JP3461247B2 - Image processing apparatus and image processing method - Google Patents

Description

Detailed Description of the Invention

[0001]

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

[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 an image forming method for performing halftone expression. These are intended to express halftones macroscopically by expressing area gradations using a small number of gradations. In other words, it is a pseudo halftone expression method. This has an effect that the load on the hardware that handles image data can be reduced because an image can be formed with a small number of gradations.

[0003]

However, when the number of gradations of an image is reduced in consideration of the simplification of hardware and a system via a network, especially when forming an image with 1 bit, scooping and texture are reduced. There was such a problem. In other words, this is a peculiar problem that occurs in the ED method and the screen method, and there are problems that dots are not printed after the characters or images in the high-density area, or that traces of insect marks appear. . To solve this problem, n
(N is an integer of 2 or more) The present inventor has filed a patent application as Japanese Patent Application No. 7-333630 in which a random number value whose absolute value is the same in pixel units and whose sign only changes regularly between positive and negative is added to the input image data. According to this method, since a random number value whose code changes periodically is added to the image data, when the input image is a halftone dot image, there is a possibility that moiré may occur due to interference with the halftone dot image or the like. all right.

The present invention eliminates the above-mentioned drawbacks of the prior art, and can solve the peculiar problems caused by the ED method and the screen method, such as roughening and texture, without increasing the feeling of roughness, and pseudo contours. It is an object of the present invention to provide an image processing device that can solve the above problem and suppress moire.

[0005]

In order to achieve the above-mentioned object, an image processing apparatus of the present invention converts input mbit image information into nbit image information (m, n are integers, and m>
an image processing apparatus for perform output gradation conversion to n), an image input unit for inputting image information mbit, 1
Random number generation means for generating a positive random number value for each pixel , random number code control means for randomly converting the sign of the random number value generated by the random number generation means into positive or negative, and a random number value of the random number code control means. In 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 is not generated by the random number generation means, the value output by the amplitude control means and the absolute value are A sign inverting means for generating a value whose sign is inverted, an adding means for adding the signal value generated by the amplitude control means and the sign inverting means to the signal value of the image input means, and the adding means. And a processing unit that performs gradation conversion processing on the obtained signal value into n-bit data.

Further, the image processing apparatus of the present invention uses the input m
Image information of bit is image information of nbit (m and n are integers
And m> n), and the image processing of performing gradation conversion and outputting.
In the apparatus, an image input unit for inputting mbit image information, a random number generation unit for generating a positive random number value every other pixel, and a random number sign generated by the random number generation unit is randomly converted into positive or negative. With the random number code control means and the pixels for which the random number value is not generated by the random number generation means,
A code inversion means for generating a value whose sign is inverted with the same absolute value as the value output by the random number code control means one pixel before, and the signal value generated by the random number code control means and the code inversion means. An amplitude control means for alternately changing the ratio of the amplitude as a function of the signal value of the image input means, an addition means for adding the signal value generated by the amplitude control means to the signal value of the image input means, And a processing unit that performs gradation conversion processing of the signal value obtained by the adding unit into n-bit data .

Further, the image processing apparatus of the present invention uses the input m
Image information of bit is image information of nbit (m and n are integers
And m> n), and the image processing of performing gradation conversion and outputting.
In the apparatus, an image input means for inputting mbit image information, a random number generation means for generating a positive or negative random number value every other pixel, and a random number value of the random number generation means for a signal value of the image input means. The amplitude control means for changing the ratio of the amplitude as a function and the pixel for which the random number value is not generated by the random number generation means have the same absolute value as the value output by the amplitude control means one pixel before and the sign is inverted. And the addition means for adding the signal value generated by the amplitude control means and the sign inversion means to the signal value of the image input means alternately, and the addition means And a processing unit that performs gradation conversion processing of the signal value into n-bit data .

