JP2004228956A - Image processor, program for processing image, and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To process black-and-white images and other images with high efficiency by means of one coder by utilizing the image compression coding technique according to the JPEG 2000, and avoid the disadvantage of the JPEG 2000. <P>SOLUTION: The bit plane coding is one of features of the compression coding according to the JPEG 2000. Even a black-and-white image must be coded in a plurality of bit planes, as in usual, so far as it is expressed with multi-value data. This results in a useless coding to deteriorate the coding 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. For the black-and-white image, some process is applied to its DC level conversion process result so that it can be handled, substantially the same as a two-value data, using a positive value plus 1 after the DC level conversion, an entropy coding process is made to dispense with useless processes, increase the processing speed and improve the coding efficiency without making a wavelet conversion and a quantizing process. <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, most documents are black and white images, but there are many documents in which images other than black and white images such as color images are partially laid out, or vice versa.
[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
[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, considering the characteristics of the compression encoding by the JPEG2000 algorithm, one of them is bit plane encoding for increasing the compression ratio, and this is a case of a monochrome image which can be treated essentially as binary data. However, since it is represented by multi-valued data, it is necessary to encode a plurality of bit planes as usual, and as a result, it has the same meaning as performing useless encoding, and the encoding efficiency is reduced. There is a problem that the processing speed is slow.
[0007]
An object of the present invention is to use image compression encoding technology based on the JPEG2000 algorithm in compressing and encoding various types of document image data and the like, and to basically improve image data having various characteristics by one encoding means. It is to be able to process efficiently and to avoid inconvenience of the JPEG2000 algorithm at that time.
[0008]
[Means for Solving the Problems]
The image processing apparatus according to the first aspect of the present invention includes a compression encoding unit that compresses and encodes document image data according to a JPEG2000 algorithm, and an image area including a monochrome image area and a non-monochrome image area mixed in the document image data. Processing content switching means for switching the processing content of the compression encoding means based on the separation signal.
[0009]
Therefore, by using a compression encoding unit that basically performs compression encoding according to the JPEG2000 algorithm, a single encoding unit can cope with a compression encoding process between a black-and-white image region and a non-monochrome image region, and the configuration is simple. In addition to the high efficiency, by switching the processing content of the compression encoding means based on the image area separation signal between the black and white image area mixed with the document image data and the non-black and white image area, the characteristics of the JPEG2000 algorithm can be further utilized. This makes it possible to avoid the inconvenience of the leverage JPEG2000 algorithm.
[0010]
According to a second aspect of the present invention, there is provided the image processing apparatus according to the first aspect, wherein a black and white image region and a non-black and white image region mixed in the document image data are separated to output an image region separation signal. Means.
[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 includes at least a DC level conversion, a color space conversion, a two-dimensional wavelet conversion, a quantization, and an entropy coding. The document image data is compression-encoded by a procedure called processing, and the processing content switching means sets a normal encoding mode to an area separated as an image area other than black and white by an image area separation signal, and sets the DC level. All the encoding processes from the conversion process are performed, and the region separated as a black and white image region by the image area separation signal is set to the black and white encoding mode, and a value obtained by adding 1 to a positive value after DC level conversion is used. Further, the processing content in the compression encoding means is switched so that the wavelet division level is set to 0 and the entropy encoding processing is performed.
[0013]
Therefore, considering the characteristics of the compression encoding by the JPEG2000 algorithm, one of them is bit plane encoding for increasing the compression ratio, and this is a case of a monochrome image which can be treated essentially as binary data. However, since it is represented by multi-valued data, it is necessary to encode a plurality of bit planes as usual, and as a result, it has the same meaning as performing useless encoding, and the encoding efficiency is reduced. Paying attention to the disadvantage that the processing speed is poor, the specific content of the invention according to claim 1 or 2 is that, in the case of a black and white image, the DC level conversion processing result is modified. By allowing the data to be treated substantially in the same manner as binary data and performing only entropy coding processing without performing two-dimensional wavelet transform processing or quantization processing, unnecessary processing is omitted. Bets can be, high-speed processing, it is possible to improve the coding efficiency. That is, when it is determined that the image is a monochrome image, the value is set to 0: white (or black), 255: black (for an 8-bit image or white), and after DC level conversion, the values are -128 and 127. become. Adding 1 to this positive value results in -128 and 128. When this value is subjected to the following three coding passes (three passes to the -bit plane: JPEG2000 standard) without performing the wavelet transform at the wavelet division level 0, both +128 and -128 are obtained. , Only the 7th bit has a value (that is, the 7th bit is 1 and the other 0th to 6th bits and the 8th bit and above are 0). When this is coded, only the seventh bit is to be coded, so that in the case of a black-and-white mixed image, the coding efficiency is increased.
