JP2005204065A - Image processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus, capable of preventing image quality deterioration by improving compressibility at compression processing. <P>SOLUTION: The image processing apparatus divides image data to be processed into preprocessing blocks corresponding to pixel blocks at the time of compression, executes preprocessings by each preprocessing block, divides the image data after the preprocessing into pixel blocks of a predetermined size, and performs compression by the specified processing by each pixel block. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus that performs compression processing of image data.

  Raster image data (hereinafter simply referred to as “image data” unless otherwise distinguished) includes many images with different properties, such as character (text) portions and natural image portions (pattern portions). Elements can be included. Due to the difference in properties of these image elements, it is often preferable to perform different image processing for each image element, for example, compression by a different method is suitable for compression processing. Therefore, conventionally, image processing called T / I separation has been researched and developed to separate a character part from a picture part, and generate image data consisting of a character part and image data consisting of a picture part. A processing method for performing suitable compression processing is known (for example, Patent Document 1).

Also, for example, in the image data consisting of the pattern part, the pixel value of the part that was originally the pixel of the character part is generally set to the pixel value around the part, filled in the hole, and then compressed. is there.
Japanese Patent Laid-Open No. 2002-76631

  However, in the above-described conventional method, when a compression process is performed on a block of a predetermined size such as JPEG (Joint Picture Experts Group) compression, a plurality of types of pixel values set for filling the hole are included in the block. When they are mixed, there is a problem that the compression rate is lowered, and block noise, color turbidity, and the like are generated, and image quality is likely to be deteriorated.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image processing apparatus capable of improving the compression rate and preventing deterioration of image quality.

  The present invention for solving the above-described problems of the conventional example is an image processing apparatus, wherein preprocessing means for performing preprocessing on image data to be processed, and image data after the preprocessing are predetermined. A compression unit that divides the pixel block into a size and compresses the pixel block according to a predetermined process for each pixel block, wherein the preprocessing unit divides the image data into preprocessing blocks corresponding to the pixel blocks in the compression unit. The predetermined preprocessing is executed for each preprocessing block.

  In addition, the present invention for solving the problems of the conventional example is an image processing apparatus that divides image data to be processed into pre-processed blocks of a predetermined size, Pre-processing means for executing processing, and compression means for dividing the pre-processed image data into pixel blocks having a size corresponding to the pre-processing block, and performing compression by predetermined processing for each pixel block. It is characterized by.

  Here, an image portion constituting an image having a predetermined property is extracted from the target image data to be compressed, an image portion obtained by removing the image portion from the target image data is extracted, and each of the first partial image data And the second partial image data are generated, and the preprocessing means divides the second partial image data into the preprocessing blocks by using the second partial image data as image data to be processed. The process for adjusting the pixel value of the removed pixel may be executed as the predetermined preprocess for each preprocess block.

  Further, the preprocessing means adjusts the pixel value of the pixel that has been removed in the predetermined preprocessing based on the pixel value of the pixel that has not been removed in the preprocessing block. The value may be determined and adjusted.

  In addition, in the case where there is a pixel that has not been removed in the preprocessing block in order to adjust the pixel value of the removed pixel in the predetermined preprocessing, the preprocessing means may include a pixel of the pixel that has not been removed. A pixel value of the removed pixel is determined based on the value, and no pixel is removed in the preprocessing block to adjust the pixel value of the removed pixel in the predetermined preprocessing. Obtains a pixel value of a pixel that has not been removed in another pre-processing block, and determines a pixel value of the removed pixel based on the obtained pixel value, whereby the removed pixel The pixel value may be adjusted.

  Further, the present invention for solving the problems of the above-described conventional example is an image processing method using a computer, wherein the computer performs preprocessing on image data to be processed, and the preprocessing Dividing the subsequent image data into pixel blocks of a predetermined size and performing compression by a predetermined process for each pixel block, and in the preprocessing, before the image data corresponds to the pixel block in the compression means The processing block is divided and predetermined preprocessing is executed for each preprocessing block.

  Furthermore, the present invention for solving the problems of the above-described conventional example is an image processing method using a computer, in which image data to be processed is divided into pre-process blocks of a predetermined size, Performing predetermined preprocessing for each processing block; dividing the preprocessed image data into pixel blocks of a size corresponding to the preprocessing block; and performing compression by predetermined processing for each pixel block; It is characterized by executing.

