WO2010037262A1

WO2010037262A1 - Dot array page compressing method and apparatus

Info

Publication number: WO2010037262A1
Application number: PCT/CN2009/001080
Authority: WO
Inventors: 康俊杰; 杨斌; 赵晖
Original assignee: 北大方正集团有限公司; 北京大学; 北京北大方正电子有限公司
Priority date: 2008-09-26
Filing date: 2009-09-25
Publication date: 2010-04-08
Also published as: CN101394461A

Abstract

A method for compressing dot array pages is provided, which comprises the following steps: dividing the dot matrix pages to be compressed into at least two dot matrix page parts; processing each dot matrix page part obtained after division; determining the element type with the largest proportion in the dot matrix page part; and selecting a corresponding compressing mode to compress the dot matrix page part according to the determined element type with the largest proportion. Accordingly, an apparatus for dot array page compressing is provided. The technical proposal disclosed by the present invention can solve the problem that the same compressing method is applied to compress the whole dot matrix page in the prior art, so that the contradiction between compressing proportion and compressing rate can not be well relieved.

Description

Dot matrix page compression method and device thereof

The present invention relates to the field of computer image processing, and in particular, to a dot matrix page compression method and apparatus therefor. Background technique

In the field of computer graphics image processing, Raster Image Processor (RIP, Raster Image Processor) is a kind of programming language such as PS (PostScript, a description language used to describe page content, whose specification is developed by Adobe Corporation of the United States) Format or PDF

(Portable Document Format, an electronic document format used to describe the content of a page, whose specification is developed by Adobe, USA). The page described by the format is converted into a device of a dot matrix page. In the subsequent processing, a raster imaging device is usually used. For example, imagesetters, computer-to-plate platesetters, printers, etc. print out the dot matrix pages generated by the conversion, and before the printout, the dot matrix pages are often compressed to save storage space and processing time.

When compressing a dot matrix page, the compression method used often has a contradiction between the compression rate and the compression ratio (wherein the compression ratio = the original size of the dot matrix page / the compressed file obtained by compressing the dot matrix page) In other words, when compressing the same dot matrix page, if the dot matrix page is compressed by a compression method with a high compression ratio, the compression rate will be relatively small; if a compression rate is large, compression is performed. The method compresses the dot matrix page, although the compression rate becomes larger, but the compression ratio is lower.

Generally, when the compression mode is selected to compress the dot matrix page, a compression method with a higher compression ratio but a relatively lower compression rate is selected to compress the dot matrix page with higher complexity; A low dot matrix page will compress the compression rate with a relatively low compression ratio.

In a dot matrix page, there are often text elements, graphic elements, and image elements. In addition, there are blank areas that do not contain any text, graphics, and images. The pixels in the blank area do not contain color information, for example. Any kind of information such as gray scale information, and therefore the element type of the pixel in the blank area is called a "blank element". In the same In a dot matrix page with blank elements, text elements, graphic elements, and image elements, the portion of the image element will have a higher complexity, while the portion of the graphic element, blank element, or text element will have a lower The complexity. In the prior art, when compressing a dot matrix page, the same dot matrix page is compressed by the same compression method, thereby ignoring the difference of various elements in the dot matrix page, and thus cannot The above contradictory problems between the compression ratio and the compression rate are well alleviated. Summary of the invention

The embodiment of the invention provides a method and a device for compressing a dot matrix page, which are used to solve the problem that the compression of the entire dot matrix page is performed by using the same compression mode in the prior art, and the compression ratio and the compression rate are not well relieved. Contradictory issues.

To this end, the present invention adopts the following technical solutions:

A dot matrix page compression method includes: dividing a bitmap page to be compressed into at least two dot matrix page portions; and performing the following processing on each of the lattice page portions obtained by the division:

Determining the type of element that has the largest proportion in the bitmap page portion;

According to the determined element type with the largest proportion, the corresponding compression mode is selected to compress the page portion of the dot matrix.

Preferably, determining the type of the element that has the largest proportion in the page portion of the dot matrix comprises:

In the bitmap page portion, the number of identifier values of each element type is separately counted, wherein the element type identifier value is a different element in the bitmap page in the process of rasterizing the page content into a dot matrix page. The element type identification value respectively assigned by the type; according to the number of identification values of each element type obtained by the statistics, the element type having the largest proportion in the dot matrix page is determined.