Further, the image processing apparatus of the present invention uses the input m
In an image processing apparatus that performs gradation conversion from n-bit image information to n-bit image information (m and n are integers, m> n) and outputs the same, an image input unit for inputting m-bit image information and every other pixel. In the random number generation means for generating a positive or negative random number value and the pixel for which the random number value is not generated by the random number generation means, the absolute value is the same as the value output by the random number generation means one pixel before , The signal value generated by the random number generating means and the code inverting means is changed alternately as a function of the signal value of the image input means to change the amplitude ratio. Amplitude control means,
The image forming apparatus further includes an adding unit that adds the signal value generated by the amplitude control unit to the signal value of the image input unit, and a processing unit that performs gradation conversion processing of the signal value obtained by the adding unit into n-bit data. Further, the image processing method of the present invention is an image processing method of performing gradation conversion from input mbit image information to nbit image information (m, n are integers, m> n) and outputting the same. An image input step of inputting information, a random number generation step of generating a positive random number value every other pixel, and a random number code control step of randomly converting the sign of the random number value generated in the random number generation step into positive or negative. , An amplitude control step of changing a random number value of the random number code control step as a function of a signal value of the image input step, and a pixel whose random number value is not generated in the random number generation step, the amplitude control A sign reversing step of generating a value whose absolute value is the same as the value output by the means and whose sign is reversed;
An addition step of adding the signal value generated in the amplitude control step and the sign inversion step to the signal value of the image input step, and gradation conversion processing of the signal value obtained in the addition step into n-bit data. And a processing step.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION 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 the 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 the image of the original image 100 formed on the CCD sensor 102 via the lens 101 is converted by the CCD sensor 102
(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 the image processing unit 104.

The image processing unit 104 performs correction processing required for the reading system such as shading correction, color correction, and r correction, smoothing processing, edge enhancement, gradation conversion processing, processing, etc., and outputs it to the printer unit 105. To be done.

The printer unit 105 is composed of an exposure control unit (not shown) such as a laser, an image forming unit (not shown), a transfer paper conveyance control unit, and the like. Record the image.

The CPU circuit section 110 includes the CPU 10
6, the ROM 107, the RAM 108, and the like, and the image reading unit 109, the image processing unit 104, and the printer unit 1
05, etc., and controls the sequence of this device centrally.

<Structure 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 shown in FIG.
Input to 1. The shading correction unit 201 corrects variations in sensors for reading a document and light distribution characteristics of a document illumination lamp. The corrected image signal is converted from the luminance signal into the density data,
It is input to the gradation correction unit 202 to create density image data. The image signal converted into 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 subjected to error diffusion processing as a pseudo halftone expression.

When outputting a color image signal,
The Y, M, and C data from the gradation correction unit 202 is subjected to conversion processing in the gradation conversion processing unit 204, respectively.

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

<First Embodiment><Structure of Gradation Conversion Processing Unit> FIG. 3 is a detailed block diagram of the gradation conversion processing unit 204, which is a feature of the present embodiment.

In the gradation conversion processing section 204 shown in FIG. 1, first, in the counter 301, the timing signals of 0 and 1 are alternately generated in a cycle of two pixels. This is configured so that a signal is transmitted in synchronization with each pixel of the image and 0 is transmitted at the end. Next, the timing signal output from the counter 301 is input to the random number generation unit 302, and only when the timing signal is 0, the random number generation unit 302 generates a positive random number value. 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. Has become. That is, the output signal value from this 304 is a function of the signal from the color / monochrome conversion unit 203, and control is performed to reduce the amplitude of the output signal in the low density portion and the high density portion in the density data. Is taking place. The situation is shown in FIG. FIG. 7A shows a case without amplitude control, and FIG. 7B shows a case with amplitude control. That is, in (b) in which the amplitude control is performed, a function that makes the amplitude of the random number value smaller in the low density portion and the high density portion acts.

Next, the signal output from the amplitude control 304 is input to the memory 305 and the selector 307. The memory 305 is for temporarily storing the signal value output from the amplitude control 304. Selector 3
07 is configured to output a signal value by switching between A and A bar based on the signal of the counter 301. That is, when the signal of the counter 301 is 0, the amplitude control 30
The signal from 4 is output as it is, and when the signal of the counter 301 is 1, the signal from the sign inverting unit 306 is output. The sign inverting unit 306 is configured to output the signal from the memory 305 while inverting the sign of the 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 and output to a negative value. With such a configuration, it is possible to output a random number value in which two pixels have the same absolute value and only the sign is positive or negative or the pair of negative and positive is different.

The signal value output from the selector 307 in this manner is the V value from the color / monochrome conversion unit 203.
The error signal 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 added with, the signal value is increased to 25
Clipping to 5 or 0 is being performed. Further, although details of the error diffusion processing unit 308 are not shown, processing such as ordinary error diffusion processing for binary data and screen processing such as dithering for binary data is performed.