  According to another aspect of the present invention, a program for causing a computer to perform preprocessing on image data to be processed, and dividing the preprocessed image data into pixel blocks of a predetermined size, A step of performing compression by predetermined processing for each block, and in the preprocessing, in the preprocessing, the image data is divided into preprocessing blocks corresponding to pixel blocks in the compression unit, It is characterized by executing processing.

  Further, a program according to another aspect of the above-described conventional example, the computer divides the image data to be processed into preprocessed blocks of a predetermined size, and executes a predetermined preprocess for each preprocess block, The pre-processed image data is divided into pixel blocks having a size corresponding to the pre-process block, and compression is performed by a predetermined process for each pixel block.

  As shown in FIG. 1, the image processing apparatus according to the embodiment of the present invention includes a control unit 11, a storage unit 12, an image input unit 13, and an image output unit 14. The control unit 11 operates in accordance with a program stored in the storage unit 12 and performs each image processing described later. The contents of this image processing will be described in detail later.

  The storage unit 12 holds a program executed by the control unit 11. The storage unit 12 also operates as a work memory that stores various data generated during the process of the control unit 11. Specifically, the storage unit 12 can be implemented as a computer-readable recording medium and a device that writes data to or reads data from the recording medium (for example, a hard disk device or a memory device).

  The image input unit 13 is, for example, a scanner, and outputs image data obtained by optically reading a document to the control unit 11. Here, it is assumed that the value of each pixel is expressed in an RGB (red, green, blue) color space in the image data output from the image input unit 13. The image output unit 14 outputs image data in accordance with an instruction input from the control unit 11. For example, the image output unit 14 outputs the image data to an image forming unit (printer or the like) or transmits it to an external device via a network. Is what you do.

  Next, the content of the process of the control part 11 is demonstrated. As functionally shown in FIG. 2, the control unit 11 of the present embodiment performs image processing on the image data input from the image input unit 13 as a processing target, and an image correction unit 21 and a character image plane. A generating unit 22, a character color image plane generating unit 23, a pattern image plane generating unit 24, a character color image plane resolution converting unit 25, a character color image plane compressing unit 26, and a pattern image plane resolution converting unit 27; The pattern image plane compression unit 28, the character image plane compression unit 29, and the format unit 30 are configured.

  Hereinafter, each of these parts will be described in detail. The image correction unit 21 converts the value of each pixel of the image data (processing target image data) input from the image input unit 13 from RGB to YCbCr (value consisting of luminance and color difference). Specifically, the conversion can be performed using the following equation (1). Here, the value of each component of RGB is assumed to be a value from 0x00 (“0x” indicates a hexadecimal number) to 0xFF. Further, the image correction unit 21 may perform gradation correction on each pixel value based on the luminance and saturation of the background area. However, the gradation correction process is not always necessary.

  The character image plane generation unit 22 extracts a character / line drawing part from the image data output from the image correction unit 21 and specifies information for specifying pixels constituting the character / line drawing part (for example, the pixels constituting the character / line drawing part are “black”). , Image data in which the other pixels are “white”) is generated as a character image plane. The character color image plane generation unit 23 includes information including color information of the character / line drawing image based on the image data output from the image correction unit 21 and the character image plane output from the character image plane generation unit 22. Is generated as a character color image plane.

  These processes may be the same as those disclosed in Patent Document 1. In other words, the character image plane generation unit 22 has an image characteristic as a character from the binarized image data obtained by binarizing the corrected image data (hereinafter referred to as “original image”) to be processed. A part is extracted, and coordinate information of the image part is acquired. Then, the character color image plane generation unit 23 generates a position corresponding to the image portion represented by the coordinate information in the original image (on the original image corresponding to the black (significant pixel) area on the binarized image). Is obtained, and information including the pixel value is generated. For example, a circumscribed rectangle surrounding the character portion is generated, and the character color plane is generated by painting the inside of the circumscribed rectangle with the acquired pixel value. The character color image plane generating unit 23 may determine a representative color for each character / line image and limit the representative color to the representative color.

