JP2004351719A - Printing device and controlling method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a printing process with a small memory capacity by performing a compression or extension on a band unit when printing data is received from host equipment such as a host computer and is printed and outputted to a recording medium such as recording paper. <P>SOLUTION: Printing data described in the PDL received from a host computer is classified into band unit-specific code expressions (S302), raster data is generated for each band, objects in the data is binarized by using a dither matrix prepared for each object, and compressed into a code and stored (S303). This coding is performed by counting objects for every kind of object, and considering the periodicity of a dither matrix for the kind under which most objects fall in generating raster data for a band. When compressed coded data for a band count for a page is generated, an individual band is extended for printing (S304). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for receiving print data output from a host device such as a host computer and performing printing.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an image forming apparatus called a page printer such as a laser beam printer, one page of raster data is held in a raster memory to form an image. Raster data as such an image processing device handles not only text but also all kinds of images from simple figures to images such as photographs.
[0003]
The resolution of these image forming apparatuses has been improved in recent years. For example, a resolution of 600 dpi requires 4 Mbytes of memory to create one A4 size page. At present, the resolution tends to increase more and more, and the gray scale conventionally expressed by two gray scales (1 bit) per pixel is changed from 16 gray scales (4 bits) to 256 gray scales (8 bits). Increasingly, they require an increasingly large amount of raster memory. Furthermore, recently, a device that handles color has appeared, and requires four planes of the YMCK space as compared with monochrome, and the memory size is becoming enormous.
[0004]
In order to suppress the cost increase due to such an increase in memory, various memory saving techniques have been proposed. For example, there is a method in which one page of raster data is not stored in the raster memory as it is, but is divided into bands. In this method, one band of raster data is generated and printed. As a result, the apparatus does not require a memory for one page, and the cost can be relatively reduced.
[0005]
Furthermore, in order to realize a further printing speed while adopting this band method, raster data is generated in band units, and the band raster data is compressed, coded and stored sequentially. It is also practiced to sequentially decode the compression-encoded band data and output it to a printer engine, thereby increasing the throughput and speeding up image formation.
[0006]
[Problems to be solved by the invention]
By the way, dither processing using a dither matrix is known as a technique for forming a gradation image when the printer engine is a binary engine. When compressing raster data in band units as described above, the raster data is converted from multi-valued data to binary data, that is, one pixel is represented by one bit from a state where one pixel can be represented by many bits. Since the amount of information can be reduced by converting the binarized image into a compressed image, it is desirable that the binarized result be subjected to compression encoding.
[0007]
What is effective in compressing the image after dither processing (binary image) is to use the periodicity of the dither matrix used in the dither processing. That is, when the size of the dither matrix is assumed to be M (size in the horizontal direction) × N (size in the vertical direction), the binarization result is likely to be the same in the cycle of M pixels in the horizontal direction. The directions are likely to be the same in the cycle of N pixels. In other words, it can be said that the correlation between the pixels of each binarization result is high due to the periodicity due to the size of the dither matrix.
[0008]
Therefore, when the binarized pixel is expressed as Xi using the horizontal position i, {X0, XM, X2M...}, {X1, XM + 1, X2M + 1,. By setting 1,..., It is possible to expect a high compression ratio in which the runs of each group can be achieved.
[0009]
However, recently, in order to further improve the image quality, the dither pattern (the size of the dither matrix) is switched according to the resolution of the raster data, the dither pattern is switched according to the gradation of the raster data, and the raster data in the YMCK color space is changed. A variety of methods have been adopted, such as switching a dither pattern for each color, or switching a dither pattern for each object such as characters, images, and rectangles in raster data.
[0010]
Therefore, when a specialized dither pattern or dither matrix size is used for various objects, the correlation between the binarized results is not uniform, and a high compression ratio is hardly obtained.
[0011]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is intended to receive band print data from a host device such as a host computer and to perform compression and decompression in band units when printing out on a recording medium such as recording paper. Therefore, it is an object of the present invention to provide a technology capable of realizing a printing process with a small memory capacity.
