JP2004134962A - Image compression method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that uniform processing is performed for any of attribute portions in forming an image when one kind of attribute information is set for the entire page in the case that attribute information added to every pixel cannot be compressed to a predetermined size even if the information is compressed. <P>SOLUTION: In compressing an information plane 401 indicating attribute information for every pixel, if the compressed data obtained by compressing the information plane 401 cannot be compressed to a predetermined size, the information plane 401 is replaced with identical attribute information in the unit of blocks of a prescribed size as in the case where, for example, a block 405 mixedly including a plurality of attribute kinds is replaced by a block 406 having uniform attributes, and then the information plane 401 is re-compressed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image compression technique, and more particularly to an image compression technique for compressing an information plane indicating attribute information for each pixel of an image of one page.
[0002]
[Prior art]
In a conventional image forming apparatus, attribute information is added to each pixel in order to determine characters, figures, and images existing on an image after formation. The required memory size inevitably increases. Therefore, in the image forming apparatus, when memory is insufficient, attribute information is compressed to reduce the required memory size.
[0003]
However, for example, characters, complicated figures, and the like exist in a state where attribute information is complicated and complicated, so that a desired compression result may not be obtained. Therefore, when the attribute information does not fit in a predetermined size, a method of discarding the attribute information and setting one set of attribute information for the entire page has been adopted.
[0004]
[Problems to be solved by the invention]
However, if one piece of attribute information is set for the entire page as described above, uniform processing is performed on any part of characters, graphics, and images during image formation. Could not be used.
[0005]
The present invention has been made in order to solve the above-described problem, and when compressing an information plane indicating attribute information for each pixel, an image realizing a smaller compression size while minimizing loss of attribute information. It is intended to provide a compression technique.
[0006]
[Means for Solving the Problems]
As one technique for achieving the above object, the image compression method of the present invention includes the following steps.
[0007]
That is, an image compression method for compressing an information plane indicating attribute information for each pixel, wherein a first compression step of compressing the information plane, and the compressed data obtained in the first compression step is reduced to a predetermined size And a second compression step of compressing the information plane when the information plane does not fit. In the second compression step, after replacing the information plane with the same attribute information in block units of a predetermined size, The compression is performed on a block-by-block basis.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
[0009]
The present invention relates to an image compression method for compressing an information plane indicating attribute information of each pixel, wherein a first compression step of compressing the information plane and compressed data obtained in the first compression step are reduced to a predetermined size. And a second compression step of compressing the information plane when the information plane does not fit. In the second compression step, after replacing the information plane with the same attribute information in the block unit, a block of a predetermined size The present invention can be implemented as an image compression method characterized by performing compression in units.
[0010]
Further, in the second compression step, the information plane is compressed in units of blocks of a predetermined size by the same compression method as in the first compression step.
[0011]
The present invention as described above can be specifically expressed in the configurations shown in FIGS. 1 to 15 in correspondence with the following first to third embodiments.
[0012]
<First embodiment>
An example in which this embodiment is applied to a laser beam printer (hereinafter abbreviated as LBP) will be described. First, a configuration of an LBP to which the present embodiment is applied will be described with reference to FIG.
[0013]
FIG. 1 is a sectional view showing the internal structure of the LBP. In the figure, reference numeral 100 denotes an LBP main unit, which corresponds to a character corresponding to a character print command, various graphic drawing commands, an image drawing command, a color designation command, etc. supplied from an externally connected host computer (201 in FIG. 2). A pattern, a figure, an image, and the like are created, and an image is formed on a recording sheet as a recording medium. Reference numeral 151 denotes an operation panel on which an operation switch and an LED display or an LCD display for displaying the status of the printer are arranged. 101 denotes control of the entire LBP 100 and analysis of a character printing command supplied from a host computer. It is a printer control unit.
