JP2010200174A - Image processor and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor capable of compressing image data into a further small size in a range where an extension time of the image data is fitted in an allowable range. <P>SOLUTION: This image processor includes: compression parts 111a-111d for simultaneously compressing the same image data by a plurality of types of compression methods in parallel to one another to generate a plurality of types of compressed data for the same image data; extension time calculation parts 112a-112d for obtaining an extension time of the compressed data for each of the plurality of types of compressed data generated by the compression parts 111a-111d; a selection part 116 for selecting one of the compressed data from among the plurality of types of compressed data based on the extension times of the plurality of types of compressed data obtained by the extension time calculation parts 112a-112d and data sizes of the respective compressed data; and an output part 117 for outputting the compressed data selected by the selection part 116 as output data. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image processing apparatus and an image processing method. The present invention particularly relates to an image processing apparatus and an image processing method for compressing image data for printing.

  Products with severe cost competition such as printers need to reduce the cost of memory. For this purpose, it is effective to compress the image data to a smaller size.

  As a technique related to compression of image data, an image forming apparatus as shown in Patent Document 1 below is known. The image forming apparatus disclosed in Patent Document 1 preliminarily compresses image data in units of one line, estimates the decompression time of the image data from the data size of the compressed image data, and the decompression time exceeds the allowable value. If it is determined, the image data is compressed by changing the compression method. According to such a configuration, the decompression time of the compressed image data is surely kept within an allowable range. Therefore, in a printing method in which the print processing is executed while decompressing the compressed image data in real time, one line's worth is achieved. It is possible to prevent a printing error (overrun) from occurring because the image data decompression process is not in time for the printing process.

  However, in the image forming apparatus, the decompression time of the compressed image data is guaranteed to be within an allowable range, but the data size of the compressed image data is not taken into consideration. In the above printing method, it is desired to compress the image data to the smallest possible size within a range where the expansion time of the image data is within an allowable range.

Japanese Patent Laid-Open No. 10-23271

  The present invention has been made in view of the above-described problems. Accordingly, an object of the present invention is to provide an image processing apparatus and an image processing method capable of compressing image data to a smaller size within a range where the expansion time of the image data is within an allowable range.

  The above object of the present invention is achieved by the following means.

  (1) A compression unit that simultaneously compresses the same image data by a plurality of types of compression methods to generate a plurality of types of compressed data for the same image data, and the plurality of units generated by the compression unit For each type of compressed data, an expansion time calculation unit that calculates the expansion time of the compressed data, the expansion time of the plurality of types of compressed data determined by the expansion time calculation unit, and the data size of each compressed data And a selection unit that selects one compressed data from the plurality of types of compressed data, and an output unit that outputs the compressed data selected by the selection unit as output data. An image processing apparatus.

  (2) The image data is divided image data obtained by dividing image data for one page into a plurality of pieces, and the compression unit sequentially compresses the plurality of divided image data. The image processing apparatus according to (1) above.

  (3) an integration time calculation unit that integrates the decompression time of the compressed data that has been output as the output data to obtain an integration time of the decompression time of the compressed data that has been output; Based on the total data size of the divided image data that has become, a setting unit that sets a threshold of the integration time obtained by the integration time calculation unit, and the threshold that the integration time is set by the setting unit A determination unit that determines whether or not the total time is less than the threshold by the determination unit, the selection unit includes the plurality of types of compressed data When the determination unit determines that the integration time is equal to or greater than the threshold value, the selection unit selects the plurality of types of compression data. The image processing apparatus according to (2) from in the elongation time and selects the shortest of the compressed data.

  (4) The setting unit is configured so that the integration time of the decompression time of the output compressed data is shorter than the time required for the image printing process based on the divided image data that is the source of the output compressed data. The image processing apparatus according to (3), wherein the threshold is set based on a total data size of the divided image data.

  (5) When the determination unit determines that the accumulated time is less than the threshold value, and there are a plurality of types of compressed data with the minimum data size, the selection unit selects among the plurality of types of compressed data. The image processing apparatus according to (3) or (4), wherein the compressed data having the shortest decompression time is selected.

