JP2004228952A - Image processor, program for processing image, and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To code gray images and color images with a high efficiency by means of one coder by utilizing the image compression coding technique according to the JPEG 2000, and avoid the disadvantages of the JPEG 2000. <P>SOLUTION: The color space transform process for transforming an RGB image to a YCbCr image in the brightness color difference system is one of features of the compression coding according to the JPEG 2000 and has the need of the RGB to YCbCr color space transform and a coding process thereafter every component even for a gray image originally having no color difference component, thus making a useless encoding to deteriorate the encoding efficiency and slow the processing speed. Thereupon, an image region separating means 121 decides an image region, a process contents switching means 122 switches the process contents, based on the result. In the color space transform process of a gray image region, only its brightness components are taken for effective ones while the code value of the color difference component is set to 0, and all processes are made from the color space transform process to dispense with useless processes, increase the processing speed and improve the coding efficiency. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to various image processing apparatuses such as a digital copying machine (including a multifunction peripheral = MFP), a printer, a scanner, and a personal computer, an image processing program, and a storage medium.
[0002]
[Prior art]
Generally, there are various types of document image data handled by this type of image processing apparatus. For example, some documents are mostly gray images, but have partially laid out color images such as photographs.
[0003]
As a high-definition image compression / decompression technology capable of restoring a high-quality image with a high compression ratio, an image compression / encoding technology based on the JPEG2000 algorithm has attracted attention.
[0004]
[Patent Document 1]
JP 2001-297303 A
[0005]
[Problems to be solved by the invention]
If the JPEG2000 algorithm is used, several high-efficiency encoding processes are included, and high-efficiency, high-compression-rate compression encoding is basically possible. Depending on the characteristics, it is not always effective, and it may be a wasteful process, rather deteriorating the coding efficiency and hindering high-speed processing.
[0006]
That is, in consideration of the feature of the compression encoding by the JPEG2000 algorithm, one of them is a color space conversion that converts an RGB image into a luminance / color difference YCbCr image (Y: luminance component, Cb, Cr: color difference component). There is a process for increasing the compression efficiency of the image, and even for a gray image originally having no color difference components, it is necessary to perform RGB → YCbCr color space conversion and subsequent encoding processes for each component, and the final code formation Although it is possible to remove the chrominance component of that part at the stage, it has the same meaning as the result of performing useless encoding, resulting in poor encoding efficiency and slow processing speed. .
[0007]
SUMMARY OF THE INVENTION An object of the present invention is to use image compression encoding technology based on the JPEG2000 algorithm in compressing and encoding various document image data and the like. And the inconvenience of the JPEG2000 algorithm at that time can be avoided.
[0008]
[Means for Solving the Problems]
2. The image processing apparatus according to claim 1, wherein the image encoding apparatus compresses and encodes the document image data according to a JPEG2000 algorithm, and an image area separation signal for a color image area and a gray image area mixed in the document image data. Processing content switching means for switching the processing content by the compression encoding means based on the
[0009]
Therefore, by using the compression encoding means which basically performs compression encoding according to the JPEG2000 algorithm, the compression encoding processing of the color image area and the gray image area can be handled by a single encoding means, and the configuration is simple and highly efficient. In addition, by switching the processing contents of the compression encoding means based on an image area separation signal of a color image area and a gray image area mixed in the document image data, the JPEG2000 algorithm can be further utilized by utilizing the features of the JPEG2000 algorithm. Can be avoided.
[0010]
According to a second aspect of the present invention, in the image processing apparatus according to the first aspect, an image area separating unit that separates a color image area and a gray image area mixed in the document image data and outputs an image area separation signal. Prepare.
[0011]
Therefore, when the applicable model is, for example, a personal computer or the like, the image area separation signal may be configured to be input from the outside, but when the applicable model is, for example, an image forming apparatus such as a digital copying machine, Providing the image area separating means itself enables proper image compression encoding processing by itself.
[0012]
According to a third aspect of the present invention, in the image processing apparatus according to the first or second aspect, the compression encoding unit performs at least a procedure of a color space conversion process, a two-dimensional wavelet transform process, a quantization process, and an entropy encoding process. The image data is compression-encoded, and the processing content switching means sets a color encoding mode for an area separated as a color image area by an image area separation signal, and sets all codes from the color space conversion processing. And the area separated as a gray image area by the image area separation signal is set to the gray encoding mode, the code amount of the color difference component during the color space conversion processing is set to 0, and only the luminance component is subjected to the color space conversion. The processing contents of the color space conversion processing in the compression coding means are switched so as to perform all the coding processing from the processing.