[0014]
Note that the LBP in the present embodiment converts RGB color information into M (magenta), C (cyan), Y (yellow), and K (black), and forms and develops them in parallel. It has an image forming and developing mechanism. The printer control unit 101 generates a print image of each of MCYK, converts the print image into a video signal, and outputs the video signal to the laser driver of each of MCYK.
[0015]
An M (magenta) laser driver 110 is a circuit for driving the semiconductor laser 111, and switches on / off a laser beam 112 emitted from the semiconductor laser 111 according to an input video signal. The laser beam 112 is swung right and left by a rotating polygon mirror 113 to scan on an electrostatic drum 114. As a result, an electrostatic latent image of a character or graphic pattern is formed on the electrostatic drum 114. The latent image is developed by a developing unit (toner cartridge) 115 around the electrostatic drum 114 and then transferred to a recording sheet.
[0016]
C, Y and K have the same image forming and developing mechanism as M, and 120, 121, 122, 123, 124 and 125 are image forming and developing mechanisms for C, 130, 131, 132, 133, 134, 135 is an image forming / developing mechanism for Y, and 140, 141, 142, 143, 144, and 145 are image forming / developing mechanisms for K. These individual functions are the same as those of the image forming / developing mechanism of M, and the description thereof is omitted.
[0017]
A cut sheet is used as a recording sheet, and the cut sheet recording sheet is stored in a sheet cassette 102 mounted on the LBP and is kept at a certain height by a spring 103. The sheet is taken into the apparatus, is placed on the sheet conveying belt 107, and passes through each image forming / developing mechanism of MCYK.
[0018]
The MCYK toner (powder ink) transferred to the recording paper is fixed to the recording paper by heat and pressure by a fixing device 108, and the recording paper is output to the upper portion of the LBP main body by conveyance rollers 109 and 150.
[0019]
FIG. 2 is a block diagram showing a schematic configuration of the printer control unit 101 of the LBP shown in FIG.
[0020]
The printer control unit 101 inputs data 214 including characters, graphics, and image drawing commands and color information sent from the host computer 201, which is a source of print information, and prints document information and the like in page units. I do.
[0021]
An input / output interface unit 202 exchanges various information with the host computer 201, and an input buffer 203 temporarily stores various information input via the input / output interface unit 202. Reference numeral 204 denotes a character pattern generator, which includes a font information section 218 storing attributes such as the width and height of a character and an address of an actual character pattern; a character pattern section 219 storing a character pattern itself; It consists of a control program. The read control program is included in the ROM 215, and has a code conversion function of calculating an address of a character pattern corresponding to the character code when the character code is input.
[0022]
Reference numeral 205 denotes a RAM, which is a font cache area 207 for storing a character pattern output from the character pattern generator 204, and a storage area 206 for storing external character fonts and form information sent from the host computer 201, the current printing environment, and the like. Contains. By storing the pattern information once expanded into the character pattern as the font cache in the font cache area 207 as described above, it is not necessary to decode the same character again and develop the pattern when printing the same character. Development into patterns is faster.
[0023]
A CPU 208 controls the entire control system of the printer, and controls the entire apparatus by a control program stored in the ROM 215. An intermediate buffer 209 is an internal data group generated based on the input data 214. After the reception of one page of data is completed, the data is converted into simpler intermediate data and stored in the intermediate buffer, then rendered by the renderer 210 in band units, and output to the band buffer 211 as a print image.
[0024]
There are three renderers 210 that are completely equivalent in function to renderers A, B, and C, and each can operate independently. That is, the LBP of the present embodiment can render up to three bands at the same time.
[0025]
In the renderer 210, a drawing plane RGB 24 bits and an information plane 3 bits are generated. When data is transmitted from the band buffer 211 to the renderer 212, color space conversion from RGB 24 bits to CMYK 32 bits is performed using the drawing plane and the information plane. .
[0026]
A print image for at least eight bands can be stored in the band buffer 211, and the print image output to the band buffer 211 is converted into a video signal by the output interface unit 212 and output to the printer print unit 213. Reference numeral 213 denotes a printing mechanism of a page printer that prints image information based on a video signal from the output interface unit 212.