[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 between a normal encoding mode and a monochrome 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 normal encoding mode and the black-and-white encoding mode in units of the entire document image data, the inventions of 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 means includes a normal encoding mode and a black-and-white 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 a normal encoding mode and a black-and-white encoding mode.
[0019]
Therefore, switching between the normal encoding mode and the black-and-white encoding mode is performed by dividing a document image data into a plurality of small areas and encoding them, for example, a tile as in the seventh aspect of the present invention, and a eighth 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 normal encoding mode applied to each tile in a main header area of the encoded data, and a black and white code. 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 includes a normal encoding mode and a black-and-white 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 apparatus according to the seventh aspect, the compression encoding unit includes a normal encoding mode and a black-and-white encoding mode applied to the tile of the encoded data of each tile. 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 normal encoding mode and a black and white 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 the computer has a compression encoding function of compressing and encoding document image data according to a JPEG2000 algorithm, and a black-and-white 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 an image area separation signal from an image area other than a monochrome image.
[0029]
Therefore, by using a compression coding function for performing compression coding in accordance with the JPEG2000 algorithm, a single coding unit can be used for the compression coding processing of the black-and-white image area and the image area other than the black-and-white image. In addition, the JPEG2000 algorithm is more efficient by switching the processing contents by this compression encoding function based on the image area separation signal between the black and white image area mixed with the document image data and the image area other than the black and white image. It is possible to avoid the disadvantage of the JPEG2000 algorithm by utilizing
[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 the present embodiment, in addition to the compression encoding means 106 according to the JPEG2000 algorithm, in the present embodiment, black-and-white image regions and image regions other than the black-and-white image region included in the document image data to be processed are mixed. And an image area separation unit 121 as an image area separation unit that outputs an image area separation signal by separating the image signal and a process in the compression encoding unit 106 according to the determination signal output from the image characteristic determination unit 121. Further, a selector 122 is provided as processing content switching means for making the processing content of the compression encoding different.
[0059]
The image area separation unit 121 separates a black-and-white image area and an image area other than a black-and-white image in order to perform optimal image processing that matches the characteristics of the image. A method such as that disclosed in Patent Document 1 in which a background color is specified for the target document image data and a region identification result of the document image is obtained bottom-up using the background color may be used, and details thereof are omitted. I do. The separation of the image area in the case of Patent Document 1 is separation of an image area other than a black-and-white image from a black-and-white / black-and-white image area. For the identification, the lower limit level and the upper limit level of the black and white image recognition are appropriately set, and if they belong to these level ranges, the black and white image region may be recognized and the black and white image region may be excluded.
[0060]
The selector 122 selects the processing of the document image data to be processed in the compression coding means 106 according to the image area separation signal and makes the processing content of the compression coding different, and in particular, JPEG2000 In the algorithm, the processing of the DC level conversion unit 101a, the processing of the color conversion unit 101b, the processing of the two-dimensional wavelet conversion unit 102a, the processing of the quantization unit 103a, and the processing of the arithmetic coding unit 104b are discarded according to the image area separation signal. As a selection target, the processing content of the compression encoding is made different depending on the characteristics of the image data.
[0061]
For example, for the area separated as an image area other than black and white by the image area separation signal, the normal coding mode is set, all the processing by the compression coding unit 106 is enabled, and all the coding processing from the DC level conversion processing is performed. Let On the other hand, the area separated as a black-and-white image area by the image area separation signal is set to the black-and-white encoding mode, and a value obtained by adding 1 to a positive value to the value after DC level conversion by the DC level shift unit 101a is used. Further, the entropy encoding process is performed with the wavelet division level set to 0. That is, the processing of the color conversion unit 101b, the processing of the two-dimensional wavelet conversion unit 102a, the processing of the quantization unit 103a, and the processing of the arithmetic coding unit 104b are omitted.
