JP2003134338A - Method for converting binarized image data into multi- level one, image processing and forming apparatus, program, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for converting a binarized image data into a multi-level one whereby the improvement of the image quality having a high cost-performance can be performed by a simple processing, to provide an image processing and forming apparatuses using the same method, and further, to provide the program and computer- readable recording medium used for the same apparatuses. SOLUTION: In a multi-level processing portion 31, the binarized image data is converted into a multi-level one by extracting the binarized image data from each local region, by so regarding each local area as a picture element as to convert an original binarized image data into the image data having a first resolution lower than the resolution of the original binarized image data, and further, and by so applying to each converted picture element a multivalued dither matrix having the matrix size of a second resolution higher than the first resolution as to subject the converted image data to a multivalued dither processing. Also, the multi-level processing portion 31 is mounted on a digital-color composing machine 1, by providing the portion 31 in a color-picture processing apparatus 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for binarizing binary image data, an image processing apparatus and an image forming apparatus using the same, and a program and a computer-readable recording medium used therefor.

[0002]

2. Description of the Related Art Conventionally, a binary image has been used mainly in an image forming apparatus for holding and processing image data while suppressing memory consumption, and the binary image is multivalued. There is a way.

[0003] For example, in Japanese Patent No. 2878695, for image information that is expressed in pseudo gradation such as a dither image, the pseudo gradation image is converted from the pseudo gradation image while maintaining the gradation and sharpness of the pseudo gradation image. A method for estimating a multi-valued image is provided. This method requires a process of determining what kind of image the target pixel is included in,
Further, it is necessary to perform smoothing processing with different aperture sizes depending on the type of the image. Although the smoothing process is performed in parallel with a plurality of apertures, a line memory corresponding to the maximum aperture size and an extra process are always required, which is considered to increase the circuit scale.

Further, Japanese Patent Application Laid-Open No. 5-37782 provides a low-priced image forming apparatus capable of high-quality multi-gradation recording with a small-capacity image memory. In this image forming apparatus, a multi-valued image is created from a binary 8-color image signal, the multi-valued image is converted into a continuous tone image, and the subsequent processing is performed. When processing an image signal, it is necessary to have a part for determining whether it should be a binary image or a multi-valued image, and after that, it is necessary to make the binary image and the multi-valued image each a continuous tone separately. Although the amount of memory used is small, the amount of processing will increase and the circuit scale will increase accordingly.

As described above, in the conventional method, the processing is complicated, the circuit scale is large, and the image quality is not sufficiently improved.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a binary image data multi-valued method capable of improving image quality with high cost performance by simple processing, an image processing apparatus and an image forming apparatus using the method. An object is to provide an apparatus, a program used for the apparatus, and a computer-readable recording medium.

[0007]

SUMMARY OF THE INVENTION The present invention is a multi-valued method of binary image data, in which binary image data is extracted for each local area and each local area is regarded as one pixel. Is converted to a first resolution lower than the first resolution, and multi-valued dither processing is performed on each converted pixel using a multi-valued dither matrix having a matrix size of the second resolution higher than the first resolution. A multi-valued method of binary image data is characterized in that the binary image data is converted into multi-valued image data by performing the operation.

According to the present invention, the binary image data is not directly converted into the multi-valued image data having the same resolution, but is converted into the low-resolution image data once and then is converted into the multi-valued image data to obtain a smooth image. Tone reproduction is possible.

Further, in the present invention, the local area is 200 to
It is characterized in that it is a region equivalent to 300 μm square.

According to the invention, the local area is between 200 and 30
Since the area is equivalent to 0 μm square, when the printed image is viewed, human eyes average the area of about 300 μm square to judge the light and shade, so that multi-value quantization is performed by applying the human visual characteristic. Since it can be done, it can be converted into a multi-valued image that is not much different from the human eyes.

The present invention is also characterized in that the local region is a region close to a diamond. According to the present invention, since the local area is close to a rhombus, it is possible to perform image processing suitable for the human visual spatial frequency characteristic that the sensitivity in the direction of 45 degrees is lower than that in the horizontal and vertical directions.

The present invention is also characterized in that the multi-valued dither matrix has a mask shape close to a rhombus.