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

As described above, according to the present embodiment, in order to solve the problem that graininess deteriorates when a random number is added to normal image density data, 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 the same in units of two pixels and whose sign changes regularly between positive and negative is added to the VIDEO signal, it interferes with the read halftone dot image, and moire occurs. Therefore, in order to solve this problem. In addition, a signal whose absolute value is the same every 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 peculiar problems that occur in the n-bit ED method and the screen method and the texture without increasing the roughness, and the pseudo contour. There is an effect that the problem of can be solved and moire can be controlled.

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

<Second Embodiment> An image processing apparatus according to a second embodiment of the present invention will be described below. The second
In the embodiment, the same components as those in the first embodiment are designated 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 bar 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
At the time of, the signal is output from the sign inversion unit 306. The sign inverting unit 306 is configured to output the signal from the memory 305 while inverting the sign, 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 and output to a negative value. With such a configuration, 2
It is possible to output a random number value having the same absolute value and different signs only in consecutive pixels.

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

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 the error diffusion method of t and screen processing is performed.

The VIDEO signal, which has been subjected to the processing described above, is output from the image processing unit 104 and the printer unit 105.

In the second embodiment, since the amplitude control 304 is performed for each pixel as compared with the first embodiment, the odd-numbered pixel and the even-numbered pixel have the same absolute value and only the sign. Since different random numbers will not be added, accurate density storage will not be possible, but it will be possible to control without adding more data than necessary at the edges of the character part and image part, improving the reproducibility of the edge part. There is a feature such as.

<Third Embodiment> An image processing apparatus according to a third embodiment of the present invention will be described below. The third
In the embodiment, the same components as those in the first embodiment are designated 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 of the third embodiment.

In the figure, in the counter 301, as in the first embodiment, timing signals of 0 and 1 are alternately generated in a two-pixel cycle. This is configured so that a signal is transmitted in synchronization with each pixel of the image and 0 is transmitted at the end. The timing signal output from the counter 301 is input to the random number generation unit 501, and a random number value is generated from the random number generation unit 501 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.
The signal from is switched between A and A and output. The sign inverting unit 306 is configured to output the signal from the memory 305 while inverting the sign of the 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 the error diffusion method of t and screen processing is performed.

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

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

<Fourth Embodiment> An image processing apparatus according to a fourth embodiment of the present invention will be described below. In addition, in the fourth embodiment, regarding the same configuration as the first embodiment,
The same reference numerals are given and detailed description thereof is omitted.

FIG. 6 shows the gradation conversion processing unit 2 of the fourth embodiment.
FIG. 4 is a detailed block diagram of 04.

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

The signal value output from the random number generator 501 is input to the memory 305 and the selector 307. The memory 305 is for temporarily storing the signal value output from the random number generation unit 501. The selector 307 is configured to output a signal value by switching between A and A bar based on the signal of the counter 301. 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 output the signal from the memory 305 while inverting the sign of the signal, as in the first embodiment. With such a configuration, it is possible to output a random number value having the same absolute value but different signs only for two consecutive pixels.

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

In this way, the signal value output from the amplitude control 304 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 the error diffusion method of t and screen processing is performed.

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

Compared to the first embodiment, the fourth embodiment is similar to the second embodiment in that the amplitude control 3 is performed for each pixel.
Since 04 is performed, accurate density storage cannot be performed, but it is possible to perform control without adding more data than necessary at the edges of the character portion and the image portion, and the reproducibility of the edge portion is improved.

Further, as in the third embodiment, since the random number value output from the random number generation unit 501 generates a random number value with positive and negative signs, the sign inversion unit can be omitted and the hardware can be simplified. .

As described above, the image processing apparatus according to the present embodiment is
Random number generation means for generating a positive random number value every other pixel, random number code control means for randomly converting the sign of the random number value generated by the random number generation means into positive or negative, and a random number value of the random number code control means. Is the amplitude control means for changing the ratio of the amplitude as a function of the signal value of the input image data, and for the pixel for which the random number value has not been generated by the random number generation means, the value output by the amplitude control means one pixel before And an addition means for alternately adding the signal value generated by the amplitude controlling means and the sign inverting means to the signal value of the input image data With.

As a result, when 8-bit input image information is usually binarized by the ED method or the screen method, problems such as scooping and texture occur, but every other pixel depending on the input image data value. Each pixel of the input image data is controlled by randomly controlling the ratio of the amplitude value of the generated random number, and randomly changing the sign pattern of the random number value added to each pixel in units of 2 pixels and having the same absolute value by a positive / negative or negative / positive pair These problems were solved by adding to the value.

