CN101742300A - System and method for compressing satellite images with low bit rate - Google Patents
System and method for compressing satellite images with low bit rate Download PDFInfo
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- CN101742300A CN101742300A CN 200810226721 CN200810226721A CN101742300A CN 101742300 A CN101742300 A CN 101742300A CN 200810226721 CN200810226721 CN 200810226721 CN 200810226721 A CN200810226721 A CN 200810226721A CN 101742300 A CN101742300 A CN 101742300A
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Abstract
The invention discloses a system and a method for compressing satellite images with low bit rate. The system comprises a control module, a wavelet transformation module, a CCSDS scanning coding module and a code stream splicing module. In the system and the method, image data are divided into a plurality of 32X32 (or 64X64 and 128X128) small images; then, the small images are transmitted into the wavelet transformation module, the scanning coding module and the code stream splicing module for obtaining compressing code streams. The wavelet transformation module, the scanning coding module and the code stream splicing module are used for line production among image blocks; and the scanning coding module is used for the line production along bit planes. The compressing effect of the system and the method for compressing the images is between JPEG 2000 and EZW; when the compression is carried out at a low bit rate, the compressing effect is equivalent to JPEG2000; a decoding re-synchronization mechanism is adopted for preventing error codes of space data from diffusing in transmission, with low power consumption; and extensively used parallel operation and a line structure increase the processing speed of a chip and meet the macro compressing requirement of the satellite images.
Description
Technical field
The present invention relates to the image compression field, particularly relate to a kind of space spaceborne image compression system of low bit rate and method that use, that meet the CCSDS standard of being suitable for.
Background technology
In recent years, fast development along with China's Aerospace Technology, on the star sensing and detecting devices on quantity still is precision all than increasing greatly in the past, the image data amount that satellite obtains in effective observation time section is increasing, and these " magnanimity " view data have brought great pressure for storage and transmission.Because the capacity of memory is limited by the infinitely increase of restriction of aspects such as volume, weight, power consumption on the star, the transmittability of same clock star-ground down link is limited by the limited visual time restriction of transmission bandwidth and ground station, so just become an indispensable link of data processing on the star in the rail image compression.Just become the inevitable choice that solves spatial data storage and transmission problem and develop high performance spaceborne low bit rate image compression system.
Star loaded camera often adopts to push away sweeps the mode images acquired, the bit-depth of pixel is generally 8～16bits, data transfer rate is big, this just requires spaceborne image compression system processing capability in real time strong, require system must satisfy requirements such as volume is little, in light weight, low in energy consumption simultaneously, the number abominable of delivering a letter in space requires the error-resilient performance height of compression algorithm in addition.3 set chained lists that need add use based on the spiht algorithm of wavelet transformation make storage demand big; The spiht algorithm of no chained list has reduced storage demand, has also reduced compression performance simultaneously; And general JPEG2000 is difficult to be applicable to space field because of its algorithm too complicated (each pixel operation times is above 300 times).General algorithm generally is to do convolution with whole frame image data when realizing wavelet transformation, and calculation of complex and memory space that need be a large amount of can't satisfy the demand that spatial image compresses.At this problem, F.W.Wheeler and W.A.Pearlman propose the spiht algorithm that piecemeal independently carries out.(The Consultative Committee forSpace Data Systems, CCSDS) FIY wavelet transformation and the strip-type JPEG2000 compression algorithm that proposed once are the transition coding based on fixing row view data in consultative committee for space data system.The ICER algorithm of JPL also is conversion of segmentation independence and coding.The spatial image that divides block transform coding to be fit to push-scanning image is handled, and can reduce requirement to memory capacity, help to realize the hardware system of best area-time-power, and can limit the error code diffusion.Can greatly reduce master, the objective quality of reconstructed image yet each piece independently carries out " blocking effect " brought of wavelet transformation (data outside the block boundary are obtained by cycle data continuation in the piece or mirror image continuation), this situation is particularly serious when low bit rate compresses.