According to the present invention, since the multi-valued dither matrix has a mask shape close to a rhombus, the image processing suitable for the human visual spatial frequency characteristic that the sensitivity in the direction of 45 degrees is lower than that in the horizontal and vertical directions. It can be performed.

Further, according to the present invention, the multi-valued dither matrix has a plurality of layers corresponding to gradations, and the matrix coefficients arranged in each layer have a coefficient within a predetermined range of one layer. It is characterized in that the case where all of them are arranged inside and the case where the coefficients whose values are within a predetermined range are arranged over a plurality of layers are mixed.

According to the present invention, since the arrangement pattern of two types of matrix coefficients is mixed, the matrix characteristics are arranged such that the density characteristics are non-linear, so that the human eyes are required to reproduce a photographic image. The resulting photographic density characteristics are excellent, and gradation reproduction that is smooth to the human eye is possible.

Further, the present invention is a program for causing a computer to execute the multi-valued method of binary image data.

According to the present invention, the binary image data is not directly converted into the multi-valued image data of the same resolution, but is converted into the low-resolution image data and then converted into the multi-valued image data to obtain a smooth image. A computer can read and execute a multi-valued method of binary image data that enables tone reproduction, and this method can be general-purpose.

Further, the present invention is a computer-readable recording medium having the program recorded therein.

According to the present invention, the binary image data is not directly converted into the multi-valued image data of the same resolution, but is converted into the low-resolution image data once and then into the multi-valued image data to obtain a smooth image. It is possible to easily and easily provide a computer with a multivalued method of binary image data capable of reproducing tones.

Further, according to the present invention, the local area extracting means for extracting the binary image data for each local area and the means for converting each local area into one pixel and converting it into the first resolution lower than the resolution of the binary image. And for each converted pixel, the first
Multi-value dither processing is performed using a multi-value dither matrix having a matrix size of a second resolution higher than the resolution of 2
An image processing apparatus comprising: a multi-value conversion processing unit having a multi-value dither processing unit for converting value image data into multi-value image data.

According to the present invention, there is provided multi-valued processing means for converting binary image data into low-resolution image data once without converting directly into multi-valued image data having the same resolution. By providing the image processing apparatus, it is possible to provide an image processing apparatus capable of smooth gradation reproduction.

Further, according to the present invention, there is mounted an image input device for inputting an image, the image processing device, and an image output device for outputting the image processed by the image processing device. Is.

According to the present invention, by mounting the image processing device, smooth gradation reproduction is possible, so that an image forming device capable of outputting a high quality image can be provided. Further, since it can be realized by a simple method, the cost increase of the image forming apparatus can be suppressed.

[0024]

1 is a block diagram showing the configuration of a digital color multi-function peripheral 1 including a color image processing apparatus 20 according to an embodiment of the present invention. The color image processing device 20 is an image processing device that uses the multivalued method of binary image data according to the present invention.

The digital color multifunction device 1 includes a color image processing device 20 and a color image input device 10 connected to the color image processing device 20.
And a color image output device 40, and an external input interface unit 50 and an external output interface unit 60 which are external connection units. External input interface unit 50 and external output interface unit 6
Reference numeral 0 indicates, for example, an interface unit as a network printer via Ethernet (registered trademark) and an interface unit with a telephone line for transmitting / receiving facsimile.

The color image input device 10 is an image reading means, for example, a charge coupled device (CCD: Charge Coupl).
ed Device) is included in the scanner unit, and the reflected light image from the document is converted into RGB (R: red, G:
It is read as image data of analog signals of green, B: blue) and input to the color image processing device 20. The analog signal read by the color image input device 10 is subjected to various kinds of processing in the color image processing device 20, and CM
YK (C: cyan, M: magenta, Y: yellow, K:
It is output to the color image output device 40 as image data of a digital color signal of (black).

The color image processing apparatus 20 includes an A / D (analog / digital) conversion section 21 and a shading correction section 2.
2, input tone correction unit 23, area separation processing unit 24, color correction unit 25, black generation undercolor removal unit 26, spatial filter processing unit 2
7, an output gradation correction unit 28, a gradation reproduction processing unit 29, an image buffer 30, and a multi-valued processing unit 31.