[0013]
Therefore, in consideration of the feature of the compression encoding by the JPEG2000 algorithm, one of them is a color space conversion which converts an RGB image into a YCbCr image of a luminance / color difference system (Y: luminance component, Cb, Cr: color difference component). There is a process for increasing the compression efficiency of the image, and even for a gray image originally having no color difference components, it is necessary to perform RGB → YCbCr color space conversion and subsequent encoding processes for each component, and the final code formation Although it is possible to remove the chrominance component of that part at the stage, it has the same meaning as the result of performing useless encoding, resulting in poor encoding efficiency and slow processing speed. Focusing on the point, as a specific content of the invention according to claim 1 or 2, regarding the gray image area, the code amount of the color difference component is set to 0 as the color space conversion processing and the luminance component is set. And effective themselves, by causing all processing from the color space conversion processing, it is possible to omit useless processing, faster processing, thereby improving the coding efficiency. That is, useless component processing can be omitted for an image area determined to be a gray image area.
[0014]
According to a fourth aspect of the present invention, in the image processing apparatus according to any one of the first to third aspects, the processing content switching means switches a color encoding mode and a gray encoding mode for the entire document image data. The processing contents are switched so as to apply either one.
[0015]
Therefore, by switching between the color encoding mode and the gray encoding mode in units of the entire document image data, the invention according to claims 1 to 3 can be most simply realized.
[0016]
According to a fifth aspect of the present invention, in the image processing apparatus according to the fourth aspect, the compression encoding unit is configured to switch between a color encoding mode and a gray encoding mode applied to a main header area of the encoded data. Describe any one of the encoding mode information.
[0017]
Accordingly, since the encoding mode information is described in the main header area of the compression-encoded code data, decoding of the code data can be performed without error by referring to the coding mode information.
[0018]
According to a sixth aspect of the present invention, in the image processing apparatus according to any one of the first to third aspects, the processing content switching unit is configured to divide the document image data into a plurality of pieces and encode the document image data in a plurality of small area units. The processing content is dynamically switched between the color encoding mode and the gray encoding mode.
[0019]
Therefore, switching between the color encoding mode and the gray encoding mode is performed by dividing a document image data into a plurality of small areas and encoding the divided document image data, for example, a tile as in the seventh aspect of the present invention. By performing the operation in units of raster lines as in the invention of the first aspect, the inventions of the first to third aspects can be realized finely according to the state of the document image data.
[0020]
According to a ninth aspect of the present invention, in the image processing apparatus according to the seventh aspect, the compression encoding means includes a color encoding mode and a gray code applied to each tile in a main header area of the encoded data. Any coding mode information with the coding mode is described.
[0021]
Therefore, since the encoding mode information is described for each tile in the main header area of the encoded data, the decoding can be performed without error by referring to the encoding mode information when decoding the encoded data. .
[0022]
According to a tenth aspect of the present invention, in the image processing apparatus according to the eighth aspect, the compression encoding unit is configured to switch between a color encoding mode and a gray encoding mode applied to a main header area of the encoded data. The coding mode information on the switching raster line is described.
[0023]
Therefore, since the encoding mode information on the switching raster line is described in the main header area of the encoded data, the decoding can be performed without error by referring to this encoding mode information when decoding the encoded data. .
[0024]
According to an eleventh aspect of the present invention, in the image processing device according to the seventh aspect, the compression encoding means includes a color encoding mode and a gray encoding mode applied to the tiles in the code data of each of the compressed and encoded tiles. Is described.
[0025]
Accordingly, since the coding mode information applied to each tile is described in the code data of each compression-coded tile, decoding can be performed without error by referring to the coding mode information when decoding the code data. .
[0026]
According to a twelfth aspect of the present invention, in the image processing apparatus according to the seventh aspect, the compression encoding means relates to a raster line for switching between a color encoding mode and a gray encoding mode applied to the encoded data. Describe the encoding mode information.
[0027]
Accordingly, the coding mode information on the switching raster line is described in the code data of each tile that has been compressed and coded, so that decoding of the code data can be performed without error by referring to the coding mode information.
[0028]
An image processing program according to claim 13 is installed in a computer, and stores, in the computer, a compression encoding function for compressing and encoding document image data in accordance with a JPEG2000 algorithm and a color image area mixed in the document image data. And a processing content switching function of switching the processing content by the compression encoding function based on the image area separation signal from the gray image area.
[0029]
Therefore, by using a compression coding function for compression coding according to the JPEG2000 algorithm, a single coding means can handle compression coding processing for a color image area and a gray image area with a simple configuration and high efficiency. In addition, by switching the processing contents by the compression encoding function based on an image area separation signal between a color image area and a gray image area mixed in the document image data, the JPEG2000 algorithm can be further utilized by utilizing the features of the JPEG2000 algorithm. Can be avoided.
[0030]
A computer-readable storage medium according to a fourteenth aspect stores the image processing program according to the thirteenth aspect.
[0031]
Therefore, an effect similar to that of the thirteenth aspect is obtained.
[0032]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings.
[0033]
[Outline of JPEG2000]
The present embodiment utilizes the JPEG2000 algorithm. First, JPEG2000 will be briefly described.
[0034]
FIG. 1 is a functional block diagram for explaining the basics of the JPEG2000 algorithm. As shown in FIG. 1, the JPEG2000 algorithm includes a color space transform / inverse transform unit 101, a two-dimensional wavelet transform / inverse transform unit 102, a quantization / inverse quantize unit 103, an entropy encoding / decode unit 104, a tag process It is configured by the unit 105. Hereinafter, each unit will be described.