Summary of the invention
The object of the invention is, spaceborne image compression processing system of a kind of low bit rate and method are provided, with solve the space use in the high power compression problem of image, develop a kind of be suitable for that use in the space, meet the bottleneck problem of FPGA image compression chip CCSDS 122.0-B-1 standard, that have best area-time-power to solve the spatial data storage and to transmit.
In order to achieve the above object, the present invention proposes spaceborne image compression processing system of a kind of low bit rate and method.This system and method compresses the small images that original image is divided into 32*32 (perhaps 64*64,128*128), (specifically dividing block size to be decided by concrete application demand) carries out lossless coding, ac coefficient to DC coefficient and adopts bit-plane coding technology in conjunction with entropy coding, between compression performance and encoder complexity, obtained compromise, be fit to the space and use.
The spaceborne image compression processing system of a kind of low bit rate provided by the invention comprises:
One control module is used to coordinate the running of image block, wavelet transformation, scanning encoding and code stream concatenation module;
One wavelet transformation module is used for the view data of input is carried out band decomposition, does the processing of decorrelation, obtains the coefficient of wavelet decomposition of this view data, and this coefficient of wavelet decomposition is sent into CCSDS scanning encoding module.
One CCSDS scanning encoding module is used for coefficient of wavelet decomposition is scanned and encodes, and coding is sent into the code stream concatenation module.And
One code stream concatenation module, it is the code stream of unit that the coding that is used for importing is spliced into the word.
Wherein, described control module is divided into view data the small images of 32*32 (perhaps 64*64,128*128) earlier, then this small images is sent into the wavelet transformation module and carries out wavelet transformation.Between wavelet transformation module and scanning encoding module, the code stream concatenation module flowing water between image block and the image block; The scanning encoding module is to carry out flowing water between each bit-planes.
Wherein, described control module is at first by judging the synchronous head and the length and width of image, the frame head information of compression multiple, the position No. of computing block head (piece top left corner pixel); Row by pixel in the piece is set number and row number are judged the progress that image reads then; At last by position No., image first address, ram numbering in the piece, (perhaps 4096,16384) the individual data of exporting 1024 are continuously finished the blocking process to view data.The core design of this system is to carry out computing at small images, adopts the heavy synchronization mechanism of decoding can prevent that the error code in the spatial data transmission from spreading, low in energy consumption (≤1watt/Msamples/sec); In addition, a large amount of concurrent operations of adopting and the flowing structure processing speed (data processing speed when frequency is 100MHz is 20Mpixels/s) that improved system.
Wherein, described wavelet transformation module adopts foldable structure, utilizes two one-dimensional wavelet transform nuclears successively the data of input to be carried out the row, column conversion, finally obtains the 2-d wavelet decomposition coefficient.Be characterized in having reused one-dimensional wavelet transform nuclear, saved logical resource on the sheet,, alleviated the complexity of addressing by adopting two block caches.Specific rate is slower mutually with carrying out the row, column transform framework simultaneously for this framework, but the processing speed of wavelet transformation is not the bottleneck of whole compressibility, and it is a kind of rational way that sacrifice speed saving logical resource takies.Simultaneously, adopt two two-port RAMs, buffer memory MemoryA and buffer memory MemoryB have used free IP core, need not external RAM, have not only optimized design, have improved the speed of service, have also shortened the development time.
Wherein, DC coefficient coding and the parallel processing of ac coefficient coding in the described CCSDS scanning encoding module.
Wherein, described CCSDS scanning encoding module comprises: block scan module and entropy coding module.
The scanning sequency of described block scan inside modules is by first grandson's coefficient, the day after tomorrow subsystem number, last father's coefficient, and single pass obtains the ac coefficient degree of depth of 16 " j-trees "; The escape word of 16 j-trees of parallel computation; Wherein, the memory space buffer memory opened up in addition in the escape word greater than 1 bit;
Described entropy coding module calculation code option time-division two parts parallel processing, first finishes the reading of the escape word copy of 0～7 j-tree, and second portion is finished reading the escape word copy of 8～15 j-trees.