The A / D converter 21 converts the RGB analog signals input from the color image input device 10 into digital signals. Shading correction unit 22
Is the digital RG sent from the A / D converter 21.
The B signal is subjected to processing for removing various distortions occurring in the illumination system, the imaging system and the imaging system of the color image input device 10.

The input tone correction unit 23 is an RGB signal (RG) from which various distortions have been removed by the shading correction unit 22.
The reflectance signal (B) is subjected to a process for adjusting the color balance and a process for converting it into a signal such as a density signal which can be easily handled by the image processing system employed in the color image processing apparatus 20.

The area separation processing section 24 includes an input gradation correction section 2.
On the basis of the RGB signals sent from the No. 3, each pixel in the input image is separated into a character area, a halftone dot area and a photographic area. Further, the area separation processing unit 24
Based on this separation result, an area identification signal indicating which area the pixel belongs to is output to the black generation undercolor removal section 26, the spatial filter processing section 27, and the gradation reproduction processing section 29, and the input gradation The input signal output from the correction unit 23 is directly output to the color correction unit 25 in the subsequent stage.

The color correction unit 25 converts input image data of RGB signals into output image data of CMY signals.

The black generation undercolor removal unit 26 is used for the CM after color correction.
A black generation process for generating a black (K) signal from three Y color signals and a lower color removal process for subtracting the K signal obtained by the black generation process from the original CMY signal to generate a new CMY signal are performed. Then, the CMY three-color signal is converted into a CMYK four-color signal.

As an example of the black generation processing, there is a method (general method) for generating black by skeleton black. In this method, the input / output characteristics of the skeleton curve are y
= F (x), input data is C, M, Y, output data is C ', M', Y ', K', UCR (Under Co
When the lor removal rate is α (0 <α <1), the black generation undercolor removal process is expressed by the following equation (1).

[0034]

[Equation 1]

The spatial filter processing unit 27 performs a spatial filter process by a digital filter on the image data of the CMYK signals input from the black generation and undercolor removal unit 26 based on the area identification signal to obtain a spatial frequency characteristic. The correction is performed to prevent blurring of the output image and deterioration of graininess. Similarly to the spatial filter processing unit 27, the tone reproduction processing unit 29 also performs predetermined processing on the image data of the CMYK signals based on the area identification signal.

For example, the image data separated into the character areas by the area separation processing unit 24 is high in the sharpness enhancement processing in the spatial filter processing by the spatial filter processing unit 27 in order to improve the reproducibility of black characters or color characters in particular. The frequency emphasis amount is increased. At the same time, in the gradation reproduction processing unit 29, binarization or multi-value conversion processing on a high resolution screen suitable for reproduction of high frequency is selected.

The image data separated into the halftone dot areas by the area separation processing section 24 is subjected to a low-pass filter processing for removing the input halftone dot component in the spatial filter processing section 27. After that, the output gradation correction unit 28
An output gradation correction process for converting a signal such as a density signal into a halftone dot area ratio, which is a characteristic value of the color image output device 40, is performed, and then the gradation reproduction processing unit 29 finally determines an image pixel. The gradation reproduction processing, that is, the halftone generation processing is performed so as to reproduce each gradation separately.

Further, the image data separated into the photographic area by the area separation processing section 24 is subjected to binarization or multi-value conversion processing on the screen with an emphasis on gradation reproducibility.

The image data which has been subjected to the above various processes is temporarily stored in a storage means (not shown), read at a predetermined timing, and input to the color image output device 40.

The color image output device 40 outputs image data onto a recording medium such as paper, and examples thereof include a color image output device using an electrophotographic system or an inkjet system, but are not particularly limited. Not a thing.

The gradation reproduction processing unit 29 performs binarization processing of multi-valued input image data, stores the result in the image buffer 30, reads it out when necessary, and multi-values processing unit 31. It is also possible to perform a multi-valued processing at and output to the color image output device 40. That is, the image data read from the color image input device 10 can be stored in the image buffer 30 while being subjected to the above-described image processing and output from the color image output device 40.

