CN105245888A - Image compression method and image compression device - Google Patents

Abstract

The invention provides an image compression method and an image compression device. The image compression method comprises the steps of scanning each pixel in an image coding unit, and acquiring a plurality of pixel sets; distributing a unique index value for a gray value set of each pixel set, and generating an index table, wherein two pixel sets with a symmetry characteristic are identical in index value, and identification information is added to the two pixel sets with the symmetry characteristic so as to differentiate pixel sets with a forward order or a reverse order; and carrying out entropy coding on the coding unit according to the index value of each pixel set in the index table and the image coding unit, wherein if the reverse order of M continuous pixels is matched with other M continuous pixels, the M continuous pixels and the other M continuous pixels are determined to have the symmetry characteristic. The technical scheme provided by the invention utilizes the symmetry characteristics of characters in coding, thereby being capable of reducing the amount of data for expressing an image, reducing the space occupation of data, and improving the data transmission efficiency.

Description

Image compression method and image compression device

technical field

The present invention relates to the technical field of image processing, in particular, to an image compression method and an image compression device.

Background technique

Image compression is used to reduce the amount of data required to represent digital images. The reason why images can be compressed is because there is redundancy in the data. The purpose of data compression is to reduce the number of bits required to represent data by removing these data redundancies. . Due to the huge amount of image data, it is more difficult to store, transmit, and process, so image data compression is very important. Image compression can be either lossy or lossless data compression. However, whether it is lossless data compression or lossy data compression, the current image compression methods do not take into account the symmetry characteristics of characters.

Contents of the invention

In view of this, the present invention proposes a new image compression technology, which utilizes the symmetry feature existing in characters to encode images, further reducing the amount of image compression.

In view of this, according to one aspect of the present invention, an image compression method is provided, including: scanning each pixel in the image coding unit to obtain multiple pixel sets; assigning a unique index to the gray value set of each pixel set value, generate an index table, wherein the index values of the two pixel sets with symmetry characteristics are the same, and add identification information to the two pixel sets with symmetry characteristics to distinguish the pixel sets in the forward order or reverse order ; Perform entropy coding on the coding unit according to the index table and the index value of each pixel set in the image coding unit, wherein, if the reverse order of one consecutive M pixels matches another consecutive M pixels , it is determined that there is a symmetry feature between the one continuous M pixel and the other continuous M pixel.

According to another aspect of the present invention, an image compression device is also provided, including: a scanning unit that scans each pixel in the image coding unit to obtain a plurality of pixel sets; The degree value set is assigned a unique index value, and an index table is generated, wherein the index values of the two pixel sets with symmetry characteristics are the same, and identification information is added to the two pixel sets with symmetry characteristics to distinguish the forward order Or a set of pixels in reverse order; the coding unit performs entropy coding on the coding unit according to the index table and the index value of each pixel set in the image coding unit, wherein, if the reverse order of a consecutive M pixels If matched with another consecutive M pixels, then it is determined that there is a symmetry feature between the one consecutive M pixels and the other consecutive M pixels.

According to still another aspect of the present invention, there is also provided an electronic device, which includes the above-mentioned image compression device.

According to still another aspect of the present invention, there is also provided a program product storing machine-readable instruction codes. When the program product is executed, the above-mentioned machine can execute the above-mentioned image compression method.

In addition, according to other aspects of the present invention, there is also provided a computer-readable storage medium on which the above-mentioned program product is stored.

The above-mentioned image compression device, image compression method, and electronic equipment according to the embodiments of the present invention scan the encoding unit to generate an index table. In the index table, the index values of two sets of pixels with symmetry characteristics are the same, and can at least achieve the following One of the beneficial effects: reducing the number of index values and further reducing the amount of data representing images; it is especially suitable for compressing computer-generated images or screenshot images.

These and other advantages of the present invention will be more apparent through the following detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings.