Wherein, described block scan module is to 16 j-trees and line scanning; Described entropy coding module is in the process of coding, and the option that the code word size that travels through all the encoding options is selected the code length minimum is the optimum code option, then according to the option coding of tabling look-up.
Wherein, the data among described wavelet transformation module and the block scan module reuse Dwt_ram; DC coefficient code stream and ac coefficient encoding code stream that described scanning encoding module produces enter the code stream concatenation module by the alternative selector; The code stream that original image frame header that transmits via inner buffer FIFO1 and code stream concatenation module obtain enters inner buffer FIFO2 output by the alternative selector; Wherein, described alternative selector is controlled by control module.
Wherein, described code stream concatenation module is added digit counter in the link of code word splicing and output, if counter has satisfied compression ratio, then stops coding at once.Can save unnecessary work like this, reduce power consumption.
The spaceborne image compress processing method of a kind of low bit rate provided by the invention may further comprise the steps:
(1) control module is sent view data into the wavelet transformation module by the sequence ground of original image;
(2) the wavelet transformation module is carried out band decomposition to the view data of input, does the processing of decorrelation, obtains the coefficient of wavelet decomposition of this view data, and this coefficient of wavelet decomposition is sent into CCSDS scanning encoding module;
(3) CCSDS scanning encoding module scans coefficient of wavelet decomposition and encodes, and coding is sent into the code stream concatenation module;
(4) to be spliced into the word be the code stream of unit to the coding that will import of code stream concatenation module;
Wherein, described control module is divided into view data the small images of 32*32 (perhaps 64*64,128*128) earlier, then this small images is sent into the wavelet transformation module and carries out wavelet transformation.Between wavelet transformation module and scanning encoding module, the code stream concatenation module flowing water between image block and the image block; The scanning encoding module is to carry out flowing water between each bit-planes.
Wherein, described step (1) further comprises: control module is at first by judging the synchronous head and the length and width of image, the frame head information of compression multiple, the position No. of computing block head (piece top left corner pixel); The row number of pixel in the piece and row number are set then, are used to the progress of judging that image reads; At last by piece position No., image first address, ram numbering, (perhaps 4096,16384) the individual data of exporting 1024 continuously are to the step of wavelet transformation module.
Wherein, described step (2) further comprises: the wavelet transformation module adopts foldable structure, utilizes two one-dimensional wavelet transform nuclears successively the data of input to be carried out the row, column conversion, finally obtains the step of 2-d wavelet decomposition coefficient.
Wherein, described step (3) further comprises: the step of DC coefficient coding and the parallel processing of ac coefficient coding in the CCSDS scanning encoding module.
Wherein, described step (3) further comprises:
By first grandson's coefficient, the day after tomorrow subsystem number, last father's coefficient, single pass obtains the ac coefficient degree of depth of 16 " j-trees " to the scanning sequency of coefficient of wavelet decomposition; The escape word of 16 j-trees of parallel computation; Wherein, the memory space buffer memory opened up in addition in the escape word greater than 1 bit; The parallel processing of calculation code option time-division two parts, first finishes the reading of the escape word copy of 0～7 j-tree, and second portion is finished the step that reads to the escape word copy of 8～15 j-trees.
Wherein, described step (3) further comprises: to 16 j-trees and the line scanning of coefficient of wavelet decomposition; In the process of coding, the option that the code word size that travels through all the encoding options is selected the code length minimum is the optimum code option, then according to the table look-up step of coding of option.
Wherein, described step (2) and (3) further comprise: the data among wavelet transformation module and the block scan module reuse Dwt_ram; DC coefficient code stream and ac coefficient encoding code stream that CCSDS scanning encoding module produces enter the code stream concatenation module by the alternative selector; The code stream that original image frame header that transmits via inner buffer FIFO1 and code stream concatenation module obtain enters the step of inner buffer FIFO2 output by the alternative selector; Wherein, described alternative selector is controlled by control module.
Wherein, described step (4) further comprises: the code stream concatenation module is added digit counter in the link of code word splicing and output, if counter has satisfied compression ratio, then stops the step of encoding at once.
