JP2009212692A - Image processor and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor and image forming apparatus applying synthetic processing that prevents deterioration in the image quality with respect to image data of different resolution. <P>SOLUTION: An upsampling module 314 transmits a notification signal to a DMA (Direct Memory Access) 311 for a high-resolution line, when a DMA 313 for a low resolution line stores a background layer read from a main memory 7 into a line buffer. The DMA 311 for a high-resolution line acquiring the notification signal reads a foreground layer 71 from the main memory 7, to transmit the foreground layer to a delay circuit 312, and transmits a synchronization signal to the upsampling module 314. The upsampling module 314 for acquiring the synchronization signal performs upsampling processing on the foreground layer 72 stored in the line buffer and transmits the upsampled background layer 72 to a synthesis circuit 310. The delay circuit 312 stores the acquired foreground layer 71 for a prescribed time and subsequently transmits the acquired foreground to the synthesis circuit 310. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image processing apparatus that synthesizes a plurality of image data having different resolutions, and an image forming apparatus including the image processing apparatus.

In recent years, digital image systems have made remarkable progress, and the construction of digital image processing technology is progressing. In the field of copiers and multi-function peripherals using the electrophotographic system or ink jet system, for example, documents (originals, images) read by a scanner are stored as electronic data, the stored document files are managed, It is required to use. In addition, the document file is compressed and transmitted by e-mail.
In general, since an image (scanned image) read by a scanner has a large file size, an image compression technique is indispensable when storing or transmitting a scanned image.

  One compression technique for realizing a high compression ratio is an image compression technique based on layer separation. The image compression technique based on layer separation is to separate an image into a foreground layer and a background layer, compress the image using a compression technique suitable for each layer, and finally generate a highly compressed image. The foreground layer is a layer representing characters and line drawings, and is compressed using lossless compression techniques such as JBIG (Joint Bi-level Image experts Group), MMR (Modified Modified Read code), and LZW (Lempel Ziv Welch). It is common. On the other hand, the background layer is a layer representing image content other than characters and line drawings, and is generally compressed using an irreversible compression technique such as JPEG (Joint Photographic Experts Group).

When developing image data compressed using such an image compression technique based on layer separation, it is necessary to consider that the foreground layer resolution and the background layer resolution are different. When a high resolution layer and a low resolution layer are simply combined, there is a problem that, for example, the low resolution layer becomes rough.
In addition, the process of developing image data compressed using an image compression technique based on layer separation can be executed by software when there is no need to consider the processing speed. When image data stored in a storage unit such as the above is expanded in a multi-function peripheral, real-time processing is required. Therefore, it is more realistic that the image data is executed by hardware.

A technique for synthesizing image data having different resolutions depending on hardware is disclosed in Patent Document 1, for example. The technique disclosed in Patent Document 1 is a technique for synthesizing a high-resolution character image and a low-resolution photographic image by hardware, and when synthesizing a high-resolution character image and a low-resolution photographic image. A contour designating circuit and a LUT (Look Up Table) are prepared, and photographic image data with a resolution equivalent to 100 dpi (dot per inch) is converted into photographic image data with a resolution equivalent to 400 dpi and synthesized. With such a configuration, it is possible to solve the problem that a low-resolution photographic layer becomes rough when a high-resolution character image and a low-resolution photographic image are simply combined.
Japanese Patent Laid-Open No. 4-14372

  However, the above-described technology requires a memory for image of character / line drawing (image memory) and a memory for photographic image (image memory) separately from the hard disk and main memory, and the image data has a high resolution. As a result, there is a problem that an image memory having a large capacity is required. Further, in the above-described technology, an outline designating circuit and an LUT are used in order to improve the image quality as much as possible when combining a high-resolution character image and a low-resolution photographic image. The configuration of the apparatus becomes complicated and also causes an increase in cost.

  The present invention has been made in view of such circumstances, and an object of the present invention is to reduce the amount of memory and prevent deterioration in image quality of image data with different resolutions without providing a complicated configuration. Another object of the present invention is to provide an image processing apparatus capable of executing the combined processing at a high speed and an image forming apparatus including the image processing apparatus.

  An image processing apparatus according to the present invention comprises: a storage unit that stores image data; and a plurality of image data in an image processing apparatus that combines image data having a first resolution and image data having a second resolution lower than the first resolution. Synthesizing means for synthesizing the image data, a first reading unit for reading image data of the first resolution from the storage means, and holding the image data of the first resolution read by the first reading unit for a predetermined time and then sending it to the synthesizing means And a second reading unit that reads out the second resolution image data from the storage unit, and performs conversion processing to the first resolution on the second resolution image data read out by the second reading unit. A resolution converter, and the synthesizing unit is configured to synthesize the image data sent from the delay circuit and the image data converted by the resolution converter. And wherein the Rukoto.

  According to the present invention, when image data having different resolutions are combined, the low resolution (second resolution) image data is subjected to the conversion processing to the high resolution (first resolution), and then both are combined. Thus, it is possible to solve the problem that the low-resolution image data becomes rough when the image data with different resolutions are simply combined. Further, according to the present invention, the low resolution image data read from the storage means is converted to high resolution, and the high resolution image data read from the storage means is held for a predetermined time, thereby reducing the low resolution image data. It is possible to synchronize the timing for sending the resolution image data to the synthesizing means and the timing for sending the high-resolution image data to the synthesizing means.

  Further, the image processing apparatus includes a reading unit (second reading unit) that reads low-resolution image data from the storage unit, and a resolution conversion unit that performs conversion processing of high-resolution on low-resolution image data. Since the reading process and the conversion process to the high resolution can be executed in parallel, the processing speed can be increased even when the low resolution image data is divided into a plurality of pieces and stored in the storage unit. It becomes possible.

  In the image processing apparatus according to the present invention, the resolution conversion unit stores a line buffer that stores image data of the second resolution read by the second reading unit, and the image data stored in the line buffer. A conversion processing unit that performs conversion processing to one resolution, detection means for detecting that image data of the second resolution is stored in the line buffer, and that the detection means stores image data in the line buffer. And a means for sending a notification signal indicating that image data can be read from the line buffer to the first reading unit when detected, and the first reading unit acquires the notification signal. The first resolution image data is read from the storage means and sent to the delay circuit, and the image data is sent to the delay circuit. When the processing is started, it has means for sending a synchronization signal to the resolution conversion unit. When the resolution conversion unit obtains the synchronization signal, the image data stored in the line buffer is sent to the conversion processing unit. It is characterized by starting the process to send out.

