JP4111863B2 - Image processing apparatus, image forming apparatus, image processing program, and storage medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus having an image compression function for compressing an image, an image forming apparatus including the image processing apparatus, a program for image processing, and a storage medium storing the program.
[0002]
[Prior art]
Conventionally, in order to improve the operability of compression-encoded image data, the original image data is divided into a plurality of regions, each region is independently encoded as a compression code, and when this compression code is decoded, A technique is known in which the order of regions to be decoded is changed according to the processing content after decoding. Here, “independently” means that information on other regions is not used when decoding each region, and therefore decoding is performed regardless of whether image data in other regions is decoded. Means that it is possible. An example of improving the operability by dividing and encoding the image data into a plurality of areas is that the process of rotating the direction of the image can be executed by changing the order of the areas to be decoded. .
[0003]
For example, Patent Document 1 discloses a technique for executing a rotation process or the like using a fixed-length encoding method. Patent Document 2 discloses a technique for storing addresses of blocks of compression codes that are variable-length-encoded in units of blocks and switching the addresses to be accessed according to the decoding order. In general, since variable-length coding has a higher compression rate than fixed-length coding, the method disclosed in Patent Document 2 has an advantage of a higher compression rate than a fixed-length coding method.
[0004]
In addition, the concept of tile is also introduced in JPEG2000, which is an image compression method that has become an international standard, and image data divided into regions is obtained by dividing the image data into tiles and encoding each tile. It becomes possible. Since each tile is a unit that is independently encoded, image rotation processing or the like can be easily performed by changing the order of tiles to be read.
[0005]
Patent Document 3 discloses a technique for performing variable length compression when recording on the maximum size recording paper and performing fixed length compression when recording on recording paper other than the maximum size.
[0006]
In addition, when image data is divided into a plurality of regions, parallel processing can be performed when encoding or decoding processing is performed. Patent Document 4 discloses a technique for allocating an upper limit information amount to each tile and performing compression so that each tile does not exceed the upper limit value in order to control the compression code amount when the tile is divided. Yes. Furthermore, Patent Document 5 proposes a technique for adaptively selecting an expansion pixel creation method in accordance with the state of a tile boundary.
[0007]
[Patent Document 1]
JP 2001-160904 A (see paragraph [0003])
[Patent Document 2]
JP 2002-125116 A
[Patent Document 3]
JP 2000-101851 A
[Patent Document 4]
JP 2000-134623 A
[Patent Document 5]
JP 2001-217718 A
[0008]
[Problems to be solved by the invention]
By the way, the compression code that can rotate the direction of the conventional image often has a larger code amount than the compression code that cannot be rotated, so it is preferable because the data amount is large from the viewpoint of storing in the memory. Absent. For example, a fixed-length code can rotate an image, but does not use entropy coding, and therefore has a lower compression rate than a variable-length code. In addition, when an image is divided into small areas such as blocks or tiles and encoding is performed in units of small areas, correlation with pixels outside the area cannot be used, or entropy encoding is performed because the area is small. The learning effect becomes insufficient, and the compression rate deteriorates. Further, in hierarchical encoding using wavelet transform or the like, the compression rate deteriorates particularly in the data of the hierarchy with the highest resolution.
[0009]
On the other hand, a medium (paper, OHP, etc.) of the maximum size (for example, A3 size) that can be handled by an image forming apparatus such as an electrophotographic printer or a copier generally has a long side for reducing the size of the image forming apparatus. The paper is transported so that is substantially parallel to the transport direction. Therefore, since the short side is not transported so as to be substantially parallel to the transport direction, it is not necessary to rotate and output the image.
[0010]
Thus, paying attention to the fact that the necessity of image rotation processing changes according to the size of the image, the applicant of the present invention in the case of recording an image on the maximum size recording paper in Patent Document 3 described above. A technique has been proposed in which variable-length compression is performed and fixed-length compression is performed when an image is recorded on a recording sheet other than the maximum size.
[0011]
However, a system that executes variable-length compression and fixed-length compression separately has a problem that the scale of a circuit that realizes the compression becomes large.
[0012]
Therefore, it is desired to realize an image rotation function by area division while suppressing the circuit scale by unifying the compression encoding system and suppressing an unnecessary increase in code amount due to area division. In other words, for example, A3 size compression encoding cannot be rotated, but encoding is performed with an encoding method that provides a high compression rate, and the compression rate is reduced for A4 size images. However, it is desirable to satisfy the request with a single encoding means in response to a request to perform encoding with an encoding method that can obtain a compression code capable of rotating an image.
[0013]
Further, there may be a demand for outputting an image that has been output once in a smaller size. For example, there is a case where printing is performed in A3 size, but printing is performed again in A4 size because it is inconvenient to carry.
[0014]
For example, when outputting a plurality of copies by electronic sorting at the time of output in A4, or the long side of A3 size paper is substantially parallel to the paper transport direction, while the short side of A4 size paper is When the paper is stored in a direction substantially parallel to the paper transport direction, or the long side of the A3 size paper is substantially parallel to the paper transport direction, whereas the short side of the A4 size paper is The A4 size paper stored with the long side stored in the direction substantially parallel to the transport direction and the long side stored in the direction substantially parallel to the transport direction has been cut. If so.
[0015]
In particular, the image once output is stored in the image forming apparatus according to a predetermined condition (for example, a condition such as storing for a certain period), and the date and time when the image is scanned is specified later. Thus, in an image forming apparatus having a function of searching for a specific image stored in the image forming apparatus and printing it out, the image stored in the maximum size is stored at a later date when image data is stored. It is assumed that the data is reduced and output as a reference material of low importance. Further, a plurality of copies may be output while electronically sorting the images.
[0016]
In each case as described above, when trying to cope with the technique disclosed in Patent Document 3, when the image processing apparatus is configured to perform encoding and decoding of image data in band units, Decoding the image in band units, re-encoding it as a rotatable compression code of the image, and then reading out the compressed compression code of the image again in the direction that was on the recording paper to form an image Processing had to be done.
[0017]
On the other hand, digital copiers, multi-function peripherals, etc. have recently been used as image servers due to the increase in storage capacity of their storage devices. It has been compressed and encoded and stored in a storage device such as a computer, and can be arbitrarily used by a personal computer or the like as necessary.
[0018]
Under such circumstances, an image forming apparatus such as a digital copying machine, a multi-function peripheral (MFP), or a printer as an image processing apparatus can divide an image only when necessary, and is accompanied by the area division. Although it is desired that the deterioration of the compression ratio of the image can be suppressed, in general, an image processing apparatus such as a personal computer does not need to consider a large size such as A3 size unlike the case of the image forming apparatus. There is also a need to ensure consistency when the stored code data is used by an external device such as a personal computer.
[0019]
Furthermore, when variable length coding is performed for each tile and the obtained compressed code is stored in the memory, the variable length coding is difficult to predict the compression rate unlike the fixed length coding method. May not fit in memory. In such a case, it is necessary to reduce the amount of information of the image data so that the compressed code can be stored in the memory. For this reason, if the image divided into regions is quantized, image quality deterioration occurs at the boundary of the regions. Such image quality degradation is called tile boundary distortion in JPEG2000, where each area encoded independently is called a tile.
[0020]
As a technique for reducing such tile boundary distortion, it is conceivable to adaptively select a method for creating an extended pixel according to the state of the tile boundary as disclosed in Patent Document 5.
[0021]
However, the technique disclosed in Patent Document 5 has a problem that the tile boundary distortion cannot be essentially prevented.
[0022]
The object of the present invention is to enable image segmentation only when necessary, to suppress deterioration in image compression rate due to region segmentation and distortion occurring at the boundary of the region due to frequency conversion, and to a personal computer or the like This is to ensure consistency with external equipment.
[0023]
[Means for Solving the Problems]
The image processing apparatus of the present invention When the image data is divided into a plurality of areas and the code sequence is generated by hierarchically compressing and encoding the image data with different resolutions, an image processing apparatus that processes the code sequence decodes the code sequence In the processing of the hierarchy corresponding to the resolution that can rotate the image data In the hierarchy being processed Coding is performed by changing the number of divisions of the area of the image data with respect to the processing of the layer not corresponding to the resolution that can be rotated. Compression coding Means and said Compression coding A storage device for storing a code string compressed and encoded by the means, and a correction output means for outputting a correction code string obtained by extracting a code string from the code string up to a hierarchy in which the number of divisions of the region does not change; , And the processing of the layer that does not correspond to the resolution that can be rotated is performed before the processing of the layer that corresponds to the resolution that can be rotated. It is characterized by.

[0024]
Therefore, when generating a code string by compressing and encoding image data, the encoding is performed by changing the number of divisions of the area from the middle layer, for example, a large size in which the orientation of the image cannot be rotated. With regard to the frequency conversion coefficient for decoding the image (for example, A3), the frequency for decoding a small size (for example, A4, A5) that can rotate the direction of the image without performing area division such as tile division. With regard to the conversion coefficient, it is possible to divide the image into only the necessary layers, such as by dividing the area, such as tile division. Therefore, it is possible to improve the image quality by suppressing the deterioration of the compression rate due to the area division. . In addition, it is possible to create a code that is a target of region division and a code that is not a target by using a single algorithm, and it is possible to simplify a circuit related to image compression processing as compared with a case where a coding method is properly used. it can .