[0012]
[Means for Solving the Problems]
In order to solve such a problem, for example, a printing apparatus according to the present invention has the following configuration. That is,
A printing device that receives print data from a higher-level device and forms an image on a predetermined recording medium,
Means for classifying the received print data for each band;
Raster data generating means for generating raster data subjected to pseudo halftone processing in band units based on print data classified for each band,
Encoding means for compression-encoding the generated band raster data;
Means for expanding and printing out the raster data of the encoded band,
The encoding unit determines the type of the representative object based on the frequency for each type of object when generating raster data in the band of interest, and performs compression encoding corresponding to the determined type of object. It is characterized by performing.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0014]
FIG. 1 is a sectional view showing an internal structure of a laser beam printer (hereinafter abbreviated as LBP) in the embodiment. This LBP enables registration of a character pattern and registration of a fixed format (form data) from a host computer (see FIG. 2).
[0015]
In the figure, reference numeral 1000 denotes an LBP main body, which inputs and stores character information (character code), form information, macro instructions, and the like supplied from an externally connected host computer (2001 in FIG. 2); A corresponding character pattern or form pattern is created according to the information, and an image is formed on a recording sheet as a recording medium. Reference numeral 1012 denotes an operation panel on which switches for operation, an LCD display, and the like are arranged. Reference numeral 1001 denotes a printer control unit that controls the entire LBP 1000 and analyzes character information supplied from a host computer. The control unit 1001 mainly converts character information into a video signal of a corresponding character pattern and outputs the video signal to the laser driver 1002. The laser driver 1002 is a circuit for driving the semiconductor laser 1003, and switches on and off a laser beam 1004 emitted from the semiconductor laser 1003 according to an input video signal. The laser 1004 is swung right and left by a rotating polygon mirror 1005 to scan on an electrostatic drum 1006. As a result, an electrostatic latent image of a character pattern is formed on the electrostatic drum 1006. This latent image is developed by a developing unit 1007 around the electrostatic drum 1006 and then transferred to a recording sheet. A cut sheet is used as the recording paper. The cut sheet recording paper is stored in a paper cassette 1008 mounted on the LBP 1000, is taken into the apparatus by a paper feed roller 1009 and transport rollers 1010 and 1011, and is transferred to an electrostatic drum 1006. Supplied.
[0016]
2, reference numeral 2001 denotes an external device such as a host computer, 2002 denotes the entire printer controller, and 2003 denotes an address / data / control bus. Reference numeral 2004 denotes a host I / F including a buffer unit; 2005, a CPU that controls a printer controller unit; 2006, a ROM that stores programs and font data for performing controller control and the like; 2007, a DMAC controlled by the CPU 2005; An operation panel unit 2009 is an I / F circuit unit including an output buffer unit for storing data to be sent to the engine 2011 (see FIG. 1), and 2010 is a RAM unit.
[0017]
In the above configuration, the operation in the embodiment will be described below.
[0018]
FIG. 3 is a flowchart illustrating the overall operation processing procedure of the LBP 1000 according to the embodiment.
[0019]
First, in step S301, print data described in PDL (page description language including bitmap data) is input from an external device 2001 such as a host computer via the host I / F unit 2004.
[0020]
In step S302, the PDL in step 301 is analyzed to create a band coded expression. The term "band-coded representation" as used here refers to drawing objects such as "bitmaps", "run-lengths", "trapezoids", "boxes", and "high-speed boundary-coded bitmaps" divided into bands. This is a general term for patterns and drawing logic for drawing them in a raster memory. In short, it is a process of classifying each band.
[0021]
Next, in step S303, processing for creating a compressed page is performed. In the present embodiment, the PDL data is analyzed, rendered and binarized by a dither matrix prepared for each object, and then subjected to band-by-band compression and storage. When the compression processing of all the bands constituting one page is completed, in step S304, processing of expanding the data in units of compressed bands and outputting the expanded data to the printer engine is performed.