[0035]
The color space transform / inverse transform unit 101 and the two-dimensional wavelet transform / inverse transform unit 102 will be described with reference to FIGS.
[0036]
FIG. 2 is a schematic diagram illustrating an example of each of the divided components of an original image that is a color image. In a color image, as shown in FIG. 2, components R, G, and B (111) of the original image are generally separated by, for example, an RGB primary color system. Then, the components R, G, and B of the original image are further divided by the tiles 112, which are rectangular regions. Each tile 112, for example, R00, R01, ..., R15 / G00, G01, ..., G15 / B00, B01, ..., B15 constitutes a basic unit when executing the compression / decompression process. Therefore, the compression / expansion operation is performed independently for each of the components R, G, B (111) and for each tile 112.
[0037]
Here, at the time of encoding the image data, the data of each tile 112 is input to the color space conversion / inverse conversion unit 101 shown in FIG. At 102, a two-dimensional wavelet transform (forward transform) is applied and spatially divided into frequency bands.
[0038]
FIG. 3 is a schematic diagram showing subbands at each decomposition level when the number of decomposition levels is three. The two-dimensional wavelet transform / inverse transform unit 102 performs a two-dimensional wavelet transform on the tile original image (0LL) (decomposition level 0) obtained by dividing the original image into tiles, Separate the bands (1LL, 1HL, 1LH, 1HH). Then, the two-dimensional wavelet transform / inverse transform unit 102 continuously performs a two-dimensional wavelet transform on the low-frequency component 1LL in this layer, and outputs the sub-bands (2LL, 2HL, 2LH, 2HH) shown in the decomposition level 2. Is separated. Similarly, the two-dimensional wavelet transform / inverse transformer 102 sequentially performs the two-dimensional wavelet transform on the low-frequency component 2LL, and separates the sub-bands (3LL, 3HL, 3LH, 3HH) shown in the decomposition level 3. I do. In FIG. 3, subbands to be encoded at each decomposition level are shown in gray. For example, if the number of decomposition levels is 3, the gray subbands (3HL, 3LH, 3HH, 2HL, 2LH, 2HH, 1HL, 1LH, 1HH) are to be encoded, and the 3LL subband is not encoded. .
[0039]
Next, in the quantization / inverse quantization unit 103, after bits to be encoded are determined in the specified encoding order, a context is generated from bits around the target bits.
[0040]
FIG. 4 is a schematic diagram illustrating a precinct. The wavelet coefficients after the quantization process are divided into non-overlapping rectangles called “precincts” for each subband. This was introduced to make efficient use of memory in the implementation. As shown in FIG. 4, one precinct is composed of three rectangular regions that spatially match. Furthermore, each precinct is divided into non-overlapping rectangular “code blocks”. This is a basic unit when performing entropy coding.
[0041]
FIG. 5 is a schematic diagram showing an outline of a process of decomposing the values of the two-dimensional wavelet coefficients after the two-dimensional wavelet transform into “bit planes” and ranking the “bit planes” for each pixel or code block. . The coefficient value after the wavelet transform can be quantized and coded as it is. However, in JPEG2000, in order to increase the coding efficiency, the coefficient value is decomposed into "bit planes" and " A "bit plane" can be ranked. FIG. 5 briefly shows the procedure. In this example, the original image (32 × 32 pixels) is divided into four 16 × 16 pixel tiles, and the size of the precinct at the decomposition level 1 and the size of the code block are each 8 × 8 pixels. And 4 × 4 pixels. The precinct and code block numbers are assigned in raster order. The pixel expansion outside the tile boundary is performed by using a mirroring method, performing a wavelet transform using a reversible (5, 3) filter, and obtaining a wavelet coefficient value of decomposition level 1.
[0042]
FIG. 5 also shows a conceptual schematic diagram of a representative “layer” for tile 0 / precinct 3 / code block 3. The layer structure is easy to understand when the wavelet coefficient value is viewed from the horizontal direction (bit plane direction). One layer is composed of an arbitrary number of bit planes. In this example, layers 0, 1, 2, and 3 are respectively composed of three bit planes of 1, 3, and 1. Then, a layer including a bit plane closer to the LSB is subject to quantization first, and conversely, a layer closer to the MSB remains unquantized to the end. A method of discarding from a layer close to the LSB is called truncation, and it is possible to finely control the quantization rate.
[0043]
Next, the entropy encoding / decoding unit 104 will be described with reference to FIG. FIG. 6 is a schematic diagram illustrating a code stream of encoded image data. The entropy encoding / decoding unit 104 (see FIG. 1) encodes each component RGB tile 112 by probability estimation from the context and the target bit. In this way, the encoding process is performed on all the components RGB of the original image in tile 112 units.