[0041]
Of the present invention The image forming apparatus Any one of the present invention Based on the image processing apparatus, decoding means for decoding the code string compressed and encoded by the image compression means of the image processing apparatus and stored in the storage device, and based on the image data decoded by the decoding means A printer engine that performs image formation.
[0042]
Therefore, with respect to a frequency conversion coefficient for decoding an image of a large size (for example, A3) in which the image orientation cannot be rotated, area division such as tile division is not performed, and the image orientation can be rotated. As for frequency transform coefficients for decoding the size (for example, A4, A5), it is possible to divide the image only when necessary, such as dividing the region such as tile division. The deterioration of the rate can be suppressed. In addition, it is possible to create a code that is a target of region division and a code that is not a target by using a single algorithm, and it is possible to simplify a circuit related to image compression processing as compared with a case where a coding method is properly used. it can .
[0043]
By the image processing apparatus of the present invention The action is Of the present invention Image processing programs, Of the present invention It can also be played by a storage medium.
[0044]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
A first embodiment of the present invention will be described with reference to FIGS. In the present embodiment, an example of application to a full-color digital copier (which may be an MFP = MFP) 1 is shown as an image forming apparatus, for example, as shown in FIG. A system configuration in which a personal computer 100 or the like is connected via a network 4 such as a LAN is assumed.
[0045]
FIG. 2 is a block diagram showing a schematic configuration of the digital copying machine 1 according to the present embodiment. The digital copying machine 1 includes a printer engine 2 that forms an image on a sheet or the like by a known electrophotographic process, and a scanner 3 that reads an image of a document. The digital copying machine 1 includes a controller 5 having a microcomputer. Specifically, the controller 5 includes a main controller that controls the entire digital copying machine 1 and a plurality of sub-controllers that control each part of the main controller 5. Here, the controller 5 is illustrated as a single controller 5. To do. The CPU of the controller 5 executes processing described later based on a control program stored in a ROM (storage medium).
[0046]
The printer engine 2 includes a photoconductor, a developing device, a cleaning device, and a charging device, and a process for forming dry toner images of K, M, C, and Y (black, magenta, cyan, and yellow) colors. Electrostatic latent images of K, M, C, and Y color images are formed on the photoreceptors of the cartridges 11K, 11M, 11C, and 11Y, the transfer belt 12, the fixing device 13, and the process cartridges 11K, 11M, 11C, and 11Y. Optical writing devices 14K, 14M, 14C, and 14Y for optical writing are provided. The digital copying machine 1 also includes paper feed trays 15a to 15c that store media (such as paper and OHP) for recording color images. Each of the process cartridges 11K, 11M, 11C, and 11Y is formed by superimposing toner images of K, M, C, and Y colors on the transfer belt 12, and the superimposed toner images are illustrated from the paper feed trays 15a to 15c. The image is transferred to a medium supplied by a conveyance device that does not, and fixed by a fixing device 13.
[0047]
The digital copying machine 1 also includes a band buffer 22, a color conversion unit 31, an inverse color conversion unit 32, a compression encoding unit or encoding units 23a and 23b that realize a compression encoding function, a decoding unit or a decoding function. An image processing device 26 including a decoding unit 24a, 24b to be realized and a page memory 25 as a storage device is provided.
[0048]
In FIG. 2, a band buffer 22 is a buffer for storing pixel data included in one band among a plurality of bands constituting image data for one page. Here, a band is an area of image data composed of a predetermined number of pixel lines.
[0049]
The color conversion unit 31 converts the image data stored in the band buffer 22 into a luminance color difference such as YCrCb. Since color conversion is a well-known technique, description thereof is omitted. The reverse color conversion unit 32 performs reverse conversion of the color conversion unit 31.
[0050]
The encoding unit 23a converts the image information or luminance color difference information of the image data into a low resolution image (first low resolution image) and detailed information (first detailed information) (first conversion means, first conversion unit). 1 conversion processing) and an entropy encoding unit (first entropy encoding means, first entropy encoding processing) for entropy encoding the first detailed information. For example, the conversion unit converts the image information or the luminance color difference information into a low frequency component (first low frequency component) that is a first low resolution image and first detailed information that is higher in frequency than the first low frequency component. It can be decomposed into a high frequency component (first high frequency component) as a component by frequency conversion.
[0051]
In this example, such an encoding unit 23a performs frequency conversion on the luminance color difference information converted by the color conversion unit 31 by wavelet conversion of a predetermined hierarchy, and encodes the obtained high frequency component without dividing the tile. It is the encoding apparatus for converting. Hereinafter, the compression code encoded by the encoding unit 23a is referred to as a “first compression code”.
[0052]
That is, the encoding unit 23a in this example includes at least a conversion unit that performs wavelet conversion and an entropy encoding unit that entropy-encodes the high-frequency component of the wavelet coefficient converted by the conversion unit. The entropy encoding unit may entropy encode data obtained by quantizing the wavelet coefficients or data obtained by performing predetermined conversion on the wavelet coefficients.
[0053]
Several function forms are known as wavelet transforms. In this example, a filter that overlaps with adjacent pixels is used, such as a 5 × 3 filter used in the international standard JPEG2000. When a filter that overlaps adjacent pixels is used, there is an advantage that block distortion does not occur during quantization. In this example, in order to overlap the adjacent pixels even at the band boundary, the necessary number of adjacent pixels together with the pixels constituting the band are stored in the band buffer 22. In addition, arithmetic coding is used as entropy coding.
[0054]
The encoding unit 23b divides the low resolution image (first low resolution image, first low frequency component) in the encoding unit 23 into regions such as a plurality of tiles, and the low resolution image existing in each region is divided. A conversion unit (second) that decomposes a low-resolution image existing in another area without using it and obtains a low-resolution image (second low-resolution image) and detailed information (second detailed information) for each area Conversion means, a second conversion function), and an entropy encoding unit (second entropy encoding means, second entropy encoding processing) for entropy encoding this detailed information. For example, the conversion unit converts the low-frequency component (first low-frequency component) in the encoding unit 23a into the low-frequency component (second low-frequency component) that is the second low-resolution image and the second detailed information. It can be decomposed by frequency conversion into a high frequency component (second high frequency component) which is a higher frequency component than the second low frequency component.
[0055]
In this example, the encoding unit 23b divides image information into tiles of a predetermined size for an image output to an A4 size medium, and independently compresses and encodes each tile, and outputs the result to an A3 size medium. For the image to be processed, the low frequency component obtained by the encoding unit 23a is divided into tiles of a predetermined size, and then each tile is independently compression encoded. Here, “independent” means that encoding is performed without using pixel information in other tiles at the time of encoding. That is, the encoding unit 23b includes at least a high-frequency component among the conversion unit that performs wavelet transform of a predetermined layer on the coefficients included in each tile and the frequency components (low-frequency component and high-frequency component) obtained thereby. Is composed of an entropy coding unit for entropy coding. In this example, the same wavelet as that used in the encoding unit 23a is used as the wavelet transform. Hereinafter, the compression code encoded by the encoding unit 23b is referred to as a “second compression code”.
[0056]
The decoding unit 24b performs the inverse transformation of the encoding unit 23b. That is, an entropy decoding unit (second entropy decoding means, second entropy decoding function) that decodes detailed information (second detailed information) for the code strings created by the encoding units 23a and 23b, From the detailed information decoded by the entropy decoding unit and the low resolution image (second low resolution image), an inverse conversion unit (second inverse conversion means, second low resolution image) decodes the low resolution image (first low resolution image). 2 inversion function).
[0057]
The entropy decoding unit may decode a high frequency component (second high frequency component) that is a higher frequency component than a low frequency component (second low frequency component) that is detailed information (second detailed information). it can. The inverse conversion unit reverses the frequency conversion used when decomposing the low frequency component (second low frequency component) and the second high frequency component into the second low frequency component and the second high frequency component. Conversion can be performed to decode the low-frequency component (first low-frequency component).
[0058]
The decoding unit 24a performs the inverse transformation of the encoding unit 23a. That is, the decoding unit 24a includes an entropy decoding unit (first entropy decoding unit, first entropy decoding function) that decodes detailed information (first detailed information), and the decoded detailed information and decoding unit. An inverse conversion unit (first inverse conversion means, first inverse conversion function) that decodes image information or luminance color difference information from the low-resolution image decoded by 24b.
[0059]
In this way, the image data decoded by the decoding unit 24b or the decoding units 24a and 24b is output to the RGB → CMYK conversion unit 28.
[0060]
The digital copying machine 1 can receive image data from a predetermined network 4 such as a LAN via a communication interface (not shown). When the image data input via the network 4 is data in the PDL (page description language) format, the RIP unit 21 performs drawing processing on a band basis and converts it into a bitmap format, and the image processing device 26 Output to.