  The pattern image plane generation unit 24 removes pixels included in the character image plane information from the image data output from the image correction unit 21 and the character image plane output from the character image plane generation unit 22, thereby A picture image plane that specifies an image portion that does not contain the image (in other words, a pixel area corresponding to the picture) is generated. One characteristic of this embodiment is that the picture image plane generation unit 24 adjusts the pixel value of the removed pixel so that the pixel has a size determined in relation to the subsequent compression processing. Dividing into blocks, the pixel values of the removed pixels are determined for each pixel block based on the pixel values of the pixels not removed in the block. More detailed processing contents of the pattern image plane generation unit 24 will be described in detail later.

  Specifically, the character color image plane, the character image plane, and the pattern image plane generated by these processes are as shown in FIG. That is, if the character string “ABC” written in red characters, the character string “123” written in blue characters, and a photo image are included on the original image, the character image plane An image in which the columns “ABC” and “123” are described in black characters (FIG. 3A), and the character color image plane has a rectangular area including a circumscribed rectangle of the character string “ABC” as the color of the character string. It includes an image painted in red and an image in which a rectangular area including the circumscribed rectangle of the character string “123” is painted in blue, which is the color of the character string (FIG. 3B). Further, image data including only a photographic image excluding these character portions is generated as a pattern image plane (FIG. 3C).

  Here, the character image plane and the character color image plane for reproducing the character image correspond to the first partial image data referred to in the present invention, and the picture image plane corresponds to the second partial image data.

  The character color image plane resolution conversion unit 25 converts the resolution of the image data of the character color image plane. As described above, the character color image plane does not include a character-shaped image, but a relatively large area such as a rectangular area is filled, so that the image quality is deteriorated even at a relatively low resolution. Therefore, the resolution is reduced and the compression rate is increased.

  The character color image plane compression unit 26 compresses the image data of the character color image plane after the resolution conversion. Here, since the character color image plane has a plurality of bits per pixel (for example, 24), an irreversible compression method for multi-valued images that can be processed in real time using a general-purpose image processing chip such as JPEG compression is applied. It is preferable. However, if irreversible compression is applied, the color may change, so it may be reversible compression.

  The pattern image plane resolution conversion unit 27 performs resolution conversion processing on the pattern image plane to reduce the resolution. This reduction in resolution is to improve the compression rate, but is not essential and the reduction in resolution may not be performed. The pattern image plane compression unit 28 compresses the image data of the pattern image plane output from the pattern image plane resolution conversion unit 27. In this compression process, the image data of the picture image plane is divided into pixel blocks of a predetermined size, and compression is performed by a predetermined process for each pixel block. As this compression method, for example, there is JPEG compression (compression processing is performed for each block of 8 × 8 pixels).

  The character image plane compression unit 29 compresses the image data of the character image plane. In the compression processing here, since the number of bits per pixel is 1 (that is, binary) in the character image plane, MH (Modified Huffman), MR (Modified Reed), MMR (Modified Modified Reed), etc. are adopted. be able to. Further, by adopting these, real-time processing can be easily realized using a general-purpose image processing chip.

  The format unit 30 uses a character color image plane after compression processing, a pattern image plane after compression processing, and a character image plane after compression processing for a predetermined image format (for example, PDF (Portable Document Format) or Internet FAX). Wrapped to TIFF-FX).

  Here, more detailed processing contents of the pattern image plane generation unit 24 will be described. The picture image plane generation unit 24 performs pre-compression processing and sets the pixel values of the removed pixels in order to increase the compression rate in the picture image plane compression unit 28. Specifically, the pattern image plane generation unit 24 starts the processing shown in FIG. 4 and first divides the original image into blocks (called processing blocks) corresponding to the pixel blocks generated by the pattern image plane compression unit 28. (S1).

  Here, the size of the processing block is determined by the size of the pixel block used by the picture image plane compression unit 28 and the resolution conversion ratio in the picture image plane resolution conversion unit 27. Specifically, when the picture image plane compression unit 28 performs JPEG compression, the pixel block is assumed to be 8 × 8, and the resolution conversion by the picture image plane resolution conversion unit 27 performs 1/2 times conversion. The size of the processing block is 16 × 16 pixels. When sub-sampling is performed here, for example, when sub-sampling is performed for Cb and Cr (and when conversion for halving the resolution is performed), the size of the processing block may be changed accordingly.