[0044]
Next, the tag processing unit 105 will be described. The tag processing unit 105 combines all encoded data from the entropy encoding / decoding unit 104 into one code stream and performs a process of adding a tag to the code stream. FIG. 6 briefly shows the structure of the code stream. Tag information called a header is added to the head of such a code stream and the head of a partial tile constituting each tile 112, and thereafter, encoded data of each tile 112 follows. Then, a tag is placed again at the end of the code stream.
[0045]
On the other hand, at the time of decoding, image data is generated from the code stream of each tile 112 of each component RGB, contrary to the encoding. Such a process will be briefly described with reference to FIG. The tag processing unit 105 interprets the tag information added to the code stream input from the outside, decomposes the code stream into a code stream of each tile 112 of each component RGB, and a code stream of each tile 112 of each component RGB. A decryption process is performed for each. At this time, the positions of the bits to be decoded are determined in the order based on the tag information in the code stream, and the quantization / dequantization unit 103 sets the peripheral bits of the target bit positions (decoding has already been performed. Is generated from the sequence of Then, the entropy coding / decoding section 104 performs decoding by probability estimation from the context and the code stream to generate a target bit, and writes it to the position of the target bit. Since the data decoded in this manner is spatially divided for each frequency band, the two-dimensional wavelet transform / inverse transform unit 102 performs an inverse two-dimensional wavelet transform on the data to obtain each component in the image data. Each tile 112 in RGB is restored. The restored data is converted into the original color system data by the color space conversion / inversion unit 101.
[0046]
Next, an example of a JPEG2000 code format will be described. FIG. 7 is a schematic diagram showing a code format of JPEG2000. The code format starts with an SOC (Start of Codestream) marker indicating the start of code data, followed by a main header describing coding parameters and quantization parameters, and further followed by actual code data. It is. Actual code data starts with an SOT (Start of Tile-part) marker, and is composed of a tile header, a SOD (Start of Data) marker, and tile data (code). After the code data corresponding to the entire image, an EOC (End of Codestream) marker indicating the end of the code is added.
[0047]
[Overall configuration of digital full-color copying machine]
Next, a configuration example of a digital full-color copying machine that is an image processing apparatus according to the present embodiment will be described with reference to FIG.
[0048]
The digital color copying machine 1 also functions as an MFP = multifunction machine having a data storage function, and includes a printer 2 which is a color printer functioning as a printer engine, and an image reading device installed on the upper part of the printer 2. And a scanner 3 which is a color image scanner.
[0049]
The printer 2 forms an image by an electrophotographic method in an image forming unit 4 based on image data of a document optically read by a scanner 3 and image data transmitted from an external device, and sends the image to a paper feeding unit. 5 is transferred to a sheet P which is a recording medium conveyed through a sheet conveying path 7 by a sheet conveying section 6, and the sheet P on which an image is transferred is conveyed to a fixing section 9 by a conveying belt 8, and the transferred image of the sheet P is transferred. Is heated and pressurized by a fixing unit 9 and is discharged and discharged to a discharge tray 10.
[0050]
The image forming unit 4 includes a charging unit 12 that uniformly charges the surface of the photoconductor 11 around the rotating drum-shaped photoconductor 11, and an image for each color obtained by exposing and scanning the uniformly charged surface of the photoconductor 11. Exposure unit 13 for forming an electrostatic latent image based on data on photoconductor 11, electrostatic latent image for each color including cyan (C), magenta (M), yellow (Y), and black (K) toners A revolver type color developing unit 14 for forming a visible toner image by adhering toner corresponding to the image, and an intermediate for sequentially transferring toner images of respective colors onto an intermediate transfer belt 15 supported by a plurality of rollers. The transfer unit 16 is formed by arranging a photoconductor cleaning unit 17 for scraping off toner remaining on the photoconductor 11 without being transferred onto the intermediate transfer belt 15, a charge removing unit 18 for removing charges on the photoconductor 11, and the like. Have Further, a transfer unit 19 for collectively transferring the toner images on the intermediate transfer belt 15 onto the sheet P and a belt cleaning unit 20 for scraping off the toner remaining on the intermediate transfer belt 15 without being collectively transferred onto the sheet P are provided. Is formed.
[0051]
Next, the scanner 3 will be described. The scanner 3 includes a scanner body 21 and an ADF (automatic document feeder) 22 which is a document feeder provided on the upper part of the scanner body 21. On the upper surface of the housing 23 of the scanner body 21, a placed original glass 24 on which an original is placed when reading an original image in the original fixed mode, and a transport used when reading the original image in the original transport mode. A document glass 25 is provided. Here, the document fixing mode is an operation mode for reading an image of a document placed on the placed document glass 24, and the document transport mode is for automatically feeding a document by the ADF 22 and automatically feeding the document. This is an operation mode in which an image of a paper document is read when the paper document passes over the glass sheet 25 for conveyance.
[0052]
Further, an illumination lamp (high-intensity Xe lamp) 26 and a mirror 27 as exposure means for irradiating the original with light are provided at a position inside the housing 23 and facing the placed original glass 24 from below. One traveling body 28 is disposed movably in the sub-scanning direction along the placed original glass 24. A second traveling body 31 including two mirrors 29 and 30 is arranged on the reflected light path of the first traveling body 28 so as to be movable in the sub-scanning direction along the placed document glass 24. An SBU (Sensor Board Unit) 34 mounted with a CCD (Charge Coupled Device) 33 which is a color line sensor via a lens 32 is located in the reflected light path of the two-wheeled vehicle 31. Note that the CCD 33 functions as a photoelectric conversion element.