[0061]
The page memory 25 is a storage device for storing (storing) image data for a predetermined page as a compression code string. The page memory 25 of this example can store a compression code string for one page of A4 size image data. The hard disk 27 is a memory provided for acquiring and storing the compression code string stored in the page memory 25 and re-storing the compression code string in the page memory 25 as necessary.
[0062]
The image scaling unit 33 is provided to scale the image. In this example, the image scaling unit 33 performs a function of enlarging a low resolution image of A5 size to A4 size.
[0063]
The RGB → CMYK conversion unit 28 receives image data expressed by RGB (red, green, blue) color signals decoded by the decoding unit 24a or 24b, and converts them into CMYK signals. The K, M, C, and Y color gradation processing units 29K, 29M, 29C, and 29Y each have a function of reducing the multivalue data of K, M, C, and Y colors and converting it into write data. In this example, the band buffer 22 stores 600 dpi image data of 8 bits per pixel, which is converted into 1200 dpi image data of 1 bit per pixel by the K, M, C, and Y color gradation processing units 29K, 29M, 29C, and 29Y. Convert to.
[0064]
The K, M, and C color write data are stored in the line memories 16K, 16M, and 16C to adjust the image formation start timing, and the K, M, and C color data are timed so that the images of the respective colors overlap on the medium. , Y, color writing devices 14K, 14M, 14C, 14Y.
[0065]
Next, the operation of the digital copying machine 1 will be described.
[0066]
The digital copying machine 1 of this example can execute the electronic sort function when outputting A4 size. When the electronic sort function is executed, an image is recorded on the A4 paper stored in the paper feed tray 15a (or the paper feed tray 15b) at the time of printing the first copy, and the paper feed tray 15b at the time of printing the second copy. An image is recorded on the A4 paper stored in (or the paper feed tray 15a), and then the images are sequentially recorded on the A4 paper stored in the paper feed tray 15a (or the paper feed tray 15b) when the odd number of copies are output. When an even number of copies are output, an image is recorded on A4 paper stored in the paper feed tray 15b (or the paper feed tray 15a), and so on. At this time, the image is output without being rotated when the odd number of copies is output, and the image is rotated by 90 degrees and output when the even number of copies is output.
[0067]
Further, the digital copying machine 1 of this example has a paper feed tray automatic switching function for forming an image on a medium stored in one of the paper feed trays 15a and 15b when the medium stored in the other is consumed. However, even at this time, by rotating the image direction by 90 degrees, it is possible to output the image in a direction suitable for the medium stored in the paper feed tray as the switching destination.
[0068]
In this example, when an image is formed on an A3 size recording sheet, the image is not rotated. When an image is formed on an A4 size recording sheet, the image is rotated.
[0069]
Details of the image forming operation will be described.
[0070]
Image data read from the scanner 3 or sent from the network 4 is stored in the band buffer 22 in band units. The capacity of image data that can be stored in the band buffer 22 of this example is a capacity that can store image data of 8 bits per pixel of 600 dpi by a quarter of A4 size. However, as described above, the image data for adjacent pixels to be referred to when the wavelet transform overlaps can be stored separately.
[0071]
The image data for one band stored in the band buffer 22 is color-converted by the color conversion unit 31 and then compressed and encoded by the encoding unit 23a and the encoding unit 23b. As described above, in this example, the image orientation is not rotated when an image is formed on an A3 size recording sheet, and the image orientation is rotated when an image is formed on an A4 size recording sheet. To implement.
[0072]
For this reason, the controller 5 uses the first size encoding process as a process for compressing and encoding an image of a size to be recorded on A3 paper, and the low frequency component obtained by the nth (≧ 1) size encoding process. Is defined as the (n + 1) th size encoding process, the first size encoding process is compression encoded by the encoding unit 23a, and the second size encoding process is encoded. The compression unit 23b performs compression encoding.
[0073]
If A5 size paper is stored instead of A4 size paper and image rotation is performed on A5 size paper, the low frequency obtained by wavelet transforming A3 size for two layers. Since the component is an object of image rotation processing, the first and second sizes are compressed and encoded by the encoding unit 23a, and the third size is compressed and encoded by the encoding unit 23b.
[0074]
FIG. 3 is a flowchart of processing executed by the digital copying machine 1. Such processing implements compression instruction means. As shown in FIG. 3, in step S1, the controller 5 obtains the size of the image in the XY directions based on the image size information of the image data acquired from the network 4 and information from the document size detection device. The size of the image here means the size of the visible image formed on the medium. When the acquired image is scaled and output, it means the size after scaling. Here, the X direction is a conveyance direction of a medium such as paper, and the Y direction is a direction orthogonal to the conveyance direction of a medium such as paper.
[0075]
In step S2, the controller 5 reads A from the memory stored therein. _size4 And B _size4 Is read. Where A _size4 Is the length (about 29 cm) of the longest side that can form an image on an A4 size medium, _size4 Is the length (about 21 cm) of the shortest side of the maximum size that can form an image on an A4 size medium. These two values are stored to indicate the maximum size of an image that can be subjected to image rotation processing.
[0076]
In step S3, the controller 5 determines that “X is A _size4 And Y is B _size4 Is "or" Y is A _size4 And X is B _size4 It is determined whether or not any of the following conditions is satisfied.
[0077]
As a result of the determination in step S3, if the condition is not satisfied (Y in step S3), it is determined that the image does not fit in the A4 size, and the process proceeds to step S5. If the condition is satisfied (N in step S3), the process proceeds to step S4.
[0078]
In step S4, it is determined whether the medium designated as the output destination for image formation is designated as an A3 size medium, and if it is designated to be output on an A3 size medium (Y in step S4). The process proceeds to step S5. If it is not specified to output to an A3 size medium (N in step S4), the process proceeds to step S6.
[0079]
In step S5, the encoding unit 23a compresses and encodes the image data without dividing the tile. The low frequency component obtained by the encoding unit 23a in step S5 is sent to the encoding unit 23b.
[0080]
In step S6, since the encoding unit 23b is N in the determination in step S4, the image data sent directly to the encoding unit 23b without being processed by the encoding unit 23a or the processing in step S5 Encoding is performed on the low-frequency component of the wavelet transform obtained by the encoding unit 23a.
[0081]
By such processing, the compression code string encoded by the encoding unit 23 a and the encoding unit 23 b is quantized according to the set quantization rate in accordance with an instruction from the controller 5. The quantization rate is set so that no quantization is performed at the beginning of encoding, but the setting is changed as necessary based on the relationship between the capacity of the page memory 25 and the code amount of the compression code string. To go.
[0082]
That is, from the total code amount F2 of the encoded bands stored in the page memory 25, the capacity F1 of the page memory 25, the total number of bands N constituting one page of image data, and the number of encoded bands n. It is determined whether or not the relationship of (F1 / N × n) <F2 ”is established. If this relationship is established, the quantization rate is reset. The resetting of the quantization rate means resetting the quantization rate so that the degree of quantization of the entire page becomes stronger.
[0083]
The meaning of the determination formula “(F1 / N × n) <F2” will be described. When (F1 / N × n) is assumed that the information amount of each band is equal, the processing for n bands is completed. The upper limit of the amount of information stored in the page memory 25. For example, when N is 4 and n is 3, “F1 / N × n = F1 × 0.75” is obtained, which means that the compression code string should occupy 75% or less of the page memory 25. That is, “the quantization rate is reset when the relationship of (F1 / N × n) <F2 is satisfied” means that the expected information amount (F1 / N × n) when the information amount of each band is assumed to be equal. On the other hand, if the total code amount F2 of a band that has actually been encoded exceeds even a little, it means that the quantization rate is reset.
[0084]
When the relationship of “(F1 / N × n) <F2” is established and the quantization rate is reset, the quantization rate of the band to be encoded after resetting is quantized with the newly set quantization rate. In addition to this, it is necessary to re-quantize the compressed code stored in the page memory 25. The reason is that if the quantization rate varies within an image of one page, the image quality varies within the page, and the viewer may feel uncomfortable. Therefore, the data to be quantized is deleted from the page memory 25 as well. Various methods are known as quantization methods. In this example, a predetermined bit plane is reduced from the compression code string.
[0085]
After performing the quantization on the compression code string stored in the page memory 25, the controller 5 determines whether the band to be processed is the last band among the bands constituting one page. If not, the band buffer 22 is cleared. However, the pixel value necessary for wavelet transform of the band to be encoded is not cleared but is left in the band buffer 22 and used for compression encoding. As a result, it is possible to prevent boundary distortion from occurring at the band boundary when quantization is performed. Next, the controller 5 reads the image data of the next band into the band buffer 22 and starts encoding of the image data constituting the newly read band. If it is the last band, the encoding process by the encoding unit 23a ends.