  The pattern image plane generation unit 24 selects one of the processing blocks (S2). Then, it is checked whether or not there is a removed pixel in the selected block (S3). Here, if there is no removed pixel (that is, if all the pixels in the block are pixels constituting the pattern portion), it is checked whether there is a processing block that has not yet been processed (S4), If there is a processing block that has not been processed, the process returns to step S2 to select the next processing block and continue the processing. If there is no processing block that has not yet been processed in step S4 (that is, when processing has been completed for all processing blocks), the processing ends.

  In the process S3, if there is a pixel that has been removed, a pixel that is not removed from the selected processing block (ie, a pixel constituting the pattern portion) is extracted (S5), and the value of the extracted pixel is set. A statistic (for example, an average value of the extracted pixel values) is calculated, and the result of the calculation is determined as the pixel value of the removed pixel (S6). Note that, instead of the statistic itself, a pixel value closest to the statistic may be selected and determined as the pixel value of the removed pixel from the values of the pixels constituting the pattern portion in the processing block.

  Then, the picture plane generation unit 24 sets all the values of the removed pixels among the pixels in the selected processing block to the pixel values determined in the processing S6 (S7), and proceeds to the processing S4. Continue processing. That is, the process of the picture image plane generating unit 24 corresponds to the preprocessing referred to in the present invention.

  As described above, the picture image plane generation unit 24 determines one pixel value for each block unit at the time of compression processing as the value of the removed pixel, so that the compression rate and the image quality are not deteriorated. .

  In the process shown in FIG. 4, when there is no pixel constituting the picture part in step S <b> 5, the pixel constituting the picture part may be extracted from another block different from the selected processing block. Here, the other blocks are, for example, neighboring blocks (e.g., eight blocks of upper, lower, right, left, upper left, upper right, lower left, and lower right).

  Next, the operation of the image processing apparatus according to this embodiment will be described. When the image input unit 13 optically reads image data for a plurality of pages and outputs the image data to the control unit 11, the control unit 11 sets the image data of each page as image data to be processed and sequentially selects the target image data.

  Then, the control unit 11 extracts a character image plane from the target image data, generates a character color image plane corresponding to the character image plane, and stores the character image plane and the character color image plane in the storage unit 12. Further, the control unit 11 generates a pattern image plane obtained by removing the character image plane from the target image data, and stores the generated pattern image plane in the storage unit 12. At this time, the control unit 11 determines the size of the processing block based on the compression processing parameter of the pattern image plane to be performed later and the resolution conversion parameter, and divides the target image data into processing blocks of the determined size. Thus, for each processing block, the value of the pixel to be excluded among the pixels in the processing block is determined based on the value of the pixel that is not excluded.

  The control unit 11 converts the resolution of the character color image plane and the pattern image plane stored in the storage unit 12, respectively, and further compresses the character image plane, and the character color image plane and the pattern image plane after the resolution conversion. And stored in the storage unit 12. Here, both resolution conversion and compression processing for the pattern image plane are performed by processing parameters related to the size of the processing block. The control unit 11 further checks whether there is image data of a page not selected as the target image data. If there is such image data, one of the image data of the unselected page is selected as the target image data. The above process is repeated.

  Further, if the processing of the image data of all pages is completed, the control unit 11 converts the compressed image data related to each plane of each page stored in the storage unit 12 into image data of a predetermined format such as PDF. The converted image data is output from the image output unit 14.

  The converted image data obtained in this way is decompressed for each plane, for example, on the receiving side. The receiving side converts the resolution so that the resolution of the character color image plane and the pattern image plane is restored to the original (original image) resolution, and corresponds to the black pixel on the character image plane of the character color image plane. Reproduce the image data from which the pixel values have been extracted (this will reproduce the image of the character part including the color) and overwrite the reproduced image data of the character part at the corresponding position on the design image plane. Thus, the original image data is reproduced.

  In the above description, when generating the pattern image plane, processing blocks are generated in consideration of processing parameters for resolution conversion and compression processing to be performed later, and processing is performed for each processing block. Instead of this, the image image plane data is generated by dividing into processing blocks of a predetermined size when generating the pattern image plane, and resolution conversion or compression processing is performed based on the size of the processing block. Processing parameters may be determined. For example, when the size of the processing block is 16 × 16, the size of the pixel block in the compression processing is set to 16 × 16.