A dot matrix page compression device, comprising: a dividing unit, configured to divide a dot matrix page to be compressed into at least two dot matrix page portions; and a determining unit, configured to divide each dot matrix page portion obtained by the dividing unit, respectively Determining an element type that has the largest proportion in the bitmap page portion; and selecting a unit, configured to compress the bitmap page portion according to the element type that has the largest proportion determined by the determining unit, and select a corresponding compression manner. Preferably, the determining unit specifically includes a statistic module, configured to calculate, according to each bitmap page portion obtained by dividing the unit, the number of each element type identifier value in each bitmap page portion, wherein the element type identifier value is In the process of rasterizing page content into a dot matrix page, respectively, respectively, a unique identifier value respectively assigned to different element types in the dot matrix page; a determining module, configured to identify values of each element type according to statistics module statistics Number, determines the type of element that has the largest proportion of each dot matrix page.

A dot matrix page compression method includes: determining an element type included in a dot matrix page to be compressed; and selecting different compression modes to respectively compress a page portion where different element types are located according to the determination result.

A dot matrix page compressing device, comprising: a determining unit, configured to determine an element type included in a dot matrix page to be compressed; and a selecting unit, configured to select different compression modes for different element types according to the determining result of the determining unit The portion of the page where it is located is compressed.

In the embodiment of the present invention, the dot matrix page to be compressed is divided into at least two dot matrix page portions; and for each dot matrix page portion obtained by the partitioning, the element type having the largest proportion in the dot matrix page portion is determined. And according to the determined element type with the largest proportion, the corresponding compression mode is selected to compress the page portion of the dot matrix, so that the contradiction between the compression ratio and the compression rate can be well relieved. DRAWINGS

Figure 1 is a schematic diagram of a dot matrix page containing various types of elements;

2 is a schematic flowchart of a dot matrix page compression method according to an embodiment of the present invention;

FIG. 3 is a schematic flowchart of a specific implementation process of a dot matrix page compression method according to an embodiment of the present invention; FIG.

4 is a schematic diagram of a dot matrix page for generating an intermediate format from an original page according to an embodiment of the present invention;

5 is a schematic diagram of the element type identification value in the element type dot matrix corresponding to the pixel point in the dot matrix page;

FIG. 6 is a schematic structural diagram of a dot matrix page compression apparatus according to an embodiment of the present invention; FIG. 7 is a schematic flowchart of another method for compressing a dot matrix page according to an embodiment of the present disclosure;

FIG. 8 is a schematic structural diagram of another dot matrix page compression apparatus according to an embodiment of the present disclosure;

Figure 9 is a diagram showing portions of two dot matrix pages obtained by dividing a CMYK dot matrix page in an embodiment of the present invention. detailed description

The embodiment of the present invention provides a dot matrix page compression scheme, which is used to solve the problem that the compression of the entire dot matrix page is performed by using the same compression mode in the prior art, and the problem of the contradiction between the compression ratio and the compression rate cannot be well relieved.

The main implementation principles, the specific embodiments, and the corresponding beneficial effects that can be achieved by the technical solutions of the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

As shown in FIG. 1 , it is a schematic diagram of a dot matrix page, which includes various element types such as blank elements, text elements, graphic elements, and image elements, for example, the letters in the figure. And Arabic numerals are text elements; stars and hexagons are graphic elements; landscape pictures are called image elements; and blank areas except text, graphics, and images are blank elements.

Generally, the complexity of a dot matrix page can be represented by the proportion of each of the above elements in the page, for example, when the proportion of each element type in a dot matrix page is: blank element 50 %, text elements account for 30%, graphic elements account for 15%, image elements account for 5%, you can judge the dot matrix page is less complex; and when a dot matrix page, the proportion of each element is: Image elements account for 70%, text elements for 10%, graphic elements for 15%, and blank elements for 5%, which can be judged to be more complex.

Therefore, according to the correspondence between the proportion of the element type in the dot matrix page and the complexity of the dot matrix page, the embodiment of the present invention provides a dot matrix page compression method, and the specific process schematic diagram of the method is as shown in FIG. 2, including:

Step 21, dividing the dot matrix page to be compressed into at least two dot matrix page portions; Step 22, respectively determining the proportion of each dot matrix page portion obtained by the partitioning Large element type;

Step 23: According to the determined element type with the largest proportion, respectively, select a corresponding compression mode to compress each bitmap page portion.