[0086]
Where most resolution The wavelet transform coefficient with high is next to the wavelet coefficient in the first layer and the wavelet coefficient in the nth layer. Low resolution If the wavelet transform coefficients are defined as the (n + 1) th layer wavelet coefficients, the first layer wavelet coefficients (high frequency components) that are not divided into tiles are entropy in the page memory 25 by the above processing. Entropy of the encoded first compression code and wavelet coefficients (high frequency component and low frequency component (however, the low frequency component may not be entropy encoded)) of the second and higher layers divided into tiles The encoded second compression code is stored.
[0087]
FIG. 4 schematically shows this state. FIG. 4 shows an example in which the low-frequency component of the first layer is divided into four tiles and the compression encoding by the encoding unit 23b is performed in the second size encoding process. If the low frequency component is LL, the high frequency component is HL, LH, HH, and the number of layers is an index, the first compression code HL1, LH1, HH1 is not divided into tiles in FIG. The codes LL3, HL3, LH3, HH3, HL2, LH2, and HH2 are divided into tiles.
[0088]
For this reason, in the digital copying machine 1 of this example, the direction of an A3 size image cannot be rotated, but since the tile is not divided, the compression rate is good. Further, since an A5 size image is divided into tiles, a compression code capable of rotating the image direction is obtained. Therefore, the electronic sort function or the paper feed tray automatic switching function can be realized with a small code amount as compared with the case where tiles are divided for all layers.
[0089]
Next, the image rotation process will be described in detail.
[0090]
FIG. 5 shows an example in which the wavelet coefficients of the second layer are divided into 16 tiles. In the second compression code, when the leading address is stored in the controller 5 for each tile of 1 to 16 and the long side of the A4 sheet is conveyed in the conveying direction, as shown in FIG. With reference to the memory in the controller 6, the compression codes of the first to fourth tiles (indexes 1 to 4) are read from the page memory 25, and the compression code is decoded by the decoding unit 24b and is stored in the band buffer 22 as image data. Expand. Then, this image data is read in the direction of the arrow shown in FIG. On the other hand, when transporting so that the short side of the A4 paper is in the transport direction, referring to the memory in the controller 5, as shown in FIG. The compressed code of the 13 tiles (indexes 1, 5, 9, and 13) is read from the page memory 25, and this compressed code is decoded by the decoding unit 24b and the image data is developed in the band buffer 22. Then, this image data is read in the direction of the arrow shown in FIG. Accordingly, it is possible to rotate the image by changing the tile number to be read and the read direction after decoding.
[0091]
That is, in order to realize a decoding instruction means, when decoding a compression code obtained by compression encoding an A3 size image, if decoding is performed in A3 size, the decoding units 24a and 24b perform the first Decoding up to the compression code may be performed without rotating the image. On the other hand, when outputting while rotating the image in A4 size, only the second compression code is read out by the decoding unit 24b, and the tile number to be read and the decoding as described with reference to FIG. By changing the reading direction later, it is possible to rotate the image.
[0092]
Here, since the low frequency component obtained by converting the A3 size image by one layer frequency conversion is A5 size, when the rotation operation is executed, the image zoom unit 33 uses the A5 size image data developed in the band buffer 22. Is enlarged and converted to A4 size. Since this scaling method is well known, detailed description thereof is omitted.
[0093]
Note that the bit length of the low frequency component is not necessarily equal to the bit length of the original image data. Therefore, when the low frequency component is used as an output image, the bit length is appropriately adjusted (a predetermined lower bit). Reduction).
[0094]
Note that JPEG 2000, which is an international standard, can be used for encoding / decoding processing in the encoding units 23a and 23b and the decoding units 24a and 24b. In JPEG2000, image data can be encoded by color conversion, wavelet conversion, and entropy encoding, and can be quantized in the state of compression code. It is possible to demonstrate. Specifically, when the x layer is encoded by the encoding process of the encoding unit 23a, and the y layer is divided into z tiles and encoded by the encoding process of the encoding unit 23b, tiles are used. The first compression code and the low frequency component are obtained with the number = 1 and the composition level (hierarchy) = y, and then the tile number = z and the decomposition level (hierarchy) = x with respect to the low frequency component. The process of obtaining the compression code 2 may be performed while rewriting the header information of the JPEG2000 code.
[0095]
If the JPEG2000 system is used in this way, the above-described processing can be performed only by adding the processing of changing the number of tiles in the middle layer, so that the encoding units 23a and 23b can be used in common. Efficient.
[0096]
As described above, according to the digital copying machine 1 of this example, only wavelet coefficients necessary for decoding an image up to A4 size that can be rotated are tiled and encoded, and the image is rotated. Wavelet coefficients necessary only for decoding an A3-size image that cannot be encoded are encoded without being tiled, so that the image rotation can be performed without causing a reduction in the compression rate of high-frequency components with a large amount of information. Possible compression codes can be obtained. Even if the wavelet coefficients of the first layer are reduced by quantization, tile boundary distortion does not occur because the first layer is not divided into tiles. When the wavelet coefficients in the second and subsequent layers are quantized, tile boundary distortion occurs. Even in this case, if some information on the wavelet coefficients in the first layer remains, the wavelet coefficients in the first layer are Since tiles are not divided, tile boundary distortion can be made inconspicuous.
[0097]
Also, since the encoding process is a uniform process regardless of whether or not the image is rotated, there is no need to prepare multiple circuits necessary for image compression / decompression, and there is no need for a determination circuit and processing time for switching the process. It becomes. Furthermore, even when an image that has been output once is left in the memory and the image is rotated and output while being reduced, it is not necessary to decode it to A3 size once, and high-speed processing is possible.
[0098]
Note that the recording paper to be rotated is the same as the low frequency component of the recording paper that does not rotate, as in the case of having A3 size paper and A5 size paper and storing the A5 size recording paper in two transport directions. In the case of having a size, an image zoom device is not always necessary.
[0099]
Note that the encoding method of the encoding unit 23b may be a DCT-based JPEG method (DCT + Huffman encoding) instead of the wavelet base. That is, the encoding unit 23b divides the low frequency component into tiles, and then encodes each tile independently by a known JPEG method. In this case, the encoding unit 23b and the encoding unit 23a have low commonality in configuration, but the image is rotated by a single ASIC or the like that performs both wavelet-based processing and JPEG processing. It is possible to deal with the case of not performing the case.
[0100]
Further, the encoding method of the encoding unit 23b may be GBTC which is fixed length compression.
[0101]
Furthermore, the wavelet transform function of the encoding unit 23b may be different from the wavelet transform function of the encoding unit 23a. Specifically, a 9 × 7 filter with a long overlap can be used in the encoding unit 23a, and a 5 × 3 filter with a short overlap can be used in the encoding unit 23b. When performing tile division, a 5 × 3 filter with a short overlap is used to reduce the load such as mirroring processing at the tile boundary.
[0102]
Next, an output form of the digital copying machine 1 when the code string compressed and encoded by the digital copying machine 1 of this example and stored in the page memory 25 or the HDD 27 is used in an external device such as the personal computer 100 will be described. To do.
[0103]
As described above, in the digital copying machine 1 of the present example, by providing the encoding units 23a and 23b, the number of tile divisions can be changed in the wavelet division hierarchy in the middle for improving image quality. . Thereby, for example, the first layer is encoded with no tiles without tile division, and the second and subsequent layers are encoded in a state of being divided into a plurality of tiles. Corresponding to the two-stage compression coding by the coding sections 23a and 23b, two-stage decoding sections 24a and 24b are also prepared. According to such a configuration, it can be said that this is a compression coding system that has good image quality and efficiency for use in the digital copying machine 1 and other printers, MFPs (MFPs), and the like for print processing. When it is desired to use the compression-encoded code string file on the personal computer 100, the personal computer 100 having only standard decoding means cannot decode the code string.
[0104]
Therefore, in the digital copying machine 1 of this example, in the image processing apparatus 26, for example, it is implemented as a correction output means or a correction output function in the output path from the page memory 25 (or HDD 27) to the personal computer 100 (network 4). A modified output unit 51 is added so that the above-described code string is modified into a standard modified code string that can be decoded by a standard decoding unit and output. In this case, the correction processing in the correction output unit 51 is to use a code string extracted from the code string obtained from the page memory 25 to the middle layer where the number of tile divisions does not change is used as the correction code string. For example, when the number of tile divisions in the second and third layers is 4 (= tile division 1) and the number of tile divisions in the first layer is 0 (no tile = tile division 2) as shown in FIG. The code sequence extracted up to the third and second hierarchies in the middle of the column where the number of tile divisions does not change (= tile division 1) is the modified code sequence, and the tile division number (tile division 2) is changed first. It is distinguished from the code string related to the hierarchy.
[0105]
FIG. 6 pays attention to such a change (switching) of the number of tile divisions (tile divisions 1 and 2), handling as an internal code in the digital copying machine 1 and handling as an external code for the personal computer 100. As shown schematically, the internal code in the digital copying machine 1 is handled in a state where the code string of tile division 1 and the code string of tile division 2 are integrated in the state following the main header. The external code for 100 is restricted to a modified code string in which only the code string of tile division 1 is integrated following the main header by the correction output unit 51, and the code string of tile division 2 is discarded as indicated by a broken line, for example. The In this case, information on the number of tile divisions related to tile division 1 is described in the tile.