  (6) A step (a) of simultaneously compressing the same image data by a plurality of types of compression methods to generate a plurality of types of compressed data for the same image data, and generating in the step (a) For each of the plurality of types of compressed data, the step (b) of obtaining the decompression time of the compressed data, the decompression time of the plurality of types of compressed data obtained in step (b), and each compressed data A step (c) of selecting one compressed data from the plurality of types of compressed data based on the data size, and a step of outputting the compressed data selected in the step (c) as output data An image processing method comprising: (d).

  (7) The image data is divided image data obtained by dividing image data for one page into a plurality of pieces, and the plurality of divided image data are sequentially compressed in the step (a). The image processing method according to (6), characterized in that it is characterized in that

  (8) Step (e) of accumulating the decompression time of the compressed data that has been output as the output data to obtain an integral time of the decompression time of the compressed data that has been output; Based on the total data size of the divided image data, the step (f) for setting the threshold value for the integration time obtained in the step (e), and the integration time is set in the step (f). A step (g) for determining whether or not the integrated time is less than the threshold in the step (g). In c), the compressed data having the smallest data size is selected from the plurality of types of compressed data, and in the step (g), the integration time is equal to or greater than the threshold value. If it is determined, in the step (c), the compressed data having the shortest decompression time is selected from the plurality of types of compressed data. Image processing method.

  (9) In step (f), the integration time of the decompression time of the compressed data that has been output is shorter than the time required for image printing processing based on the divided image data that is the source of the compressed data that has been output. The image processing method according to (7), wherein the threshold is set based on a total data size of the divided image data.

  (10) In the case where it is determined in the step (g) that the integration time is less than the threshold value, and there are a plurality of types of compressed data having the minimum data size, in the step (c), the plurality of types The image processing method according to (8) or (9), wherein the compressed data having the shortest decompression time is selected from the compressed data.

  According to the present invention, one compressed data is selected from a plurality of types of compressed data generated in parallel based on the decompression time and data size of each compressed data, and is output as output data. Therefore, when selecting compressed data to be output as a compression result of image data from among a plurality of types of compressed data, it is possible to select the optimal compressed data by referring to the decompression time and data size of each compressed data. It becomes possible. As a result, the image data can be compressed to a smaller size within a range where the decompression time of the image data is within an allowable range.

1 is a configuration diagram illustrating a schematic configuration of a printer including an image processing apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a schematic configuration of an image processing unit in the printer illustrated in FIG. 1. It is a block diagram which shows schematic structure of the compression module in the image processing part shown by FIG. 4 is a flowchart for explaining compression processing of image data in the compression module shown in FIG. 3.

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

  FIG. 1 is a block diagram illustrating a schematic configuration of a printer including an image processing apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, the printer 1 includes a CPU 11, a ROM 12, a RAM 13, an image processing unit 14, a data output unit 15, a printing unit 16, an I / F control unit 17, and a host I / F 18. The CPU 11, the ROM 12, the RAM 13, the image processing unit 14, the data output unit 15, the I / F control unit 17, and the host I / F 18 are connected to each other via a bus. The printing unit 16 is connected to the data output unit 15.

  The printer 1 is connected to a host PC 2 that instructs printing of a document via a network, and executes a printing process based on a printing instruction from the host PC 2. Note that the printer 1 and the host PC 2 may be directly connected (locally connected) between devices without going through a network.

  The CPU 11 executes control of each part and various arithmetic processes according to a program. The ROM 12 stores various programs and various data.

  The RAM 13 temporarily stores programs and data as a work area. The RAM 13 stores bitmap image data 30 and compressed image data 40 obtained by compressing the image data 30.

  The image processing unit 14 performs image processing such as color conversion and screen processing on the bitmap format image data 30. The image processing unit 14 also generates compressed image data 40 in which the data size is reduced by compressing the image data 30.