Since the RIP generates an intermediate format dot matrix page represented by the gray value of the pixel in the process of converting the original page such as the PS or PDF format into a dot matrix page, the method proposed in this embodiment can be The dot matrix page of the intermediate format determines the element type of each pixel in the generated dot matrix page, and further determines the element type that has the largest proportion among the divided dot matrix page parts, and selects the corresponding compression mode pair point. The page portion is compressed. The specific process diagram of this process is shown in FIG. 3, including: Step 31: Input the original page of the PS or PDF format description into the RIP, and the RIP is set to: According to the original page input, 600 output per inch is required. Pixel point (600DPI) for printing four color separation (CMYK, Cyan - Cyan, Magenta - Magenta, Yellow - Yel low, Black - Black) dot matrix page, where the output of the dot matrix page Each pixel needs to use 1 byte to represent the information of one of the four color separations, that is, the four color divisions of each pixel need to be represented by 4 bytes;

Step 32: Assign a unique element type identifier value to different element types, for example, may, but is not limited to, assign an element identifier value 1 to a pixel point whose element type is an image type, and assign an element identifier to a pixel point whose element type is a non-image type. a value of 0, or, respectively, assigning element identification values 11, 10, 01, 00 to pixel points whose element type is image type, graphic type, text type, and blank type;

Step 33: The RIP converts the original page into a dot matrix page of an intermediate format represented by a gray value of the pixel, and generates an element type dot matrix corresponding to the dot matrix page of the intermediate format according to the assigned element type identification value;

Step 34: The RIP further generates a CMYK dot matrix page based on the dot matrix page of the intermediate format according to the color information in the original page;

Step 35: Divide the generated CMYK dot matrix page into at least two dot matrix page parts. For example, each part of the dot matrix page output by the RIP segment may be used as a part of the divided dot matrix page, as shown in FIG. Dividing a dot matrix into two segments, so that two threads can be used simultaneously to process the two lattice portions, thereby doubling the conversion speed; Step 36, the lattice of the element types generated in step 33 Have the same element type The number of pixels is counted to determine the type of the element that has the largest proportion in the page portion of each dot matrix. When counting the pixels with the same element type, the point-by-point statistical method may be used, or 8 The neighborhood is a unit for statistical calculation. For example, when the element type of a pixel is an image element, the image is calculated according to the 8 pixel points in the 8 fields adjacent to the pixel. Statistical methods can speed up statistics and improve statistical efficiency;

Step 37: Select a corresponding compression mode according to the determined element type having the largest proportion in each dot matrix page portion, and respectively compress each dot matrix page portion.

The specific implementation process of the foregoing step 33 is as follows:

First, the RIP interprets and forms the corresponding contour vector description according to the contour description of the image, the graphic and the text in the original page, and then fills the area formed by the contour by using the filling algorithm, so that the original page is converted into grayscale. The dot matrix page of the intermediate format indicated by the value, when filling, the area of the image outline can be filled according to the gray value of the pixel point of 255, and the area formed by the graphic outline, the area composed of the text outline, and the rest of the blank The area is not filled; the area of the image outline can be filled according to the gray value of the pixel point of 255, and the area formed by the outline of the image is filled according to the gray value of the pixel point of 170, and the area formed by the outline of the text is The gray value of the pixel is filled with 85, and the remaining blank areas are not filled, as shown in FIG. 4, which is a schematic diagram of the dot matrix page generated by the original page in the process;

After the dot matrix page of the intermediate format is generated by the above process, according to the element identification value assigned to each element type in step 32, an element type dot matrix corresponding to the element type of each pixel point is further generated, for example, when the image is not The element type identifier value of the type is set to 0, and when the element type identifier value of the image type is set to 1, the dot matrix page of the intermediate format obtained after the filling may be correspondingly generated to represent each pixel point element in the page. The type of element type dot matrix, as shown in Figure 5, is the schematic diagram of the element type identifier value in the generated element type dot matrix corresponding to the pixel point in the dot matrix page of the intermediate format. It can be seen that the element type point The element types of the pixels in the matrix and the dot matrix page are in one-to-one correspondence, and in the dot matrix, the element type for representing the pixel point only needs 1/8 byte, and therefore, the storage space occupied by the dot matrix Compared to a CMYK dot matrix page with a 4-byte representation of a pixel, the dot matrix occupies less storage space and generates an element type dot matrix The interval is only about 1% of the time of generating CMYK dot matrix. Similarly, when the element type is image type, graphic type, text type, and blank type, the pixel identification values are set to 11, 10, 01, 00. At the same time, it is also possible to generate a corresponding element type dot matrix, which is only required to represent the pixel point element type in only 1/4 byte.