[0053]
A stepping motor 35 is connected to the first traveling body 28 and the second traveling body 31 as sub-scanning means by pulleys, wires, or the like (neither is shown). The body 31 is movable in the same sub-scanning direction from the left side to the right side in FIG. 7 at a speed ratio of 2: 1. Note that the digital color copying machine 1 of the present embodiment has a scaling function, and at the time of enlarging / reducing copying, the speed of the stepping motor 35 is controlled in accordance with the scaling factor so that the first step is performed. By changing the moving speed of the second traveling bodies 28 and 31 with respect to the original, the magnification change processing in the sub-scanning direction is mechanically performed. The scaling in the main scanning direction is performed by an electrical scaling process described later.
[0054]
Such a digital full-color copying machine 1 is controlled by a control system including a plurality of microcomputers. FIG. 9 is a schematic block diagram showing an electrical connection of a control system related to image processing among these control systems. In this control system, a CPU 41, a ROM 42, a RAM 43, an operation panel 44, and the like are connected by a bus 45. The CPU 41 performs various calculations and centrally controls processing such as image processing. The ROM 42 stores various programs and fixed data related to the processing executed by the CPU 41. The RAM 43 is a work area for the CPU 41. The IPU (Image Processing Unit) 46 includes hardware related to various types of image processing. The ROM 42 serving as a storage medium includes a non-volatile memory such as an EEPROM or a flash memory, and a program stored in the ROM 42 is controlled by the CPU 41 through an external device (not shown) through an I / O port 47. It can be rewritten to a program downloaded from. That is, in the present embodiment, programs for realizing various functions are stored in the ROM 42, and the ROM 42 functions as a storage medium storing the programs.
[0055]
Further, the digital copying machine 1 of the present embodiment includes each functional block of the JPEG2000 algorithm described with reference to FIG. 1, and performs compression encoding of image data by the above-described JPEG2000 algorithm. That is, the functions of the compression encoding unit and the decoding unit as shown in FIG. 1 are executed by the processing performed by the hardware by the IPU 46, but are executed by the processing performed by the CPU 41 based on the program stored in the ROM 42. May be. As a result, digital image data of a plurality of images read by the scanner 3 and subjected to various image processing such as white shading correction by the IPU 46 are compression-encoded by the JPEG2000 algorithm, and the code of each image is basically converted. Create a stream. That is, basically, an image is divided into one or a plurality of rectangular areas (tiles), and pixel values are discrete wavelet-transformed for each of the rectangular areas and compression-coded hierarchically.
[0056]
[Image compression encoding process]
When the compression encoding means based on the JPEG2000 algorithm shown in FIG. 1 is rewritten, it can be shown as in FIG. That is, the DC level shift unit 101a, the color conversion unit 101b, the wavelet transform unit 102a, the quantization unit 103a, the coefficient modeling unit 104a, the arithmetic coding unit 104b, and the code order control unit 105a are arranged in the processing order, so that the compression coding means is arranged. 106 is configured. Here, the DC level shift unit 101a and the color conversion unit 101b belong to the color space conversion / inverse conversion unit 101, and the DC level shift unit 101a determines that the input image signal is a positive number such as an RGB signal value. In some cases, a predetermined conversion formula is used to perform a level shift process of subtracting の of the signal dynamic range from each signal value, and the color conversion unit 101b converts the RGB image into a luminance / color difference YCbCr image. A process for increasing the compression efficiency of the color image is performed. The wavelet transform unit 102a belongs to the two-dimensional wavelet transform / inverse transform unit 102, and performs the above-described conversion processing to wavelet coefficients. The quantization unit 103a belongs to the quantization / dequantization unit 103, and performs processing for reducing the dynamic range of wavelet coefficients in order to perform efficient compression. As an example of this quantization processing, there is a post-quantization method for performing quantization by truncating lower bit planes of a completed code sequence by utilizing the fact that entropy coding described later is a bit plane.
[0057]
The coefficient modeling unit 104a and the arithmetic coding unit 104b belong to the entropy coding / decoding unit 104 that performs block-based bit plane coding. Among them, the coefficient modeling unit 104a creates a bit model for binary arithmetic coding from the multivalued wavelet coefficients to be coded, and the coding method is determined by this processing. As a coding method in the arithmetic coding unit 104b, a method called MQ-Coder, which is a new binary image coding method, is used. The code order control unit 105a is included in the tag processing unit 105.