  The data output unit 15 reads the compressed image data 40 from the RAM 13 and transfers it to the printing unit 16 while expanding it in real time. The data output unit 15 transfers the compressed image data 40 to the printing unit 16 while expanding the compressed image data 40 according to the paper conveyance speed in the printing unit 16.

  The printing unit 16 prints an image based on the image data transferred from the data output unit 15 on a recording medium such as paper using a known image forming process such as an electrophotographic process.

  The I / F control unit 17 controls the host I / F 18. The host I / F 18 is an interface for communicating with other devices via a network, and standards such as Ethernet (registered trademark), token ring, and FDDI are used.

  FIG. 2 is a block diagram showing a schematic configuration of the image processing unit in the printer shown in FIG.

  As shown in FIG. 2, the image processing unit 14 is configured as an ASIC (Application Specific Integrated Circuit), and includes a ReadDMA circuit 101, an image processing module 102, a compression module 103, and a WriteDMA circuit 104.

  The ReadDMA circuit 101 acquires image data to be processed. The ReadDMA 101 reads the bitmap-format image data 30 stored in the RAM 13 in a band unit of a predetermined number of lines and passes it to the image processing module 102.

  The image processing module 102 performs image processing on the image data. The image processing module 102 performs image processing such as color conversion processing, screen processing, γ correction processing, and edge enhancement processing on the image data for one band passed from the ReadDMA circuit 101.

  The compression module 103 compresses image processed image data. The compression module 103 compresses the image data for one band subjected to image processing by the image processing module 102 in units of data of a predetermined size. The compression module 103 uses a plurality of types of compression algorithms to reduce the data size of the compressed image data within a range in which the decompression time for each line of the compressed image data is within an allowable range. Compress data.

  The Write DMA circuit 104 outputs compressed image data. The Write DMA circuit 104 writes the image data for one band compressed by the compression module 103 back to the RAM 13.

  FIG. 3 is a block diagram showing a schematic configuration of the compression module in the image processing unit shown in FIG.

  As shown in FIG. 3, the compression module 103 includes first to fourth compression algorithm circuits 111a to 111d, first to fourth expansion time detection circuits 112a to 112d, a size information comparison circuit 113, an expansion time comparison circuit 114, and an expansion. A time integration circuit 115, a selection circuit 116, and a data selection circuit 117 are included.

  The first to fourth compression algorithm circuits 111a to 111d generate compressed data by compressing image data using different compression algorithms. The first to fourth compression algorithm circuits 111a to 111d compress 16-byte divided image data obtained by dividing image data for one line in parallel, and simultaneously compress four types of image data into one divided image data. Generate compressed data. The first to fourth compression algorithm circuits 111a to 111d are connected to the corresponding first to fourth decompression time detection circuits 112a to 112d and the size information comparison circuit 113, respectively, and each output a signal indicating the data size of the compressed data. Send it out. Details of the compression algorithm executed by the first to fourth compression algorithm circuits 111a to 111d will be described later.

  The first to fourth decompression time detection circuits 112a to 112d detect decompression times (number of clocks) of the compressed data generated by the corresponding first to fourth compression algorithm circuits 111a to 111d. The first to fourth decompression time detection circuits 112a to 112d detect the decompression time of the compressed data based on the signals from the first to fourth compression algorithm circuits 111a to 111d. The first to fourth decompression time detection circuits 112a to 112d are connected to the decompression time comparison circuit 114 and the decompression time integration circuit 115, respectively, and send signals indicating the decompression time of the compressed data.

  The size information comparison circuit 113 compares the data sizes of the four types of compressed data generated by the first to fourth compression algorithm circuits 111a to 111d. The size information comparison circuit 113 compares the data sizes of the four types of compressed data based on the signals from the first to fourth compression algorithm circuits 111a to 111d, and identifies the compressed data having the smallest data size. The size information comparison circuit 113 is connected to the expansion time integration circuit 115 and the selection circuit 116, and sends a signal indicating the compressed data having the minimum data size.