[0062]
More specifically, when it is determined that the image is a black-and-white image, the value is set to 0: white (or black), 255: black (for an 8-bit image or white), and after the DC level conversion, the value becomes −. 128 and 127. Adding 1 to this positive value results in -128 and 128 (= 10000000). When this value is subjected to the following three coding passes (three passes to the -bit plane: JPEG2000 standard) without performing the wavelet transform at the wavelet division level 0, both +128 and -128 are obtained. , Only the 7th bit has a value (that is, the 7th bit is 1 and the other 0th to 6th bits and the 8th bit and above are 0). When this is coded, only the seventh bit is to be coded, so that in the case of a black-and-white mixed image, the coding efficiency is increased. That is, it can be handled similarly to binary data. Further, bit plane encoding by the arithmetic encoding unit 104b after encoding of such bit data is not performed (not necessary). At this time, since the conversion process in the wavelet conversion unit 102a is also omitted, the number of wavelet divisions is set to 0, and information without quantization is described in a header or the like as described later. By the way, such an operation results in a value exceeding the value that the pixel can take at the time of decoding (128 × 2 = 10000000 = 256), but the clipping process is performed, and the maximum value that the pixel can take becomes the original value. Is restored.
[0063]
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.
[0064]
In general, when considering the characteristics of the compression encoding by the JPEG2000 algorithm, one of them is bit plane encoding by an arithmetic encoding unit for increasing the compression ratio. Even in the case of an image, since it is represented by multi-valued data, it is necessary to encode a plurality of bit planes as usual, and as a result, it has the same meaning as performing unnecessary encoding. However, there is a problem that the coding efficiency is low and the processing speed is low. In this regard, according to the present embodiment, in the case of a black-and-white image, the result of the DC level conversion processing is modified so that it can be treated substantially in the same way as binary data, and the two-dimensional wavelet conversion processing and the quantization processing are performed. By performing only the entropy coding process without performing the pit plane coding, the unnecessary process can be omitted, and the processing speed can be increased and the coding efficiency can be improved.
[0065]
[Specific processing example]
Now, several examples of processing when document image data of a document 133 in which a black-and-white image area 131 and an image area 132 other than a black-and-white image are mixed as schematically shown in FIG. explain.
[0066]
First, as a first example, in the simplest case, for example, black-and-white encoding is performed on the entire document image data according to the ratio of the black-and-white image area 131 and the image area 132 other than the black-and-white image in the document image data. The selector 122 can be configured to switch so as to apply either the mode or the normal encoding mode. 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.
[0067]
In this case, as shown in FIG. 12, the compression encoding means 106 determines whether the mode applied to the main header area of the encoded data is the normal encoding mode or the black-and-white encoding mode. If the coding mode information (including the number of wavelet divisions in the black and white coding mode being 0 and no quantization) is described, by referring to the coding mode information at the time of decoding the code data, no mistake is made. Decryption becomes possible. The example shown in FIG. 12 is a tile encoding method (see FIG. 11B), and shows an example in which the entire document image data is black-and-white coded by applying the black-and-white coding mode.
[0068]
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. It is also possible to switch between the processing contents for the black and white coding mode and the normal coding mode.
[0069]
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 FIG. 13, the mode applied to the main header area is a normal encoding mode or a monochrome 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.
[0070]
However, not only the method described in the main header area but also the mode individually applied to the code data (tile header portion) of each compression-coded tile as shown in FIG. 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.
[0071]
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 black and white encoding mode and for normal encoding mode.
[0072]
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 normal encoding mode or a monochrome 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, the processing in the monochrome encoding mode is performed from raster line 0, the normal encoding mode is switched on the raster line y1, the monochrome encoding mode is switched on the raster line y3, and so on.
[0073]
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 the normal coding mode and the black-and-white 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.
[0074]
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.
[0075]
【The invention's effect】
According to the image processing apparatus of the first aspect of the present invention, the compression encoding means for compressing and encoding the image in accordance with the JPEG2000 algorithm is basically used. In addition to being simple and efficient with a single encoding means, the processing content of this compression encoding means can be separated into black and white image areas mixed with document image data and non-black and white image areas. Since the switching is performed based on the signal, it is possible to avoid the inconvenience of the JPEG2000 algorithm by utilizing the features of the JPEG2000 algorithm.
[0076]
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.