[0058]
In addition to the compression encoding means 106 according to the JPEG2000 algorithm, the present embodiment separates a color image area and a gray image area mixed in the document image data input as a processing target into the data. An image area separation unit 121 as an image area separation unit that outputs an image area separation signal, and a color conversion unit 101b in the compression encoding unit 106 according to the image area separation signal output from the image area separation unit 121. A selector 122 is provided as processing content switching means for switching the processing content. The image area separation unit 121 separates a color image area and a gray image area in order to perform optimal image processing that matches an image feature, and is a known image area separation technique, for example, an object. A method as disclosed in Patent Document 1 in which a background color is specified for the document image data and a region identification result of the document image is obtained using the background color in a bottom-up manner may be used, and details thereof are omitted. The gray image area and the black-and-white image area can be identified by appropriately setting the lower limit level and the upper-limit level of the black-and-white image recognition.
[0059]
The selector 122 switches the processing content of the document image data to be processed in the color conversion unit 101b in the compression encoding unit 106 according to the image area separation signal. Has no chrominance component from the beginning, so that in the gray coding mode, the code amount of the chrominance components Yb and Yr is set to 0, and the subsequent coding process is not performed. On the other hand, in the case of an image area separation signal that is a color image area, all processing by the compression encoding unit 106 is performed as usual without restricting the processing of the color conversion unit 101b as a color encoding mode suitable for a color image. The processing contents are switched so as to be performed.
[0060]
The functions of the image area separation unit 121 and the selector 122 may also be executed by processing performed by the CPU 41 based on a program stored in the ROM 42.
[0061]
In general, when considering the features of compression encoding by the JPEG2000 algorithm, as one of the above, a color space for converting the above-described RGB image into a YCbCr image of a luminance / color difference system (Y: luminance component, Cb, Cr: color difference component) There is a process called conversion to increase the compression efficiency of a color image. Even in a gray image region originally expressed as a gray image having no color difference component, the RGB → YCbCr color space conversion and the subsequent encoding process for each component are performed. It is necessary to perform this, and it is possible to remove the color difference component of that part at the final code formation stage, but as a result, it has the same meaning as performing useless coding, and the coding efficiency is poor, There is a problem that the processing speed is reduced. In this regard, according to the basic configuration of the present embodiment, when the document image data is compression-encoded, all the encoding processes are performed by the compression encoding unit 106 for the color image area, Regarding the area, the code amount of the color difference component is set to 0 at this time as the color space conversion process in the color conversion unit 101b, and only the luminance component is made valid, and all the encoding processes are performed from the color space conversion process. Useless processing can be omitted, and processing can be speeded up and coding efficiency can be improved. That is, useless component processing can be omitted for an image area determined to be a gray image area.
[0062]
[Specific processing example]
Now, a description will be given of several processing examples in which document image data of a document 133 in which a gray image area 131 and a color image area 132 are mixed as schematically shown in FIG.
[0063]
First, as a first example, in the simplest case, for example, gray coding mode or color coding mode is applied to the entire document image data in accordance with the ratio of the gray image area 131 and the color image area 132 in the document image data. The selector 122 can be configured to switch to apply any one of the encoding modes. In this case, the compression encoding processing method may be a tile method in which the image is divided into a plurality of tiles and encoded in tile units, or a raster method in which the image is divided into raster lines and encoded in raster line units. Is also good.
[0064]
In this case, as shown in FIG. 12, the compression encoding unit 106 determines whether the mode applied in the main header area of the encoded data is the color encoding mode or the gray encoding mode. If the encoding mode information is described, the decoding can be performed without error by referring to the encoding mode information when decoding the code data. The example shown in FIG. 12 is a tile coding method (see FIG. 11B), and shows an example in which the entire document image data is gray-coded by applying the gray coding mode.
[0065]
Next, as a second more practical example, the processing mode may be dynamically switched in a unit of a small area = a unit of a tile. For example, the document image data as shown in FIG. 11A is divided into a plurality of tiles A1, A2,..., F3 and F4 as shown in FIG. Switching between the processing contents for the gray coding mode and the color coding mode may be performed.
[0066]
FIG. 13 shows an example of a code string that has been compression-encoded by the compression-encoding means 106 according to this method. As shown in the figure, the mode applied to the main header area is a color encoding mode or a gray encoding mode. If the encoding mode information is described for each tile, decoding can be performed without error by referring to the encoding mode information when decoding the code data.
[0067]
However, not only the method described in the main header area, but as shown in FIG. 14, the modes individually applied to the code data (tile header portion) of each compression-coded tile are the color coding mode and the gray coding mode. The coding mode information indicating which of the coding modes is used may be described. According to this method, decoding of the code data can be performed without error by referring to the coding mode information.
[0068]
As a third more practical example, the processing mode may be dynamically switched in a unit of a certain small area = a unit of a raster line. For example, the document image data as shown in FIG. 11A is divided into a plurality of raster lines y0, y1,... As shown in FIG. May be switched between for gray coding mode and for color coding mode.
[0069]
FIG. 15 shows an example of a code string that has been compression-encoded by the compression-encoding means 106 according to this method. As shown in the drawing, the mode applied to the main header area is a color encoding mode or a gray encoding mode. If the encoding mode information is described by a raster line whose mode changes, decoding can be performed without error by referring to the encoding mode information when decoding the code data. . In the illustrated example, processing in the gray encoding mode is performed from raster line 0, switching to the color encoding mode is performed on the raster line y1, switching to the gray encoding mode is performed on the raster line y3, and so on.