Description of drawings

The present invention can be better understood by referring to the following description given in conjunction with the accompanying drawings, wherein the same or similar reference numerals are used throughout to designate the same or similar parts. The accompanying drawings, together with the following detailed description, are incorporated in and form a part of this specification, and serve to further illustrate preferred embodiments of the invention and explain the principles and advantages of the invention. In the attached picture:

Fig. 1 shows a schematic flow chart of an image compression method according to an embodiment of the present invention;

FIG. 2 shows a schematic flow diagram of an image compression method according to another embodiment of the present invention;

Fig. 3 shows a schematic diagram of characters with symmetry features;

Fig. 4 shows another schematic diagram of characters with symmetry features;

Fig. 5 shows a block diagram of an image compression device according to an embodiment of the present invention;

FIG. 6A shows a schematic diagram of an embodiment of an index table generation unit in the image compression device shown in FIG. 5;

FIG. 6B shows a schematic diagram of another embodiment of the index table generation unit in the image compression device shown in FIG. 5 .

detailed description

In order to understand the above-mentioned purpose, features and advantages of the present invention more clearly, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

In the following description, many specific details are set forth in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described here, therefore, the present invention is not limited to the specific embodiments disclosed below limit.

Fig. 1 shows a schematic flowchart of an image compression method according to an embodiment of the present invention.

As shown in Figure 1, the image compression method according to an embodiment of the present invention may include the following steps:

Step 102, scanning each pixel in the image coding unit to obtain a plurality of pixel sets;

Step 104, assign a unique index value to the gray value set of each pixel set, and generate an index table, wherein, the index values of the two pixel sets with symmetry characteristics are the same, and add Identification information to distinguish between forward-ordered and reverse-ordered sets of pixels;

Step 106, perform entropy coding on the coding unit according to the index table and the index value of each pixel set in the image coding unit,

Wherein, if the reverse order of one consecutive M pixels matches another consecutive M pixels, it is determined that there is a symmetry feature between one consecutive M pixels and another consecutive M pixels.

According to the technical scheme of the present invention, the symmetry feature of the characters is utilized during coding, which can greatly reduce the amount of data representing images, reduce the space occupied by data, and improve the efficiency of data transmission.

In the above step 104, the generation process of the index table includes:

Scanning the encoding unit, if the M consecutive pixels have different gray values, and no set of pixels having symmetry characteristics with the M consecutive pixels is found in the index table, then the M pixels are as a collection of pixels;

saving the gray value set of the M pixels in the index table, and assigning a unique index value to the gray value set;

If a pixel set having symmetry characteristics with the continuous M pixels is found in the index table, then use the index value corresponding to the found pixel set in the index table as the index of the continuous M pixels value.

For example, scan row by row from top to bottom in raster scan order, pixels 1, 2, and 3 are three consecutive pixels with different pixel values, so 1, 2, and 3 are regarded as a set of pixels and stored in the index table , assign an index value A to the set of pixels, then scan pixels 4, 5, and 6, and find three consecutive pixels with different pixel values, then judge whether the set of pixels 4, 5, and 6 are consistent with the index table The saved pixel set has symmetry characteristics, if not found, continue to save this group of pixels and assign a unique index value B to it. Then scan pixels 6, 5, and 4, and find that pixel sets 6, 5, and 4 have symmetry characteristics with the pixel sets 4, 5, and 6 saved in the index table, so the index value B of pixel sets 4, 5, and 6 is used as The index values of the pixel sets 4, 5, and 6 make the index values of the pixel sets 6, 5, and 4 the same as those of the pixel sets 4, 5, and 6. By analogy, the allocation of index values is completed.

When judging whether two pixel sets have symmetry characteristics, one of the pixel sets can be processed in reverse order, and the reordered pixel set is compared with the other pixel set. If the two pixel sets are the same, it means The original two sets of pixels are characterized by symmetry.

In addition, in order to accurately restore the image, identification information needs to be added during encoding to indicate which pixel set is in the forward order and which pixel set is in the reverse order. Of course, it is also possible to add only one identification information, and the set of pixels without identification information is defaulted to be the opposite.

