JP4650236B2 - Data compression apparatus, data compression method, and data compression program - Google Patents

Description

  The present invention relates to a data compression device, a data compression method, and a data compression program, and in particular, a data compression device, a data compression method, and a data compression device capable of setting a compression condition in consideration of a working memory amount when decompressing compressed data, And a data compression program.

  In recent years, a process of reading and digitizing a document printed on paper with a scanner or the like has been utilized. Since the read image data has a large amount of data, it needs to be compressed by an image compression method such as JPEG. When the image data is compressed by JPEG, a good result can be obtained in terms of compression rate and image quality for a photographic image.

  However, documents such as business sentences contain not only photographic images but also graphic elements such as letters and graphs. If these graphic elements are uniformly compressed by an irreversible compression method such as JPEG, there arises a problem that, for example, the image quality of the character portion deteriorates and cannot be read.

  In order to solve this problem, in the technique disclosed in Patent Document 1, the character part and the photograph part are separated to determine the position, size, and color of the character area, and the character area and the other areas are separated. Perform compression. As a result of processing in this way, in the character portion, the compression code compressed by the character's predetermined compression method, the coordinate value of the character, and the color of the character are output. A compressed code having the size of the entire page compressed by the compression method is output.

  In this technique, since the compression method can be arbitrarily selected for each of the separated character portion and background portion, the overall compression rate is high, and a high-quality image can be generated.

JP 2003-219187 A

  However, in the above technique, depending on the selected compression method, a large amount of working memory may be required when compressing image data or decompressing compressed data. If memory shortage occurs during image data compression (encoding), error recovery processing can be performed by selecting a different compression method or compression parameter. On the other hand, the processing environment on the receiving side of the compressed data is various, and if a memory shortage occurs at the time of decompressing (decoding) the compressed data, the decompressed and displayed compressed data cannot be performed.

  For example, instead of FAX-G4 (MMR) compression for binary image compression, T.T. Assuming that JBIG2 compression shown in the 88 recommendation is used, it is known that the compression ratio is doubled to fourfold in a document containing many symbols such as characters. Double memory may be required. For this reason, for example, when a recipient of compressed data uses a PDA (Portable Data Assistance), a problem arises in that the compressed data cannot be expanded and displayed because the RAM capacity of the PDA is small.

  The present invention has been made to solve the above problems, and an object of the present invention is to set compression conditions in consideration of the amount of working memory at the time of decompression of compressed data. An object of the present invention is to provide a data compression apparatus, a data compression method, and a data compression program that can avoid the inconvenience of being unable to perform expansion and display.

To achieve the above object, a data compression apparatus of the present invention generates a plurality of data input means for inputting multi-layered image data, data compression means for compressing the image data, and compression conditions for compressing the image data. a condition generating means for the data expansion means for expanding image data compressed the multilayer structure, for each of a plurality of compression conditions generated by the condition generation means, the image data compressed by said data compression means Expansion by the data expansion means, measure the amount of work memory at the time of expansion, acquire the amount of work memory at the time of expansion of the compressed image data, and is set in advance as the acquired amount of work memory An expansion memory inspection means for comparing the obtained allowable memory amount and inspecting whether or not the acquired working memory amount is less than or equal to the allowable memory amount, and the expansion memory inspection A condition setting means for setting a predetermined compression condition in which a working memory amount at the time of expansion is equal to or less than an allowable memory amount among a plurality of generated compression conditions with reference to the inspection result at the stage, and set by the condition setting means Data output means for compressing the image data inputted by the data compression means under the above-mentioned compression conditions and outputting compressed image data having a multilayer structure.

  In the above-described data compression apparatus, when multi-layered image data is input from the data input unit, the condition generation unit generates a plurality of compression conditions for compressing the image data. The expansion memory inspection unit acquires a working memory amount at the time of decompressing the compressed image data for each of the plurality of compression conditions generated by the condition generating unit, and the acquired working memory amount It is compared with a preset allowable memory amount to check whether the acquired working memory amount is less than or equal to the allowable memory amount.

  The condition setting means refers to the inspection result in the expansion memory inspection means, sets a predetermined compression condition in which the working memory amount at the time of expansion is equal to or less than the allowable memory amount from the plurality of generated compression conditions, and the data output means Compresses the image data input by the data compression means under the compression conditions set by the condition setting means, and outputs compressed image data having a multilayer structure. Therefore, by setting the allowable memory amount in advance according to the device that performs the decompression and display of the compressed data, it is possible to avoid the disadvantage that the compressed data cannot be decompressed and displayed due to a memory shortage.