  In the image processing apparatus of the present invention, a resolution conversion unit that performs conversion processing to high resolution on low resolution image data read from the storage means includes a line buffer that stores low resolution image data, and the line buffer. A conversion processing unit for converting the stored image data to high resolution. When it is detected that low resolution image data is stored in the line buffer, the image data is read from the line buffer. A notification signal indicating that reading is possible is transmitted to a reading unit (first reading unit) that reads high-resolution image data from the storage unit. When the first reading unit acquires the notification signal, the first reading unit starts reading the high-resolution image data from the storage unit, sequentially sends the read high-resolution image data to the delay circuit, and sends the image data to the delay circuit. When transmission is started, a synchronization signal is transmitted to the resolution conversion unit. When the resolution conversion unit acquires the synchronization signal, it starts sending low-resolution image data stored in the line buffer to the conversion processing unit.

  According to the present invention, with the configuration described above, when the image data can be read from the line buffer because the image data is stored in the line buffer, the notification signal is notified from the resolution conversion unit to the first reading unit. Is done. Based on the acquisition of the notification signal, the first reading unit reads high-resolution image data from the storage unit and starts sending it to the delay circuit, and also sends a synchronization signal to the resolution conversion unit. The resolution conversion unit starts sending the low-resolution image data stored in the line buffer to the conversion processing unit based on the acquisition of the synchronization signal. Since the delay circuit holds the image data for a predetermined time based on the time required for the processing performed by the resolution conversion unit (conversion processing unit), the output timing of the image data from the resolution conversion unit (conversion processing unit) and the delay circuit It is possible to synchronize the output timing of image data.

  In the image processing apparatus according to the present invention, the resolution conversion unit includes a plurality of the line buffers, and reads the second resolution image data stored in one of the line buffers and performs the conversion. A process of sending to the processing unit and a process of storing the image data of the second resolution read by the second reading unit in another line buffer are performed in parallel.

  According to the present invention, by providing a plurality of line buffers, a process of reading out image data from the line buffer storing the image data and sending it to the conversion processing unit; Processing stored in the buffer can be performed in parallel, and the processing speed can be further improved.

  An image forming apparatus according to the present invention includes the above-described image processing apparatus and an image forming unit that forms an output image based on image data processed by the image processing apparatus.

  In the present invention, when synthesizing image data of different resolutions, the low resolution image data is synthesized after the conversion processing to high resolution is performed, so that deterioration of image quality can be prevented. it can. In addition, when synthesizing image data with different resolutions, the timing of sending the respective image data to the synthesizing means can be synchronized. Therefore, as in the technique disclosed in Patent Document 1 described above, the hard disk and the main It is not necessary to provide an image memory separately from the memory. Therefore, since processing can be performed using only a general-purpose main memory, an increase in the amount of memory can be avoided.

  Therefore, for example, image data compressed using an image compression technique based on layer separation represented by MRC (Mixed Raster Content) can be developed at high speed using a memory with a small memory amount. In addition, since the low-resolution image data read processing from the storage means and the conversion processing to the high resolution can be executed in parallel, the low-resolution image data is stored in the storage means in a plurality of parts Even so, the processing speed can be increased.

  In the present invention, when synthesizing image data of different resolutions, the output timing to the synthesizing means of the low resolution image data subjected to the conversion processing to the high resolution, and the high timing read from the storage means. Since it is possible to synchronize the output timing of the resolution image data to the synthesizing means, an image memory is provided separately from the hard disk and the main memory, as in the technique disclosed in Patent Document 1 described above. It is not necessary, and no contour designating circuit and LUT are necessary. Therefore, it is possible to prevent the device configuration from becoming complicated and to avoid an increase in cost.

  In the present invention, the process of reading the image data from the line buffer storing the image data and sending it to the conversion processing unit, and the process of storing the image data read from the storage means in another line buffer Since the processing can be performed in parallel, the processing speed can be further improved.

  In the present invention, the image forming apparatus is provided with a configuration capable of performing high-speed synthesis processing that prevents image quality deterioration on image data having different resolutions without providing a complicated configuration as described above. be able to. Therefore, when an image based on image data compressed using an image compression technique based on layer separation is output to, for example, a recording sheet, high-speed processing is possible while maintaining image quality.

  Hereinafter, the present invention will be described with reference to the drawings illustrating embodiments. FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus 100 including an image processing apparatus according to the present invention. An image forming apparatus 100 (for example, a digital color multifunction peripheral) includes a color image input apparatus 1, a color image processing apparatus 2 (image processing apparatus), a color image output apparatus 3 as an image forming unit, and a transmission apparatus including a modem and a network card. 5. An operation panel 4 for performing various operations is provided.

  The image forming apparatus 100 also includes storage means such as a hard disk (hereinafter, representatively referred to as the hard disk 6 (see FIG. 6)), a main memory 7 (see FIGS. 6 and 7), and the like. The hard disk 6 and the main memory 7 may be provided in the color image processing apparatus 2 or may be provided outside the color image processing apparatus 2.

  Image data of RGB (R: red, G: green, B: blue) analog signals obtained by reading a document with the color image input device 1 is output to the color image processing device 2, and the color image processing device 2. Then, a predetermined process is performed and output to the color image output device 3 as a digital color signal of CMYK (C: cyan, M: magenta, Y: yellow, K: black).

  The color image input device 1 is, for example, a scanner including a CCD (Charged Coupled Device), reads a reflected light image from a document image as an RGB analog signal, and outputs the read RGB signal to the color image processing device 2. . In the present embodiment, the color image input apparatus 1 reads image data with a resolution of 600 dpi, for example. The color image output device 3 is a printer such as an electrophotographic system or an inkjet system that outputs image data of a document image onto a recording sheet. The color image output device 3 may be an image display device such as a CRT display or a liquid crystal display.

  The color image processing apparatus 2 includes an A / D conversion unit 20, a shading correction unit 21, an input tone correction unit 22, a compression processing unit 23, a region separation processing unit 24, a color correction unit 25, a black generation and under color removal unit 26, A spatial filter processing unit 27, an output gradation correction unit 28, a gradation reproduction processing unit 29, a development processing unit 30, a synthesis processing unit 31, a CPU (Central Processing Unit) that controls the operation of each of these hardware units, and the like. It is configured by an ASIC (Application Specific Integrated Circuit) or the like.

  When the analog signal read by the color image input device 1 is subjected to compression processing by the compression processing unit 23, the A / D conversion unit 20, the shading correction unit 21, and the input tone correction are performed in the color image processing device 2. Are sent in the order of the unit 22 and the compression processing unit 23, subjected to compression processing by the compression processing unit 23, and then stored in the hard disk 6 as compressed image data.

  When the analog signal read by the color image input device 1 is output by the color image output device 3 without being subjected to compression processing by the compression processing unit 23, the A / D is transmitted through the color image processing device 2. Conversion unit 20, shading correction unit 21, input tone correction unit 22, compression processing unit 23, region separation processing unit 24, color correction unit 25, black generation and under color removal unit 26, spatial filter processing unit 27, output tone correction The image data is sent to the color image output device 3 as a stream.