In the above step 104, the generation process of the index table may also include:

Scanning the coding unit in a first direction with a step size of M pixels, and scanning the coding unit in a second direction with a step size of M pixels, wherein the first direction is opposite to the second direction ;

Comparing the scanning result in the first direction with the scanning result in the second direction, if the two pixel sets are the same, then determining that the two pixel sets are two pixel sets with symmetric characteristics;

A unique index value is assigned to each pixel set, wherein the same index value is assigned to two pixel sets with symmetric features.

For example, in the first scan, scan in groups of 4 pixels, and scan from left to right, so that multiple sets of pixels are obtained, and in the second scan, still in groups of 4 pixels Scan, and scan from right to left, also get a plurality of pixel sets.

Combining the two scans for comparison, originally two sets of pixels with symmetric characteristics, after scanning in the above way, two identical sets of pixels can be obtained, so if two sets of pixels are found in the scan results If they are the same, it means that the two initial pixel sets have symmetry characteristics.

Finally, for a pixel set without symmetry features, palette coding or difference coding is used for coding to further reduce the amount of compressed data.

Fig. 2 shows a schematic flowchart of an image compression method according to another embodiment of the present invention.

As shown in Figure 2, the image compression method according to an embodiment of the present invention may include the following steps:

Step 202, scan each coding unit in raster scan order.

Step 204, if the multiple pixels are continuous and have different pixel values, the multiple pixels are regarded as a pixel set and stored in the index table, and each pixel set is assigned an index value.

Step 206, continue to scan the encoding unit, and judge whether the subsequent plurality of pixels that meet the conditions can find a set of pixels with corresponding characteristics in the index table, if found, go to step 210, if not, go to step 208 .

Step 208, use difference coding or palette coding for pixels that do not have symmetric features.

Step 210, keep the index values of the two pixel sets with symmetry characteristics the same, and add identification information to distinguish the forward order and the reverse order. When restoring to an image, the sequence of pixels can be correctly determined according to the identification information, and an accurate image can be obtained.

Step 212: Perform entropy coding on the coding unit according to the index table and the index value corresponding to each pixel set.

Fig. 3 shows a schematic diagram of characters with symmetrical features according to an embodiment of the present invention.

In complex images, especially screenshots or computer-generated images, there are a large number of characters, such as Chinese, English. For Chinese, at least 8.74% of the characters have symmetrical features, and for English, at least 50% of the characters have symmetrical features. If the method provided by the present invention is used to compress these characters, the amount of data representing the image can be greatly reduced.

As shown in FIG. 3 , an English character "O" with symmetrical features is shown. According to the image compression method of the present invention, each pixel in the coding unit is scanned, and the progressive scanning coding unit is scanned in raster scanning order, for example, in 4 pixels are the step length for pixel analysis. In Figure 3, each row of pixels can obtain 4 pixel sets. For example, in the first pixel set of the first row, the pixel values of each pixel are the same, so this pixel set is not considered ;In the second pixel set, the pixel values of each pixel are different, so it is stored in the index table and assigned an index value, such as m; in the third pixel set, the pixel value of each pixel They are not the same, so look up in the index table to determine whether there is a symmetry feature with the third pixel set in the index table, and find that there is a gap between the second pixel set saved in the index table and the third pixel set Symmetrical features (when judging, the third pixel set can be processed in reverse order, and then the processing result is compared with the second pixel set, if they are the same, it means that the third pixel set and the second pixel set set has symmetry characteristics), so the index value of the second pixel set is used as the index value of the third pixel set, so that the index values of the two pixel sets with symmetry characteristics are the same; 4 in the fourth pixel set The pixel values of the pixels are the same, so the pixel set is not processed. When the second row is scanned, the symmetry feature is judged in the above manner, and so on, which will not be repeated here.