  As described above, according to the present invention, by setting the compression condition in consideration of the working memory amount at the time of decompression of the compressed data, it is possible to avoid the inconvenience that the decompressed data cannot be decompressed and displayed due to insufficient memory. There is an effect that can be.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

<Schematic configuration of data compression apparatus>
FIG. 1 is a functional block diagram showing a schematic configuration of a data compression apparatus according to the present invention.
The data compression apparatus 10 acquires a compression condition acquisition processing unit 16 that generates a plurality of compression conditions 14 of the input layer image data 12 and a working memory amount at the time of expansion for each of the generated plurality of compression conditions 14. And checking whether or not the acquired working memory amount is less than or equal to a preset allowable memory amount, and compressing the layer image data 12 under a compression condition in which the working memory amount at the time of expansion is less than or equal to the allowable memory amount, And a decompression memory inspection unit 18 for outputting the compressed layer image data 20.

  The expansion memory inspection unit 18 includes an internal buffer 22 that temporarily stores input data, a compression processing unit 24 that compresses the input layer image data 12, and an expansion that expands the compressed layer image data. And a processing unit 26. The internal buffer 22 also functions as a condition setting unit that sets a predetermined compression condition from among a plurality of generated compression conditions.

  In the data compression apparatus 10 described above, when a user instructs a compression condition on a user interface (UI) (not shown), the compression condition acquisition processing unit 16 sets a plurality of compression conditions 14 for the layer image data 12 based on the instructed condition. Generated. The generated compression condition is input to the expansion memory inspection unit 18 and held in the internal buffer 22. The decompression memory checking unit 18 executes a “decompression memory check process” to be described later for each compression condition held in the internal buffer 22, and the working memory amount is less than the allowable memory amount among the plurality of generated compression conditions. A predetermined compression condition is selected. The selected compression condition is set in the internal buffer 22, the layer image data 12 is compressed under the compression condition set by the compression processing unit 24, and the compressed layer image data 20 is output.

<Layer image data>
Here, the layer image data will be described. The layer image data is image data having an MRC (Mixed Raster Content) structure, and is generated by separating document data created by an application into a plurality of layers (layers) and creating raster data for each layer. The layer image data can achieve a high compression rate by applying different types of compression processing to the raster data for each layer.

  2A to 2C are diagrams illustrating an example of layer image data. For example, FIG. 2A shows a configuration example of document data. The document data 30 is composed of text 32 and graphics 34 drawn in black, text 36 and graphics 38 drawn in red, and an image 40 created by taking in image data such as a photograph. FIG. 2B shows a state in which portions including images are collected in one layer 42, and the layer 42 can be compressed by a method (for example, JPEG method) for compressing multi-valued image data. Further, since this layer 42 is treated as a base, it is called a BG (Background) layer or a background layer.

  FIG. 2C shows a state in which portions including text and graphics are collected in one layer 44. Mask data 46 and 48 are formed for each area of the same color. Each can be compressed by a method (for example, MMR method) for compressing binary image data. Further, since this layer 44 is overwritten on the background, it is called an FG (Foreground) layer or a foreground layer, and each mask data includes “binary data”, “position / size”, and “color information” compressed by MMR. "Can be expressed as a combination.

  In the image data included in the MMR-compressed region of the FG layer 44, a portion where text or graphics exists corresponds to a “black” pixel. If it is defined that the “white” pixel portion is treated as a transparent area at the time of decoding, the JPEG compressed data of the BG layer 42 is expanded and then the MMR compressed data of the FG layer 44 is expanded and designated. The original document data 30 can be reproduced by coloring the color information.

<Generation of compression conditions>
FIG. 3 shows an example of compression conditions. As shown in FIG. 3, the compression condition of the layer image data 12 is expressed by a combination of four elements of “resolution”, “image quality parameter”, “background compression method”, and “foreground compression method”.

  In the present embodiment, the “resolution” is automatically selected (automatically selected) from 300, 400, and 600 dpi. The “image quality parameter” is determined in advance according to the compression method, and is automatically selected from these parameters. For example, as an example of the image quality standard, in the case of JPEG, the quality value (value from 0 to 100) can be set in advance such that compression priority is 30, standard is 55, and image quality is 85. .