In addition, the above step 37 can be implemented by, but not limited to, the following two ways: The first way: regards the graphic element, the text element and the blank element as non-image elements, so that only the image elements are included in the dot matrix page. And non-image elements, the two element types, therefore, when the determined largest element type is the image element, the first compression mode is selected to compress the bitmap page portion; and the determined proportion is the largest When the element type is a non-image element, the second compression mode is selected to compress the bitmap page portion; wherein the compression ratio of the first compression mode is higher than the compression ratio of the second compression mode, or the compression ratio of the second compression mode The compression rate is greater than the first compression mode. For example, the first compression mode may be, but not limited to, a run-length compression algorithm, and the second compression mode may be, but not limited to, a ZLIB compression algorithm.

The second mode: the element type of the dot matrix page includes an image element, a graphic element, a text element, and a blank element. When the determined element type having the largest proportion is an image element, the first compression mode is selected for the dot matrix. The page portion is compressed; when the determined largest element type is a graphic element, the second compression mode is selected to compress the bitmap page portion; when the determined largest proportion of the element type is a text element, Selecting a third compression mode to compress the bitmap page portion; when the determined largest element type is a blank element, selecting a fourth compression manner to compress the bitmap page portion; The compression method satisfies: the compression ratio of the first compression mode is higher than the compression ratio of the second compression mode, the compression ratio of the second compression mode is higher than the compression ratio of the third compression mode, and the compression ratio of the third compression mode is high. The compression ratio of the fourth compression mode; or the compression ratio of the fourth compression mode is greater than the compression of the third compression mode Rate, compression rate of compression is greater than the third rate of compression of the second compression mode, the compression rate of the second embodiment is greater than the compression rate of compression of the first compression method.

In addition to the above two methods, the method of determining the compression mode according to the proportion of any one or more element types in the dot matrix page is within the protection scope of the present invention.

Since the bitmap page obtained by compression is limited by the size of the storage space, and 0 When compressing a dot matrix page, it is also subject to the pre-specified compression efficiency requirements. Therefore, when the compression method is selected in the above two ways, similar limiting factors need to be considered. To this end, the compression ratio threshold or the compression rate threshold may be preset, so that the compression ratio of the subsequently selected compression mode must be greater than the preset compression ratio threshold, or the compression rate of the selected compression mode must be greater than the preset. The compression rate threshold and so on.

In addition, when the ratio of image elements to non-image elements is relatively close, for example, in a dot matrix page portion, the proportion of image elements is 49%, and the ratio of non-image elements is 51%. Select a compression method with a large compression ratio to compress the portion of the dot matrix. Therefore, when selecting the corresponding compression method according to the proportion of the various elements, the proportional threshold can also be set in advance, for example, setting the image element. The ratio threshold is 40%, and when the ratio of the image element to the entire page portion of the dot matrix reaches 40%, the compression method with a larger compression ratio is selected to compress the page portion of the dot matrix.

It should be noted that, in order to achieve the purpose of speeding up the compression speed and improving the compression efficiency, in the method provided by the present invention, the parallel parallel compression processing may be performed on each of the divided page portions.

Correspondingly, the embodiment of the present invention further provides a dot matrix page compression device, which is used to solve the compression of the entire dot matrix page by using the same compression mode in the prior art, and the compression ratio and the compression rate are not well relieved. The contradictory problem, the specific structure of the device is shown in Figure 6, specifically including:

a dividing unit 61, configured to divide the dot matrix page to be compressed into at least two dot matrix page portions;

a determining unit 62, configured to determine, according to each of the bitmap page portions obtained by the dividing unit 61, the element type that has the largest proportion in the bitmap page portion;

The selecting unit 63 is configured to compress the bitmap page portion according to the element type with the largest proportion determined by the determining unit 62 and select a corresponding compression manner.

The determining unit 62 specifically includes: when the determining unit 62 uses the statistic element type identifier value to determine the element type that has the largest proportion in each dot matrix page, as shown in FIG.