  In addition, when the image data (compressed image data) compressed by the compression processing unit 23 and stored in the hard disk 6 is output by the color image output device 3, a decompression processing unit 30, a composition processing unit 31, an area separation process Unit 24, color correction unit 25, black generation and under color removal unit 26, spatial filter processing unit 27, output gradation correction unit 28, and gradation reproduction processing unit 29 are sent in this order, and output as a stream to the color image output device 3 The

  The A / D (analog / digital) converter 20 converts the RGB signal input from the color image input device 1 into, for example, a 10-bit digital signal, and outputs the converted RGB signal to the shading correction unit 21. .

  The shading correction unit 21 performs a correction process for removing various distortions generated in the illumination system, the imaging system, the imaging system, and the like of the color image input apparatus 1 on the input RGB signal, and the corrected RGB signal is converted into a corrected RGB signal. Output to the input tone correction unit 22.

  The input tone correction unit 22 adjusts the color balance of the RGB signal (RGB reflectivity signal) from which various distortions have been removed by the shading correction unit 21 and at the same time provides the color image processing apparatus 2 with a density signal and the like. The signal is converted into a signal that can be easily handled by the image processing system employed. The input tone correction unit 22 performs image quality adjustment processing such as removal of background density or contrast, and outputs the processed RGB signal to the compression processing unit 23.

  The compression processing unit 23 performs a compression process on the RGB signal input from the input tone correction unit 22 in accordance with control from the CPU based on an operation mode designated by the user via the operation panel 4 and the like. The compressed image data is stored in the hard disk 6. When the CPU is not instructed to execute the compression process, the compression processing unit 23 outputs the RGB signal input from the input tone correction unit 22 to the subsequent region separation processing unit 24 as it is.

  Note that the case where the compression processing unit 23 performs the compression process means that, for example, the user sends a scan to e-mail mode (image data read from the document by the color image input device 1 by e-mail) via the operation panel 4. Mode) is designated, and a filing mode in which image data read by the color image input apparatus 1 is stored in the hard disk 6 as a document file (electronic data) may be designated.

  The compressed image data stored in the hard disk 6 is read from the hard disk 6 and attached to an e-mail when the scan to e-mail mode is designated by the user via the operation panel 4, for example. It is transmitted to the transmission destination via the transmission device 5. The compressed image data stored in the hard disk 6 is read from the hard disk 6 and output to the expansion processing unit 30 when, for example, an image output to a recording sheet is designated by the user via the operation panel 4. .

  The compression processing unit 23 according to the present embodiment is configured to perform compression processing using an image compression technique based on layer separation, and separates image data (RGB signals) into a foreground layer and a background layer. Since compression processing is performed for each layer, two pieces of compressed image data are generated. Note that the compression processing performed by the compression processing unit 23 and a more detailed configuration of the compression processing unit 23 will be described later with reference to FIGS.

  The decompression processing unit 30 reads the compressed image data stored in the hard disk 6 and performs decompression processing, and outputs the decompressed image data (RGB signal) to the subsequent composition processing unit 31. Specifically, for example, when a target document file is selected from the user via the operation panel 4 in order to output the compressed image data stored in the hard disk 6 to the recording paper by the filing function, the expansion process is performed. The unit 30 reads the selected document file from the hard disk 6, performs expansion processing, and stores it in the main memory 7. A more detailed configuration of the expansion processing unit 30 will be described later with reference to FIG.

  The composition processing unit 31 synthesizes a plurality of image data having different resolutions developed by the development processing unit 30. Note that the composition processing unit 31 up-samples image data having a lower resolution among image data having different resolutions (hereinafter referred to as low-resolution image data) to thereby obtain image data having a higher resolution (hereinafter referred to as “lower-resolution image data”). Conversion processing to a resolution (high resolution) (referred to as high resolution image data) is performed, and the image data converted to high resolution and the high resolution image data are synthesized in synchronism. The synthesis processing unit 31 outputs the synthesized image data (RGB signal) to the subsequent region separation processing unit 24. A more detailed configuration of the composition processing unit 31 will be described later with reference to FIG.

  Based on the RGB signal input from the compression processing unit 23 or the composition processing unit 31, the region separation processing unit 24 belongs to each of the pixels in the input image as a character region, a dot region, a photographic region, or the like. And each pixel is separated. Based on the separation result, the region separation processing unit 24 outputs a region identification signal indicating to which region each pixel belongs to the black generation and under color removal unit 26, the spatial filter processing unit 27, and the gradation reproduction processing unit 29. To do. The region separation processing unit 24 outputs the input RGB signal as it is to the subsequent color correction unit 25.

  The color correction unit 25 converts the input RGB signal into a CMY color space, performs color correction in accordance with the characteristics of the color image output device 3, and outputs the corrected CMY signal to the black generation and under color removal unit 26. To do. Specifically, the color correction unit 25 performs a process of removing color turbidity based on the spectral characteristics of CMY color materials including unnecessary absorption components in order to realize color reproduction fidelity.

  The black generation and under color removal unit 26 generates a K (black) signal based on the CMY signal input from the color correction unit 25 in accordance with each region indicated by the region identification signal input from the region separation processing unit 24. In addition, a black generation process is performed, and a KMY signal is subtracted from the input CMY signal to generate a new CMY signal. Then, the generated CMYK signal is output to the spatial filter processing unit 27.

  An example of black generation processing in the black generation and under color removal unit 26 will be described. For example, in the process of generating black using skeleton black, the input / output characteristic of the skeleton curve is y = f (x), the input data is C, M, Y, and the output data is C ′, M ′. , Y ′, K ′ and the UCR (Under Color Removal) rate is α (0 <α <1), the data output by the black generation and under color removal processing is K ′ = f {min (C, M, Y)}, C ′ = C−αK ′, M ′ = M−αK ′, and Y ′ = Y−αK ′.

  The spatial filter processing unit 27 performs spatial filter processing on the CMYK signal input from the black generation and under color removal unit 26 using a digital filter based on the region identification signal input from the region separation processing unit 24. As a result, the spatial frequency characteristics of the image data are corrected, and blurring of the output image in the color image output device 3 or deterioration of graininess is prevented. For example, the spatial filter processing unit 27 performs sharp enhancement processing on the region separated into character regions by the region separation processing unit 24 to enhance the reproducibility of black characters or color characters, and emphasizes high frequency components. The spatial filter processing unit 27 performs low-pass filter processing for removing the input halftone component on the region separated into the halftone dot region by the region separation processing unit 24. The spatial filter processing unit 27 outputs the processed CMYK signal to the output tone correction unit 28.

  The output gradation correction unit 28 performs an output gradation correction process for converting the CMYK signal input from the spatial filter processing unit 27 into a halftone dot area ratio that is a characteristic value of the color image output device 3, The CMYK signal after the tone correction processing is output to the gradation reproduction processing unit 29.