[0106]
Therefore, on the personal computer 100 side that receives such a modified code string, the number of tile divisions is continuous over each layer for the modified code string. For example, in the example of FIG. 4, the original image corresponding to LL1 Since it can be handled as a code string of a size (in this example, it becomes a JPEG2000 standard specification code string), even if it does not have a decoder such as the decoders 24a and 24b, a standard decoding means Can be decrypted and used. Further, the code string of tile division 2 is discarded, but the data to be discarded is a high-resolution data of no-tiles HL1, LH1, and HH1 of the first layer, and is displayed on a display or the like in an external device such as the personal computer 100. When it is displayed, it becomes useless data and can be discarded.
[0107]
Note that the code string of the layer after the number of divisions is changed, not only in the discarding method but not particularly illustrated, for example, described in the corrected code string or added to the end of the corrected code string as invalid data You may make it do. For example, in the example shown in FIG. 6, the code data related to the tile division 2 is described in the main header in the modified code sequence, described as comment data in the COM marker of the tile, or the code sequence of the tile division 1 It may be added as invalid data at the end. According to this, there is a case where the code data related to the tile division 2 may be used later, but in the standard specification, it is described in the correction code string or added to the end of the correction code string as invalid data. It can be restored and used.
[0108]
In the present embodiment, encoding is performed by dividing a tile from an intermediate layer, and as an example, as shown in FIG. 4, the low-frequency component (LL1) of the first layer is divided into four tiles. The encoding unit 23b performs compression encoding, and the high-frequency components (HL1, LH1, and HH1) of the first layer are compressed and encoded without being divided into tiles. By changing to the high frequency components (HL1, LH1, HH1) of the first layer, for example, as shown in FIG. 7, the high frequency components (HL1, LH1, HH1) are divided into four tiles, respectively, and the encoding unit 23b. On the other hand, the low-frequency component (LL1) of the first layer may be compressed and encoded without being divided into tiles (while remaining one tile). In FIG. 7, the first compression code LL1 is not divided into tiles, but the second compression codes LL3, HL3, LH3, HH3, HL2, LH2, and HH2 are divided into tiles.
[0109]
[Second Embodiment]
A second embodiment of the present invention will be described with reference to FIGS. This embodiment basically shows an example of application to a full-color digital copier (which may be an MFP = MFP) 1 as in the first embodiment. On the other hand, for example, a system configuration is assumed in which a personal computer 100 or the like is connected via a network 4 such as a LAN as shown in FIG.
[0110]
FIG. 8 is a block diagram showing a schematic configuration of the digital copying machine 1 according to the present embodiment. The configuration is basically the same as that of the first embodiment shown in FIG. 2, and the same portions are denoted by the same reference numerals.
[0111]
The digital copying machine 1 also includes a band buffer 22, a compression encoding unit or an encoding unit 23 that realizes a compression encoding function, a decoding unit or a decoding unit 24 that realizes a decoding function, and a page memory that is a storage device. 25, an image processing device 26 is provided.
[0112]
The encoding unit 23 is an image compression unit for encoding the image data stored in the band buffer 22. The encoding unit 23 includes a color conversion unit that converts image information into luminance color difference information, a wavelet conversion unit that performs wavelet conversion, and entropy encoding that entropy-encodes high-frequency components of wavelet coefficients obtained by the wavelet conversion unit. At least. The entropy encoding unit may entropy encode data obtained by quantizing the wavelet coefficients or data obtained by performing predetermined conversion on the wavelet coefficients.
[0113]
Several function forms are known as wavelet transforms. In this example, a filter that overlaps with adjacent pixels is used, such as a 5 × 3 filter used in the international standard JPEG2000. When a filter that overlaps adjacent pixels is used, there is an advantage that block distortion does not occur during quantization. In addition, arithmetic coding is used as entropy coding.
[0114]
In addition, the decoding unit 24 has at least an entropy decoding unit that entropy-decodes high-frequency components of wavelet coefficients and an inverse wavelet conversion unit for returning the wavelet coefficients obtained by the entropy decoding unit to pixel information. Here, the encoding unit 23 and the decoding unit 24 realize at least a part of the processing to be executed by hardware such as ASIC, but the CPU of the controller 5 stores all processing in the ROM. It can also be executed according to a control program. Alternatively, some can be executed by processing executed by the CPU of the controller 5 with some hardware such as ASIC and the other part.
[0115]
The page memory 25 is a storage device for storing (storing) image data for a predetermined page as a compressed code. The page memory 25 of this example can store a compression code string for one page of A4 size image data. The hard disk 27 is a memory provided for acquiring and storing the compression code string stored in the page memory 25 and re-storing the compression code string in the page memory 25 as necessary. The processes after the RGB → CMYK conversion unit 28 are the same as those in FIG.
[0116]
Next, details of the image forming operation in the digital copying machine 1 will be described.
[0117]
Image data read from the scanner 3 or sent from the network 4 is stored in the band buffer 22 in band units. The capacity of the image data that can be stored in the band buffer 22 of this example is more than the capacity that can store 16 bits of data per pixel of 600 dpi by 624 × 864 × 9 × 3 pixels. This capacity is determined as follows. That is, in this example, A4 size (about 21 cm × about 29 cm → about 4961 pixels × about 6851 pixels) image data for one page is divided into 8 × 8 = 64 tiles, and each tile is processed. This includes image information of 621 × 857 pixels (note that there is a margin in actual image data, but it is ignored for the sake of explanation). On the other hand, in this example, four-layer wavelet transform (WT transform) is performed as will be described later, so that the code block which is a unit of wavelet transform is 16 × 16. In order to perform wavelet transform of 621 pixels in four layers, 624 pixels, which is the minimum multiple of 16 above 621, are set as the short side of one tile. In addition, in order to perform wavelet transform of 857 pixels in four layers, 864 pixels, which is the minimum multiple of 16 above 857, are set as the long side of one tile. In this example, the image data is read into the band buffer 22 in the form of RGB colors. Therefore, the capacity of the band buffer 22 is a capacity that can store nine tiles for each color of RGB. The image information in this example has a depth of 8 bits, but a depth of 16 bits is prepared in consideration of an increase in the number of bits in the process of wavelet transformation. The reason for preparing the capacity for nine tiles although the number of pixels constituting one band is for eight tiles will be described later.
[0118]
The image data for one band stored in the band buffer 22 is encoded by the encoding unit 23 and stored in the page memory 25. When storing images of a plurality of pages, the compression code in the page memory 25 is sent to and stored in the hard disk 27, and subsequent pages are sequentially stored in the page memory 25.
[0119]
When the image is printed out, the compression code in the page memory 25 is decoded by the decoding unit 24 and returned to the RGB color image data, and this image data is converted into the CMYK color image data by the RGB → CMYK conversion unit 28. , K, M, C, and Y color gradation processing units 29K, 29M, 29C, and 29Y, the K, M, C, and Y colors are subjected to gradation processing and converted into binary data per pixel at 1200 dpi. . The K, M, and C color image data is temporarily stored in the line memories 16K, 16M, and 16C in order to adjust the timing of writing the electrostatic latent image to the photosensitive member, and a color image is recorded on a medium such as paper. It is sent to the writing devices 14K, 14M, and 14C in accordance with the formation timing.
[0120]
Since the image forming process used in the printer engine 2 is a well-known electrophotographic process, details of the operation are omitted, but process cartridges 11K, 11M, and 11C that form dry toner images of K, M, C, and Y colors, respectively. , 11Y, when the writing devices 14K, 14M, 14C, 14Y emit writing light according to the image information, the process cartridges 11K, 11M, 11C, 11Y are charged by the charging device. The upper exposed portion is neutralized to form an electrostatic latent image. A developing device selectively attaches dry toner particles only to the image portion to the electrostatic latent image to form a visible image, and the visible image of each color is carried on the transfer belt 12 and conveyed (a medium). A color image obtained by sequentially superimposing the image on a recording sheet or OHP is fixed by heating and pressing with a fixing device.
[0121]
Here, in the present embodiment, processing for compressing image data (image information) is performed while executing wavelet transform, which is one of frequency transforms. In this specification, original original image data is A wavelet transform is performed to obtain a low-frequency component in the first layer and a high-frequency component in the first layer, and a wavelet transform is further performed on the low-frequency component obtained by the wavelet transform in the first layer and the wavelet transform in the k-th layer. The transformation for obtaining the low frequency component of the (k + 1) th layer and the high frequency component of the (k + 1) th layer is referred to as a wavelet transform of the (k + 1) th layer.
[0122]
In addition, as shown in FIG. 9, the wavelet transform coefficient is represented by LL for low frequency components, LH for high frequency components corresponding to vertical edges, HL for high frequency components corresponding to horizontal edges, and high frequency components corresponding to diagonal edges. HH, and an index k is attached to the wavelet transform coefficient in the k-th layer. For example, the LH coefficient of the first layer is denoted as LH1.