Here, the multi-value processing unit (multi-value processing means)
The multi-value quantization processing by 31 will be described. The multi-value conversion processing unit 31 converts the binary image data into multi-value image data using the multi-value conversion method for binary image data according to the present invention. Figure 2
FIG. 3 is a block diagram showing a configuration of a multi-value quantization processing unit 31 according to an embodiment of the present invention. The multi-value quantization processing unit 31 includes a local area extraction unit (local area extraction means) 310, a continuous tone conversion unit 311, and a multi-value dither processing unit 312.

First, the binary image data in the image buffer 30 is sequentially read out to the local area extraction unit 310.
The local region extraction unit 310 extracts a binary image for each local region, and the continuous tone conversion unit 311 regards each local region of the binary image as a continuous tone of one pixel and has a resolution lower than that of the binary image. Convert to continuous tone with a resolution of 1. The continuous tone conversion unit 311 is a unit that regards each local region as one pixel and converts it into a first resolution lower than the resolution of the binary image. A multi-value dither processing unit (multi-value dither processing means) 312 performs multi-value dither processing on each converted pixel by using a multi-value dither matrix having a matrix size of a second resolution higher than the first resolution. Then, the obtained multivalued output image data is output to the color image output device 40.

As described above, the binary image data is not directly converted into the multi-valued image data having the same resolution, but is first converted into the low-resolution image data and then converted into the multi-valued image data, whereby the smooth gradation is reproduced. Is possible.

FIG. 3 is a flow chart showing the flow of processing of the multi-value quantization processing section 31. In step s1, binary image data is read from the image buffer 30 and input to the local area extraction unit 310. The input method at this time is 1
Any input method may be used, such as each pixel, each line, or each plane. In step s2, the local area extraction unit 31
In step 0, the target pixel and a predetermined neighboring pixel are extracted, and it is determined in step s3 whether or not the data of the target pixel and the predetermined required neighboring pixel are input and the extraction is completed. If it is judged that the processing is not completed, the binary image data input (s1) is repeated, and if it is judged that the processing is completed,
In step s4, the continuous tone converting unit 311 obtains the average value of the pixel values of the region of the target pixel and the predetermined neighboring pixel determined in advance, and when that value is regarded as one pixel of the entire neighboring region including the target pixel Set as the pixel value of. Next, in step s5, the multi-value dither processing unit 312 performs multi-value dither processing using the multi-value dither matrix, and in step s6.
Output to the color image output device 40 as multi-valued image data. In step s7, it is determined whether or not the processing of all the image data is completed. If it is determined that the processing is not completed, the pixel of interest is moved to extract the data of its neighboring pixels (s2), and the processing is continued.

Here, regarding the multi-valued processing of a certain pixel of interest and its neighboring pixels in the embodiment of the present invention,
This will be specifically described with reference to FIGS. FIG. 4 is a diagram showing a part of the binary image, which shows 5 × 5 25 pixels. In FIG. 4, each binary image data is represented by 8 bits for convenience and is represented as 255 and 0. FIG. 5 is a diagram showing a result of averaging pixel values of local regions by the continuous tone conversion unit 311. FIG. 6 is a diagram showing a multi-valued dither matrix of 13 pixels × 4 layers. FIG. 7 shows the local area 2
It is a figure which shows the result of multi-value conversion of value image data. Figure 8
It is a figure which shows the method of setting a target pixel.

The local area extraction unit 310 extracts, from the 25 pixels shown in FIG. 4, 13 pixels having the pixel located at the center of the pixel surrounded by the thick line as the target pixel a as a neighboring area.

In the continuous tone conversion section 311, the extracted 1
The three pixels are regarded as one low-resolution pixel, the pixel values of the thirteen pixels are averaged, and the gradation value for one low-resolution pixel is determined. In the case of FIG. 4, since 255 × 6 ÷ 13 = 118 (rounded to one decimal place), this value is set as the pixel value of each pixel as shown in FIG. At this time, only the obtained average value is held as a representative value in the register of the color image processing device 20. This eliminates the need to hold pixel value data for each pixel, and efficient processing can be performed without wasting memory or registers.