The above is just an example, and it should be understood that the scanning direction can also be scanned from top to bottom, row by row from bottom to top, or row by column from left to right. The scanning step can be between 2 pixels and 6 pixels. The more pixels, the faster the processing speed may be, and the fewer pixels may be, the more accurate the processing result may be.

In this embodiment, the image compression method according to the present invention is applied in each coding unit, and the size of the coding unit may be from 8×8 to 64×64.

Another example is the Chinese character "品" shown in Figure 4. This "品" also has a symmetrical feature as a whole. The image compression method of the present invention can greatly reduce the data volume of this type of image. Therefore, Chinese characters can also be processed according to The above processing process performs compression processing. After the above scanning and judgment, the index table shown in the following table can be obtained:

index value pixel set value 0 {240,230,225,250} 1 {230,200,220,255} … … 7 …

For pixels that do not have symmetric features, difference coding or palette coding can be used to code these pixels to further reduce the amount of data representing the image.

Next, the structure of the image compression device according to the present invention will be described with reference to FIG. 5 to FIG. 6B .

Fig. 5 shows a schematic diagram of an image compression device according to an embodiment of the present invention.

As shown in FIG. 5, an image compression device 400 according to an embodiment of the present invention includes:

A scanning unit 502, scanning each pixel in the image encoding unit to obtain a plurality of pixel sets;

The index table generation unit 504 assigns a unique index value to the gray value set of each pixel set, and generates an index table, wherein the index values of the two pixel sets with symmetry characteristics are the same, and the index values of the two pixel sets with symmetry characteristics are the same. Add identification information to a set of pixels to distinguish the set of pixels in forward order or reverse order;

The coding unit 506 is configured to perform entropy coding on the coding unit according to the index table and the index value of each pixel set in the image coding unit,

Wherein, if the reverse sequence of one consecutive M pixels matches another consecutive M pixels, it is determined that there is a symmetry feature between the one consecutive M pixels and the other consecutive M pixels.

According to the technical scheme of the present invention, the symmetry feature of the characters is utilized during coding, which can greatly reduce the amount of data representing images, reduce the space occupied by data, and improve the efficiency of data transmission.

In one embodiment, as shown in FIG. 6A, the index table generating unit 504 includes:

The first judging unit 5042 scans the encoding unit, if the M consecutive pixels have different gray values, and no pixel set with symmetry characteristics with the M consecutive pixels is found in the index table, then Taking the M pixels as a set of pixels, and if a set of pixels having symmetry characteristics with the continuous M pixels is found in the index table, use the set of pixels corresponding to the set of pixels found in the index table The index value is used as the index value of the M consecutive pixels; the first allocation unit 5044 saves the gray value set of the M pixels in the index table, and assigns the index value to the gray value set.

Further, when the first judging unit 5042 judges whether a set of pixels having symmetry characteristics with the consecutive M pixels is stored in the index table, the consecutive M pixels are processed in reverse order, and the The processing result is compared with the pixel set saved in the index table, and it is determined whether there is a pixel set with this characteristic according to the comparison result.

In another embodiment, the scanning unit 502 scans the coding unit in the first direction with a step size of M pixels, and scans the coding unit in the second direction with a step size of M pixels, wherein, the first direction is opposite to the second direction;

As shown in FIG. 6B, the index table generating unit 504 includes:

The second judging unit 5046 compares the scanning result in the first direction with the scanning result in the second direction, and if the two sets of pixels are the same, it is determined that the two sets of pixels are two sets of symmetrical features. pixel sets; the second assigning unit 5044 assigns a unique index value to each pixel set, where the same index value is assigned to two pixel sets with symmetry features.

The coding unit 506 uses palette coding or difference coding to code a set of pixels that do not have symmetric features.

The technical solution according to the present invention has been described in detail above in conjunction with the accompanying drawings. The present invention utilizes the symmetry feature of characters in encoding, which can greatly reduce the amount of data representing images, reduce the space occupied by data, and improve the efficiency of data transmission. It is especially suitable for and compress complex images, such as screenshots, computer-generated diagrams. In addition, the image compression technology according to the present invention is compatible with existing compression methods and standards, such as H.264 and HEVC.