  The decompression time comparison circuit 114 compares the decompression times of the respective compressed data detected by the first to fourth decompression time detection circuits 112a to 112d. The decompression time comparison circuit 114 compares the decompression times of the four types of compressed data based on the signals from the first to fourth decompression time detection circuits 112a to 112d, and identifies the compressed data with the shortest decompression time. The expansion time comparison circuit 114 is connected to the expansion time integration circuit 115 and the selection circuit 116, and transmits a signal indicating compressed data with the shortest expansion time.

  The expansion time integration circuit 115 calculates an integrated value of the expansion time of the compressed data output as output data. The decompression time integrating unit 115 decompresses the compressed data output as output data based on signals from the first to fourth decompression time detection circuits 112a to 112d, the size information comparison circuit 113, and the decompression time comparison circuit 114. The integrated value of is calculated. Further, the decompression time integration circuit 115 compares the integration value of the decompression time of the compressed data output as output data with a threshold set according to the data size of the image data that is the source of the compressed data. The extension time integration circuit 115 is connected to the selection circuit 116, and transmits a signal indicating the comparison result between the extension value of the extension time and the threshold value.

  The selection circuit 116 switches the operation reference of the data selection circuit 117. The selection circuit 116 is connected to the data selection circuit 117 and switches the operation reference of the data selection circuit 117 based on a signal from the expansion time integration circuit 115. The selection circuit 116 switches between a state in which the data select circuit 117 operates in response to a signal from the size information comparison circuit 113 and a state in which the data select circuit 117 operates in response to a signal from the expansion time comparison circuit 114.

  The data select circuit 117 selects and outputs one compressed data from a plurality of types of compressed data. Based on the signal from the size information comparison circuit 113 or the decompression time comparison circuit 114, the data select circuit 117 selects the data size from the four types of compressed data generated by the first to fourth compression algorithm circuits 111a to 111d. The compressed data with the shortest or compressed data with the shortest decompression time is output as output data.

  Next, four types of compression algorithms executed by the first to fourth compression algorithm circuits 111a to 111d will be described.

<First compression algorithm>
The first compression algorithm is a compression algorithm called “representative value compression”, and a specific gradation data fill pattern (for example, a 10% gray fill pattern) and 32 pixel (16 bytes) image data are obtained. It is determined whether or not they match, and if the fill pattern and the image data match, the 16-byte image data is replaced with 8-bit data, a 2-bit header is added, and the data is output as 10-bit data.

  If the fill pattern does not match the image data, the 16-byte image data is divided into four, and it is determined whether the 4-byte image data matches the fill pattern. If the 4-byte image data matches the fill pattern, the 4-byte image data is output as 10-bit data. If the 4-byte image data does not match the fill pattern, a compression result is obtained. I can't.

  Since it is necessary to refer to the RAM 13 in order to obtain a different fill pattern for each print job, when decompressing data compressed by the first compression algorithm, to restore image data of 32 pixels (16 bytes), For image data that is not divided into four, processing time of 6 clocks is required, and for image data that is divided into four, processing time of 24 clocks is required.

<Second compression algorithm>
The second compression algorithm is a compression algorithm referred to as “simple history”, which is a data that matches image data by comparing the history of past 2048 bytes of data divided in units of 4 bytes with 4 bytes of image data. 4 bytes of image data is output as 18-bit data. Note that, similarly to the first compression algorithm, a compression result by the second compression algorithm cannot be obtained depending on image data.

  In the second compression algorithm, it is necessary to use the RAM 13 in order to hold a history of data of the past 2048 bytes. When image data compressed by the second compression algorithm is expanded, image data of 32 pixels (16 bytes) is used. Is required to process 24 clocks.

<Third compression algorithm>
The third compression algorithm is a compression algorithm called “Huffman code”, and uses a data conversion table called “Huffman table” in which data is arranged in order of appearance frequency based on statistical data, and has a high appearance frequency. Data is compressed by assigning a code with a short bit length to the data. The compression result is variable according to the appearance frequency, and 4-byte image data is converted into compressed data of 10 to 46 bits.