The multi-value dither processing unit 312 performs multi-value dither processing on the previously extracted neighborhood area using the multi-value dither matrix shown in FIG. In FIG. 6, the layers are vertically connected, and the numerical value in each square of each layer is such that the upper side represents the threshold value t and the lower side represents the representative value T. When the gradation value obtained previously is equal to or larger than the threshold value of the mass of a certain layer A corresponding to the position of the pixel to be multivalued, and smaller than the threshold value of the mass of the same position of the layer B above it, The representative value of layer A is determined as the representative value of the square. For example, in the case of the pixel a in the middle of FIG. 5, the threshold value t of each layer is 1,65,13 in order from the lower layer.
The pixel value 118 is 65 or more 13
Since it is less than 0, the representative value after multi-value conversion is 69. When the other pixels are also multi-valued in the same manner as shown in FIG. When performing multi-valued conversion on each pixel in the neighboring area, the representative values held in the above-described registers are sequentially applied to the multi-valued dither matrix shown in FIG. 6 for processing. This saves you from wasting memory and registers
Efficient multi-value processing can be performed. Next, FIG.
As shown in, the target pixel is shifted so that the neighboring pixel of the target pixel a that has already been processed is included in the neighboring pixels of the next target pixel b by one pixel, and the process is performed until the multi-valued process of all pixels is completed. continue.

As shown in FIG. 6, the multi-valued dither matrix in this embodiment has multiple layers according to gradation. The matrix coefficient arranged in each layer, that is, the arrangement of the threshold value t, sets the threshold value t in each layer in order for the first layer and the second layer, and is in the range of 1 to 60 in the first layer. Threshold values are evenly arranged, and in the second layer, threshold values in the range of 65 to 125 are evenly arranged. Regarding the layers of the third layer and the fourth layer, a threshold value 130 is set for the third layer, a threshold value 135 is set for the fourth layer, a threshold value 140 is set for the third layer, a threshold value 145 is set for the fourth layer, and so on.
Thresholds in the range of 5 are arranged out of center over the two layers. That is, the matrix coefficients arranged in each layer have a case where the coefficients whose values are in a predetermined range are all arranged in one layer,
The case where the coefficients whose values are in the predetermined range are arranged over a plurality of layers is mixed.

As a result, in the multi-valued gradation data by this multi-valued dither matrix, the gradation value for 13 pixels is gradually increased as a whole when the pixel value is from 0 to less than 130, and 1
When it becomes 30 or more, the gradation value is increased from the center, and the gradation values around the center are gradually brightened. Therefore, when 13 pixels are collectively viewed, the gradation value does not simply increase, but
At first, the gradation value gradually increases overall, and from the middle, it becomes bright from the middle, and finally the gradation increases so that the entire 13 pixels become bright, so it can be regarded as a non-linear gradation characteristic. . As a result, it becomes possible to reduce the graininess of the highlight portion and to sufficiently reproduce the gradation in the high density portion. Therefore, when reproducing a photographic tone image, the photographic tone density characteristic looks good to the human eye, and it becomes possible to reproduce the gradation that the human eye feels smooth.

By providing the image forming apparatus with an image processing apparatus capable of realizing such smooth gradation reproduction, it is possible to output a high quality image. Further, since it can be realized by a simple method, the cost increase of the image forming apparatus can be suppressed.

In this embodiment, the processing is performed for every 13 pixels, but it is preferable to change the number of pixels according to the output resolution. According to human visual characteristics, when viewing a printed image, the human eye determines the shading by averaging an area of approximately 300 μm square. In addition, 600 dpi (dot pe
In the case of an output equivalent to r inch), it has been empirically proved that a maximum of about 5 pixels is required in each of the vertical and horizontal directions, considering the reproducibility of the character image in the rhombus matrix.
13 pixels in case of output equivalent to 600 dpi (max.
The diamond-shaped matrix of pixels is a region corresponding to a little over 200 μm square. Therefore, the local area to be processed is 20
It is preferable to set the area corresponding to 0 to 300 μm square,
In case of output equivalent to 600 dpi, 13 pixels (maximum of 5 pixels in the vertical and horizontal directions)
25 pixels from the diamond-shaped matrix of pixels (maximum of 7 pixels vertically and horizontally)
A matrix size of about a diamond-shaped matrix of pixels,
In the case of an output equivalent to 1200 dpi, it is necessary to perform processing with a matrix size of about 61 pixels (a diamond-shaped matrix with a maximum of 11 pixels in the vertical and horizontal directions) to 85 pixels (a diamond-shaped matrix with a maximum of 13 pixels in the vertical and horizontal directions). By doing so, it is possible to convert into a multi-valued image that is not much different from that seen by human eyes.

