JP2006093750A - Image processing apparatus and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus for carrying out dither processing in real time and effectively utilizing a storage section for storing threshold value data. <P>SOLUTION: The image processing apparatus converts a gradation value of each pixel of an input image through the dither processing using a threshold value matrix, converts the resolution of the input image and provides an output of the converted image, and is configured to include: a threshold value memory 12 for storing threshold value data of a plurality of threshold value matrices; a read address control section 11 for reading a plurality of pixels of the threshold value data in a plurality of the threshold value matrices in response to the resolution of the outputted image; buffers 0 to 3 for temporarily storing the threshold value data of a plurality of the threshold value matrices by a plurality of pixels; buffers 4 to 7 for storing the threshold value data of a plurality of the threshold value matrices read from the buffers 0 to 3 by each one pixel; and first and second selectors 13, 14 for selectively outputting the threshold value data of a threshold value matrix in use from the buffers 4 to 7. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus and an image processing method for performing dither processing using a threshold matrix.

  As one form of image processing performed in an image processing apparatus, a dither method is known in which a gradation value of an original image is converted into a gradation value that can be output (expressed) by an image output apparatus and reproduced in a pseudo manner. . In the dither method, the gradation value of the output image is determined by comparing the gradation value of each pixel constituting the original image with threshold data arranged in a threshold matrix. An output image whose tone value is binary is called a binary dither method, and a multi-value tone is called a multi-value dither method.

  FIG. 8 is a schematic diagram showing a configuration example of a conventional image processing apparatus. In the figure, an address control unit 101 designates a threshold value storage memory address (hereinafter also simply referred to as “address”) for threshold value reading to the threshold value storage memory 102. The threshold storage memory 102 stores threshold data corresponding to each position (matrix element) of a threshold matrix used for dither processing. The comparison unit 103 compares the gradation value of each pixel of the input image data input thereto with the threshold value data read out from the threshold value storage memory 102 correspondingly, and based on the comparison result. Pixel data of the output image after gradation conversion is generated.

  First, threshold value data arranged in a threshold value matrix used in the process based on the dither method (dither process) is stored in the threshold value storage memory 102. In this case, it is known to store one threshold value data at one address in the threshold storage memory 102 (see, for example, Patent Document 1).

  When the dither processing is actually performed, the address control unit 101 sequentially designates addresses in order in synchronization with a clock having a predetermined frequency and sequentially reads the threshold data from the threshold storage memory 102, and inputs the read threshold data and input The gradation value of the image is compared with the comparison unit 103, and the gradation value of the output image is generated based on the comparison result. Thereby, in the systematic dither method, which is a typical binary dither method, for example, the original image is divided into blocks of 4 × 4 pixels or 8 × 8 pixels, and the gradation value of the input pixel is determined for each block. Is larger than the threshold value data at the corresponding matrix position, white (1), and if it is smaller, the input image is binarized.

Japanese Patent Laid-Open No. 4-205675 (FIG. 4)

  By the way, when the resolution of the input image (hereinafter also referred to as “input resolution”) and the resolution of the output image (hereinafter also referred to as “output resolution”) are the same, the number of input pixels and the number of output pixels are 1: 1. It becomes a relationship. Therefore, when performing dither processing, one input pixel is compared with one threshold value data. Therefore, dithering can be performed in real time in synchronization with the clock.

  However, when the output resolution is higher than the input resolution, or when the input image is dithered in units of blocks composed of a plurality of pixels, a plurality of threshold data to be compared with the gradation value of the input pixels by the comparison unit 103 is required. become. In such a case, in the method of storing one threshold value data in one address (threshold value storage memory area for one word) as in the above-described prior art, dither processing is performed in real time in accordance with the threshold value reading operation from the threshold value storage memory 102. Can no longer do.

  Further, when the resolution of an input image is converted and output, it may be necessary to support a plurality of output resolutions such as 2400 × 600 dpi and 1200 × 1200 dpi. In this case, since the number of threshold data to be used differs depending on the output resolution, there is a problem that when the output resolution is low, a threshold storage memory 102 that is not used is created.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an image processing apparatus and an image processing method that perform dither processing in real time and effectively use a storage unit that stores threshold data. .

  In order to achieve this object, the image processing apparatus of the present invention converts the gradation value of each pixel of the input image by dither processing using a threshold matrix, and converts the resolution of the input image and outputs the converted image. A threshold memory that stores threshold data of a plurality of threshold matrices, a reading unit that reads out the threshold data of the plurality of threshold matrices for a plurality of pixels according to the resolution of an image to be output; First temporary storage means for temporarily storing threshold data of the plurality of threshold matrixes, and threshold data of the plurality of threshold matrixes read from the first temporary storage means are stored for each pixel. A second temporary storage means; and a selection means for selectively outputting threshold data of the threshold matrix to be used from the second temporary storage means. There.