  Since the “Huffman table” is prepared as fixed data, a logic circuit that does not use RAM can be realized. When decompressing data compressed by the third compression algorithm, image data of 32 pixels (16 bytes) is restored. To do this, a processing time of 12 clocks is required.

<Fourth compression algorithm>
The fourth compression algorithm is uncompressed, adds a header to the original image data, and outputs the uncompressed image data. In the fourth compression algorithm, a 3-bit header is added to 16-byte image data, and 131-bit data is generated.

  On the other hand, in order to decompress the data generated by the fourth compression algorithm, one clock is required for header analysis, and 4 bytes of data are decompressed every clock. Therefore, image data of 32 pixels (16 bytes) is obtained. Is required to process 5 clocks.

  Table 1 summarizes the compression results and decompression times of the first to fourth compression algorithms.

  As shown in Table 1, the four types of compression algorithms have different data sizes and decompression times of compressed data obtained by compressing the same image data.

  In the printer 1 of the present embodiment configured as described above, when a print job is received from the host PC 2, PDL data included in the print job is converted into bitmap format image data 30 by rasterization processing. The bitmap format image data 30 is temporarily stored in the RAM 13. Then, the image data 30 is read from the RAM 13, compressed in the image processing unit 14, and stored again in the RAM 13. The compressed image data 40 is read in units of pages, and transferred to the printing unit 16 while being decompressed in real time. Note that in the decompression process of the present embodiment, the compressed image data is restored to the original image data without degradation of resolution or the like.

  In the compression module 103 of the present embodiment, in order to prevent a printing error from occurring due to the image data decompression processing for one line not being in time for the printing processing, decompression of one line of compressed image data is performed. The image data is compressed so that the data size of the compressed image data is smaller within a time range that falls within the allowable range.

  FIG. 4 is a flowchart for explaining compression processing of image data in the compression module shown in FIG. In this embodiment, image data for one line is compressed from one end to the other in units of 16-byte (32 pixels) divided image data obtained by dividing image data for one line. .

  As shown in FIG. 4, in the compression processing of image data in the present embodiment, first, an expansion time integration counter is initialized (step S101). In this embodiment, prior to the compression processing of the image data for one line, the integration value of the expansion time in the expansion time integration circuit 115 is set to the initial value “0”.

  Next, one divided image data is compressed in parallel by the first to fourth compression algorithms (step S102). In the present embodiment, 16-byte divided image data is simultaneously input to the first to fourth compression algorithm circuits 111a to 111d, and compressed by the first to fourth compression algorithms. As a result, four types of compressed data are generated for one piece of divided image data. Accordingly, the first to fourth expansion time detection circuits 112a to 112d detect the expansion time (number of clocks) of each compressed data. The first to fourth decompression time detection circuits 112a to 112d respectively detect the decompression time of the compressed data from the data size information of the corresponding compressed data according to the relationship shown in Table 1.

  Next, it is determined whether or not the integrated value of the decompression time of the compressed data that has been output is less than the threshold value (step S103). In this embodiment, prior to selecting one compressed data to be output as output data from a plurality of types of compressed data generated by the processing shown in step S102, first, the end of image data for one line is selected. Among the divided image data that is sequentially compressed from the image data, the decompression time of the compressed data that has already been output as output data is integrated. Then, the integrated value (total number of clocks) of the decompression time of the compressed data that has been output is compared with a threshold value that is set according to the total number of divided image data that is the source of the compressed data.

  Here, the threshold value is the time required for the image printing process based on the divided image data that is the source of the compressed data that has been output, and the total number of pieces of compressed image data and the predetermined number of clocks. Represented by the product of For example, when the time required for an image printing process based on 16-byte divided image data is 20 clocks, and the total number of pieces of divided image data used as the source of output compressed data is N bytes, The threshold value is represented by N × 20/16 clock.