  Further, in the description of the present embodiment, a case has been described in which hole removal processing is performed on the removed portion when partial image data is removed, such as dividing the image data into planes. For example, it can be used for processing for removing noise and dirt (so-called artifacts) from image data.

1 is a configuration block diagram illustrating an example of an image processing apparatus according to an embodiment of the present invention. It is a functional block diagram showing the processing content performed by the control part of the image processing apparatus which concerns on embodiment of this invention. It is explanatory drawing showing the example of each image plane. It is a flowchart figure showing the process example of the pattern image plane production | generation part.

Explanation of symbols

11 control unit, 12 storage unit, 13 image input unit, 14 image output unit, 21 image correction unit, 22 character image plane generation unit, 23 character color image plane generation unit, 24 design image plane generation unit, 25 character color image plane Resolution conversion unit, 26 character color image plane compression unit, 27 pattern image plane resolution conversion unit, 28 pattern image plane compression unit, 29 character image plane compression unit, 30 format unit.

Claims (9)

Preprocessing means for performing preprocessing on image data to be processed;
Compression means for dividing the pre-processed image data into pixel blocks of a predetermined size and performing compression by a predetermined process for each pixel block;
Including
The image processing apparatus, wherein the preprocessing unit divides the image data into preprocessing blocks corresponding to the pixel blocks in the compression unit, and executes predetermined preprocessing for each preprocessing block. Preprocessing means for dividing the image data to be processed into preprocessed blocks of a predetermined size, and executing predetermined preprocessing for each preprocessed block;
Compression means for dividing the pre-processed image data into pixel blocks of a size corresponding to the pre-process block, and compressing by a predetermined process for each pixel block;
An image processing apparatus comprising: The image processing apparatus according to claim 1 or 2,
Extracting an image part constituting an image having a predetermined property from the target image data to be compressed, extracting an image part obtained by removing the image part from the target image data, Means for generating second partial image data;
The pre-processing unit divides the second partial image data into the pre-processing blocks using the second partial image data as processing target image data, and the pixel value of the removed pixel for each pre-processing block. An image processing apparatus characterized by executing a process for adjusting the predetermined pre-process. The image processing apparatus according to claim 3.
The preprocessing means adjusts the pixel value of the removed pixel in the predetermined preprocessing based on the pixel value of the pixel that has not been removed in the preprocessing block in order to adjust the pixel value of the removed pixel. Determining and adjusting the image processing apparatus. The image processing apparatus according to claim 3.
The preprocessing means, when there is a pixel that has not been removed in the preprocessing block in order to adjust the pixel value of the removed pixel in the predetermined preprocessing, the pixel value of the pixel that has not been removed And determining a pixel value of the removed pixel based on
In the predetermined preprocessing, in order to adjust the pixel value of the removed pixel, if there is no pixel that has not been removed in the preprocessing block, the pixel of the pixel that has not been removed in another preprocessing block By acquiring a value and determining the pixel value of the removed pixel based on the acquired pixel value,
An image processing apparatus for adjusting a pixel value of the removed pixel. Using a computer,
A step of pre-processing the image data to be processed;
Dividing the pre-processed image data into pixel blocks of a predetermined size and performing compression by predetermined processing for each pixel block;
And execute
In the preprocessing, the image data is divided into preprocessing blocks corresponding to pixel blocks in the compression unit, and predetermined preprocessing is executed for each preprocessing block. Using a computer,
Dividing the image data to be processed into pre-process blocks of a predetermined size, and executing the pre-process for each pre-process block;
Dividing the pre-processed image data into pixel blocks of a size corresponding to the pre-process block, and performing compression by a predetermined process for each pixel block;
An image processing method characterized in that On the computer,
A procedure for pre-processing the image data to be processed;
A procedure of dividing the pre-processed image data into pixel blocks of a predetermined size and performing compression by a predetermined process for each pixel block;
And execute
In the preprocessing, the image processing program divides the image data into preprocessing blocks corresponding to the pixel blocks in the compression unit, and executes predetermined preprocessing for each preprocessing block. On the computer,
A procedure of dividing the image data to be processed into pre-process blocks of a predetermined size and executing the pre-process for each pre-process block;
Dividing the pre-processed image data into pixel blocks of a size corresponding to the pre-process block, and performing compression by a predetermined process for each pixel block;
An image processing program for executing

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