[0027]
As described above with reference to FIG. 1, in the LBP in this embodiment, since MCYK image formation and development are performed in parallel, the output interface unit 212 includes an M output interface unit, a C output interface unit, and a Y output interface unit. , K output interface units, each of which independently reads dot data from the band buffer 211, converts the dot data into a video signal, and outputs the video signal to the laser drivers 110, 120, 130, and 140 of each plane.
[0028]
Reference numeral 216 denotes a non-volatile memory constituted by a general EEPROM or the like, which is hereinafter referred to as NVRAM (Non Volatile RAM). The NVRAM 216 stores panel setting values specified from the operation panel 151 and the like.
[0029]
Reference numeral 217 denotes data transmitted from the LBP to the host computer 201.
[0030]
Note that the ROM 215 also includes analysis of data input from the host computer 201, generation of intermediate data, a control program for the printing mechanism main body 213, and a color conversion table from the RGB color space to the MCYK color space.
[0031]
Generally, when a printing apparatus handles an image to be printed in an RGB color space, each pixel has attribute information. The attribute information is determined by a drawing command supplied from the host computer, for example, a pixel processed by a character printing command is a "character", and a pixel processed by a graphic drawing command is a "graphic". It is assumed that a pixel handled in the present embodiment has any one of three pieces of attribute information of an image 301, a graphic 302, and a character 303, as shown in FIG.
[0032]
The attribute information is used when LUT (Look Up Table) used for color conversion processing from an RGB color space to a CMYK color space or the like when data is transmitted from the band buffer 211 to the renderer 212 shown in FIG. Can be used to switch the dither processing. For example, even with the same black, black such as shadows present in a photograph is expressed using CMY in order to moderate the color change, and black such as lines in figures and characters is clearly expressed. Since it is necessary to express it, it can be used for switching such as using K single color.
[0033]
In the present embodiment, an information plane that is a plane of attribute information is compressed using the first compression method. If the compressed data obtained by the compression does not fit in a predetermined size, it is re-compressed using the second compression method.
[0034]
Hereinafter, a second compression method according to the present embodiment will be described.
[0035]
In the present embodiment, when the information plane does not reach the desired size in the first compression method, the information plane is first divided into blocks of a predetermined size as a second compression method. After the replacement with the area signal, compression is performed by the first compression method.
[0036]
Here, replacement of the image area signal in block units in the present embodiment will be described with reference to FIGS.
[0037]
In the present embodiment, for example, as shown in FIG. 4, an information plane 401 composed of an image attribute 402, a graphic attribute 403, and a character attribute 404 is expressed in units of a rectangular block 405 and the same image area signal as shown in a block 406, for example. And In this example, an image area signal of a rectangular block 405 including an image attribute 402 and a character attribute 404 is unified with an image attribute like a block 406.
[0038]
It is assumed that image area signals in block units in the present embodiment are basically unified with attribute information in blocks. For example, when a character attribute is included as in a rectangular block 505 shown in FIG. 5, the character attribute is unified as in a block 506. When a graphic attribute is included as in a rectangular block 605 shown in FIG. 6, a block 606 is used. Unify with graphic attributes like When an image attribute is included as in a rectangular block 705 shown in FIG. 7, the image attribute is unified as in a block 706.
[0039]
Further, when a plurality of attributes are mixed in a block, replacement may be performed by assigning a priority to each attribute. For example, in the example illustrated in FIG. 4, the image area signals of the rectangular block 405 in which the image attribute 402 and the character attribute 404 are mixed are unified with the image attribute as in the block 406, but the present embodiment is of course limited to this example. Not done.
