number value for every other pixel; and a positive or negative random number sign generated by the random number generation means. A random number code control unit that converts the random number into a random number, and a pixel whose random number has not been generated by the random number generation unit has a value that is the same as the absolute value of the value output by the random number code control unit one pixel before and whose sign is inverted. Sign inverting means for generating, an amplitude controlling means for alternately changing a ratio of amplitude as a function of a signal value of the image input means, and a signal value generated by the random number sign controlling means and the sign inverting means; An image, comprising: an addition unit that adds a signal value generated by a control unit to a signal value of the image input unit; and an n-value conversion unit that converts the signal value obtained by the addition unit into an n-value. Forming equipment. 3. Image input means for inputting m-bit image information; random number generation means for generating a positive or negative random number value for every other pixel; and random number value of said random number generation means as a signal of said image input means. Amplitude control means for changing the ratio of amplitude as a function of the value; and a pixel for which a random number value has not been generated by the random number generation means has the same absolute value as the value output by the amplitude control means one pixel before, and Sign inverting means for generating a value obtained by inverting the signal value; adding means for alternately adding the signal value generated by the amplitude control means and the sign inverting means to the signal value of the image input means; An n-value converting means for converting an obtained signal value into an n-value. 4. An image input unit for inputting m-bit image information, a random number generation unit for generating a positive or negative random number value every other pixel, and a pixel for which a random number value has not been generated by the random number generation unit. Sign inversion means for generating a value whose sign is inverted with the same absolute value as the value output by the random number generation means one pixel before, and the signal value generated by the random number generation means and the sign inversion means alternately Amplitude control means for changing the ratio of amplitude as a function of the signal location of the image input means; adding means for adding the signal value generated by the amplitude control means to the signal value of the image input means; An image processing apparatus comprising: an n-value conversion unit that converts an obtained signal value into an n-value.