The statistic module 621 is configured to calculate, according to each bitmap page portion obtained by the dividing unit 61, the number of identifier values of each element type in each bitmap page portion, where The element type identifier value is a unique element type identifier value respectively assigned to different element types in the dot matrix page in the process of rasterizing the page content into a dot matrix page;

The determining module 622 is configured to determine the element type that has the largest proportion in each dot matrix page according to the number of identification values of each element type obtained by the statistical module 621.

In the statistics module 621, a process of generating an element type identifier value for a different element type, and generating an element type dot matrix according to an intermediate format dot matrix page in the process of rasterizing the page content into a dot matrix page The process of description is similar and will not be described again.

According to the foregoing embodiment, the bitmap image compression scheme provided by the present invention is determined by dividing the dot matrix page to be compressed into at least two dot matrix page portions; and determining, for each bitmap page portion obtained by the partitioning, The type of the element having the largest proportion in the page portion of the dot matrix; and compressing the portion of the dot matrix page by selecting a corresponding compression mode according to the determined type of the largest component, which can solve the prior art The same compression method compresses the entire dot matrix page, which does not relieve the contradiction between the compression ratio and the compression rate.

In addition, since pixel points having the same element type are generally distributed in a dot matrix page, the present invention also provides another dot matrix page compression method, which can be solved without dividing the dot matrix page. In the prior art, the same compression method is used to compress the entire dot matrix page, which does not well alleviate the contradiction between the compression ratio and the compression rate.

A specific flow chart of another dot matrix page compression method provided by the embodiment of the present invention is as shown in FIG. 7 , including:

Step 71: Determine an element type included in the bitmap page to be compressed.

Step 72: According to the determination result, different compression modes are selected to respectively compress the page parts where different element types are located.

The foregoing step 72 can be implemented in the following two ways: The first method: the graphic element, the text element, and the blank element are regarded as non-image elements, so that only the image elements and non-images are included in the dot matrix page. The image element has two element types. Therefore, when the determined element type having the largest proportion is the image element, the first compression mode is selected to compress the bitmap page portion; and the determined proportion is the largest. When the element type is a non-image element, the second compression mode is selected to compress the bitmap page portion; wherein the compression ratio of the first compression mode is higher than the compression ratio of the second compression mode, or the second compression mode The compression rate is greater than the compression rate of the first compression mode. For example, the first compression mode may be, but not limited to, a run-length compression algorithm, and the second compression mode may be, but not limited to, a ZLIB compression algorithm.

The second mode: the element type of the dot matrix page includes an image element, a graphic element, a text element, and a blank element. When the determined element type having the largest proportion is an image element, the first compression mode is selected for the dot matrix. The page portion is compressed; when the determined largest element type is a graphic element, the second compression mode is selected to compress the bitmap page portion; when the determined largest proportion of the element type is a text element, Selecting a third compression mode to compress the bitmap page portion; when the determined largest element type is a blank element, selecting a fourth compression manner to compress the bitmap page portion; The compression mode satisfies: the compression ratio of the first compression mode is higher than the compression ratio of the second compression mode, the compression ratio of the second compression mode is higher than the compression ratio of the third compression mode, and the compression ratio of the third compression mode is higher than The compression ratio of the fourth compression mode; or the compression ratio of the fourth compression mode is greater than the compression of the third compression mode Rate, compression rate of compression is greater than the third rate of compression of the second compression mode, the compression rate of the second embodiment is greater than the compression rate of compression of the first compression method.

Correspondingly, the embodiment of the present invention further provides a dot matrix page compression device, and a specific structural diagram thereof is shown in FIG.

The determining unit 81 is configured to determine an element type included in the dot matrix page to be compressed, and the selecting unit 82 is configured to: according to the determining result of the determining unit 81, select different compression modes to respectively compress the page portion where the different element type is located .

The selection unit 82 selects different compression modes, and the process of compressing the page portions of the different element types is similar to the related description of the foregoing method embodiments, and therefore will not be described again.

It is apparent that those skilled in the art can make various modifications and variations to the invention without departing from the spirit and scope of the invention. Thus, if these modifications and variations of the invention belong to The invention is also intended to cover such modifications and variations within the scope of the appended claims.

1

Claims

Claim

A dot matrix page compression method, comprising:

Dividing the dot matrix page to be compressed into at least two dot matrix page portions; and performing, for each of the lattice page portions obtained by the partitioning, a method of determining the largest proportion of elements in the dot matrix page portion; According to the determined element type with the largest proportion, the corresponding compression mode is selected to compress the bitmap page portion.