The invention has the advantages that:
1, image compression processing system provided by the invention and method compression effectiveness are between JPEG2000 and EZW, and effect is suitable with JPEG2000 when low bit rate compression (compression ratio 8: 1 and 16: 1).
2, the core design of image compression processing system provided by the invention and method is to carry out computing at small images, adopts the heavy synchronization mechanism of decoding can prevent that the error code in the spatial data transmission from spreading, low in energy consumption (≤1watt/Msamples/sec).
3, a large amount of concurrent operations of adopting of image compression processing system provided by the invention and method and the flowing structure processing speed (data processing speed when frequency is 100MHz is 20Mpixels/s) that improved chip can satisfy the demand of spaceborne image high power compression.
4, image compression processing system provided by the invention and method are through test and checking, and systematic function can satisfy the AEROSPACE APPLICATION requirement.Algorithm support based on frame (Frame) input picture form (image that the CCD camera produces) and based on the input picture form of band (Strip) (pushing away the image that the transducer of sweeping type produces), the progressive picture compression be can carry out, near-earth observation and deep layer space exploration task are suitable for.
Description of drawings
Fig. 1 is embodiment of the invention image compression processing system and method CCSDS compression algorithm framework;
Fig. 2 is algorithm general frame figure in embodiment of the invention image compression processing system and the method;
Fig. 3 is a method of partition block diagram in embodiment of the invention image compression processing system and the method;
Fig. 4 is a two-dimensional wavelet transformation framework in the embodiment of the invention image compression processing system;
Fig. 5 is a two-dimentional DWT hardware structure diagram in the embodiment of the invention image compression processing system;
Fig. 6 is a wavelet transformation coefficient positions distribution map in embodiment of the invention image compression processing system and the method;
Fig. 7 is bit-planes inner segment coded sequence in embodiment of the invention image compression processing system and the method;
Fig. 8 sweeps table and coding module structure chart in the embodiment of the invention image compression processing system;
Fig. 9 is a code stream concatenation module structured flowchart in the embodiment of the invention image compression processing system.
Embodiment
The present invention is based on the image compression algorithm that CCSDS122.0-B-1 recommends, and the increase of the characteristics novelty of using according to the space image block pattern, the view data of input is divided into the small images of some 32*32 (perhaps 64*64,128*128) through control module; View data behind the piecemeal enters wavelet transformation module, scanning encoding module and code stream concatenation module and obtains compressed bit stream.Wherein the small echo module is used for input picture is carried out band decomposition reaching the purpose of decorrelation, and the wavelet coefficient of bit-plane coding module after to conversion scans and encode.Between wavelet transformation module and scanning encoding module, the code stream concatenation module flowing water between image block and the image block; The scanning encoding module is to carry out flowing water between each bit-planes.DC coefficient coding and the parallel processing of ac coefficient coding in the scanning encoding module.The scanning sequency of block scan inside modules guarantees that by first grandson's coefficient, the day after tomorrow subsystem number, last father's coefficient single pass can obtain the ac coefficient degree of depth of 16 " j-trees "; The escape word of 16 j-trees of parallel computation.Because the escape word of single-bit is not encoded, for reducing the reading times speed-up computation, the present invention opens up the memory space buffer memory in addition to the escape word greater than a bit, is referred to as copy.The option time-division two parts parallel processing of entropy coding module calculation code, first finishes the reading of the escape word copy of 0～7 j-tree, and second portion is finished reading the escape word copy of 8～15 j-trees.The spaceborne image compression chip compression effectiveness that the present invention realized is between JPEG2000 and EZW, and effect is suitable with JPEG2000 when low bit rate compression (compression ratio 8: 1 and 16: 1).Because the core design of chip is to carry out computing at small images, adopt the heavy synchronization mechanism of decoding can prevent that the error code in the spatial data transmission from spreading, low in energy consumption (≤1watt/Msamples/sec); In addition, the processing speed (data processing speed when frequency is 100MHz is 20Mpixels/s) that a large amount of concurrent operations of adopting and flowing structure have improved chip can satisfy the demand that spaceborne image high power is compressed.Through test and checking, systematic function can satisfy the AEROSPACE APPLICATION requirement.Algorithm support based on frame (Frame) input picture form (image that the CCD camera produces) and based on the input picture form of band (Strip) (pushing away the image that the transducer of sweeping type produces), the progressive picture compression be can carry out, near-earth observation and deep layer space exploration task are suitable for.