[0022]
Next, details of the compressed page creation processing in step S303 will be described with reference to the flowchart in FIG.
[0023]
First, in step S401, a work memory is obtained from the RAM 2010. Here, the work memory is an area for storing the data to be compressed. Next, in step S402, "N" indicating the band number is initialized to "1".
However, when the number of bands for one page is N_MAX,
It is assumed that 1 ≦ N ≦ N_MAX is satisfied.
[0024]
Next, in step S403, the band number N is N ≦ N_MAX.
Is determined.
[0025]
If N ≦ N_MAX is satisfied, it is determined that there is an unprocessed band, and the process proceeds to step S404. If it is determined that N> N_MAX, it is determined that the processing for all bands for one page has been completed. Proceed to step S407. Here, a case will be described in which it is determined that N ≦ N_MAX and the process proceeds to step S404.
[0026]
In step S404, a rendering process is performed. Details of the rendering process are performed using the flowchart of FIG.
[0027]
In step S501, the type of an object configuration (for example, a character, an image, a graphic, or the like) included in the band coded expression created in step S302 is analyzed.
[0028]
Next, in step S502, the band coded expression analyzed in step S501 is selected for each object. Also in this case, they are characters, images, figures, and the like.
[0029]
Then, in step S503, the number is counted for each type of object selected in step S502, and stored using a part of the RAM 2010 in FIG.
[0030]
Next, in step S504, the band-encoded expression of step S301 in FIG. 3 is stored as a bitmap in the work memory acquired in step S401 in FIG. 4, and binarized using the dither matrix corresponding to the object. . Next, in step S505, the processing system of the rendering process ends, and the process returns to step S404 in FIG.
[0031]
Returning to the description of FIG. When the process proceeds to step S405, compression processing of the rendered band of interest is performed. Here, the compression process indicates that the band data rendered in step S404 is subjected to the compression process in the work memory in step S401, and is stored in a page memory (not shown) that exists in a part of the RAM 2010 in FIG. I do. However, at the time of this compression, the number stored in the RAM 2010 of FIG. 2 is read out from the number of each object counted in step S503 of FIG.
[0032]
First, the case of N = 1, that is, the first band will be described. In this case, since this is the first band processing, the object having the largest number of rendered objects is selected. The reason is that the most objects are likely to be dominant when rendering the band. Then, the size of the most recently used dither matrix of the object that appears most frequently is checked, and compression encoding is performed based on the size.
[0033]
As a technique for compressing the image subjected to the dither processing, a dither cycle is used. Hereinafter, a brief description will be given.
[0034]
In general, when the dither matrix size is M × N, and the coordinates of an arbitrary pixel on the band data are expressed as (x, y), the pixel at the position of the coordinate (x + M, y) in the X-axis direction is (x, M, y). The correlation of the pixel of y) becomes strong (high). Similarly, if the coordinates of an arbitrary pixel on the band data is (x, y), the correlation between the pixel at the position of the coordinates (x, y + N) and the pixel at (x, y) in the Y-axis direction becomes strong. Therefore, by obtaining the values of the dither matrix sizes M and N and applying the values at the time of compression, it is possible to help improve the compression ratio.
[0035]
That is, when attention is paid to a certain line, M pieces of {x, x + M, x + 2M,...}, {X + 1, x + M + 1, x + 2M + 1,. When classified into groups, there is a high possibility that 0s or 1s are continuous in each group. Therefore, a high compression rate can be expected by using run-length encoding for each group.
[0036]
On the other hand, in the case of the processing after N = 2, that is, in the processing after the second band, the correlation between the pixels is derived using the result of the compression state check in step S406 described later in order to further improve the compression ratio. . This compression state check will be described in step S406.
[0037]
In step 406, the compression state of the compression band in step 405 is checked. The details of the check of the compression state will be described with reference to the flowchart in FIG.