  The gradation reproduction processing unit 29 performs predetermined processing on the CMYK signal input from the output gradation correction unit 28 based on the region identification signal input from the region separation processing unit 24. For example, the tone reproduction processing unit 29 performs binarization processing or the like so as to be suitable for reproduction of high-frequency components in the color image output device 3 in order to improve the reproducibility of the area separated into character areas, particularly black characters or color characters. Multi-value processing is performed.

  In addition, the gradation reproduction processing unit 29 performs gradation reproduction processing so that the region separated by the halftone dot region in the region separation processing unit 24 can be finally separated into pixels and the respective gradations can be reproduced. (Halftone generation) is performed. Further, the gradation reproduction processing unit 29 performs binarization processing or multi-value quantization processing on the region separated into the photographic regions by the region separation processing unit 24 so as to be suitable for the gradation reproducibility in the color image output device 3. .

  The color image processing apparatus 2 temporarily stores the image data (CMYK signal) processed by the gradation reproduction processing unit 29 in a storage unit (not shown), and stores the image data in the storage unit at a predetermined timing for image formation. And the read image data is output to the color image output device 3. These controls are performed, for example, by a CPU (not shown).

  The operation panel 4 includes, for example, a display unit configured with a liquid crystal display and the like, and an operation unit configured with a setting button and a numeric keypad for setting the operation mode of the image forming apparatus 100. Based on the information, the operations of the color image input device 1, the color image processing device 2, and the color image output device 3 are controlled.

  The image forming apparatus 100 according to the present embodiment performs image compression processing based on layer separation typified by MRC on the image data acquired by the color image input device 1 reading a document. Compressed image data compressed at a high compression rate can be generated. As a result, it is possible to reduce the amount of image data to be stored as a document file and the amount of image data to be transmitted by being attached to an e-mail. Further, when the image forming apparatus 100 according to the present embodiment restores compressed image data compressed by such an image compression process, image data having different resolutions obtained by decompressing the compressed image data, The image can be synthesized at high speed while preventing deterioration of the image quality.

  Hereinafter, a description will be given of the compression processing performed for separating image data into layers and performing the respective layers. Specifically, details of the compression processing performed by the compression processing unit 23 will be described. First, image compression processing based on layer separation represented by MRC will be described. FIG. 2 is a schematic diagram for explaining image compression processing based on layer separation.

  2A shows image data to be processed (referred to as input image data), FIG. 2B shows a foreground layer in the input image data, FIG. 2C shows a background layer in the input image data, 2D shows the foreground mask in the foreground layer, and FIG. 2E shows the foreground information in the foreground layer.

  In the input image data shown in FIG. 2A, M1 represents a first color character pixel, M2 represents a second color character pixel, M3 represents a third color character pixel, and G represents an image content. Yes. The background of the character pixel M1 is plain (white), and the background of the character pixels M2 and M3 is the fourth color. The first color, the second color, the third color, and the fourth color are arbitrary colors.

  The input image data shown in FIG. 2 (a) can be separated into a foreground layer shown in FIG. 2 (b) and a background layer shown in FIG. 2 (c), and the foreground shown in FIG. 2 (b). The layer can be separated into the foreground mask shown in FIG. 2D and the foreground information shown in FIG.

  The foreground layer is a layer representing character pixels in the input image data, and includes character pixels M1, M2, and M3 in the input image data shown in FIG. The background layer is a layer representing, for example, image content other than the foreground layer in the input image data, and includes the background region B of the character pixels M2 and M3 and the image content G in the input image data shown in FIG.

  The foreground mask is obtained by binarizing the foreground layer shown in FIG. 2B so that a pixel value larger than a predetermined value becomes 0 and a smaller pixel value becomes 1. By performing such binarization processing, as shown in FIG. 2D, the foreground mask in which the pixel values of the character pixels M1, M2, and M3 are 0 and the pixel values of the other (background) are 1. Is obtained. The foreground color information indicates the color information of each character pixel M1, M2, M3 in the foreground layer shown in FIG.

  The compression processing unit 23 according to the present embodiment separates input image data into a foreground layer and a background layer. The compression processing unit 23 indexes the pixel colors of the foreground layer and finally compresses them using a lossless compression technique typified by JBIG, MMR, and LZW. The compression processing unit 23 compresses the background layer using a lossy compression technique represented by JPEG. For the foreground layer, the compression processing unit 23 generates foreground mask and foreground information from the foreground layer, compresses the foreground mask using a lossless compression technique, and color information of each pixel (character pixel) indicated by the foreground information (Specifically, the foreground index color table described later) is compressed by a lossless compression technique or a lossy compression technique. As a result, the compression rate can be improved as compared with the case of directly compressing the multi-bit (for example, multi-gradation such as 1024 gradations) foreground layer.

  The detailed configuration of the compression processing unit 23 will be described below. FIG. 3 is a block diagram showing the configuration of the compression processing unit 23. The compression processing unit 23 includes a foreground mask generation processing unit 231, a foreground indexing processing unit 232, a background layer generation processing unit 233, a binary image generation processing unit 234, a compression processing execution unit 235, and the like.

  The foreground mask generation processing unit 231 extracts a foreground mask representing character pixels from the RGB signals (input image data) input from the input tone correction unit 22. As the foreground mask extraction process, for example, a method described in Japanese Patent No. 3777741 can be used. Specifically, differential processing is applied to the luminance value (pixel value) of the input image data to detect an edge portion where the luminance changes brightly and an edge portion where the luminance changes darkly. Character pixels are extracted based on the edge part.

  Specifically, a pixel in a range from the appearance of a positive differential value to the appearance of a negative differential value is defined as a character pixel, and the character pixel is extracted. The foreground mask generation processing unit 231 generates a foreground mask by binarizing the extracted character pixels, and the generated foreground mask and the image data (input image data) input from the input tone correction unit 22 are in the subsequent stage. The data is output to the foreground color indexing processing unit 232.

  The foreground indexing processing unit 232 indexes the colors of character pixels (also referred to as foreground pixels) in the input image data based on the input image data and the foreground mask input from the foreground mask generation processing unit 231 for each color. A foreground layer representing the index image data and a foreground index color table as shown in FIG. 4 are generated. In the foreground index color table, the color (character color) of each pixel (character pixel) included in the foreground layer and area information indicating the area of each character color are registered.

  FIG. 4 is a schematic diagram showing the registration contents of the foreground index color table. As shown in FIG. 4, the foreground index color table includes an index ID assigned to each index image data of each color obtained by indexing, a coordinate value for specifying a region of each character color, and RGB representing each character color. Is registered. Note that the coordinate values that specify the character color areas are, for example, the upper left coordinates of the input image data shown in FIG. 2A as the reference position (0, 0), and the direction indicated by the arrow x is the x coordinate axis. When the direction indicated by the arrow y is the y coordinate axis, the minimum coordinate value (minx, miny) where the x coordinate and y coordinate are both the minimum value, and the maximum coordinate where both the x coordinate and y coordinate are the maximum value It is indicated by the values (maxx, maxy).