[0123]
Next, processing performed by the encoding unit 23 will be described with reference to FIG. As shown in FIG. 10, first, in step S11, the controller 5 obtains the image sizes X and Y based on the image size information acquired from the network and the information from the document size detection device. The size of this image is such that when the image is read as a set of pixels and this set of pixels is a rectangular set, the number of pixels on the long side of the rectangle is X and the number of pixels on the short side is Y. The size of the image here means the size of the visible image formed on the medium, and means the size after scaling when the acquired image is scaled and printed out.
[0124]
In step S12, the image is subjected to necessary scaling processing. In this example, the scaling process is executed by the controller 5 enlarging or reducing the image data on the band buffer 22, but other known scaling techniques can also be employed.
[0125]
In step S13, the controller 5 determines that “X / pow (2, k) <X _tile ”K (k = 1, 2, 3,..., Max _lev ). Where X _tile Is the number of pixels on the long side of one tile, ie 864. Pow (2, k) means 2 to the power of k, and “X / pow (2, k)” means that X is divided by pow (2, k). The meaning of k is the number of wavelet transform layers when the long side of each frequency component obtained when wavelet transforming an image is below 864 for the first time. The “long side of the frequency component” is the length (pixel) of the side corresponding to the long side of the image data when the wavelet coefficients are arranged so as to form a similar shape of the image data according to the positional correlation of the image data. Number). For example, when the frequency components obtained by executing one layer of wavelet transform on the image data of the long side 64 and the short side 24 are arranged so as to form a similar shape of the image data according to the positional correlation of the image data, The frequency components of the side 32 and the short side 12 are obtained.
[0126]
Next, the controller 5 determines in step S14 that “Y / pow (2, j) <Y _tile J (j = 1, 2, 3,..., Max _lev ). Where Y _tile Is the number of pixels on the short side of one tile, ie 624. The meaning of j is the number of wavelet transform layers when the short side of each frequency component obtained when the image is wavelet transformed is below 624 for the first time.
[0127]
In step S15, “Th = max (k, j)” is calculated. max (a, b) is a symbol that means a larger value of the two values a and b, and Th is a wavelet transform in which both the long side and the short side of the obtained frequency component are smaller than the tile size. Means the number of threshold levels.
[0128]
Next, in step S <b> 16, image data for one band is read into the band buffer 22. This image data is converted into a luminance color difference by color conversion (S17). The controller 5 sets an initial value 1 to the variable I for managing the hierarchy of frequency conversion (S18). First, it is determined whether or not the variable I exceeds the threshold hierarchy number Th. The selection process is realized (S19).
[0129]
If the variable I exceeds the threshold layer number Th (Y in S19), the process proceeds to step S22, and if it does not exceed (N in S19), the wavelet transform of the I-th layer is executed for each luminance color difference, First frequency conversion means and first frequency conversion processing are realized (S20). The wavelet transform here is executed for each tile on the image data or low frequency component to be converted. Here, “for each tile” means that wavelet transformation is performed without using information in other tiles when wavelet transformation is performed on a tile to be transformed. Specifically, despite the use of the overlap function as the wavelet transform, the tile boundary is not subjected to the overlap transform using the adjacent tile information, and the predetermined value or pixel within the tile is determined. It means that overlap conversion is performed using a value calculated by mirroring the value. However, as described above, in this example, the number of pixels on the short side and the long side of the tile is set to a multiple of 16, and therefore, there is a portion where no pixel value exists in the short portion of the tile. You may make it reduce tile boundary distortion using the pixel value in an adjacent tile as the pixel value of this blank part.
[0130]
Thereafter, the value of the variable I is incremented by +1 (S21), and it is again determined whether or not the variable I exceeds the threshold hierarchy number Th (S22). If the variable I is less than or equal to the threshold hierarchy number Th in this determination (N in step S22), the process returns to step S19 and the processing is continued, and the low frequency components of each tile are further wavelet transformed.
[0131]
If the variable I exceeds the threshold number of layers Th (Y in S22), that is, in this example, when the wavelet transform of the third layer is completed, the process proceeds to step S23, and the encoding unit 23 performs the first to Th layers. Are entropy-coded and stored in the page memory 25.
[0132]
At this time, the low-frequency component in the Th layer is moved to another area in the band buffer 22. Previously, in this example, it was described that the band buffer 22 has a storage capacity of nine tiles. Here, the low frequency component of the Th layer corresponds to the ninth tile that is not used when reading image data. It will be moved to the area.
[0133]
Next, it is determined whether or not the currently processed band is the last band (S24). If it is not the last band (N in S24), the process returns to step S1 to read the next band, and if it is the last band (S24). Y of S24), the process proceeds to step S25. In step S25, the variable I is max. _lev It is determined whether or not. Where max _lev Is the maximum number of hierarchies of wavelet transform executed by the encoding unit 23 and is 4 in this example. In this determination, the variable I is max _lev If so (Y in S25), the process proceeds to step S29. Variable I is max _lev Otherwise (N in S25), the low-frequency component of the Th layer is wavelet transformed without being tiled in step S26, and the second frequency conversion means and the second frequency conversion process are realized. “Wavelet transform without tile division” specifically means that, in the tile division described above, even low frequency components existing in different tiles are referred to during overlap transformation. .
[0134]
Thereafter, the value of variable I is incremented by +1 (S27), and variable I is max. _lev It is determined whether or not (S28). I = max _lev If so (Y in S28), the process proceeds to step S29. If not (N in S28), the process returns to step S26 to continue the process. I = max _lev If (Y in S28), (Th + 1) to max _lev The wavelet coefficients of the hierarchy are entropy-coded and stored in the page memory 25 (S29), and a series of processing ends.
[0135]
The image data conversion process described above with reference to FIG. 10 will be further described with reference to FIG. FIG. 11A is a diagram illustrating eight tiles of the original original image data (reference numeral 31 indicates each tile). Each tile 41 stores image data of 621 pixels × 857 pixels × RGB three colors, and the size of the tile 41 is 624 × 864 pixels × in order to execute wavelet transform processing in units of 16 × 16 pixels. There are three RGB colors. FIG. 11A shows the tile 41 when the sub-scanning direction is the long side of the image. However, when the main scanning direction is the long side of the image, the short side of each tile 41 is The figures are arranged in contact with each other (the number of pixels is the same).
[0136]
Here, it is assumed that image data of A4 size (X = 6851, Y = 4961) is encoded. In step S13 of FIG. 10, the minimum k that is “6851 / pow (2, k) <864” is 3, and in step S14, the minimum j that is “4961 / pow (2, j) <624”. Is also three. Therefore, “Th = 3”. For this reason, up to the third level is tiled and wavelet transformed, and only the fourth level is wavelet transformed without tile division.
[0137]
FIG. 11B shows a state in which wavelet transform (steps S17 to S22 in FIG. 3) is performed up to the third layer on one-band image data. Of these coefficients, those other than the low-frequency component 32 of the third layer are entropy-coded (S23). In this example, the encoding unit 23 uses eight wavelet transformers and eight entropy encoders in order to process each tile 41 in parallel. Each tile 41 is subjected to wavelet transform and entropy coding by high-speed parallel processing, and the controller 5 stores the address of each tile 41. Then, before reading the next band into the band buffer 22, only the low-frequency component (reference numeral 42) in the third layer is moved to another area of the band buffer 22.
[0138]
FIG. 11C shows a state in which processing has progressed to three bands. The wavelet coefficients of the first band and the second band are entropy-encoded except for the low-frequency component 32 of the third layer, and the low-frequency component 32 of the third layer is stored in the band buffer 22 for three bands and other components. Is stored in a separate storage area.
[0139]
When all the bands have been processed (Y in S24). As shown in FIG. 11D, the third layer low frequency components 32 corresponding to all the image data are developed in the band buffer 22 (the left diagram in FIG. 11D). Therefore, this is regarded as information that has not been divided into regions (FIG. 11 (d) central view), and wavelet transform is performed up to the fourth layer (FIG. 11 (d) right view) (S26 to S28). Thereafter, the wavelet coefficients of the fourth layer are entropy-coded (S29).
[0140]
In this way, in this example, wavelet transform coefficients are encoded in a state where tiles are divided in the first to third layers, and wavelet transform is performed in the fourth layer without tile division.
[0141]
That is, according to this example, in the processing of the first to third layers, the processing is performed for each tile 41, so that high speed processing is possible. Further, since the fourth hierarchy is not tile-divided, the boundary distortion of the tile 41 can be reduced even when quantization is performed without the compression code being stored in the page memory 25. That is, in the conventional encoding / decoding, the data once divided into tiles is processed for each tile 41, but in this example, the tile boundary distortion can be reduced by returning to the data that is not divided into tiles during the frequency conversion. It becomes.
[0142]
By the way, when the decoding unit 24 decodes the compression code that has been compression-encoded as described above, the process of FIG. 10 is performed in reverse. That is, the frequency components of the fourth layer are first developed in the band buffer 22, and then the frequency components of the first to third layers are decoded for each band. Therefore, if the order of expanding the frequency components of the first to third layers divided into tiles in the state where the frequency components of the fourth layer are expanded in the band buffer 22 is changed, the image orientation is rotated by 90 degrees. Can be executed.