  Thus, according to the present invention, the threshold data of a plurality of threshold matrixes are read for a plurality of pixels in accordance with the resolution of the output image, and sequentially stored in the first primary storage unit and the second primary storage unit, It is assumed that threshold data of a plurality of threshold matrixes are stored for each pixel. Thereby, threshold data of a threshold matrix to be used can be selected according to the input image, and the number of screens to be used can be increased without increasing the memory and the primary storage means.

  The image processing apparatus may include a comparison unit that compares the threshold data selected by the selection unit with a gradation value of each pixel of the input pixel and outputs a comparison result.

  By comparing the selected threshold value data with the gradation value of each pixel of the input pixel and outputting the result, the gradation value of each pixel of the input image can be converted by dither processing using the threshold value matrix.

  The image processing method of the present invention is an image processing method for converting a gradation value of each pixel of an input image by dither processing using a threshold matrix and converting the resolution of the input image and outputting the converted image. Selecting threshold data of a plurality of threshold matrices for a plurality of pixels in accordance with the resolution of the image; storing threshold data of the plurality of threshold matrices in a storage unit for each pixel; and the threshold matrix to be used Selecting and outputting the threshold value data from the storage means.

  As described above, according to the present invention, the threshold data of a plurality of threshold matrices are read for a plurality of pixels in accordance with the resolution of the output image, and the threshold data of the plurality of threshold matrices are stored for each pixel. Thereby, threshold data of a threshold matrix to be used can be selected according to the input image, and the number of screens to be used can be increased without increasing the memory and the primary storage means.

  The present invention can perform dither processing in real time and can effectively use the memory.

  Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  First, the configuration of the present embodiment will be described with reference to FIG. In FIG. 1, a document 2 placed on a document table 1 is R (red) and G (green) by an image scanner including a color CCD sensor 3 via a scanning optical system including a light source and a scanning mirror. , B (blue) analog image signals. The analog image signals of R, G, and B read by the color CCD sensor 3 are converted into Y (yellow), M (magenta), C (cyan), and K (black) image images by the image processing unit 4. Image data of each color is sequentially output to ROS (Raster Output Scanner) 7C, 7M, 7Y, 7K of the forming units 5C, 5M, 5Y, 5K, and emitted from these ROS 7C, 7M, 7Y, 7K according to the image data. Laser beams are scanned and exposed on the surfaces of the respective photoconductive drums 6C, 6M, 6Y, and 6K to form electrostatic latent images. The electrostatic latent images formed on the photosensitive drums 6C, 6M, 6Y, and 6K are developed as toner images of respective colors Y, M, C, and K by the developing devices 8C, 8M, 8Y, and 8K, respectively.

  The configuration of the image processing unit 4 will be described with reference to FIG. An image processing unit 4 shown in FIG. 2 is a processing unit that performs dither processing on input image data, and can convert and output the resolution of the input image data. For example, the image processing unit 4 illustrated in FIG. 2 converts an input image having a resolution of 600 dpi × 600 dpi into an output image having a resolution of 1200 dpi × 2400 dpi or 1200 dpi × 1200 dpi.

  As shown in FIG. 2, the image processing unit 4 includes an address control unit 11, a threshold memory 12, buffers 0 to 3, buffers 4 to 7, a first selector 13, a second selector 14, and a comparator 15. And.

  The operation of the image processing unit 4 will be described with reference to the timing chart shown in FIG. In the timing chart shown in FIG. 3, when the page sync PS-i and the line sync LS-i sequentially rise in synchronization with the reference clock CLK, the rise timing of the line sync LS-i is used as a trigger for each pixel level of the input image. The gradation value data DATA-In [7: 0] is sequentially written in the buffers 0 to 3 every 1 clock CLK. When the address control unit 11 designates the address of the threshold memory 12, the threshold data of the designated address of the threshold memory 12 is recorded in the buffers 0 to 3, respectively. In this embodiment, threshold data for 8 pixels is read out in one clock and written in one of the buffers 0 to 3. That is, the threshold data for 8 pixels is written to the buffers 0 to 3 over 4 clocks (write signals of the buffers 0 to 3 shown in FIG. 3).

  The threshold data written to the buffers 0 to 3 is output to the buffers 4 to 7 in one clock (buffer 4, 5, 6, and 7 write signals shown in FIG. 3). At this time, the threshold data written to the buffer 0 is written to the first row of the buffers 4 to 7, and the threshold data written to the buffer 1 is written to the second row of the buffers 4 to 7. The threshold data written in the buffer 2 is written in the third row of the buffers 4-7, and the threshold data written in the buffer 3 is written in the fourth row of the buffers 4-7.

  The first selector 13 sequentially selects the buffers 4 to 7 and reads the threshold data written in the selected buffers 4 to 7 (buffer 4, 5, 6, and 7 read signals shown in FIG. 3). When one pixel of an input image is compared with the threshold data recorded in the buffer 4, the next one pixel is compared with the threshold data recorded in the buffer 5, and the next one pixel is sequentially compared with the threshold data recorded in the buffer 6. To go.