[0040]
For example, in the example shown in FIG. 8, if the priority is set higher in the order of the character attribute 804, the graphic attribute 803, and the image attribute 802, the character attribute 804, the graphic attribute 803, and the image attribute 802 are mixed in a block like a rectangular block 805. In this case, the character attribute is valid as shown in a block 806, and when the graphic attribute 803 and the image attribute 802 are mixed as in a rectangular block 807, the graphic attribute is valid as in a block 808.
[0041]
As described above, in the image compression method according to the first embodiment of the present invention, when a plurality of types of attribute information are mixed in a block in the second compression step, the block is assigned the same attribute information according to a predetermined priority. It is characterized by being replaced with
[0042]
The attribute information is one of an image, a graphic, and a character according to a drawing command for a pixel.
[0043]
As described above, according to the present embodiment, when the information plane indicating the attribute information for each pixel does not fit in a predetermined size by compression using a predetermined compression method, the attribute information is unified in block units of the information plane. After that, compress again.
[0044]
As a result, it is possible to obtain compressed data of a desired size or less without making the entire page the same attribute information, that is, while minimizing the loss of attribute information in the page.
[0045]
In the present embodiment, three types of attribute information, such as a character, a graphic, and an image, have been described as examples. However, the present invention is not limited to these three types of attributes, and other attribute information may be considered. Is also possible. For example, when the input R, G, and B values are all equal, attribute information such as whether or not to perform printing with only K toner (gray compensation) may be added.
[0046]
<Second embodiment>
Hereinafter, a second embodiment according to the present invention will be described.
[0047]
In the first embodiment described above, even if re-compression is performed after unifying the attribute information of the information plane in units of blocks, the information plane may not be within the predetermined compression size. In such a case, the second embodiment increases the block size. That is, the replacement of the image area signal in the unit of a block described in the first embodiment is performed in a similar manner by increasing the block size.
[0048]
For example, as shown in FIG. 9, if the desired compression size is not reached with the predetermined block size 905, the attribute information is unified in units of a larger block size 906, and recompression is attempted.
[0049]
A smaller compressed size can be obtained by performing such block size expansion and recompression a plurality of times, but the number of recompressions may be limited in order to suppress loss of image area information.
[0050]
For example, when the number of times of recompression is set to 5, as shown in FIG. 10, as the first recompression, recompression is performed after replacing with the same image area signal in a block unit 1005 of 3 pixels × 3 pixels. As the second recompression, recompression is performed after replacing the same image area signal in block units 1006 of 5 pixels × 5 pixels. Similarly, a 7 pixel × 7 pixel block unit 1007 is used as the third recompression, a 9 pixel × 9 pixel block unit 1008 is used as the fourth recompression, and a 15 pixel × 15 pixel is used as the fifth recompression. Replacement with the same image area signal and recompression are performed in block units 1009.
[0051]
When the number of times of recompression is set to 3, as shown in FIG. 11, a block unit 1105 of 3 pixels × 3 pixels is used as the first recompression, and 7 pixels × 7 pixels is used as the second recompression. Is replaced with the same image area signal and recompressed in a block unit 1107 of 15 pixels × 15 pixels as third recompression.
[0052]
As described above, in the image compression method according to the second embodiment of the present invention, in the second compression step, the block size is adjusted so that the compressed size of the information plane falls within a predetermined size. Is what you do.
[0053]
In the second compression step, the block size is repeatedly expanded and compressed until the compressed size of the information plane falls within a predetermined size.
[0054]
Further, the number of times of compression in the second compression step is limited to a predetermined number of times, and a block size is determined for each number of times of compression.
[0055]
As described above, according to the second embodiment, when performing compression in units of blocks in the above-described first embodiment, the block size is appropriately expanded and recompression is performed, thereby achieving compression of a desired size or less. Data can be obtained.
[0056]
Further, by determining the block size according to the number of times of recompression, it is possible to adjust the quality and compression size of the compressed image area signal, the time required to reach a predetermined compression size, and the like.
[0057]
<Third embodiment>
Hereinafter, a third embodiment according to the present invention will be described.