CCSDS122.0-b-1 be issue in 2005 for AEROSPACE APPLICATION formulation Standard of image compression, its low bit rate compression effectiveness is better than JPEG2000, code check is adjustable continuously.Algorithm has adopted a kind of transition coding model of extensive use, CCSDS compression algorithm framework as shown in Figure 1, wherein the small echo module is used for input picture is carried out band decomposition reaching the purpose of decorrelation, and the wavelet coefficient of bit-plane coding module after to conversion scans and encode.
The compression algorithm general frame
Compression algorithm general frame figure as shown in Figure 2, according to algorithm characteristic, with the data input-buffer, wavelet transformation, bit-plane coding (comprises the piece interscan, the ac coefficient entropy coding, code word splicing) and output buffers be in turn connected to form level Four flowing water, be the flowing water between image block and the image block between wavelet transformation module and scanning encoding module, the code stream concatenation module, the scanning encoding module is to carry out flowing water between each bit-planes, and the coordination of flowing water intermodule is finished by interface control module.Because DC coefficient coding and ac coefficient coding are independent fully, the inner scanning sequency of block scan module (BlockScan) guarantees that by first grandson's coefficient, the day after tomorrow subsystem number, last father's coefficient single pass can obtain the ac coefficient degree of depth of 16 " j-trees "; The escape word of 16 j-trees of parallel computation.Because the escape word of single-bit is not encoded, for reducing the reading times speed-up computation, the present invention opens up the memory space buffer memory in addition to the escape word greater than a bit, is referred to as copy.The option time-division two parts parallel processing of entropy coding module calculation code, first finishes the reading of the escape word copy of 0～7 j-tree, and second portion is finished reading the escape word copy of 8～15 j-trees.
Utilize the buffer structure of poll can realize view data is sent into buffer memory continuously, wavelet transformation is when handling current image block, and buffer memory receives the image of next piece simultaneously.Each buffer area can be stored an image block separately at least, when one of them carries out wavelet transformation, imports next piece image to another buffer memory, and after all finishing, the buffer memory task function works on successively.So reduce the data buffering time, guaranteed the continuous processing of view data.
Input of 8bit gray level image and method of partition
The method of partition block diagram as shown in Figure 3.Getting 512*512 size 8bit gray scale image is experimental subjects, add synchronous head and figure image width, high, compression multiple, after the headers such as valid data number, send into FIFO1, in a single day FIFO1 is non-NULL, and the spacing wave of its FIFO1 will be put low, and in a single day input and output and buffer memory control (IO and Ram ctrl) module receive this signal, at first judge whether to have empty external cache (External Ram), if no, with abort operation, if having, to begin reading of data from FIFO1, and judge synchronous head simultaneously, and unsuccessful if synchronous head reads, then abandon data, continue the interpretation synchronous head, if synchronous head reads success, then send into, then by fifo2_sel signal gating FIFO2 and with the header of synchronous head and image, the subsequent images data are sent in the external cache, and external cache is (to comprise 2) more than 2 to have the static ram that can store the piece image capacity.Meanwhile, whether input and output and buffer memory control module detect external cache constantly the sign that is filled with piece image, in case detect, then send the send_ready signal, notice BPE_Ctrl module has been ready to send, and the send_start signal of wait BPE_Ctrl module, in case receive this signal, then with this image block output.Dividing block size is 32*32 (perhaps 64*64,128*128), because dividing block size fixes, so can calculate the piece first address, each pixel in the Row Column traversal piece successively again realizes the individual pixel of gapless continuous output 1024 (perhaps 4096,16384).In the time of output pixel, put high Data_in_en, make the wavelet transformation module receive the data of input.