In addition, an embodiment of the present invention also provides an electronic device, which includes the above apparatus for counting target objects based on an image. In the specific implementation of the above-mentioned electronic device according to the embodiment of the present invention, the above-mentioned electronic device can be any one of the following devices: computer; tablet computer; personal digital assistant; multimedia playback device; mobile phone and electronic paper book, etc. Wait. Wherein, the electronic device has various functions and technical effects of the above-mentioned apparatus for counting objects based on an image, which will not be repeated here.

Each constituent unit, subunit, module, etc. of the image-based object counting apparatus according to the embodiment of the present invention may be configured by software, firmware, hardware or any combination thereof. In the case of realization by software or firmware, the program constituting the software or firmware can be installed from a storage medium or a network to a machine with a dedicated hardware structure, and when the machine is installed with various programs, it can execute the above-mentioned constituent units and sub-units. Various functions of the unit.

In addition, the present invention also proposes a program product storing machine-readable instruction codes. When the above instruction code is read and executed by a machine, the image-based target object counting method according to the embodiment of the present invention can be executed. Accordingly, various storage media such as magnetic disks, optical disks, magneto-optical disks, semiconductor memories, etc. for carrying such program products are also included in the disclosure of the present invention.

In addition, the methods in the various embodiments of the present invention are not limited to being executed in the time sequence described in the description or shown in the drawings, and may also be executed in other time sequences, in parallel or independently. Therefore, the execution order of the methods described in this specification does not limit the technical scope of the present invention.

In addition, obviously, each operation process of the above method according to the present invention can also be implemented in the form of computer executable programs stored in various machine-readable storage media.

Moreover, the purpose of the present invention can also be achieved in the following manner: the storage medium storing the above-mentioned executable program code is directly or indirectly provided to a system or device, and the computer or central processing unit in the system or device reads and Execute the above program code.

At this time, as long as the system or device has the function of executing the program, the embodiment of the present invention is not limited to the program, and the program can also be in any form, for example, an object program, a program executed by an interpreter, or a program provided to an operating system. script programs, etc.

The above-mentioned machine-readable storage media include, but are not limited to: various memories and storage units, semiconductor devices, magnetic disk units such as optical, magnetic and magneto-optical disks, and other media suitable for storing information, and the like.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

To sum up, in the embodiments according to the present invention, the present invention provides the following solutions but not limited thereto:

Additional Note 1. An image compression method, comprising:

scanning each pixel in the image coding unit to obtain multiple pixel sets;

Assign a unique index value to the gray value set of each pixel set, and generate an index table, wherein the index values of the two pixel sets with symmetry characteristics are the same, and add identification to the two pixel sets with symmetry characteristics information to distinguish between forward-ordered and reverse-ordered sets of pixels;

performing entropy coding on the coding unit according to the index table and the index value of each pixel set in the image coding unit,

Wherein, if the reverse sequence of one consecutive M pixels matches another consecutive M pixels, it is determined that there is a symmetry feature between the one consecutive M pixels and the other consecutive M pixels.

Additional note 2. according to the image compression method described in additional note 1, wherein, the generation process of described index table comprises:

Scanning the encoding unit, if the M consecutive pixels have different gray values, and no set of pixels having symmetry characteristics with the M consecutive pixels is found in the index table, then the M pixels are as a collection of pixels;

saving the gray value set of the M pixels in the index table, and assigning a unique index value to the gray value set;

If a pixel set having symmetry characteristics with the continuous M pixels is found in the index table, then use the index value corresponding to the found pixel set in the index table as the index of the continuous M pixels value.

Supplement 3. The image compression method according to Supplement 2, wherein, when judging whether to store a set of pixels having symmetry characteristics with the M consecutive pixels in the index table, the M consecutive The pixels are processed in reverse order, the processing result is compared with the pixel set saved in the index table, and whether there is a pixel set with this characteristic is determined according to the comparison result.