  The foreground indexing processing unit 232 finally indexes the foreground layer by updating the foreground index color table as shown in FIG. 4 for the foreground pixels. When the foreground indexing processing unit 232 determines that the pixel color of each foreground pixel has already been registered in the foreground index color table for each foreground pixel (character pixel in the foreground layer), the foreground index color table. The index ID of the closest color is assigned. When the foreground indexing processing unit 232 determines that the pixel color of the foreground pixel is not registered in the foreground index color table, the foreground index index processing unit 232 newly assigns an index ID, and assigns the index ID, coordinate value, Register RGB values.

  The foreground color indexing processing unit 232 indexes the foreground pixels by repeating such processing. The foreground indexing processing unit 232 outputs the generated foreground layer and foreground index color table and the input image data input from the foreground mask generation processing unit 231 to the subsequent background layer generation processing unit 233.

  The background layer generation processing unit 233 generates a background layer by removing the foreground pixels from the input image data input from the foreground color indexing processing unit 232. In general, the background layer generation processing unit 233 performs a filling process on the removed foreground pixels using the background layer pixels around the foreground pixels in order to improve the compression ratio of the background layer. Specifically, the background layer generation processing unit 233 refers to a pixel (background pixel) around the removed foreground pixel in the input image data, and uses the average value of the background pixel to determine the location of the removed foreground pixel. To create a background layer.

  In addition, when no background pixel exists in the vicinity (periphery) of the removed foreground pixel, for example, when no background pixel exists in a reference range (for example, an area composed of 5 × 5 pixels), the filling process is already performed. Processing is performed with reference to the result. Specifically, for the pixel to be filled, even if the pixel on the left side or the pixel on the upper side of this pixel has already been filled in by the hole filling process, Alternatively, the pixels may be used to fill the holes. Alternatively, filling may be performed using the average value of the left adjacent pixel or the upper adjacent pixel.

  Also, the background layer generation processing unit 233 reduces the resolution of the background layer obtained by executing the hole filling process to, for example, 150 dpi. As a method for reducing the resolution, an interpolation method such as a nearest neighbor method, a bilinear method, or a bicubic method can be used. The nearest neighbor method is a method in which a pixel value of an existing pixel closest to a pixel to be interpolated (interpolated pixel) or a pixel value of an existing pixel having a predetermined positional relationship with respect to the interpolated pixel is used as the pixel value of the interpolated pixel. is there. The bilinear method is a method in which the pixel values of four existing pixels surrounding the interpolation pixel are weighted with values proportional to the distance from the interpolation pixel, and the average value of the obtained values is used as the pixel value of the interpolation pixel. In the bicubic method, a value calculated based on pixel values of 16 existing pixels obtained by adding 12 existing pixels including them to 4 existing pixels surrounding the interpolation pixel is used as a pixel value of the interpolation pixel. It is.

  As described above, the background layer generation processing unit 233 removes the foreground pixels from the input image data, performs the hole filling process, and reduces the resolution, and the foreground layer input from the foreground indexing processing unit 232 The foreground index color table and the foreground index color table are output to the subsequent binary image generation processing unit 234.

  The binary image generation processing unit 234 performs binarization processing on each index image data included in the foreground layer using the foreground layer and the foreground index color table input from the background layer generation processing unit 233, and generates The foreground index color table and background layer input from the binary foreground layer and background layer generation processing unit 233 are output to the subsequent compression processing execution unit 235.

  The compression processing execution unit 235 executes compression processing corresponding to each of the foreground layer, the foreground index color table, and the background layer input from the binary image generation processing unit 234. As described above, the compression processing execution unit 235 performs compression processing using a lossless compression technique represented by JBIG, MMR, and LZW (hereinafter referred to as MMR) for the foreground layer and the foreground index color table. Execute. The compression processing execution unit 235 executes compression processing using a lossy compression technique typified by JPEG for the background layer.

  In this way, the compression processing execution unit 235 converts the multi-bit foreground layer shown in FIG. 2B into the foreground mask which is binary data shown in FIG. The compression ratio can be further improved by decomposing and compressing the color information (specifically, foreground index color table) relating to one or more of the character colors shown.

  The compression processing execution unit 235 associates compressed image data obtained by executing appropriate compression processing for each of the foreground layer, the foreground index color table, and the background layer, and stores them in the hard disk 6. For example, the compression processing execution unit 235 is partially common to the compressed image data of the foreground layer, the foreground index color table, and the background layer in one piece of image data, and the foreground layer, the foreground index color table, and the background. A file name that distinguishes the layers is added and stored in the hard disk 6.

  Next, the operation of the color image processing apparatus 2 will be described. FIG. 5 is a flowchart showing a procedure of compression processing by the compression processing unit 23. The compression process is not only configured by a dedicated hardware circuit such as the compression processing unit 23, but a computer program that defines the procedure of the compression process is loaded into a personal computer including a CPU, a RAM, a ROM, and the like. This can also be performed by a CPU (both not shown). In the following description, the compression processing unit 23 of the color image processing apparatus 2 is referred to as a “processing unit”.

  Image data acquired by the color image input device 1 reading a document is sent to the color image processing device 2, and when the color image processing device 2 acquires image data, the A / D conversion unit 20, the shading correction unit 21, and The input tone correction unit 22 performs each process on the acquired image data, and outputs the processed image data to the subsequent compression processing unit 23.

  The processing unit extracts character pixels from the image data (RGB signal) acquired from the input tone correction unit 22, and binarizes the extracted character pixels to generate a foreground mask (S1). The processing unit indexes the color of the character pixel (foreground pixel) in the image data based on the image data acquired from the input tone correction unit 22 and the foreground mask (S2), and sets the foreground layer representing the index image data. The foreground index color table is generated (S4).

  The processing unit removes the foreground pixels from the image data acquired from the input tone correction unit 22 to generate a background layer (S5), and sets the foreground pixels removed from the image data as pixels of the background layer around the foreground pixels. Is used to fill the hole (S6). The processing unit lowers the resolution of the background layer subjected to the hole filling process (S7). The processing unit performs a binarization process on the foreground layer (index image data) generated as described above to generate a binary foreground layer (S8).

  The processing unit executes appropriate compression processing on the foreground layer, the foreground index color table, and the background layer generated as described above (S9), and associates the obtained compressed image data with each other and stores them in the hard disk 6.

  As described above, in the present embodiment, the image data is separated into the foreground layer and the background layer, and compressed by the compression process optimal for each layer, thereby improving the compression ratio for the entire image data. Further, in the present embodiment, the foreground layer is further separated into the foreground mask and the color information of the foreground pixels and compressed, so that the compression rate can be further improved as compared with the case where the foreground layer is directly compressed.

  In the following, processing for expanding compressed image data compressed by the processing by the compression processing unit 23 described above, and processing for combining image data of different resolutions obtained by the expansion will be described. Specifically, details of the unfolding process performed by the unfolding processing unit 30 and the combining process performed by the combining processing unit 31 will be described. In the following description, it is assumed that the compression processing unit 23 performs MMR compression processing on the foreground layer and JPEG compression processing on the background layer.