The wavelet transformation framework
Wavelet transformation is an important component part of compression algorithm, and the present invention has adopted the less foldable structure of a kind of resource occupation (as shown in Figure 4) to realize wavelet transformation.This framework utilizes one-dimensional wavelet transform nuclear, carries out the row, column conversion successively and obtains the 2-d wavelet decomposition coefficient, is characterized in having reused one-dimensional wavelet transform nuclear, has saved logical resource on the sheet, by adopting two block caches, has alleviated the complexity of addressing.Specific rate is slower mutually with carrying out the row, column transform framework simultaneously for this framework, but the processing speed of wavelet transformation is not the bottleneck of whole compressibility, and it is a kind of rational way that sacrifice speed saving logical resource takies.
9/7 integer wavelet transformation is that the non-linear of 9/7 discrete wavelet approached, the operation that rounds in the decorrelation process has brought non-linear to algorithm, this nonlinear transformation is not real wavelet transform strictly speaking, yet but exists strict inversion to bring the realization lossless compress.Algorithm adopts the mode of symmetric extension to handle the border, and its formula is as follows:
Input image data x
i, calculate high-pass coefficient D according to (1) formula
j, and then according to formula (2) calculating low-pass coefficients C
jBy the wavelet arithmetic formula as can be seen, mainly be plus and minus calculation and division arithmetic, and division mainly is the power divided by 2, in hardware, can realize quick computing by simple right-shift operation, it realizes that statement is as follows:
Go through＜=Xdj-SHIFT_RIGHT (Xb+Xc+1,1)-SHIFT_RIGHT (Xb+Xc-Xa-Xd, 4);
Cj＜＝Xcj+SHIFT_RIGHT(Da+Db-2，2)；
The hardware circuit of two dimension DWT, as shown in Figure 5.Mainly contain two one-dimensional wavelet transform processes in the hardware structure diagram, line translation Prow and rank transformation Pcol; Two two-port RAMs, buffer memory MemoryA and buffer memory MemoryB have used free IP core, need not external RAM, have not only optimized design, have improved the speed of service, have also shortened the development time; Control unit Ctrl Unit controls the process of whole wavelet transformation: the generation of address signal, the progression of wavelet transformation etc.Datain_P1 and Datain_P2 are original image data, deposit among the MemoryA at first, IN2n and IN2n+1 are two subset data after dividing, after line translation, be stored among the MemoryB, Adr_MB_P1 and Adr_MB_P2 are the address signal of MemoryB, wavelet coefficient after the line translation is stored among the MemoryA behind rank transformation again, Adr_MA_P1 and Adr_MA_P2 are the address signal of MemoryA, control signal Sol_Prow, Eol_Prow, Sol_Pcol and Eol_Pcol are used to control BORDER PROCESSING, and the wavelet transformation final result is stored among the MemoryA.
Bit-plane coding
Bit-plane coding is a kind of effective progressively-encode method, helps carrying out flexibly Rate Control, realizes the progression transmission and blocks at random.Bit-plane coding mainly comprises three steps: scanning, escape word entropy coding (hereinafter to be referred as entropy coding) and code stream splicing.The scanning encoding module is to carry out flowing water between each bit-planes.DC coefficient coding and the parallel processing of ac coefficient coding in the scanning encoding module.The scanning sequency of block scan inside modules guarantees that by first grandson's coefficient, the day after tomorrow subsystem number, last father's coefficient single pass can obtain the ac coefficient degree of depth of 16 " j-trees "; The escape word of 16 j-trees of parallel computation.Because the escape word of single-bit is not encoded, for reducing the reading times speed-up computation, the present invention opens up the memory space buffer memory in addition to the escape word greater than a bit, is referred to as copy.The option time-division two parts parallel processing of entropy coding module calculation code, first finishes the reading of the escape word copy of 0～7 j-tree, and second portion is finished reading the escape word copy of 8～15 j-trees.