2. The method according to claim 1, wherein determining an element type that has the largest proportion in the dot page portion, specifically comprising - separately counting each element type in the dot page portion The number of identifier values, wherein the element type identifier value is an element type identifier value respectively assigned to a different element type in the bitmap page in the process of rasterizing the page content into a dot matrix page;

Based on the number of statistically identified values for each element type, the type of element that has the largest proportion in the bitmap page is determined.

3. The method of claim 1, wherein the element type comprises an image element and a non-image element;

According to the determined element type with the largest proportion, the corresponding compression mode is selected to compress the page portion of the dot matrix, which specifically includes:

When the determined largest element type is an image element, the first compression mode is selected to compress the bitmap page portion;

When the determined largest element type is a non-image element, the second compression mode is selected to compress the bitmap page portion;

The compression ratio of the first compression mode is higher than the compression ratio of the second compression mode, or the compression rate of the second compression mode is greater than the compression rate of the first compression mode.

4. The method according to claim 1, wherein the element type comprises an image element, a graphic element, a text element, and a blank element; The part of the dot matrix page is compressed according to the determined type of the largest element, and the corresponding compression mode is selected, which includes:

When the determined largest element type is a graphic element, the second compression mode is selected to compress the bitmap page portion;

When the determined largest element type is a text element, the third compression mode is selected to compress the bitmap page portion;

When the determined largest element type is a blank element, the fourth compression mode is selected to compress the bitmap page portion;

The compression ratio of the first compression mode is higher than the compression ratio of the second compression mode, the compression ratio of the second compression mode is higher than the compression ratio of the third compression mode, and the compression ratio of the third compression mode is higher than the fourth compression mode. The compression ratio of the shrink mode; or

The compression rate of the fourth compression mode is greater than the compression rate of the third compression mode, the compression rate of the third compression mode is greater than the compression rate of the second compression mode, and the compression rate of the second compression mode is greater than that of the first compression mode. rate.

The method according to claim 1, wherein the processing is performed on each of the divided page portions obtained by the division.

A dot matrix page compression device, comprising: a dividing unit, configured to divide a dot matrix page to be compressed into at least two dot matrix page portions;

a determining unit, configured to determine, for each partitioned page portion obtained by dividing the unit, the element type having the largest proportion in the dot page portion;

And a selecting unit, configured to compress the bitmap page portion according to the element type with the largest proportion determined by the determining unit, and selecting a corresponding compression manner.

The device according to claim 6, wherein the determining unit specifically includes: The statistics module is configured to calculate, according to each bitmap page part obtained by dividing the unit, the number of identifier values of each element type in each bitmap page part, wherein the element type identifier value is to rasterize the page content into a dot matrix page. In the process, respectively, a unique identifier value respectively assigned to different element types in the dot matrix page;

The determining module is configured to determine the type of the element that has the largest proportion in each dot matrix page according to the number of identification values of each element type obtained by the statistical module.

8. A dot matrix page compression method, comprising:

Determining the type of elements contained in the bitmap page to be compressed;

According to the determination result, different compression modes are selected to compress the page parts where different element types are located.

9. The method of claim 8, wherein the element type comprises an image element and a non-image element;

Selecting the first compression method to compress the portion of the page where the image element is located, and selecting the second compression method to compress the portion of the page where the non-image element is located,

10. The method of claim 8, wherein the element type comprises an image element, a graphic element, a text element, and a blank element;

Selecting the first compression method to compress the page portion where the image element is located, selecting the second compression method to compress the page portion where the graphic element is located, selecting the third compression method to compress the page portion where the text element is located, and selecting the first The four compression method compresses the portion of the page where the blank element is located;

The compression ratio of the first compression mode is higher than the compression ratio of the second compression mode, the compression ratio of the second compression mode is higher than the compression ratio of the third compression mode, and the compression ratio of the third compression mode is higher than the fourth compression mode. The compression ratio of the mode; or

The compression rate of the fourth compression mode is greater than the compression rate of the third compression mode, the compression rate of the third compression mode is greater than the compression rate of the second compression mode, and the compression of the second compression mode. The shrink rate is greater than the compression rate of the first compression mode.

11. A dot matrix page compression device, comprising:

a determining unit, configured to determine an element type included in the bitmap page to be compressed; and a selecting unit, configured to select different compression modes according to the determining result of the determining unit, respectively compressing the page portion where the different element types are located.