  First, the expansion process performed by the expansion processing unit 30 will be described. FIG. 6 is a block diagram illustrating a configuration of the expansion processing unit 30. The expansion processing unit 30 includes an MMR decoder 301, an MMR decoder DMA (Direct Memory Access) 302, a JPEG decoder 303, a JPEG decoder DMA 304, and the like. The expansion processing unit 30 expands the compressed image data compressed by the compression processing unit 23 and stored in the hard disk 6 on the main memory 7 as described above. The compressed image data obtained by compressing the foreground layer is referred to as MMR image data 61, and the compressed image data obtained by compressing the background layer is referred to as JPEG image data 62.

  The MMR decoder 301 expands the MMR image data 61 stored in the hard disk 6. The MMR decoder 301 expands the compressed foreground index color table, and writes the area information of each index image data registered in the obtained foreground index color table to the foreground layer 71 on the main memory 7. It is converted into an address (coordinate) and set in the register of the MMR decoder DMA302, and color information of each index image data registered in the foreground index color table is set as a color when the foreground layer 71 is written on the main memory 7. To do.

  The MMR decoder DMA 302 sequentially writes the foreground layer 71 developed by the MMR decoder 301 into the main memory 7 based on the address and color set by the MMR decoder 301. The MMR decoder 301 and the MMR decoder DMA 302 expand the image data of the foreground layer 71 for one page on the main memory 7 by repeating such processing for the number of index image data registered in the foreground index color table. can do. As a result, a foreground layer 71 similar to the foreground layer before being compressed by the compression processing unit 23 is written on the main memory 7.

  FIG. 6 illustrates a configuration in which the foreground index color table is directly input to the MMR decoder DMA302, but the compression processing unit 23 of the present embodiment also compresses the foreground index color table with MMR. Actually, the foreground index color table is developed by the MMR decoder 301 and then sent to the MMR decoder DMA 302.

  The JPEG decoder 303 expands the JPEG image data 62 stored in the hard disk 6, and the JPEG decoder DMA 304 sequentially writes the background layer 72 expanded by the JPEG decoder 303 into the main memory 7. In FIG. 6, the foreground layer 71 expanded in the main memory 7 has a resolution of, for example, 300 dpi, the background layer 72 expanded in the main memory 7 is, for example, 75 dpi, and the background layer 72 is lower than the foreground layer 71. Resolution.

  Next, the synthesis process performed by the synthesis processing unit 31 will be described. FIG. 7 is a block diagram showing a configuration of the composition processing unit 31. The synthesis processing unit 31 includes a synthesis circuit 310, a high resolution line DMA 311, a delay circuit 312, a low resolution line DMA 313, an upsampling module 314, and the like. As described above, the composition processing unit 31 combines the foreground layer 71 and the background layer 72 having different resolutions developed on the main memory 7 (storage unit) by the development processing unit 30. Note that the synthesized image data 73 is stored in the main memory 7.

  The high-resolution line DMA 311 and the delay circuit 312 process the foreground layer 71, which is high-resolution (first resolution) image data, in units of lines. The high-resolution line DMA 311 is a first reading unit that reads the foreground layer 71 from the main memory 7, and sequentially sends the foreground layer 71 read at a predetermined timing to the delay circuit 312. The delay circuit 312 holds the foreground layer 71 acquired from the high resolution line DMA 311 for a predetermined time, and then sends it to the synthesis circuit 310.

  The low resolution line DMA 313 and the upsampling module 314 process the background layer 72, which is low resolution (second resolution) image data, in units of lines. The low resolution line DMA 313 is a second reading unit that reads the background layer 72 from the main memory 7, and sequentially sends the background layer 72 read at a predetermined timing to the upsampling module 314. The upsampling module 314 operates as a resolution converting unit that converts the background layer 72 acquired from the low resolution line DMA 313 to the same resolution as the foreground layer 71, and combines the background layer 72 with the converted resolution. Send to 310.

  FIG. 8 is a block diagram showing the configuration of the upsampling module 314. As shown in FIG. 8A, the upsampling module 314 includes a line buffer 314a, an upsampling unit 314b, and the like. The line buffer 314a sequentially stores the background layer 72 acquired from the DMA 313 for low resolution lines, stores the background layer 72 for one line, and sends it to the upsampling unit 314b at a predetermined timing.

  Specifically, if the line buffer 314a is empty, the upsampling module 314 sends a signal requesting the background layer 72 to the low resolution line DMA 313. If the image data of the background layer 72 is expanded on the main memory 7, the DMA 313 for low resolution line reads out the background layer 72 having the data amount requested from the upsampling module 314 from the main memory 7 and reads the upsampling module 314. To send.

  The upsampling module (detection means) 314 sequentially stores the background layer 72 acquired from the low resolution line DMA 313 in the line buffer 314a, and determines whether or not the background layer 72 for one line is stored in the line buffer 314a. Detect. When the background layer 72 for one line is stored in the line buffer 314a, the line data of the background layer 72 can be output from the upsampling module 314 to the synthesis circuit 310. When the upsampling module 314 detects that the background layer 72 for one line is stored in the line buffer 314a, the upsampling module 314 sends a notification signal indicating that the background layer 72 can be read from the line buffer 314a to the DMA 311 for high resolution line. To send.

  When acquiring the notification signal from the upsampling module 314, the high resolution line DMA 311 starts the process of reading the foreground layer 71 from the main memory 7 and sending it to the delay circuit 312. The high-resolution line DMA 311 starts a process of sending the foreground layer 71 to the delay circuit 312 and outputs a signal (synchronization signal) synchronized with the output of the foreground layer 71 to the delay circuit 312 to the upsampling module 314. Send it out.

  When the synchronization signal is acquired from the high resolution line DMA 311, the upsampling module 314 starts a process of sending the background layer 72 for one line stored in the line buffer 314 a to the upsampling unit 314 b. The upsampling unit (conversion processing unit) 314b performs resolution conversion processing on the background layer 72 sequentially acquired from the line buffer 314a, converts the background layer 72 to the same resolution as the foreground layer 71, and sequentially converts the obtained background layer 72. The data is sent to the synthesis circuit 310.

  Note that the conversion process (interpolation process) performed by the upsampling unit 314b uses an interpolation method such as a nearest neighbor method, a bilinear method, or a bicubic method, similarly to the resolution conversion process performed by the background layer generation processing unit 233. it can.

  Here, since the time for which the delay circuit 312 holds the foreground layer 71 is set to be the same as the time required for the upsampling process (conversion process) by the upsampling module 314, the delay circuit 312 to the synthesis circuit 310 is set. The output timing of the foreground layer 71 and the output timing of the background layer 72 from the upsampling module 314 to the synthesis circuit 310 are synchronized.