  In the “compression method”, candidates are set in advance for each of the background layer and the foreground layer of the layer image data, and are automatically selected from these. The “background compression method” is a compression method for multi-valued images, and JPEG, JPEG2K, and deflate are set as candidates. The “foreground compression method” is a binary image compression method, and MMR and JBIG2 are set as candidates. Here, actual compression formats that can be used up to 1.5 specifications of PDF are illustrated as candidates.

  In the compression condition acquisition processing unit 16, compression conditions are generated by the number of combinations of the four elements described above. For example, in the example illustrated in FIG. 2, 3 × 3 × 3 × 2 = 54 types of compression conditions are generated, and the plurality of generated compression conditions are input to the expansion memory inspection unit 18.

<Expansion memory inspection process>
FIG. 4 is a flowchart showing a processing routine of “development memory inspection processing”. This processing routine is executed by the compression condition acquisition processing unit 16.
When a plurality of compression conditions generated by the compression condition acquisition processing unit 16 are input to the expansion memory inspection unit 18, first, in step 100, the plurality of compression conditions are held in the internal buffer 22 of the expansion memory inspection unit 18. To do. In the next step 102, a predetermined compression condition is selected. That is, one of the combinations of the four elements described above is selected. In the next step 104, when the layer image data 12 is compressed under the selected compression condition, the compression rate of the compressed data and the amount of working memory necessary for decompressing the compressed data are measured. "Measurement process" is executed.

  Next, in step 106, the allowable memory amount held in the internal buffer 22 is read, the working memory amount at the time of expansion is compared with the allowable memory amount, and whether the working memory amount at the time of expansion is less than the allowable memory amount or not. Judging. As the allowable memory amount, a plurality of candidate values may be set in advance according to a device that performs decompression and display of compressed data, and may be selected by the user. For example, if the device is a mobile phone, it is 1 megabyte, if it is a PDA, it is 10 megabytes, and if it is a personal computer, there is no limit. If the determination is negative, the process proceeds to step 108, the target compression condition is removed from the internal buffer, and the process returns to step 102 to select the next compression condition. As a result, it is possible to avoid the inconvenience that the compressed data cannot be expanded and displayed in the device that has received the compressed data due to a lack of working memory.

  If the determination is affirmative, the process proceeds to step 110 to determine whether there is another compression condition. If the determination is affirmative, the process returns to step 102 to select the next compression condition. On the other hand, in the case of negative determination, it means that the “decompression memory check process” has been completed for the plurality of generated compression conditions, so that the process proceeds to the next step 112 and the allowable compression conditions held in the internal buffer 22. Are selected, and an allowable compression condition in which the compression ratio is the highest is selected. Then, the selected allowable compression condition is set in the internal buffer 22 as the actual compression condition, and the routine ends.

<Measurement processing of working memory amount>
FIG. 5 is a flowchart showing a subroutine of “measurement process of working memory amount”.
In step 200, the layer image data 12 is compressed according to the compression condition selected by the compression processing unit 24. In step 202, the compression rate is measured from the compressed data obtained by actually executing the compression process, and in step 204, the measured compression rate is stored in the internal buffer 22. Next, in step 206, the decompression processing unit 26 decompresses the compressed data. In step 208, the amount of work memory actually required for the expansion process is measured. In step 210, the measured amount of work memory is stored in the internal buffer 22, and the routine is terminated. Note that the working memory usage at the time of development refers to the amount of memory excluding the image data that is the result of the development out of the amount of memory dynamically secured by the development program at the time of development.

  As described above, in the present embodiment, the layer image data compression process and the compressed data decompression process are performed for all the compression conditions to actually measure the compression rate and the working memory amount at the decompression. As the actual compression condition used for the compression process, the compression condition is set so that the working memory amount at the time of decompression is equal to or less than the preset allowable memory amount and the compression rate is the highest among the plurality of generated compression conditions. It is possible to avoid the inconvenience that the compressed data cannot be expanded and displayed due to a lack of working memory.

  In the above embodiment, an example has been described in which both the compression processing of the layer image data and the decompression processing of the compressed data are performed to actually measure the compression rate and the working memory amount necessary for decompression. Only the compression process may be performed to actually measure the compression rate and calculate the working memory amount at the time of decompression from the compressed data. Further, the compression rate and the working memory amount at the time of decompression may be calculated without performing any of the compression process and the decompression process.