[0038]
In step S601, the result of the compression processing in step S405 in FIG. 4 is checked. The result of the compression processing is to set a predetermined value for the correlation between pixels and the compression ratio set in step S404 in advance, and determine the state of the compression efficiency by comparison with the predetermined value. However, in the present embodiment, the default value of the compression ratio is a value depending on the size of the memory previously allocated for storing compressed pages from the RAM 2010 in FIG. If the result of comparison in step S601 indicates that the compression ratio is better than the specified value, the flow advances to step 603 to end the processing system for checking the compression state. That is, the pixel correlation shows that there is no problem at present. On the other hand, if the result of comparison in step S601 indicates that the compression ratio is lower than the default value, the process proceeds to step S602.
[0039]
In step S602, the correlation between the pixels indicates that there is a problem at present from the comparison result in step S601. Therefore, the correlation between the pixels is improved. A method for improving the correlation between pixels will be described below.
[0040]
First, in the rendering processing of FIG. 5, the correlation of pixels is obtained from the matrix cycle of the dither pattern of the object, paying attention to the object having the largest number of rendered objects. However, in this case, the matrix period is not necessarily the same as the matrix period of the dither pattern of another object. If not, the deviation of this period affects the compression ratio. Therefore, attention is paid to the second most frequently rendered object, and the correlation with the matrix period with the most frequently rendered object is derived. In the case of the present embodiment, the least common multiple of the matrix period of the dither pattern of the object with the largest number of the rendered result and the matrix period of the dither pattern of the object with the second largest number of the rendered result is used as the correlation between the pixels. Shall be used.
[0041]
The result is used at the time of rendering and compression of the next band N + 1. This is because in the adjacent bands such as the N band and the N + 1 band, it is expected that there is a similar state of the object in both bands. Therefore, such a method is applied. This makes it possible to derive an optimal correlation, which is effective in terms of coding efficiency.
[0042]
Next, proceeding to step 603, the processing system for checking the compression state is terminated, and step S406 in FIG. 4 is terminated.
[0043]
Next, in step 407, the band number "N" is updated by increasing it by "1" so as to indicate the next band.
[0044]
Then, it is checked again in step S403 whether or not N ≦ N_MAX is satisfied. If the condition is satisfied, the steps from step 404 are processed as described above. If N> N_MAX, the process proceeds to step S408, where the processing system for creating the compressed page in step 400 ends, step S303 in FIG. 3 ends, and the printing process in step S304 is performed.
[0045]
Here, the printing process in step S304 will be described with reference to the flowchart in FIG.
[0046]
First, in step S701, "N" indicating a band number is initialized to "1".
Where N is an integer value,
1 ≦ N ≦ N_MAX
Shall be satisfied.
However, N_MAX is the number of bands on one page,
It is an integer value satisfying 1 ≦ N_MAX.
[0047]
Next, in step S702, the band number N is N ≦ N_MAX.
Investigate whether is satisfied.
[0048]
If N ≦ N_MAX, it is determined that the printing process for one page is not completed, and the process proceeds to step S703. If N> N_MAX, it is determined that printing of one page has been completed, and the process proceeds to step S705. Here, a case where N ≦ N_MAX will be described.
[0049]
In step S703, N band shipping is performed. Here, “Shipping” means that band data is converted into a video signal and transmitted to the engine unit 2011 of FIG. Further, in the compressed page creation processing of FIG. 4, since this page has already been compressed, it needs to be decompressed. Here, it is assumed that shipping can be performed simultaneously with expansion.
[0050]
Next, proceeding to step S704, the band number "N" is updated by increasing it by "1" so as to indicate the next band number, and the process returns to step S702.
[0051]
By repeating the processes of steps S703 and S704 in this manner, the relationship finally becomes N> N_MAX, and the printing process ends.
[0052]
As described above, according to the present embodiment, when encoding is performed using an encoding method that uses the correlation between pixels, various types of information of raster data that has been complicated due to high image quality are verified and the correlation between pixels is checked. By deriving the relationship and performing the corresponding encoding, a high compression rate can be expected, and the throughput and memory of the printing process can be used effectively.