Additional note 4. according to the image compression method described in additional note 2, wherein, the generation process of described index table comprises:

Scanning the coding unit in a first direction with a step size of M pixels, and scanning the coding unit in a second direction with a step size of M pixels, wherein the first direction is opposite to the second direction ;

Comparing the scanning result in the first direction with the scanning result in the second direction, if the two pixel sets are the same, then determining that the two pixel sets are two pixel sets with symmetric characteristics;

A unique index value is assigned to each pixel set, wherein the same index value is assigned to two pixel sets with symmetric features.

Supplementary Note 5. According to the image compression method described in Supplementary Note 3, palette coding or difference coding is used to code a set of pixels that do not have symmetric features.

Supplement 6. The image compression method according to any one of Supplements 1 to 4, wherein the coding unit is a coding unit in a screenshot image or a computer-generated image.

Additional note 7. An image compression device, comprising:

a scanning unit, scanning each pixel in the image encoding unit to obtain multiple pixel sets;

The index table generation unit assigns a unique index value to the gray value set of each pixel set, and generates an index table, wherein the index values of the two pixel sets with symmetry characteristics are the same, and the index values of the two pixel sets with symmetry characteristics are the same. Add identification information to the pixel set to distinguish the pixel set in forward order or reverse order;

a coding unit, performing entropy coding on the coding unit according to the index table and the index value of each pixel set in the image coding unit,

Wherein, if the reverse sequence of one consecutive M pixels matches another consecutive M pixels, it is determined that there is a symmetry feature between the one consecutive M pixels and the other consecutive M pixels.

Supplement 8. The image compression device according to Supplement 7, wherein the index table generation unit includes:

The first judging unit scans the encoding unit, if the M consecutive pixels have different gray values, and no set of pixels having symmetry characteristics with the M consecutive pixels is found in the index table, then the The M pixels are used as a set of pixels, and if a set of pixels having symmetry characteristics with the continuous M pixels is found in the index table, an index corresponding to the set of pixels found in the index table is used value as the index value of the continuous M pixels;

A first allocating unit, saving the gray value set of the M pixels in the index table, and assigning an index value to the gray value set.

Supplement 9. According to the image compression device described in Supplement 8, when the first judging unit judges whether a set of pixels having symmetry characteristics with the continuous M pixels is stored in the index table, the continuous The M pixels are processed in reverse order, the processing result is compared with the pixel set saved in the index table, and whether there is a pixel set with this characteristic is determined according to the comparison result.

Supplement 10. The image compression device according to Supplement 8, wherein the scanning unit scans the encoding unit in the first direction with a step of M pixels, and scans in the second direction with a step of M pixels The encoding unit, wherein the first direction is opposite to the second direction;

The index table generation unit includes:

The second judging unit compares the scanning result in the first direction with the scanning result in the second direction, and if the two pixel sets are the same, it is determined that the two pixel sets are two symmetrical features. collection of pixels;

The second allocation unit allocates a unique index value for each pixel set, wherein the same index value is assigned to two pixel sets with symmetry characteristics.

Supplement 11. The image compression device according to Supplement 9, wherein the coding unit uses palette coding or difference coding to code a set of pixels that do not have symmetric features.

Supplement 12. The image compression device according to any one of Supplements 7 to 11, wherein the coding unit is a coding unit in a screenshot image or a computer-generated image.

Supplement 13. An electronic device, comprising the image compression device according to any one of Supplements 7 to 12 above.

Claims (10)

1. a method for compressing image, comprising:

Each pixel in scan image coding unit, obtains multiple pixel set;

For the gray value set of each pixel set distributes unique index value, generating indexes table, wherein, the index value with two pixel set of symmetric characteristics is identical, described have in two pixel set of symmetric characteristics add identification information, to distinguish the pixel set of forward sequence or reverse order;

Index value according to each pixel set in described concordance list and described image coding unit carries out entropy code to described coding unit,

Wherein, if the opposite sequence of a continuous print M pixel and another continuous print M pixel matching, then determine, between a described continuous print M pixel and another continuous print described M pixel, there is symmetric characteristics.