[0070]
However, not limited to the method described in the main header area, as shown in FIG. 16, a raster in which the mode individually applied to the compression-coded code data is switched between a color coding mode and a gray coding mode. Information about lines may be described as encoding mode information. According to this method, decoding of the code data can be performed without error by referring to the coding mode information.
[0071]
Further, in the present embodiment, the digital copying machine has been described as including the image area separating unit 121, but a configuration in which the digital copying machine does not have them and can be obtained as an external signal may be used. That is, if the applicable model as the image processing apparatus is, for example, a personal computer, the image area separation signal may be configured to be input from the outside, but the applicable model as the image processing apparatus is, for example, the present embodiment. In the case of an image forming apparatus such as a digital copying machine as in the embodiment, since the image forming apparatus itself includes the image area separating unit 121, appropriate image compression encoding processing can be performed by itself.
[0072]
【The invention's effect】
According to the image processing apparatus of the first aspect of the present invention, by using the compression encoding means that basically performs compression encoding according to the JPEG2000 algorithm, a single compression encoding process for the color image area and the gray image area is performed. In addition to being able to cope with the encoding means, having a simple configuration and high efficiency, the processing content of the compression encoding means is switched based on an image area separation signal between a color image area and a gray image area mixed in the document image data. Therefore, it is possible to avoid the inconvenience of the JPEG2000 algorithm by utilizing the features of the JPEG2000 algorithm.
[0073]
According to the second aspect of the present invention, in the image processing apparatus according to the first aspect, when the applicable model is, for example, a personal computer, the image processing apparatus may be configured to receive the image area separation signal from outside. In the case where the applicable model is an image forming apparatus such as a digital copying machine, for example, the image forming apparatus itself includes the image area separating means, so that the apparatus itself can perform an appropriate image compression / encoding process by itself.
[0074]
According to the third aspect of the present invention, in the image processing apparatus according to the first or second aspect, in consideration of the feature of compression encoding by the JPEG2000 algorithm, one of the features is to convert an RGB image into a luminance / color difference YCbCr image ( (Y: luminance component, Cb, Cr: color difference components) is a process of increasing the compression efficiency of a color image called color space conversion. Even if a gray image originally has no color difference components, it is possible to perform RGB → YCbCr color space conversion. It is necessary to perform encoding processing for each component thereafter, and it is possible to remove the color difference component of that part at the final code formation stage, but as a result it is the same as performing unnecessary encoding Paying attention to the point that there is a problem that the encoding efficiency is low and the processing speed is low, as a specific content of the invention according to claim 1 or 2, Then, as the color space conversion processing, the code amount of the chrominance component is set to 0 and only the luminance component is made valid, and all the processing is performed from the color space conversion processing, so that unnecessary processing can be omitted. It is possible to increase the processing speed and the coding efficiency. That is, useless component processing can be omitted for an image area determined to be a gray image area.
[0075]
According to a fourth aspect of the present invention, in the image processing apparatus according to any one of the first to third aspects, switching between the color encoding mode and the gray encoding mode is performed in units of the entire document image data. Thus, the inventions of claims 1 to 3 can be most easily realized.
[0076]
According to the fifth aspect of the present invention, in the image processing apparatus according to the fourth aspect, the encoding mode information is described in the main header area of the compression-encoded code data. By referring to the encoding mode information, decoding can be performed without error.
[0077]
According to a sixth aspect of the present invention, in the image processing apparatus according to any one of the first to third aspects, the switching between the color encoding mode and the gray encoding mode is performed by dividing the document image data into a plurality of pieces. Since a certain small area to be converted, for example, a tile as in the invention of claim 7 and a raster line as in the invention of claim 8 are performed, the invention of claims 1 to 3 is performed. It can be realized finely according to the state of the document image data.
[0078]
According to the ninth aspect of the present invention, in the image processing apparatus according to the seventh aspect, the encoding mode information is described for each tile in the main header area of the compression-encoded code data. Can be decoded without error by referring to the encoding mode information.
[0079]
According to the tenth aspect of the present invention, in the image processing apparatus according to the eighth aspect, the encoding mode information relating to the switching raster line is described in the main header area of the compression-encoded code data. Can be decoded without error by referring to the encoding mode information.
[0080]
According to the eleventh aspect of the present invention, in the image processing apparatus according to the seventh aspect, the coding mode information applied to the tile is described in the code data of each compression-coded tile. Can be decoded without error by referring to the encoding mode information.
[0081]
According to the twelfth aspect of the present invention, in the image processing apparatus according to the seventh aspect, the encoding mode information on the switching raster line is described in the code data of each compressed and encoded tile. At the time of decoding, by referring to the encoding mode information, decoding can be performed without error.