  The synthesis circuit (synthesizing unit) 310 synthesizes the image data of the foreground layer 71 acquired from the delay circuit 312 and the image data of the background layer 72 acquired from the upsampling module 314 for each pixel, and synthesizes the image data 73. Is stored in the main memory 7. Note that the composition circuit 310 refers to the registered contents of the foreground index color table and reproduces the color of each character for the foreground layer.

  Note that the upsampling module 314 is not limited to the configuration illustrated in FIG. 8A, and may be configured to include two line buffers 314a as illustrated in FIG. 8B, for example. When configured as shown in FIG. 8B, the background layer 72 read from the main memory 7 by the low resolution line DMA 313 is written to one line buffer 314a, and the background stored in the other line buffer 314a. It is possible to execute the upsampling process (resolution conversion process) performed on the layer 72 in parallel. Therefore, the processing speed can be improved by using the two line buffers 314a and 314a.

  Further, the development processing unit 30 and the composition processing unit 31 are not limited to the configurations illustrated in FIGS. 6 and 7, and may be configured as illustrated in FIGS. 9 and 10, for example. FIG. 9 is a block diagram showing a modification example of the configuration of the expansion processing unit 30, and FIG. 10 is a block diagram showing a modification example of the composition processing unit 31. The development processing unit 30 illustrated in FIG. 9 includes an MMR decoder 301, an MMR decoder DMA 302, two JPEG decoders 303 and 305, two JPEG decoders DMA 304 and 306, and the like.

  In the development processing unit 30 having such a configuration, one MMR image data 61 (foreground layer) development process and two JPEG image data 62a and 62b (background layer) development processes can be executed in parallel. . Therefore, for example, the background layer is further separated into medium-resolution image data (photo data, etc.) and low-resolution image data (thing that does not need to be processed at a higher resolution than photo data, background data, etc.) Even if the resolution is reduced to a different resolution and then compressed and stored in the hard disk 6, the processing speed can be increased.

  Specifically, the MMR image data 61 stored in the hard disk 6 is developed by the MMR decoder 301 and the MMR decoder DMA 302, and the foreground layer 71 (for example, 300 dpi) is written on the main memory 7. Further, the JPEG image data 62a stored in the hard disk 6 is developed by the JPEG decoder 303 and the JPEG decoder DMA 304, and the medium resolution (for example, 75 dpi) image data 72a in the background layer is written on the main memory 7, and the JPEG decoder The JPEG image data 62 b stored in the hard disk 6 is expanded by the 305 and the JPEG decoder DMA 306, and the low resolution (for example, 37.5 dpi) image data 72 b in the background layer is written on the main memory 7.

  The synthesis processing unit 31 shown in FIG. 10 includes a synthesis circuit 310, a high resolution line DMA 311, a delay circuit 312, a low resolution line DMA 313, two upsampling modules 314 and 316, a medium resolution line DMA 315, and the like. . The high-resolution line DMA 311, the delay circuit 312, the low-resolution line DMA 313, and the upsampling module 314 have the same configurations as those shown in FIG. 7, and the medium-resolution line DMA 315 and the upsampling module 316 are shown in FIG. The low-resolution line DMA 313 and the upsampling module 314 shown in FIG.

  As described above, the composition processing unit 31 having such a configuration includes the foreground layer 71 having different resolution developed on the main memory 7 by the development processing unit 30, the medium resolution image data 72a in the background layer, and the background layer. The low-resolution image data 72b is synthesized. Note that the synthesized image data 73 is stored in the main memory 7.

  The high resolution line DMA 311 and the delay circuit 312 process the foreground layer 71, which is high resolution image data, in units of lines. The low-resolution line DMA 313 and the upsampling module 314 process the image data 72b in the background layer, which is low-resolution image data, in units of lines. The medium resolution line DMA 315 and the upsampling module 316 process the image data 72a in the background layer, which is medium resolution image data, in units of lines.

  The medium resolution line DMA 315 reads the medium resolution image data 72a from the main memory 7 and sequentially sends it to the upsampling module 316 at a predetermined timing. The upsampling module 316 operates as a resolution conversion unit that converts the image data 72a acquired from the medium resolution line DMA 315 to the same resolution as the foreground layer 71, and combines the image data 72a with the converted resolution. Send to 310. The upsampling module 316 also includes a line buffer and an upsampling unit (both not shown), like the upsampling module 314.

  In the composition processing unit 31 having the configuration shown in FIG. 10, if the line buffer 314a is empty, the upsampling module 314 sends a signal requesting the image data 72b in the background layer to the low resolution line DMA 313. The low resolution line DMA 313 reads out the image data 72b having the data amount requested from the upsampling module 314 from the main memory 7 and sends it to the upsampling module 314.

  The upsampling module 314 sequentially stores the image data 72b acquired from the DMA 313 for low resolution lines in the line buffer 314a. When the upsampling module 314 detects that one line of image data 72b is stored in the line buffer 314a, the line buffer 314a A notification signal indicating that the image data 72b can be read from 314a is sent to the DMA 311 for high resolution line.

  Similarly, if its line buffer is empty, the upsampling module 316 sends a signal requesting the image data 72a in the background layer to the DMA 315 for the medium resolution line, and the DMA 315 for the medium resolution line Image data 72 a having a data amount requested from the sampling module 316 is read from the main memory 7 and sent to the upsampling module 316. The upsampling module 316 sequentially stores the image data 72a acquired from the DMA 315 for medium resolution lines in the line buffer. When the upsampling module 316 detects that one line of image data 72a is stored in the line buffer, the upsampling module 316 reads the image data 72a from the line buffer. A notification signal indicating that the data 72a can be read out is sent to the high-resolution line DMA 311.

  When the high-resolution line DMA 311 acquires the notification signal from each of the upsampling module 314 and the upsampling module 316, the high-resolution line DMA 311 reads the foreground layer 71 from the main memory 7 and sends it to the delay circuit 312. A signal (synchronization signal) synchronized with the output to the circuit 312 is sent to the upsampling module 314 and the upsampling module 316, respectively.

  When each of the upsampling modules 314 and 316 obtains a synchronization signal from the high resolution line DMA 311, the upsampling modules 314 and 316 start sending the image data 72 b and 72 a for one line stored in the line buffer 314 a to the upsampling unit 314 b. . The upsampling unit 314b of the upsampling modules 314 and 316 performs resolution conversion processing (correction processing) on the image data 72b and 72a sequentially obtained from the line buffer 314a, and converts the image data to the same resolution as that of the foreground layer 71. The obtained image data 72b and 72a are sequentially sent to the synthesis circuit 310.

  The upsampling modules 314 and 316 operate independently of each other. The upsampling module 314 stores the image data 72b in the line buffer 314a and the upsampling module 316 stores the image data 72a in the line buffer. It is executed separately from the processing. Therefore, the high-resolution line DMA 311 can start reading the foreground layer 71 from the main memory 7 and sending it to the delay circuit 312 only after obtaining notification signals from both the upsampling modules 314 and 316. The high-resolution line DMA 311 needs to send a synchronization signal to both the upsampling modules 314 and 316.