[0058]
The third embodiment is characterized in that if a desired compression size is not reached even after performing re-compression a predetermined number of times in the above-described second embodiment, the entire page is replaced with the same image area signal and re-compressed. And
[0059]
Hereinafter, the information plane compression processing according to the third embodiment will be described with reference to the flowcharts of FIGS.
[0060]
FIG. 12 is a flowchart showing the main processing of the information plane compression processing in the third embodiment.
[0061]
First, block size setting is initialized in step S1201, and information plane compression processing is performed in step S1202. Then, in step S1203, it is determined whether or not the compressed data fits in a predetermined compressed size, and if so, the process ends.
[0062]
On the other hand, if the size does not fit in the predetermined compressed size, the process proceeds to step S1204, where the block size setting process is performed, and then the in-block attribute determination process is performed in step S1205. The details of these processes will be described later.
[0063]
Then, in step S1206, after compressing the information plane in which the attribute in the block is determined, the process proceeds to step S1203, and the compression size is examined. By repeating the above processing, recompression is continued until the compression size is reduced to the predetermined compression size in step S1203.
[0064]
FIG. 13 is a flowchart showing details of the block size setting initialization process shown in step S1201 of FIG. First, in step S1301, the number-of-compression counter is initialized, and in step S1302, the upper limit number of recompressions is acquired. Here, it is assumed that the upper limit of recompression is set so that the page size eventually becomes the block size. As a result, when the compressed size is less than the desired size, the same image area signal is designated for the entire page. In step S1303, a block size corresponding to each recompression count is set, and the process returns to step S1201 in FIG.
[0065]
FIG. 14 is a flowchart showing details of the block size setting process shown in step S1204 of FIG. First, in step S1401, the block size for the current compression number counter is obtained, then in step S1402, the compression number counter is updated, and the flow returns to step S1204 shown in FIG.
[0066]
FIG. 15 is a flowchart showing details of the in-block attribute determination processing shown in step S1205 of FIG.
[0067]
First, in step S1501, it is determined whether or not there is a character attribute in the block. If there is a character attribute, the process proceeds to step S1502 to unify the inside of the block with the character attribute, and then returns to step S1205 in FIG.
[0068]
On the other hand, if the character attribute does not exist in the block in step S1501, the flow advances to step S1503 to determine whether or not there is a graphic attribute in the block. If the graphic attribute exists, the flow advances to step S1504 and the flow advances to step S1504. After unifying the graphics attributes, the process returns to step S1205 in FIG.
[0069]
On the other hand, if there is no graphic attribute in the block in step S1503, the flow advances to step S1505 to determine whether or not there is an image attribute in the block. After unifying the image attributes, the process returns to step S1205 in FIG.
[0070]
On the other hand, if the image attribute does not exist in the block in step S1505, the process proceeds to step S1507 to unify the inside of the block with the initial attribute, and returns to step S1205 in FIG.
[0071]
As described above, in the image compression method according to the third embodiment of the present invention, in the second compression step, when the compression size of the information plane does not fall within the predetermined size after the predetermined number of compressions is completed, It is characterized in that one page of the information plane is compressed as one block.
[0072]
As described above, according to the third embodiment, if the desired compression size is not reached after performing the re-compression a predetermined number of times in the above-described second embodiment, the entire page is replaced with the same image area signal. By recompressing, a maximum compression ratio can be obtained.
[0073]
By applying the image compression method described in each of the above embodiments to the image forming apparatus, a drawing plane is generated based on the input drawing command, and the attribute information for each pixel of the entire image is generated based on the drawing command. Is generated, the information plane is compressed by the image compression method described in each of the above embodiments, and an image is formed based on the compressed information plane in accordance with the attribute information of each pixel. it can. Thus, for example, in LBP, when performing image formation according to attribute information using a compressed information plane, more effective image processing according to the attribute can be performed, and the same image processing can be performed on the entire page. Can be avoided.