  More specifically, when the compression processing is completed from one end of the image data for one line to the fourth divided image data and the output data has already been output, the total number of divided image data is 64 ( 16 × 4) bytes and the threshold is set to 80 (64 × 20/16) clocks. The 80 clocks are compared with the integrated value M of the expansion time of the output data up to the fourth. Note that the time (for example, 20 clocks) required for image printing processing based on image data of a predetermined size is determined in consideration of characteristics such as the paper conveyance speed of the printing unit 16.

  When it is determined that the decompression time integrated value M is less than the threshold value (step S103: YES), the compressed data with the smallest data size is selected from a plurality of types of compressed data (step S104). In the present embodiment, since the decompression time of the compressed data is shorter than the time required for the image printing process based on the divided image data after decompression, it is assumed that no print error occurs, and a plurality of data generated by the process shown in step S102 is performed. The compressed data having the smallest data size is selected from the types of compressed data. For example, when M <N × 20/16, compressed data having the smallest data size is selected from four types of compressed data.

  The selected compressed data is output as output data (step S105). In the present embodiment, the compressed data having the smallest data size selected in the process shown in step S104 is output as output data. Note that when there are two or more pieces of compressed data having a minimum data size, compressed data having a shorter decompression time is selected.

  Next, the decompression time of the compressed data output as output data is added to the integration time of the decompression time (step S106). In the present embodiment, the decompression time of the compressed data having the smallest data size selected in the process shown in step S104 is added to the decompression time integration value stored in the decompression time integration circuit 115.

  As described above, according to the processing shown in steps S101 to S106, first, divided image data obtained by dividing image data for one line is compressed in parallel by a plurality of types of compression algorithms, and a plurality of types of compression are performed. Data is generated. Next, a threshold value set according to the total number of pieces of divided image data that have been output as output data is compared with the integrated value of the decompression time of the compressed data that has been output. When it is determined that the integration value of the decompression time is less than the threshold value, the compressed data having the smallest data size is selected from a plurality of types of compressed data.

  On the other hand, when it is determined in the process shown in step S103 that the expansion time integrated value M is equal to or greater than the threshold (step S103: NO), the compressed data with the shortest expansion time is selected from a plurality of types of compressed data. (Step S107). In this embodiment, since the decompression time of the compressed data is longer than the time required for the image printing process based on the decompressed divided image data, a print error may occur, and the process shown in step S102 is performed. The compressed data with the shortest decompression time is selected from the plurality of types of compressed data. For example, when M ≧ N × 20/16, compressed data having the shortest decompression time is selected from four types of compressed data.

  The selected compressed data is output as output data (step S108). In the present embodiment, the compressed data with the shortest decompression time selected in the process shown in step S107 is output as output data.

  Next, the decompression time of the compressed data output as output data is added to the integrated value of the decompression time (step S109). In the present embodiment, the decompression time of the compressed data having the shortest decompression time selected in the process shown in step S107 is added to the decompression time integration value stored in the decompression time integration circuit 115.

  As described above, according to the processing shown in steps S107 to S109, when it is determined that the integrated value of the decompression time of the compressed data that has been output is greater than or equal to the threshold value, the compressed data having the shortest decompression time from among a plurality of types of compressed data. Is selected.

  Next, it is determined whether or not the compression process has been executed up to the end of the image data for one line (step S110). In the present embodiment, whether or not the compression processing that is sequentially executed for each 16-byte divided image data from one end of the image data for one line is performed up to the other end of the image data for one line. Is judged.

  When it is determined that the compression process has not been executed up to the end of the image data for one line (step S110: NO), the step is performed until the compression process is performed on the divided image data at the end of the image data for one line. The processing from S102 onward is repeated.

  On the other hand, when it is determined that the compression process has been executed up to the end of the image data for one line (step S110: YES), it is determined whether or not the compression process has been completed up to the last line of the image data of a plurality of lines. Determination is made (step S111). In the present embodiment, it is determined whether or not the compression process has been completed up to the last line of the image data acquired in band units.

  If it is determined that the compression process has not been completed up to the final line (step S111: NO), the process from step S101 is repeated until the final line compression process is completed. On the other hand, when it is determined that the compression process has been completed up to the final line (step S111: YES), the process ends.