[0143]
Next, this image rotation processing will be described in detail. FIG. 12 shows an example in which the wavelet coefficients of the second hierarchy are divided into 16 tiles 41 (similar to the case of FIG. 5). When the compression code is stored in the controller 5 for each tile 41 of 1 to 16, the printer engine 2 transports a medium such as a sheet such that the long side of the A4 sheet is in the transport direction (see FIG. As shown in b), the compressed code of the first to fourth tiles (indexes 1 to 4) is read from the page memory 25 with reference to the memory in the controller 5, and the compressed code is decoded by the decoding unit 24. The image data is decoded by expanding the frequency components of the first to third layers in the band buffer 22 and performing inverse wavelet transform together with the already decoded low frequency component 32 (see FIG. 11) of the fourth layer. Then, this image data is read in the direction of the arrow shown in FIG.
[0144]
On the other hand, when the printer engine 2 transports the medium so that the short side of the A4 paper is in the transport direction, as shown in FIG. The compressed codes of the fifth, ninth, and thirteenth tiles (indexes 1, 5, 9, and 13) are read from the page memory 25, and the compressed code is decoded by the decoding unit 24 and stored in the first to third band buffers 22. Image data is expanded by expanding the frequency component of the layer and performing inverse wavelet transform together with the frequency component 32 (see FIG. 11) of the fourth layer that has already been decoded. Then, this image data is read in the direction of the arrow shown in FIG. Therefore, it is possible to rotate the direction of the image by changing the number of the tile 41 to be read and the reading direction after decoding.
[0145]
In addition, since the code of the fourth layer is address-managed without being divided into tiles, it is easy to call a thumbnail image.
[0146]
As described above, the encoding / decoding method of the present example has an excellent effect that it is possible to perform image rotation processing and high-speed processing while reducing tile boundary distortion.
[0147]
Note that JPEG 2000, which is an international standard, can also be used as an encoding / decoding algorithm in the encoding unit 23 and the decoding unit 24 in this example.
[0148]
Next, an output form of the digital copying machine 1 when the code string compressed and encoded by the digital copying machine 1 of this example and stored in the page memory 25 or the HDD 27 is used in an external device such as the personal computer 100 will be described. To do.
[0149]
As described above, in the digital copying machine 1 of this example, in order to reduce the boundary distortion of the tile 41, the number of tile divisions can be changed depending on the processing hierarchy. That is, in the processing of the first to third layers, high-speed processing can be performed by dividing the tiles 41 into a plurality of tiles 41, and processing is performed for each tile 41, and the page memory 25 can be processed without tile division in the fourth layer. Even when the compression code is not fully contained and quantization is performed, the boundary distortion of the tile 41 can be reduced. According to such a configuration, it can be said that this is a compression coding system that has good image quality and efficiency for use in the digital copying machine 1 and other printers, MFPs (MFPs), and the like for print processing. When it is desired to use the compression-encoded code string file on the personal computer 100, since the number of tile divisions is not uniform for all hierarchies, standard specification decoding means (for example, JPEG2000 standard specification decoding means) ), The personal computer 100 that only holds the code string cannot be decoded.
[0150]
Therefore, in the digital copying machine 1 of this example, as in the case of the first embodiment, in the image processing apparatus 26, for example, in the output path from the page memory 25 (or HDD 27) to the personal computer 100 (network 4). A modified output unit 52 implemented as a modified output means or a modified output function is added to the above, and the above-described code string is modified into a standard modified code string that can be decoded by the standard decoding means and output. Is. The correction processing in the correction output unit 51 in this case is the same as in the case of the correction output unit 51, and the code string extracted from the code string obtained from the page memory 25 to the middle layer where the number of tile divisions does not change. Is a modified code string. For example, in the example as shown in FIG. 11 and the like, the code example extracted from the code string to the first to third layers divided into the plurality of tiles 41 is a modified code string, and the number of tile divisions is changed ( (No tile division) This is distinguished from the code string related to the fourth layer.
[0151]
In this case, the processing of the modified code string and the unnecessary code string (discard, invalid data, etc.) due to the change in the number of tile divisions may be the same as described with reference to FIG.
[0152]
Therefore, on the personal computer 100 side that receives such a modified code string, the number of tile divisions is continuous over each hierarchy with respect to the modified code string. For example, in the example of FIG. Since it can be handled as a code string having no four-level code string (in this example, it is a code string with a standard specification of JPEG 2000), it can be decoded and used by a standard decoding means.
This embodiment According to the above, when the image data is basically compressed and encoded to generate the code string, it is divided into a plurality of regions from the middle layer and encoded. The frequency transform coefficient for decoding an image of a certain large size (for example, A3) is not divided into regions such as tile division, and a small size (for example, A4, A5) that can rotate the direction of the image is decoded. As for the frequency conversion coefficient for this purpose, it is possible to divide the image into only the necessary layers, such as by dividing the area such as tile division, so that the deterioration of the compression rate associated with the area division is suppressed and the image quality is improved. be able to. Further, it is possible to create a code that is an object of region division and a code that is not an object by a single algorithm, and it is possible to simplify a circuit related to image compression processing as compared with a case where an encoding method is selectively used. On the other hand, when a code string by such compression coding is used by an external device such as a personal computer, the number of area divisions changes in the middle of the hierarchy, so it cannot be decoded by standard decoding means, but is output to the outside. In such a case, a standard code string is obtained by outputting a code string from the code string up to the middle layer where the number of divisions of the region does not change, as a modified code string. It is possible to ensure consistency so that decoding can be performed with
This embodiment According to the above, when outputting to the outside, the code sequence is extracted from the code sequence up to the middle layer where the number of divisions of the region does not change, but at this time, the number of divisions does not change Since the number of divisions of the code string up to the second layer is described in the modified code string, it is possible to perform an appropriate decoding process according to the number of divisions in the external device.
This embodiment In general, when considering the relationship between an image forming apparatus or the like as an image processing apparatus and a personal computer, for example, the layer portion for encoding without dividing the area has a high resolution. Since it becomes useless information, even when the code string of the layer after such a change in the number of divisions is discarded when it is output to an external device, there is no particular problem.
This embodiment In general, when considering the relationship between an image forming apparatus or the like as an image processing apparatus and a personal computer, for example, the layer portion for encoding without dividing the area has a high resolution. Since it becomes useless information, there is no problem in discarding the code string of the layer after such a change in the number of divisions when outputting to an external device. Since it has been described in, it can be restored and used in the standard specification.
This embodiment In general, when considering the relationship between an image forming apparatus or the like as an image processing apparatus and a personal computer, for example, the layer portion for encoding without dividing the area has a high resolution. Since it becomes useless information, there is no problem in discarding the code string of the layer after such a change in the number of divisions when outputting to an external device, but there are cases where it is desired to use it. Since it is added at the end of the modified code string, it can be restored and used in the standard specification.
This embodiment According to, for example, the frequency conversion coefficient for decoding an image of a large size (for example, A3) whose image orientation cannot be rotated can be rotated without dividing the region such as tile division. As for frequency transform coefficients for decoding a small size (for example, A4 and A5), it is possible to divide an image only when necessary, such as dividing an area such as tile division. The accompanying deterioration of the compression rate can be suppressed. Further, it is possible to create a code that is an object of region division and a code that is not an object by a single algorithm, and it is possible to simplify a circuit related to image compression processing as compared with a case where an encoding method is selectively used. Furthermore, in the case where the image output once is stored in the image forming apparatus or the like, and then the same image is output again, it is designated to output to a medium of a different size each time it is output. Can output at high speed. For example, it is possible to respond at high speed when the A3 image is reduced and output, but it is difficult to see and output again in A3 size, or when the A3 output is performed once but the A4 output is performed the second time.
This embodiment Therefore, it is possible to suppress the deterioration of the compression rate due to the region division, simplify the circuit, etc. using frequency conversion.
This embodiment According to the above, since the low frequency component is not divided into regions, the distortion generated at the boundary of the region when the component is quantized can be reduced, and such frequency transform coefficients are compressed by entropy coding. A code can be generated.
This embodiment According to the JPEG2000 algorithm, it is possible to suppress the deterioration of the compression rate due to the area division, simplify the circuit, and output the file as a JPEG2000 algorithm file when outputting to an external device. be able to.
This embodiment According to the image forming apparatus, This embodiment Because it is equipped with the image processing device Image processing apparatus according to the present embodiment The same effect can be achieved.
This embodiment According to the storage medium This embodiment Since the image processing program is stored, Image processing program according to the present embodiment The same effect can be achieved.
[0153]
【The invention's effect】
The present invention According to the above, when the image data is basically compressed and encoded to generate the code string, it is divided into a plurality of regions from the middle layer and encoded. The frequency transform coefficient for decoding an image of a certain large size (for example, A3) is not divided into regions such as tile division, and a small size (for example, A4, A5) that can rotate the direction of the image is decoded. As for the frequency conversion coefficient for this purpose, it is possible to divide the image into only the necessary layers, such as by dividing the area such as tile division, so that the deterioration of the compression rate associated with the area division is suppressed and the image quality is improved. be able to. In addition, it is possible to create a code that is a target of region division and a code that is not a target by using a single algorithm, and it is possible to simplify a circuit related to image compression processing as compared with a case where a coding method is properly used. it can .