[0074]
[Other embodiments]
Note that the present invention can take the form of, for example, a system, an apparatus, a method, a program, a storage medium, and the like. Specifically, a plurality of devices (for example, a host computer, an interface device, a reader, and a printer) Etc.), or may be applied to an apparatus (for example, a copying machine, a facsimile machine, etc.) including one device.
[0075]
Further, an object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and a computer (or CPU or MPU) of the system or apparatus to store the storage medium. Needless to say, this can also be achieved by reading out and executing the program code stored in the.
[0076]
In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.
[0077]
As a storage medium for supplying the program code, for example, a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM, or the like is used. I can do it.
[0078]
When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also an OS (Operating System) running on the computer based on the instruction of the program code. It goes without saying that a case where a part of the actual processing is performed and the function of the above-described embodiment is realized by the processing is also included.
[0079]
Further, after the program code read from the storage medium is written into a memory provided on a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that a CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.
[0080]
【The invention's effect】
As described above, according to the present invention, when compressing the information plane indicating the attribute information for each pixel, it is possible to realize a smaller compression size while minimizing the loss of the attribute information.
[Brief description of the drawings]
FIG. 1 is a side sectional view of a laser beam printer according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a control configuration of an LBP main body shown in FIG.
FIG. 3 is a table showing attribute information of pixels handled in the embodiment.
FIG. 4 is a diagram illustrating the concept of image area signal replacement processing in block units according to the present embodiment.
FIG. 5 is a diagram illustrating a processing example when a character attribute exists in a block according to the embodiment;
FIG. 6 is a diagram illustrating a processing example when a graphic attribute exists in a block according to the present embodiment.
FIG. 7 is a diagram illustrating a processing example when an image attribute exists in a block according to the embodiment;
FIG. 8 is a diagram illustrating a processing example in a case where a character attribute, a graphic attribute, and an image attribute are mixed in a block according to the embodiment;
FIG. 9 is a diagram illustrating an example of changing a block size in the second embodiment.
FIG. 10 is a diagram illustrating an example of performing block size adjustment five times in the second embodiment.
FIG. 11 is a diagram illustrating an example in which three block size adjustments are performed in the second embodiment.
FIG. 12 is a flowchart illustrating a main process of an information plane compression process according to the third embodiment.
FIG. 13 is a flowchart illustrating initialization processing of block size setting according to the third embodiment.
FIG. 14 is a flowchart illustrating a block size setting process according to the third embodiment.
FIG. 15 is a flowchart illustrating an in-block attribute determination process according to the third embodiment.
[Explanation of symbols]
REFERENCE SIGNS LIST 100 Printer main unit 101 Printer control unit 102 Paper feed cassette 103 Spring 104 Paper feed roller 105 Paper transport roller 106 Paper transport roller 107 Paper transport belt 108 Fixing device 109 Paper transport rollers 110, 120, 130, 140 Laser drivers 111, 121, 131 , 141 Semiconductor laser emitting device 112.122.132.142 Laser beam 113, 123, 133, 143 Rotating polygon mirror 114, 124, 134, 144 Electrostatic drum 115, 125, 135, 145 Toner cartridge 150 Paper transport roller 151 Operation Panel 202 Host computer 202 Input / output interface unit 203 Input buffer 204 Character pattern generator 205 RAM
206, 209 storage area 207 font cache area 208 CPU
210 Renderer 211 Output interface unit 213 of band buffer 212 Printing mechanism unit 215 ROM
216 NVRAM
218 Font information section 219 Character pattern section

Claims (1)

An image compression method for compressing an information plane indicating attribute information for each pixel,
A first compression step of compressing the information plane;
A second compression step of compressing the information plane when the compressed data obtained in the first compression step does not fit in a predetermined size;
The image compression method according to claim 2, wherein, in the second compression step, the information plane is replaced with the same attribute information in units of blocks of a predetermined size and then compressed in units of blocks.

Images