[0082]
According to the image processing program of the present invention, since the compression coding function for compression coding according to the JPEG2000 algorithm is basically used, the compression coding processing of the color image area and the gray image area is performed. It can be handled by a single encoding means, has a simple configuration and is highly efficient.In addition, the processing content of this compression encoding function is based on the image area separation signal of the color image area and the gray image area mixed in the document image data. Since the switching is performed, the inconvenience of the JPEG2000 algorithm can be avoided by taking advantage of the features of the JPEG2000 algorithm.
[0083]
According to the computer-readable storage medium of the fourteenth aspect, the same effects as those of the thirteenth aspect can be obtained.
[Brief description of the drawings]
FIG. 1 is a functional block diagram of a system for realizing a basic algorithm of the JPEG2000 system which is a premise of an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a divided rectangular area of each component of an original image.
FIG. 3 is an explanatory diagram showing subbands at each decomposition level when the number of decomposition levels is three.
FIG. 4 is an explanatory diagram showing a precinct.
FIG. 5 is an explanatory diagram showing an example of a procedure for ranking bit planes. It is.
FIG. 6 is a schematic diagram illustrating a code stream of encoded image data.
FIG. 7 is a schematic diagram showing a code format of JPEG2000.
FIG. 8 is a schematic configuration diagram illustrating a digital full-color copying machine as an image processing apparatus according to an embodiment of the present invention.
FIG. 9 is a schematic block diagram showing the control system.
FIG. 10 is a block diagram illustrating a compression encoding processing portion serving as a characteristic portion.
FIG. 11 is an explanatory diagram illustrating an example of document image data to be processed;
FIG. 12 is an explanatory diagram showing an example of code data at the time of processing in page units.
FIG. 13 is an explanatory diagram showing an example of code data at the time of processing in units of tiles.
FIG. 14 is an explanatory diagram showing another example of code data at the time of processing in units of tiles.
FIG. 15 is an explanatory diagram showing an example of code data at the time of processing in units of raster lines.
FIG. 16 is an explanatory diagram showing another example of code data at the time of processing in units of raster lines.
[Explanation of symbols]
121 Image area separation means
122 Processing content switching means
131 Gray image area
132 color image area

Claims (14)

Compression encoding means for compressing and encoding the document image data according to the JPEG2000 algorithm;
Processing content switching means for switching processing content by the compression encoding means based on an image area separation signal of a color image area and a gray image area mixed in the document image data;
An image processing apparatus comprising: 2. The image processing apparatus according to claim 1, further comprising an image area separating unit that separates a color image area and a gray image area mixed in the document image data and outputs an image area separation signal. The compression encoding means compresses and encodes the document image data by at least a procedure of a color space conversion process, a two-dimensional wavelet transform process, a quantization process, and an entropy encoding process.
The processing content switching means sets a color coding mode to an area separated as a color image area by the image area separation signal, performs all the coding processing from the color space conversion processing, and sets a gray level by the image area separation signal. The region separated as the image region is set to the gray encoding mode, the code amount of the color difference component during the color space conversion process is set to 0, and only the luminance component is subjected to all the encoding processes from the color space conversion process. Switching the processing content of the color space conversion processing in the compression encoding means,
The image processing device according to claim 1. 4. The processing content switching unit according to claim 1, wherein the processing content switching unit switches the processing content so as to apply one of a color encoding mode and a gray encoding mode to the entire document image data. 5. Image processing device. The image according to claim 4, wherein the compression encoding unit describes one of a color encoding mode and a gray encoding mode applied in a main header area of the encoded data. Processing equipment. The processing content switching means dynamically switches the processing content between a color encoding mode and a gray encoding mode in a unit of a small area in which the document image data is divided into a plurality of parts and encoded. The image processing apparatus according to any one of claims 1 to 3. The image processing apparatus according to claim 6, wherein the certain small area unit is a tile unit in which the document image data is divided into a plurality of pieces and encoded. 7. The image processing apparatus according to claim 6, wherein the certain small area unit is a raster line unit in which document image data is divided and scanned into a plurality of pieces and encoded. 8. The compression encoding unit according to claim 7, wherein in a main header area of the compression-encoded code data, any one of a color encoding mode and a gray encoding mode applied to each tile is described. The image processing apparatus according to claim 1. 9. The image according to claim 8, wherein said compression coding means describes coding mode information on a raster line for switching between a color coding mode and a gray coding mode applied in a main header area of the code data obtained by compression coding. Processing equipment. 8. The compression coding unit according to claim 7, wherein the compression coding unit describes, in the code data of each compression-coded tile, any one of a color coding mode and a gray coding mode applied to the tile. Image processing device. The image processing apparatus according to claim 8, wherein the compression encoding unit describes encoding mode information on a raster line for switching between a color encoding mode and a gray encoding mode applied to the encoded data. A compression encoding function installed on a computer, for compressing and encoding document image data in accordance with the JPEG2000 algorithm;
A processing content switching function of switching processing content by the compression encoding unit based on an image area separation signal of a color image area and a gray image area mixed in the document image data;
An image processing program that executes A computer-readable storage medium storing the image processing program according to claim 13.

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