[0077]
According to the third aspect of the present invention, in the image processing apparatus according to the first or second aspect, when the features of the compression encoding by the JPEG2000 algorithm are considered, one of them is bit plane encoding for increasing the compression ratio. Yes, even in the case of a black-and-white image that can be treated as equivalent to binary data, it is necessary to perform encoding of a plurality of bit planes as usual since it is represented by multi-valued data. 3. It has the same meaning as performing useless encoding, and has a problem that the encoding efficiency is low and the processing speed is reduced. In the case of a black-and-white image, the result of the DC level conversion processing is modified so that it can be treated substantially in the same way as binary data, without performing two-dimensional wavelet conversion processing and quantization processing. Since so as to perform Ntoropi encoding process only, it is possible to omit wasteful processing, faster processing, thereby improving the coding efficiency. That is, when it is determined that the image is a monochrome image, the value is set to 0: white (or black), 255: black (for an 8-bit image or white), and after the DC level conversion, the values are -128 and 127. When 1 is added to this positive value, it becomes -128 and 128. Therefore, the wavelet at the wavelet division level 0, that is, the next three coding passes (- When the bit plane is subjected to three passes: JPEG2000 standard, both +128 and -128 have a value only in the seventh bit (that is, the seventh bit is 1 and the other 0 to 6th and 8th bits). The above is 0), and when this is coded, only the seventh bit is to be coded. Therefore, in the case of a black and white mixed image, the coding efficiency can be improved.
[0078]
According to the fourth aspect of the present invention, in the image processing apparatus according to any one of the first to third aspects, switching between the normal encoding mode and the black-and-white 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.
[0079]
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.
[0080]
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 normal encoding mode and the monochrome 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.
[0081]
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.
[0082]
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.
[0083]
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.
[0084]
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.
[0085]
According to the image processing program of the present invention, since the compression coding function for performing compression coding in accordance with the JPEG2000 algorithm is basically used, the compression coding of the black and white image area and the image area other than the black and white image is performed. The encoding process can be handled by a single encoding means, the configuration is simple and efficient, and the processing contents of this compression encoding function can be combined between black and white image areas mixed in the document image data and image areas other than the black and white image. Since the switching is performed based on the image area separation signal, the inconvenience of the JPEG2000 algorithm can be avoided by utilizing the features of the JPEG2000 algorithm.
[0086]
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 separating means 122 Processing content switching means 131 Black and white image area 132 Image area other than black and white image

Claims (14)

Compression encoding means for compressing and encoding the document image data according to the JPEG2000 algorithm;
Processing content switching means for switching the processing content by the compression encoding means based on an image area separation signal of a monochrome image area and a non-black and white 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 black and white image area and a non-black and white 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 at least in the order of DC level conversion, color space conversion processing, two-dimensional wavelet conversion processing, quantization processing, and entropy coding processing.
The processing content switching means sets a normal coding mode for an area separated as an image area other than black and white by the image area separation signal, and performs all coding processing from the DC level conversion processing. Is set to a black and white encoding mode for a region separated as a black and white image region, a value obtained by adding 1 to a positive value after DC level conversion is used, and a wavelet division level is set to 0 to perform entropy encoding processing. Switching the processing contents in the compression encoding means so that
The image processing device according to claim 1. 4. The processing method according to claim 1, wherein the processing content switching unit switches the processing content so that one of a normal encoding mode and a black-and-white encoding mode is applied to the entire document image data. Image processing device. The image according to claim 4, wherein the compression coding unit describes one of coding mode information of a normal coding mode and a black-and-white coding mode applied in a main header area of the compression-coded code data. Processing equipment. The processing content switching means dynamically switches the processing content between a normal encoding mode and a black-and-white encoding mode in a unit of a certain small area in which the document image data is divided 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, encoding mode information of one of a normal encoding mode and a monochrome encoding mode applied to each tile is described. An image processing apparatus as described in the above. 9. The image according to claim 8, wherein said compression coding means describes coding mode information relating to a raster line for switching between a normal coding mode and a black and white coding mode applied in a main header area of the compression-coded code data. Processing equipment. 8. The compression encoding device according to claim 7, wherein the compression encoding unit describes, in the code data of each tile that has been compression encoded, one of encoding mode information of a normal encoding mode and a monochrome encoding mode applied to the tile. Image processing device. 9. The image processing apparatus according to claim 8, wherein said compression encoding means describes encoding mode information on a raster line for switching between a normal encoding mode and a black-and-white 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 monochrome image area and a non-black and white 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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