According to the algorithm of CCSDS 122.0-B-1, the wavelet coefficient to 9/7 wavelet transformation obtains according to decomposing the back in the position of each frequency band correspondence, forms quad-tree structure, and the wavelet conversion coefficient location map as shown in Figure 6.By this structure, each member (DC coefficient) of LL3 subband, corresponding j-tree ({ father p
i, son C
i, grandson H
I0, H
I1, H
I2, H
I3, i=1,2,3) totally 63 ac coefficients, form a square that comprises 64 coefficients, as a scanning element.Because continuous zone of the corresponding original image of these 64 coefficients is stronger with the intersubband statistic correlation in the subband, so help by scanning further decorrelation.
Before each block scan, at first carry out preliminary treatment, the coefficient of different frequency bands is weighted.Calculate the ac coefficient degree of depth (ACDepth), then the DC coefficient and the ac coefficient degree of depth are quantized, parallel afterwards DC coefficient coding and the ac coefficient depth coding of carrying out.DC coefficient coding and ac coefficient depth coding carry out the Rice coding according to the method for CCSDS agreement.
Ac coefficient is encoded to comprise by bit-planes and is scanned and entropy coding two parts content.When scanning by bit-planes, earlier with each scanning element according to the putting in order of coefficient among the LL3, Row Column scans one by one.Wherein, to the scan method of each piece as described in the CCSDS 122.0-B-1, the present invention is with 16 continuous scanning elements also line scanning simultaneously, for each bit-planes, the escape word correspondence that scanning forms is sent into dual port RAM in 16 sheets, 16 scanning elements form the content of a section (segment), and entropy coding is carried out in unification, and the coding of each bit-planes is uncorrelated mutually.During coding, at first read 16 scanning results among the ram, calculate optimum option by the traversal the encoding option of tabling look-up, encode according to this option then, the method for specifically tabling look-up is seen CCSDS122.0-B-1.The ac coefficient coding is according to bit-planes scanning successively from high to low, and the top of bit-planes determined that by the ac coefficient degree of depth entropy coding order in the bit-planes in the section as shown in Figure 7.
Coding between each bit-planes is mutually independently, but in the process of scanning, the scanning result of following one deck and the scanning result of last layer are closely related, and can form flowing structure between bit-planes.At first, scan module scans by bit-planes, and scanning result is sent into dual port RAM; Coding module can be encoded then, and scan module can carry out the scanning on next plane simultaneously.For improving sweep speed, the present invention sweeps table and coding module structure chart, as shown in Figure 8 to 16 j-trees and line scanning.In the process of coding, the option that the code word size that travels through all the encoding options is selected the code length minimum is the optimum code option, then according to the option coding of tabling look-up.The specific coding process of bit-planes b is as follows:
Stage 0: b most important bit during the complement code of coding DC coefficient is expressed.
Stage 1: paternal number types encodes
b[P], signs
b[P].
Stage 2: coding son coefficient
1)tran
B，
2) tran
D, at tran
B≠ 0 and t
Max(B) ≠-1 under the situation
3) types
b[C
i] and signs
b(C
i) each i there is t
Max(D
i) ≠ 0 ,-1.(i＝0，1，2)。
Stage 3: coding grandson coefficient
If tran
B=0 or t
Max(B)=-1, then need not carry out the stage3 coding, otherwise:
1)tran
G，
2)
3) types
b[H
Ij] and signs
b[H
Ij]; Each i there is t
Max(G
i) ≠ 0 ,-1; Each j there is t
Max(H
Ij) ≠ 0 ,-1
Stage 4: the type of coding value is b the bit value of 2 AC, and for each j-tree, the bit strings of output is by types value t
bB bit value of ac coefficient (x)=2 formed in the following order:
P
i(i＝0，1，2)，
C
i(i＝0，1，2)，
H
ij(i＝0，1，2；j＝0，1，2，3)；
Annotate: P={p
0, p
1, p
2----father's set in the j-tree
B={D
0, D
1, D
2----j-tree offspring set
D
i={ C
i, G
i----offspring's coefficient of i family in the j-tree
Types
bThe binary word that b the bit value of each coefficient x constitutes among the coefficient sets ψ under [ψ]----bit-planes b is so that t
b(x)=0or1.