  The second selector 14 selects only the threshold data used for comparison by the comparison unit 15 from the threshold data of the buffers 4 to 7 selected by the first selector 13 and outputs the selected threshold data to the comparator 14. For example, when the resolution of the input image is 600 dpi × 600 dpi and the resolution is converted to 1200 dpi × 2400 dpi, one pixel is compared with 2 × 4 threshold data as shown in FIG. All of the threshold data written in is required. On the other hand, when the resolution of the input image is converted to 1200 dpi × 1200 dpi, one pixel is compared with a 2 × 2 threshold as shown in FIG. For this reason, the buffers 0 to 3 may use either the buffer (0, 1) or the buffer (2, 3), and the buffers 4 to 7 may use the upper half or the lower half. . FIG. 5 shows a buffer used when the resolution of the input image is converted to 1200 dpi × 1200 dpi.

  The comparator 15 performs dither processing by comparing the input image data and threshold data, and outputs the comparison result as output data.

  In the conventional image processing apparatus, the buffer usage method has not been changed in accordance with the resolution of the output image. Therefore, for example, in order to prepare two screens for characters, line drawings, and images, even when the resolution of the input image is converted to 1200 dpi × 1200 dpi, the threshold memory 12 and the buffer 0 are displayed as shown in FIG. -3 and buffers 4-7 had to be prepared according to the number of screens. Further, since the screens are recorded one by one in the threshold memory 12, if the number of screens is increased, the set size of each screen is determined by the size of the threshold memory 12.

  On the other hand, in this embodiment, when the resolution of the input image is converted to 1200 dpi × 1200 dpi, a plurality of screens are stored in the threshold memory 12 as shown in FIG. In this embodiment, two types of screens, screen 1 and screen 2, are recorded in the threshold memory 12. Under the control of the address control unit 1, the threshold data of the screen 1 is written in the buffer 0 and the buffer 1 and the threshold data of the screen 2 is sequentially written in the buffer 2 and the buffer 3 over 4 clocks. Then, all the values of the buffers 0 to 3 are written in the buffers 4 to 7 at a timing of once every four clocks, and the threshold data used by the screen 1 and the screen 2 is selected by the second selector. As a result, when the resolution of the input image is converted to 1200 dpi × 1200 dpi, the number of threshold memories 12 and buffers can be reduced as compared with the configuration shown in FIG. 6, and the screen can be changed without changing the configuration of the threshold memory 12. You can increase the number. Further, since the threshold memory 12 is sized to store a plurality of screens, the screen size can be freely set.

  The embodiment described above is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

It is a figure which shows the structure of an image processing apparatus. It is a block diagram which shows the structure of an image process part. It is a timing chart which shows the operation timing of an image processing part. It is a figure which shows the threshold value data required for resolution conversion. It is a figure which shows the buffer which is not used by the resolution to convert. It is a figure which shows the structure of the conventional image processing part. It is a figure which shows operation | movement of the image process part of a present Example. It is a figure which shows the structure of the conventional image processing part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Original stand 2 Original 3 Color CCD sensor 4 Image processing part 5C, 5M, 5Y, 5K Image forming unit 6C, 6M, 6Y, 6K Photosensitive drum 7C, 7M, 7Y, 7K ROS
8C, 8M, 8Y, 8K Developer 11 Address controller 12, 16 Threshold memory 13 First selector 14 Second selector 15 Comparator

Claims (3)

An image processing device that converts a gradation value of each pixel of an input image by dither processing using a threshold matrix, and converts and outputs the resolution of the input image,
A threshold memory for storing threshold data of a plurality of threshold matrices;
Reading means for reading out the threshold data of the plurality of threshold matrixes for a plurality of pixels according to the resolution of the image to be output;
First temporary storage means for temporarily storing threshold data of the plurality of threshold matrixes for the plurality of pixels;
Second temporary storage means for storing threshold data of the plurality of threshold matrixes read from the first temporary storage means for each pixel;
Selection means for selectively outputting threshold data of the threshold matrix to be used from the second temporary storage means;
An image processing apparatus comprising:   The image processing apparatus according to claim 1, further comprising a comparison unit that compares the threshold data selected by the selection unit with a gradation value of each pixel of the input pixel and outputs a comparison result. An image processing method for converting a gradation value of each pixel of an input image by dither processing using a threshold matrix, and converting and outputting the resolution of the input image,
Selecting a plurality of pixels of threshold data of a plurality of threshold matrices according to the resolution of the image to be output;
Storing threshold data of the plurality of threshold matrices in a storage unit for each pixel;
Selecting and outputting threshold data of the threshold matrix to be used from the storage means;
An image processing method comprising:

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