  As described above, according to the processing shown in steps S110 to S111, the compression processing of image data for one line executed in units of 16-byte divided image data is executed for a plurality of lines constituting one band. Is done. As a result, the image data for one band is compressed, and the compressed image data is stored again in the memory 13.

  Then, according to the processing of the flowchart shown in FIG. 4, when the integrated value of the decompression times of the divided image data that has already been compressed out of the plurality of divided image data constituting the image data for one line is less than the threshold. The compressed data having the smallest data size is selected from a plurality of types of compressed data on the assumption that the expansion time of the image data is sufficient. On the other hand, if the integrated value of the decompression time of the divided image data that has been compressed and output is equal to or greater than the threshold value, the compressed data with the shortest decompression time is selected from a plurality of types of compressed data, assuming that the decompression time of the image data is not sufficient Is selected.

  According to such a configuration, one line of image data is sequentially compressed from one end to the other end in units of 16 bytes, and compressed data having the smallest data size is output as output data. The data size and the decompression time are optimized by switching between the process to perform and the process to output the compressed data with the shortest decompression time as output data according to the comparison result of the decompression time integrated value and the threshold value. One line of compressed image data is acquired.

  As a result, in a printing method in which printing processing is executed while decompressing compressed image data in real time, it is possible to prevent a printing error from occurring because the decompression processing of image data for one line is not in time for the printing processing. The Further, since the image data is compressed to the smallest possible data size, the amount of use of the RAM 13 is minimized.

  As described above, according to the present embodiment, one compressed data is selected from a plurality of types of compressed data generated in parallel by a plurality of types of compression algorithms based on the decompression time and data size of each compressed data. Selected and output as output data. Therefore, when selecting compressed data to be output as a compression result of image data from among a plurality of types of compressed data, it is possible to select the optimal compressed data by referring to the decompression time and data size of each compressed data. It becomes possible. As a result, the image data can be compressed to a smaller size within a range where the decompression time of the image data is within an allowable range.

  In addition, according to the present embodiment, since image data is compressed in parallel by a plurality of types of compression algorithms, the image data can be compressed more efficiently than when the compression method is changed and the image data is compressed again. it can. Further, it is not necessary to retain the original image data in order to recompress the image data, and the amount of memory used can be saved.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims.

  For example, in the above-described embodiment, the compressed data with the smallest data size or the compressed data with the shortest decompression time is selected from a plurality of types of compressed data according to the comparison result between the integrated value of the decompression time and the threshold value. . However, the method for selecting one compressed data from a plurality of types of compressed data is not limited to the above embodiment. For example, rather than comparing the integrated value of decompression time with a threshold value, the decompression time of a plurality of types of compressed data is compared with a predetermined allowable value, thereby reducing the decompression time of the plurality of types of compressed data below the allowable value. The compressed data having the smallest data size may be selected from the compressed data that have been narrowed down to the compressed data.

  In the above-described embodiment, the image data compression processing is executed in units of divided image data obtained by dividing image data for one line. However, for example, the image data may be compressed in units of image data for one line, or the image data may be compressed in bands of a predetermined number of lines or predetermined blocks.

  The means and method for performing various processes in the image processing apparatus according to the present embodiment can be realized by either a dedicated hardware circuit or a programmed computer. The program may be provided by a computer-readable recording medium such as a flexible disk and a CD-ROM, or may be provided online via a network such as the Internet. In this case, the program recorded on the computer-readable recording medium is normally transferred to and stored in a storage unit such as a hard disk. The program may be provided as a single application software, or may be incorporated in the software of the device as one function of the device.

1 printer,
11 CPU,
12 ROM,
13 RAM,
14 Image processing unit,
15 data output section,
16 Printing department,
17 I / F control unit,
18 Host I / F,
2 host PC,
101 ReadDMA circuit,
102 image processing module,
103 compression module,
104 Write DMA circuit,
111a, 111b, 111c, 111d first to fourth compression algorithm circuits,
112a, 112b, 112c, 112d first to fourth extension time detection circuits,
113 Size information comparison circuit,
114 expansion time comparison circuit,
115 extension time integration circuit,
116 selection circuit,
117 Data select circuit.