Further, in the present embodiment, the local area in which the multi-valued processing is performed by regarding one pixel is an area close to a diamond. This applies the fact that the spatial frequency characteristics of human vision are inferior in the direction of 45 degrees compared to the horizontal and vertical directions, and image processing suitable for human visual characteristics can be performed by making a local region close to a rhombus. It can be carried out.

The image data that has been subjected to such multi-value conversion processing by the multi-value conversion processing unit 31 may be output from the color image output device 40, and may be output via the external output interface unit 60 to the external output interface unit. It may be output from an image forming apparatus connected to 60 and capable of expressing a multivalued image.

Further, in the present embodiment, the multi-value processing unit 31 may be realized by a dedicated LSI (Large Scale Integrated circuit), and a computer-readable recording medium in which a program to be executed by a computer is recorded is described above. It is also possible to record a program for performing the multivalued method of the binary image data and to make the computer execute the multivalued method of the binary image data. As a result, the computer can read and execute the multi-valued method of the binary image data, the method can be general-purpose, and a program for performing the multi-valued method of the binary image data can be provided. The recorded recording medium can be provided easily and freely.

In the present embodiment, the recording medium is a memory (not shown) such as ROM (Read Only Memor) because the processing is performed by the microcomputer.
y) itself may be a program medium,
Further, a program reading device is provided as an external storage device,
It may be a program medium that can be read by inserting a recording medium therein.

In any case, the stored program may be accessed and executed by the microprocessor, or the program may be read out and downloaded to the program storage area of the microcomputer for execution. May be used. It is assumed that this download program is stored in the main body device in advance.

Here, the program medium is a recording medium which can be separated from the main body, and is a tape system such as a magnetic tape or a cassette tape, a magnetic disk such as a flexible disk or a hard disk, and a CD-RO.
M (Compact Disk-Read Only Memory), MO (Magneto
Optical) disk, MD (Mini Disk), DVD (Digi
disk system such as optical disk such as tal versatile disk), IC (Integrated Circuit) including memory card
Cards such as cards and optical cards, or mask R
OM, EPROM (Erasable Programmable Read Only)
Memory), EEPROM (Electrically Erasable Progr
It may be a medium that holds a program fixedly, including a semiconductor memory such as an ammable read only memory) and a flash ROM.

Further, in the present embodiment, since the system configuration is such that a communication network including the Internet can be connected, it may be a medium that carries the program fluidly so as to download the program from the communication network. When the program is downloaded from the communication network in this way, the program for downloading may be stored in the main body device in advance, or may be installed from another recording medium.

The recording medium is a digital color compound machine 1.
Also, it is possible to execute the above-mentioned image processing method by being read by a program reading device provided in a computer system.

The computer system is an image input device such as a flatbed scanner, a film scanner or a digital camera, a computer in which various processes such as the above-described image processing method are performed by loading a predetermined program, a process of the computer. It is configured to include an image display device such as a CRT (Cathode Ray Tube) display and a liquid crystal display for displaying the result, and a printer for outputting the processing result of the computer onto paper or the like. Further, a modem or the like is provided as a communication means for connecting to a server or the like via a network.

[0063]

As described above, according to the present invention, in the multi-valued method of binary image data, the binary image data is not directly converted into the multi-valued image data of the same resolution, but the low resolution image data is once converted. By converting to multi-valued image data after converting to, smooth tone reproduction is possible.

Further, according to the present invention, by selecting a region having a specific area as the local region of the multi-valued processing, it is possible to perform multi-valued processing applying human visual characteristics.
It can be converted into a multi-valued image that is not much different from that seen by the human eye.

Further, according to the present invention, a region close to a rhombus is selected as the local region of the multi-value quantization process, and a mask shape close to a rhombus is selected as the form of the multi-valued dither matrix. It is possible to perform image processing suitable for the spatial frequency characteristic of human vision that the sensitivity in the 45-degree direction is poor.

Further, according to the present invention, since the matrix characteristics of the multi-valued dither matrix are mixed with the specific two types of array patterns, the matrix characteristics are arranged so that the density characteristics are non-linear, and therefore, the photo-like appearance is obtained. When an image is reproduced, it has a photographic density characteristic that looks good to the human eye, and gradation reproduction that feels smooth to the human eye is possible.