2. method for compressing image according to claim 1, wherein, the generative process of described concordance list comprises:

Scan described coding unit, if a continuous print M pixel has different gray values, and in concordance list, do not find the pixel set with a described continuous print M pixel with symmetric characteristics, then using a described M pixel as a pixel set;

In described concordance list, preserve the gray value set of a described M pixel, and be that described gray value set distributes unique index value;

If find the pixel set with a described continuous print M pixel with symmetric characteristics in concordance list, then use index value corresponding with the pixel set found out in described concordance list as the index value of a described continuous print M pixel.

3. method for compressing image according to claim 2, wherein, judge whether to preserve in described concordance list with a described continuous print M pixel, there is the pixel set of symmetric characteristics time, opposite sequence process is carried out to a described continuous print M pixel, the pixel set of having preserved in result and described concordance list is compared, determines whether that there is the pixel set to this property feature according to comparison result.

4. method for compressing image according to claim 2, wherein, the generative process of described concordance list comprises:

In a first direction with M pixel for coding unit described in step scan, in a second direction with M pixel for coding unit described in step scan, wherein, described first direction is contrary with described second direction;

Scanning result in a first direction and scanning result are in a second direction compared, if two pixel set are identical, then determines that described two pixel set are two pixel set with symmetric characteristics;

For each pixel set distributes unique index value, wherein, give identical index value to two pixel set with symmetric characteristics.

5. the method for compressing image according to claim 3 or 4, adopts palette coding or differential coding to encode to the pixel set without symmetric characteristics.

6. an image compressing device, comprising:

Scanning element, each pixel in scan image coding unit, obtains multiple pixel set;

Concordance list generation unit, for the gray value set of each pixel set distributes unique index value, generating indexes table, wherein, the index value with two pixel set of symmetric characteristics is identical, described have in two pixel set of symmetric characteristics add identification information, to distinguish the pixel set of forward sequence or reverse order;

Coding unit, the index value according to each pixel set in described concordance list and described image coding unit carries out entropy code to described coding unit,

Wherein, if the opposite sequence of a continuous print M pixel and another continuous print M pixel matching, then determine, between a described continuous print M pixel and another continuous print described M pixel, there is symmetric characteristics.

7. image compressing device according to claim 6, wherein, described concordance list generation unit comprises:

First judging unit, scan described coding unit, if a continuous print M pixel has different gray values, and in concordance list, do not find the pixel set with a described continuous print M pixel with symmetric characteristics, then using a described M pixel as a pixel set, if and in concordance list, find the pixel set with a described continuous print M pixel with symmetric characteristics, then use index value corresponding with the pixel set found out in described concordance list as the index value of a described continuous print M pixel;

First allocation units, preserve the gray value set of a described M pixel in described concordance list, and are described gray value set allocation index value.

8. image compressing device according to claim 7, described first judging unit judge whether to preserve in described concordance list with a described continuous print M pixel, there is the pixel set of symmetric characteristics time, opposite sequence process is carried out to a described continuous print M pixel, the pixel set of having preserved in result and described concordance list is compared, determines whether that there is the pixel set to this property feature according to comparison result.

9. image compressing device according to claim 7, described scanning element in a first direction with M pixel for coding unit described in step scan, in a second direction with M pixel for coding unit described in step scan, wherein, described first direction is contrary with described second direction;

Described concordance list generation unit comprises:

Second judging unit, compares scanning result in a first direction and scanning result in a second direction, if two pixel set are identical, then determines that described two pixel set are two pixel set with symmetric characteristics;

Second allocation units, for each pixel set distributes unique index value, wherein, give identical index value to two pixel set with symmetric characteristics.

10. image compressing device according to claim 8 or claim 9, described coding unit adopts palette coding or differential coding to encode to the pixel set without symmetric characteristics.