  In the above embodiment, an example in which “development memory inspection process” is executed for all the generated compression conditions has been described. The “memory inspection process” can be omitted. For example, when the memory becomes insufficient at 300 dpi, it is expected that the memory will normally become insufficient even at 400 dpi and 600 dpi. In such a case, 400 dpi and 600 dpi processing can be omitted.

  In the above-described embodiment, an example in which each element of the compression condition is automatically selected has been described. However, some elements may be fixed. FIG. 6 shows another example of the compression condition. This compression condition is also expressed by a combination of the above four elements. In this example, “resolution” is a fixed value, which is 300 dpi. The “image quality parameter” is a fixed value and has compression priority. The “background compression method” is a fixed value, and JPEG is set. The “foreground compression method” is a compression method for binary images, and is automatically selected from MMR and JBIG2. As an example of immobilization, there is a case where the user directly designates “resolution”, “image quality parameter” or the like on the UI. Also, some elements may be fixed due to the specifications of the actually operating device. For example, the upper limit of the resolution of the apparatus is 600 dpi.

It is a functional block diagram which shows schematic structure of the data compression apparatus of this invention. (A) thru | or (C) are figures which show an example of layer image data. It is a figure which shows an example of compression conditions. It is a flowchart which shows the processing routine of "the memory test process at the time of expansion | deployment". It is a flowchart which shows the subroutine of "the measurement process of working memory amount". It is a figure which shows another example of compression conditions.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Data compression apparatus 12 Layer image data 14 Compression condition 16 Compression condition acquisition process part 18 Expansion memory test | inspection part 20 Layer image data 22 Internal buffer 24 Compression process part 26 Expansion process part 30 Document data 32 Text 34 Graphics 36 Text 38 Text 40 image 42 layer 44 layer 46 mask data

Claims (6)

Data input means for inputting image data having a multilayer structure;
Data compression means for compressing the image data;
Condition generating means for generating a plurality of compression conditions for compressing the image data;
Data expansion means for expanding the compressed image data of the multilayer structure;
For each of the plurality of compression conditions generated by the condition generation means, the image data compressed by the data compression means is expanded by the data expansion means, the amount of working memory at the time of expansion is measured, and the compressed data Acquire the working memory amount when expanding image data, compare the acquired working memory amount with a preset allowable memory amount, and determine whether the acquired working memory amount is less than or equal to the allowable memory amount Expansion memory inspection means for inspecting
Condition setting means for referring to the inspection result in the expansion memory inspection means and setting a predetermined compression condition in which the working memory amount at the time of expansion is equal to or less than the allowable memory amount from among the plurality of generated compression conditions;
Data output means for compressing the image data input by the data compression means under the compression conditions set by the condition setting means, and outputting compressed image data having a multilayer structure;
A data compression apparatus comprising: The expansion memory inspection unit obtains a compression rate when the image data is compressed together with a work memory amount at the time of expansion, and the condition setting unit includes a compression memory that has a work memory amount at the time of expansion that is equal to or less than an allowable memory amount. The data compression apparatus according to claim 1, wherein a predetermined compression condition is set such that becomes the highest. The data compression apparatus according to claim 1 , wherein the compression condition includes a compression method, an image quality parameter, and a resolution. The data compression apparatus according to claim 3 , wherein the image quality parameter is set at a plurality of levels according to the compression method. The data compression apparatus according to claim 3 , wherein a part of the compression condition is a fixed condition. By computer
A condition generation step for generating a plurality of compression conditions for compressing the input multilayered image data;
A data expansion step of expanding the compressed image data of the multilayer structure;
For each of the plurality of compression conditions generated in the condition generation step, the image data compressed by the data compression unit is expanded by the data expansion unit, the working memory amount at the time of expansion is measured, and the compressed Acquire the working memory amount when expanding image data, compare the acquired working memory amount with a preset allowable memory amount, and determine whether the acquired working memory amount is less than or equal to the allowable memory amount Expansion memory inspection step for inspecting
A condition setting step for setting a predetermined compression condition in which the amount of working memory at the time of expansion is equal to or less than an allowable memory amount from among a plurality of generated compression conditions with reference to the inspection result in the expansion memory inspection step;
A data output step of compressing the input image data under the compression conditions set in the condition setting step and outputting compressed image data of a multilayer structure;
Data compression program that executes

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