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a system example of a first embodiment of the present invention.
FIG. 2 is a block diagram showing a schematic configuration of the digital copying machine.
FIG. 3 is a flowchart illustrating an example of processing executed by the digital copying machine.
FIG. 4 is an explanatory diagram illustrating a data configuration of a code string created by an encoding unit.
FIG. 5 is an explanatory diagram illustrating image orientation rotation processing;
FIG. 6 is an explanatory diagram schematically showing an example of a code string that is different in the inside and outside.
FIG. 7 is an explanatory diagram illustrating a modification example of the data configuration of a code string created by an encoding unit.
FIG. 8 is a block diagram showing an overall configuration of a digital copying machine according to a second embodiment of the present invention.
FIG. 9 is an explanatory diagram illustrating wavelet transform coefficients in the present embodiment.
FIG. 10 is a flowchart showing an example of processing in the present embodiment.
FIG. 11 is an explanatory diagram for explaining processing in the present embodiment;
FIG. 12 is an explanatory diagram illustrating an image orientation rotation process according to the present embodiment.
[Explanation of symbols]
1 Image forming device
2 Printer engine
23a, 23b, 23 Image compression means, image compression function
24a, 24b, 24 decoding means
25, 27 storage device
26 Image processing device
51, 52 Correction output means, correction output function
100 External equipment

Claims (20)

When the image data is divided into a plurality of areas and the code sequence is generated by hierarchically compressing and encoding the image data with different resolutions, an image processing device that processes the code sequence decodes the code sequence in the processing of the corresponding hierarchy resolution that can rotate the image data, the number of divisions of regions of the image data in the hierarchy to be the process, the processing of the hierarchy that does not correspond to the resolution that can be said rotating Compression encoding means for encoding by changing, and
A storage device for storing a code string which has been compressed and encoded by said compressing and encoding means,
A correction output means for outputting a correction code string extracted from the code string up to a hierarchy where the number of divisions of the region does not change, and output to the outside ,
The image processing apparatus according to claim 1, wherein the processing of the layer not corresponding to the resolution that can be rotated is performed before the processing of the layer corresponding to the resolution that can be rotated .   2. The image processing apparatus according to claim 1, wherein the correction output unit describes the number of divisions of the code string up to a middle layer where the number of divisions does not change in the correction code string.   The image processing apparatus according to claim 1, wherein the correction output unit discards the code string of the hierarchy after the division number is changed.   The image processing apparatus according to claim 1, wherein the correction output unit describes a code string of a layer after the number of divisions is changed in the correction code string.   The image processing apparatus according to claim 1, wherein the correction output unit adds a code string of a layer after the number of divisions is changed as invalid data to an end of the correction code string. The compression encoding means includes
First conversion means for decomposing image information or luminance color difference information of image data into a first low-resolution image and first detailed information;
First entropy encoding means for entropy encoding the first detailed information;
The first low-resolution image is divided into a plurality of areas, and the first low-resolution image existing in each area is decomposed without using the first low-resolution image existing in another area. A second conversion means for obtaining a second low-resolution image and second detailed information for each area;
Second entropy encoding means for entropy encoding the second detailed information;
An image processing apparatus according to any one of claims 1 to 5, further comprising: The first conversion unit in the compression encoding unit converts the image information or the luminance / color difference information into the first low-frequency component that is the first low-resolution image and the first detailed information. Is decomposed by frequency conversion into a first high frequency component that is a higher frequency component than a low frequency component
The second conversion means in the compression encoding means uses the second low-frequency component that is the second low-resolution image as the first low-frequency component and the second detailed information as the second low-frequency component. Decompose by frequency conversion into a second high frequency component which is a higher frequency component than the low frequency component,
The image processing apparatus according to claim 6. The compression encoding means frequency-converts image information to decompose a low-frequency component and a high-frequency component that is higher in frequency than the low-frequency component, and repeats the process of performing the frequency conversion again on the low-frequency component. The image information is frequency-converted into n-layer frequency components, and the process for converting the frequency of the original image information is obtained by the frequency conversion of the first layer and the frequency conversion of the m-th layer. When the process of further converting the frequency of the low frequency component is the (m + 1) th layer frequency conversion,
In the frequency conversion from the first layer to the m-th layer (1 ≦ m <n), a first frequency conversion is performed without dividing the image information or a low-frequency component of a region corresponding to the image information. In the frequency conversion means and the frequency conversion from the (m + 1) th layer to the nth layer, for the low frequency component corresponding to each region of the low frequency component of the mth layer divided into a plurality of regions, Second frequency conversion means for performing frequency conversion without using the low-frequency component existing in the other region;
Entropy encoding means for entropy encoding each frequency conversion coefficient after the frequency conversion to generate a compression code;
An image processing apparatus according to any one of claims 1 to 5, further comprising:   The image processing apparatus according to claim 7 or 8, wherein the compression encoding method is JPEG2000. An image processing apparatus according to any one of claims 1 to 9,
A decoding means for decoding a code string stored in the storage device is compressed and encoded by the compression encoding unit of the image processing apparatus,
A printer engine for forming an image based on the image data decoded by the decoding means;
An image forming apparatus comprising: When the image data is divided into a plurality of areas and the code sequence is generated by hierarchically compressing and encoding the image data with different resolutions, an image processing apparatus that processes the code sequence decodes the code sequence The processing of the layer that does not correspond to the resolution that can rotate the image data is performed before the processing of the layer that corresponds to the resolution that can be rotated , and the processing of the layer that corresponds to the resolution that can be rotated. Is a compression encoding function for encoding by changing the number of divisions of the area of the image data in the layer to be processed with respect to the processing of the layer not corresponding to the resolution that can be rotated,
A function of storing the code sequence which has been compressed and encoded by said compressing and encoding functions in the storage device,
A correction output function for outputting a correction code string obtained by extracting a code string from the code string up to a hierarchy where the number of divisions of the region does not change; and
An image processing program for causing a computer to execute the above.   12. The image processing program according to claim 11, wherein the modified output function describes the number of divisions of a code string up to a middle layer where the number of divisions does not change in the modified code string.   The image processing program according to claim 11 or 12, wherein the correction output function discards a code string of a layer after the number of divisions is changed.   13. The image processing program according to claim 11, wherein the correction output function describes a code string of a layer after the number of divisions is changed in the correction code string.   The image processing program according to claim 11 or 12, wherein the correction output function adds a code string of a layer after the number of divisions is changed as invalid data to the end of the correction code string. The compression encoding function is:
A first conversion function for decomposing image information or luminance color difference information of image data into a first low-resolution image and first detailed information;
A first entropy encoding function for entropy encoding the first detailed information;
The first low-resolution image is divided into a plurality of areas, and the first low-resolution image existing in each area is decomposed without using the first low-resolution image existing in another area. A second conversion function for obtaining a second low-resolution image and second detailed information for each area;
A second entropy encoding function for entropy encoding the second detailed information;
16. The image processing program according to claim 11, wherein the image processing program is executed by the computer. The first conversion function in the compression encoding function is the first low-frequency component that is the first low-resolution image and the first detailed information that is the image information or the luminance / color-difference information. Is decomposed by frequency conversion into a first high frequency component that is a higher frequency component than a low frequency component of
The second conversion function in the compression encoding function is configured such that the first low-frequency component is the second low-frequency component that is the second low-resolution image and the second detailed information is the second low-frequency component. Decomposed by frequency conversion into a second high frequency component, which is a higher frequency component than the low frequency component,
The program for image processing according to claim 16. The compression encoding function repeats the process of performing frequency conversion on image information and decomposing the image information into a low frequency component and a high frequency component higher in frequency than the low frequency component, and performing the frequency conversion again on the low frequency component. The image information is frequency-converted into n-layer frequency components, and the process for converting the frequency of the original image information is obtained by the frequency conversion of the first layer and the frequency conversion of the m-th layer. When the process of further converting the frequency of the low frequency component is the (m + 1) th layer frequency conversion,
In the frequency conversion from the first layer to the m-th layer (1 ≦ m <n), a first frequency conversion is performed without dividing the image information or a low-frequency component of a region corresponding to the image information. In the frequency conversion function and the frequency conversion from the (m + 1) th layer to the nth layer, for the low frequency component corresponding to each region of the low frequency component of the mth layer divided into a plurality of regions, A second frequency conversion function for performing frequency conversion without using the low frequency component existing in the other region;
An entropy encoding function for entropy encoding each frequency conversion coefficient after the frequency conversion to generate a compression code;
16. The image processing program according to claim 11, wherein the image processing program is executed by the computer.   19. The image processing program according to claim 17, wherein the compression encoding method is JPEG2000.   A computer-readable storage medium storing the program according to claim 11.

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