[0053]
In the embodiment, after the band for one page is compressed, the band is decompressed and the printing process is performed. However, the number of bands to be compressed is not limited to one page, and may be compressed and stored over a plurality of pages as the memory capacity allows. You may make it. At this time, when performing the printing process, it may be determined based on whether or not the compressed data of at least the number of bands for one page has been generated.
[0054]
Further, in the above-described embodiment, the case where a plurality of dither patterns are used for a band to be rendered is dealt with, but a single band may be used. In that case, a processing system that acquires the cycle of the dither pattern based on the resolution, gradation, color, and the like may be used.
[0055]
Further, in the above-described embodiment, the case where a single compression method is used is dealt with. However, a case where a form is selected from a plurality of compression methods may be used.
[0056]
Furthermore, in the embodiment, no particular distinction is made between monochrome and color. However, a case where processing is limited to monochrome or color processing may be used.
[0057]
Further, in the embodiment, the case where the correlation with the target pixel is obtained is dealt with, but it is not limited to the pixel unit, but may be the byte unit or another unit.
[0058]
Further, in the embodiment, the case of processing for acquiring a special object of the object inside the controller is handled.However, the processing for acquiring the characteristics of the object with an external device such as a host computer, and the case of transmitting the characteristic to the controller unit by a command or the like. It does not matter.
[0059]
Furthermore, in the embodiment, the printing apparatus using the PDL is dealt with, but other image processing apparatuses may be used.
[0060]
【The invention's effect】
As described above, according to the present invention, when print data is received from a host device such as a host computer and printed out on a recording medium such as recording paper, compression and decompression in band units are performed, thereby reducing The printing process can be realized with the memory capacity.
[Brief description of the drawings]
FIG. 1 is a sectional structural view of a printing apparatus according to an embodiment.
FIG. 2 is a block diagram of a printing apparatus according to the embodiment.
FIG. 3 is a flowchart illustrating a processing procedure of the printing apparatus according to the embodiment.
FIG. 4 is a flowchart illustrating a processing procedure of the printing apparatus according to the embodiment.
FIG. 5 is a flowchart illustrating a processing procedure of the printing apparatus according to the embodiment.
FIG. 6 is a flowchart illustrating a processing procedure of the printing apparatus according to the embodiment.
FIG. 7 is a flowchart illustrating a processing procedure of the printing apparatus according to the embodiment.

Claims (5)

A printing device that receives print data from a host device and forms an image on a predetermined recording medium,
Means for classifying the received print data for each band,
Raster data generating means for generating raster data subjected to pseudo halftone processing in band units based on print data classified for each band,
Encoding means for compression-encoding the generated band raster data;
Means for expanding and printing out the encoded band raster data,
The encoding means determines the type of the representative object based on the frequency of each type of the object when generating the raster data in the band of interest, and performs compression encoding corresponding to the determined type of the object. A printing device characterized by performing. The printing apparatus according to claim 1, wherein the representative object is an object that has been generated most frequently when raster data is generated. Further, means for comparing the encoded data amount of the band after compression with a predetermined threshold,
3. The printing apparatus according to claim 2, further comprising: means for performing encoding based on the types of the two most frequent objects as representative objects when the encoded data amount exceeds the threshold. 2. The printing apparatus according to claim 1, wherein when the type of encoding is determined, the type of encoding is reflected in the type of encoding of the next band. A method of controlling a printing apparatus that receives print data from a host device and forms an image on a predetermined recording medium,
Classifying the received print data for each band;
A raster data generating step of generating raster data subjected to pseudo halftone processing in band units based on print data classified for each band;
An encoding step of compressing and encoding the generated band raster data;
Decompressing and printing out the encoded band raster data,
The encoding step determines the type of the representative object based on the frequency for each type of object when generating raster data in the band of interest, and performs compression encoding corresponding to the determined type of object. A method for controlling a printing apparatus, the method comprising:

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