Further, according to the present invention, the computer can read and execute the program for executing the multi-valued method of the binary image data, and the method can be general-purpose. Further, by recording this program on a recording medium, it is possible to provide the computer with the multi-valued method of the binary image data easily and freely.

Further, according to the present invention, it is possible to provide an image processing apparatus capable of smooth gradation reproduction by using the binary image data multi-valued method. Further, by mounting this image processing device, it is possible to output a high quality image, and it is possible to provide an image forming device in which the cost increase is suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a digital color multi-function peripheral 1 including a color image processing device 20 according to an embodiment of the present invention.

FIG. 2 is a multi-value quantization processing unit 3 according to the embodiment of the present invention.
2 is a block diagram showing a configuration of No. 1.

FIG. 3 is a flowchart showing a processing flow of a multi-value quantization processing section 31.

FIG. 4 is a diagram showing a part of a binary image.

FIG. 5 is a diagram showing a result of averaging pixel values in a local area by a continuous tone conversion unit 311.

FIG. 6 is a diagram showing a multi-valued dither matrix of 13 pixels × 4 layers.

FIG. 7 is a diagram showing a result of multi-value conversion of binary image data of a local area.

FIG. 8 is a diagram showing a method of setting a target pixel.

[Explanation of symbols]

1 Digital color compound machine 10 Color image input device 20 Color image processor 21 A / D converter 22 Shading correction section 23 Input tone correction section 24 area separation processing unit 25 color correction section 26 Black generation undercolor removal unit 27 Spatial filter processing unit 28 Output gradation correction unit 29 gradation reproduction processing unit 30 image buffer 31 Multi-value processing unit 40 color image output device 50 External input interface 60 External output interface 310 Local Area Extraction Unit 311 Continuous tone converter 312 Multi-level dither processing unit

Continued front page    F term (reference) 2C262 AA24 AB13 AC07 BB01 BB06                       BB22 BB25 DA16 EA04                 5B057 CA01 CA02 CA08 CA12 CA16                       CB01 CB02 CB06 CB12 CB16                       CC01 CE11 CE13 CH07 CH08                 5C077 LL17 MP01 MP08 NN02 NN08                       PP46 PP68 PQ12 PQ18 RR09                       SS02 TT02 TT06

Claims (9)

[Claims] 1. A multi-valued method of binary image data, comprising: extracting the binary image data for each local region, regarding each local region as one pixel, and lowering the resolution of the binary image. Binary image data is obtained by performing multi-value dither processing on each converted pixel by using a multi-value dither matrix having a matrix size of a second resolution higher than the first resolution. Is converted into multi-valued image data, and a multi-valued method of binary image data. 2. The local region according to claim 1, wherein the local region is a region corresponding to a square of 200 to 300 μm.
Value image data multi-valued method. 3. The multivalued method of binary image data according to claim 1, wherein the local area is an area close to a rhombus. 4. The multivalued method for binary image data according to claim 1, wherein the multivalued dither matrix has a mask shape close to a diamond shape. 5. The multi-valued dither matrix has multiple layers according to gradation, and matrix coefficients arranged in each layer are all coefficients within a predetermined range of values within one layer. 5. The binary image data according to any one of claims 1 to 4, wherein a case where the binary image data is arranged and a case where coefficients having a predetermined value range are arranged over a plurality of layers are mixed. Valuation method. 6. A program for causing a computer to execute the binary image data multivalued method according to claim 1. Description: 7. A computer-readable recording medium on which the program according to claim 6 is recorded. 8. A local area extracting means for extracting binary image data for each local area, a means for converting each local area into one pixel and converting the local area into a first resolution lower than the resolution of the binary image, A multivalued dither process is performed on each of the generated pixels using a multivalued dither matrix having a matrix size of a second resolution higher than the first resolution, and multivalued image data is converted into multivalued image data. An image processing apparatus comprising multi-valued processing means having value dither processing means. 9. An image forming device, comprising: an image input device for inputting an image; an image processing device according to claim 8; and an image output device for outputting an image processed by the image processing device. apparatus.