Claims (10)

A compression unit that simultaneously compresses the same image data by a plurality of types of compression methods and generates a plurality of types of compressed data for the same image data;
For each of the plurality of types of compressed data generated by the compression unit, an expansion time calculation unit that calculates the expansion time of the compressed data;
A selection unit that selects one compressed data from the plurality of types of compressed data based on the decompression time of the plurality of types of compressed data obtained by the decompression time calculation unit and the data size of each compressed data;
An image processing apparatus comprising: an output unit that outputs the compressed data selected by the selection unit as output data. The image data is divided image data obtained by dividing image data for one page into a plurality of pieces,
The image processing apparatus according to claim 1, wherein the compression unit sequentially compresses the plurality of divided image data. An integration time calculation unit that integrates the decompression time of the compressed data that has been output as the output data, and calculates an integration time of the decompression time of the compressed data that has been output;
A setting unit that sets a threshold value of the integration time obtained by the integration time calculation unit based on the total data size of the divided image data that is the source of the output compressed data;
A determination unit that determines whether or not the accumulated time is less than the threshold set by the setting unit;
When the determination unit determines that the integration time is less than the threshold, the selection unit selects compressed data having a minimum data size from the plurality of types of compressed data, and the determination unit When the integration time is determined to be equal to or greater than the threshold, the selection unit selects the compressed data with the shortest decompression time from the plurality of types of compressed data. Item 3. The image processing apparatus according to Item 2.   The setting unit is configured so that the integration time of the decompression time of the output compressed data is shorter than the time required for the image printing process based on the divided image data that is the source of the output compressed data. The image processing apparatus according to claim 3, wherein the threshold is set based on a total data size of the divided image data.   When the determination unit determines that the integration time is less than the threshold value, and there are a plurality of types of compressed data with the smallest data size, the selection unit selects the decompression from the plurality of types of compressed data. 5. The image processing apparatus according to claim 3, wherein compressed data having the shortest time is selected. A step (a) of simultaneously compressing the same image data by a plurality of types of compression methods and generating a plurality of types of compressed data for the same image data;
For each of the plurality of types of compressed data generated in step (a), obtaining a decompression time of the compressed data;
Step (c) of selecting one compressed data from among the plurality of types of compressed data based on the decompression time of the plurality of types of compressed data obtained in step (b) and the data size of each compressed data. When,
And (d) outputting the compressed data selected in step (c) as output data. The image data is divided image data obtained by dividing image data for one page into a plurality of pieces,
The image processing method according to claim 6, wherein in the step (a), the plurality of divided image data are sequentially compressed. (E) calculating the integration time of the decompression time of the compressed data that has been output by integrating the decompression time of the compressed data that has been output as the output data;
A step (f) of setting a threshold value of the integration time obtained in the step (e) based on a total data size of the divided image data that is a source of the output compressed data;
And (g) determining whether the accumulated time is less than the threshold value set in the step (f),
If it is determined in step (g) that the accumulated time is less than the threshold value, compressed data having the smallest data size is selected from the plurality of types of compressed data in step (c). When it is determined in step (g) that the accumulated time is equal to or greater than the threshold value, in step (c), compressed data with the shortest decompression time is selected from the plurality of types of compressed data. The image processing method according to claim 7, wherein the image processing method is selected.   In the step (f), the integration time of the decompression time of the outputted compressed data is made shorter than the time required for the image printing process based on the divided image data that is the source of the outputted compressed data. The image processing method according to claim 7, wherein the threshold is set based on a total data size of the divided image data.   If it is determined in step (g) that the accumulated time is less than the threshold value, and there are a plurality of types of compressed data with the smallest data size, in step (c), the plurality of types of compressed data 10. The image processing method according to claim 8, wherein the compressed data having the shortest decompression time is selected from the inside.

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