The feature is that moire can also be controlled while solving the problem that graininess deteriorates when a random number is added to normal image density data.
Further, this patent is not limited to image formation in which gradation conversion from 8 bits to 1 bit is performed, but 2 bits are used.
The present invention is characterized in that 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 solved at the same time while suppressing moire.

[0054]

As described above, according to the present invention, there are peculiar problems caused by the ED method and the screen method.
There is an effect that it is possible to solve the scooping and texture without increasing the feeling of roughness, solve the problem of pseudo contour, and suppress moire.

[Brief description of 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 the fourth embodiment.

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

[Explanation of symbols]

301 counter 302 random number generator 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

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Claims (5)

(57) [Claims] 1. The input mbit image information is nbit
Of the image information (m, n are integers, m> n) and outputs the image by performing gradation conversion. Image input means for inputting mbit image information, and a positive random value for every other pixel. Random number generation means for generating, random number code control means for randomly converting the sign of the random number value generated by the random number generation means into positive or negative, the random number value of the random number code control means, the signal value of the image input means Amplitude control means for changing the ratio of the amplitude as a function of, and in the pixels for which the random number value is not generated by the random number generation means, the value output by the amplitude control means is the same in absolute value and its sign is inverted. Sign inversion means for generating, addition means for adding the signal value generated by the amplitude control means and the sign inversion means to the signal value of the image input means, and the signal value obtained by the addition means of nbit The image processing apparatus characterized by having processing means for tone conversion processing over data. 2. The input mbit image information is nbit
Of the image information (m, n are integers, m> n) and outputs the image by performing gradation conversion. Image input means for inputting mbit image information, and a positive random value for every other pixel. Random number generating means for generating, random number code control means for randomly converting the sign of the random number value generated by the random number generating means into positive or negative, and one pixel in the pixel for which the random number value is not generated by the random number generating means. A code inversion means for generating a value whose sign is inverted with the same absolute value as the value output by the random number code control means, and a signal value generated by the random number code control means and the code inversion means are alternated. An amplitude control means for changing an amplitude ratio as a function of the signal value of the image input means, an addition means for adding the signal value generated by the amplitude control means to the signal value of the image input means, and the addition means. so An image forming apparatus, comprising: a processing unit that performs gradation conversion processing on the obtained signal value into n-bit data. 3. The input mbit image information is nbit
Image information (m and n are integers, m> n), and an image processing device for performing gradation conversion and outputting, image input means for inputting mbit image information, and positive or negative disturbance every other pixel. A random number generating means for generating a numerical value; an amplitude control means for changing the random number value of the random number generating means as a function of the signal value of the image input means; and a random value not generated by the random number generating means. In the pixel, a sign inverting means for generating a value having the same absolute value as the value outputted by the amplitude controlling means one pixel before and the sign inverted, and a signal generated by the amplitude controlling means and the sign inverting means. Image processing characterized by comprising: an addition unit for alternately adding a value to the signal value of the image input unit; and a processing unit for performing gradation conversion processing of the signal value obtained by the addition unit into n-bit data. apparatus. 4. The input mbit image information is nbit
Image information (m and n are integers, m> n), and an image processing device for performing gradation conversion and outputting, image input means for inputting mbit image information, and positive or negative disturbance every other pixel. In the random number generating means for generating a numerical value and the pixel for which the random number value is not generated by the random number generating means, a value whose absolute value is the same as the value output by the random number generating means one pixel before and whose sign is inverted is generated. A sign reversing means, an amplitude controlling means for alternately changing the signal value generated by the random number generating means and the sign reversing means as a function of the signal value of the image inputting means, and the amplitude controlling means. An image comprising: an addition unit that adds the generated signal value to the signal value of the image input unit; and a processing unit that performs gradation conversion processing of the signal value obtained by the addition unit into n-bit data. processing Location. 5. The input mbit image information is nbit
In the image processing method of performing gradation conversion on the image information (m and n are integers and m> n) and outputting the image information, an image input step of inputting the image information of mbit, and a positive random number value every other pixel. A random number generation step of generating, a random number code control step of randomly converting the sign of the random number value generated in the random number generation step into positive or negative, a random number value of the random number code control step, a signal value of the image input step Amplitude control step of changing the ratio of the amplitude as a function of, in the pixel for which the random number value is not generated in the random number generation step, the value output by the amplitude control means and the absolute value is the same as the inverted value A sign inversion step of generating, an addition step of adding the signal value generated in the amplitude control step and the sign inversion step to the signal value of the image input step, and the signal value obtained in the addition step of nbit An image processing method characterized by having a process of tone conversion processing over data.