  Also here, the time for which the delay circuit 312 holds the foreground layer 71 is set to be the same as the time required for the upsampling processing (resolution conversion processing) by the upsampling modules 314 and 316. The output timing of the foreground layer 71 to 310, the output timing of the image data 72b from the upsampling module 314 to the synthesis circuit 310, and the output timing of the image data 72a from the upsampling module 316 to the synthesis circuit 310 are synchronized. Will be.

  The synthesis circuit 310 pixelally converts the foreground layer 71 image data acquired from the delay circuit 312, the background layer image data 72 b acquired from the upsampling module 314, and the background layer image data 72 a acquired from the upsampling module 316. The combined image data 73 is stored in the main memory 7. Note that the composition circuit 310 refers to the registered contents of the foreground index color table and reproduces the color of each character for the foreground layer.

  As described above, even when the background layer 72 is decomposed into a plurality of image data and processed, the upsampling modules 314 and 316 that process the image data with different resolutions. This can be dealt with by adding a configuration for sending a notification signal to the DMA 311 for high resolution lines and a configuration for sending a synchronization signal from the DMA 311 for high resolution lines to the respective upsampling modules 314 and 316.

  As described above, the composition processing unit 31 according to the present embodiment converts the foreground layer 71 into the resolution of the foreground layer 71 with respect to the low-resolution background layer 72 when compositing the foreground layer 71 and the background layer 72 having different resolutions. Since the two are combined after performing the above, it is possible to perform a combining process that prevents deterioration in image quality. Also, the output timing of the high-resolution foreground layer 71 output from the delay circuit 312 to the synthesis circuit 310, and the low-resolution (and medium-resolution) background layer output from the upsampling module 314 (and 316) to the synthesis circuit 310. 72 (image data 72b, 72a) can be synchronized with the output timing of the image data, the image memory, the contour designating circuit and the LUT as in the prior art are not required in addition to the hard disk and the main memory. Accordingly, the amount of memory can be reduced and the configuration of the apparatus can be simplified, so that an increase in cost can be avoided.

  In addition, since the synthesis processing unit 31 includes the low resolution line DMA 313 and the upsampling module 314, the image data reading process from the main memory 7 and the resolution conversion process for the read image data are executed in parallel. Therefore, for example, even when image data (foreground layer or background layer) having the same resolution (high resolution or low resolution) is separated into a plurality of images and compressed, the processing speed can be increased.

  In the image forming apparatus 100 described in the above-described embodiment, for example, when performing facsimile transmission, the modem (transmission apparatus 5) performs a transmission procedure with the other party and secures a state where transmission is possible. Image data compressed in a predetermined format (image data read by a scanner) is read from the memory (hard disk 6), subjected to necessary processing such as changing the compression format, and sequentially transmitted to the other party via a communication line. . When receiving a facsimile, the transmission device 5 receives the image data transmitted from the other party while performing a communication procedure and outputs the image data to the color image processing device 2. The color image processing device 2 receives the received image data. Is decompressed by a compression / decompression processing unit (not shown). The decompressed image data is subjected to rotation processing and resolution conversion processing as necessary, subjected to output tone correction and tone reproduction processing, and is output from the color image output device 3.

Further, the image forming apparatus 100 is configured to perform data communication with a computer and other digital multi-function peripherals connected to the network via the transmission device 5. Therefore, the compressed image data compressed as described above and stored in the hard disk 6 can be transmitted to an external device via the network, and the compressed image data can also be received from the external device. Further, the present invention can be applied not only to a digital color multifunction peripheral but also to a multifunction peripheral that handles monochrome images, a digital color copying machine that has only a copier function and a printer function, and a facsimile communication apparatus that has only a facsimile communication function. Can do.
You may apply to.

1 is a block diagram illustrating a configuration of an image forming apparatus including an image processing apparatus according to the present invention. It is a schematic diagram for demonstrating the image compression process based on layer separation. It is a block diagram which shows the structure of a compression process part. It is a schematic diagram which shows the registration content of a foreground index color table. It is a flowchart which shows the procedure of the compression process by a compression process part. It is a block diagram which shows the structure of an expansion | deployment process part. It is a block diagram which shows the structure of a synthetic | combination process part. It is a block diagram which shows the structure of an upsampling module. It is a block diagram which shows the modification of a structure of an expansion | deployment process part. It is a block diagram which shows the modification of a structure of a synthetic | combination process part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming device 1 Color image input device 2 Color image processing device 3 Color image output device 30 Development processing unit 31 Composition processing unit 310 Composition circuit (composition means)
311 DMA for high resolution line (first reading unit)
312 Delay circuit 313 DMA for low resolution line (second reading unit)
314 Upsampling module (resolution converter, detection means)
314a Line buffer 314b Upsampling unit (conversion processing unit)

Claims (4)

In an image processing apparatus for synthesizing first resolution image data and second resolution image data lower than the first resolution,
Storage means for storing image data;
A combining means for combining a plurality of image data;
A first reading unit for reading image data of a first resolution from the storage unit;
A delay circuit for sending image data of the first resolution read by the first reading unit to the combining unit after holding the image data for a predetermined time;
A second reading unit for reading image data of the second resolution from the storage means;
A resolution conversion unit that performs conversion processing on the second resolution image data read by the second reading unit to the first resolution;
The image processing apparatus, wherein the synthesizing unit is configured to synthesize the image data sent from the delay circuit and the image data subjected to conversion processing by the resolution conversion unit. The resolution converter
A line buffer for storing image data of the second resolution read by the second reading unit;
A conversion processing unit for converting the image data stored in the line buffer into the first resolution;
Detecting means for detecting that image data of the second resolution is stored in the line buffer;
And a means for sending a notification signal indicating that the image data can be read from the line buffer to the first reading section when the detecting means detects that the image data is stored in the line buffer. ,
The first reading unit is configured to start a process of reading the image data of the first resolution from the storage unit and sending the image data to the delay circuit when the notification signal is acquired, and delays the image data. When starting the processing to send to the circuit, it has means for sending a synchronization signal to the resolution converter,
The said resolution conversion part is comprised so that the process which sends out the image data stored in the said line buffer to the said conversion process part may be started when the said synchronizing signal is acquired. The image processing apparatus described. The resolution converter has a plurality of the line buffers, reads out the second resolution image data stored in one of the line buffers, and sends the image data to the conversion processor; and The image processing apparatus according to claim 2, wherein the image processing apparatus is configured to perform parallel processing of storing the second resolution image data read by the second reading unit in another line buffer.   4. An image forming apparatus comprising: the image processing apparatus according to claim 1; and an image forming unit that forms an output image based on image data processed by the image processing apparatus. .

Images