Signs
bThe binary word that the sign bit of each coefficient x constitutes among the coefficient sets ψ under [ψ]-----bit-planes b is so that t
b(x)=1.
Tword[Λ]----expression Λ={ λ
0, λ
1, Λ λ
lIn types value be 0 or 1 λ
iThe binary word that sequence is formed.
The code word splicing
Output code flow is that unit transmits with 16 word among the present invention, and therefore the scattered avriable length codes of coding output must be spliced into the word is the code stream of unit.Code stream concatenation module structure as shown in Figure 9.Scattered code word is at first intercepted significance bit,,, and new remaining bit is moved to right if form new unit code stream then export with residue code stream splicing; If it is be not enough to form new unit code stream, then together temporary after the splicing as remaining bit.Simultaneously, for the compression ratio to lossy compression method is controlled flexibly, requirement can be blocked code stream at any time, just need add the position counting in the link of code word splicing and output, in case counter has satisfied compression ratio, will stop coding work at once.Do like this and can save unnecessary work, reduce power consumption.
Claims (16)
1. spaceborne image compression processing system of low bit rate, described system comprises:
One control module is used to coordinate the running of image block, wavelet transformation, scanning encoding and code stream concatenation module;
One wavelet transformation module is used for the view data of input is carried out band decomposition, does the processing of decorrelation, obtains the coefficient of wavelet decomposition of this view data, and this coefficient of wavelet decomposition is sent into CCSDS scanning encoding module;
One CCSDS scanning encoding module is used for coefficient of wavelet decomposition is scanned and encodes, and coding is sent into the code stream concatenation module; And
One code stream concatenation module, it is the code stream of unit that the coding that is used for importing is spliced into the word;
It is characterized in that described control module is divided into view data the small images of 32*32 or 64*64,128*128 earlier, then this small images is sent into the wavelet transformation module.
2. image compression processing system according to claim 1 is characterized in that, described control module is at first by judging the synchronous head and the length and width of image, the frame head information of compression multiple, the position No. of computing block head; Row by pixel in the piece is set number and row number are judged the progress that image reads then; By position No., image first address, ram numbering in the piece, accordingly, export 1024 or 4096,16384 data continuously at last, finish blocking process view data to the wavelet transformation module.
3. image compression processing system according to claim 1 is characterized in that, described wavelet transformation module adopts foldable structure, utilizes two one-dimensional wavelet transform nuclears successively the data of input to be carried out the row, column conversion, finally obtains the 2-d wavelet decomposition coefficient.
4. image compression processing system according to claim 1 is characterized in that, DC coefficient coding and the parallel processing of ac coefficient coding in the described CCSDS scanning encoding module.
5. image compression processing system according to claim 1 is characterized in that, described CCSDS scanning encoding module comprises: block scan module and entropy coding module;
The scanning sequency of described block scan inside modules is by first grandson's coefficient, the day after tomorrow subsystem number, last father's coefficient, and single pass obtains the ac coefficient degree of depth of 16 " j-trees "; The escape word of 16 j-trees of parallel computation; Wherein, the memory space buffer memory opened up in addition in the escape word greater than 1 bit;
Described entropy coding module calculation code option time-division two parts parallel processing, first finishes the reading of the escape word copy of 0～7 j-tree, and second portion is finished reading the escape word copy of 8～15 j-trees.
6. image compression processing system according to claim 5 is characterized in that, described block scan module is to 16 j-trees and line scanning; Described entropy coding module is in the process of coding, and the option that the code word size that travels through all the encoding options is selected the code length minimum is the optimum code option, then according to the option coding of tabling look-up.
7. image compression processing system according to claim 5 is characterized in that, described wavelet transformation module and block scan module reuse buffer memory Dwt_ram; DC coefficient code stream and ac coefficient encoding code stream that described scanning encoding module produces enter the code stream concatenation module by the alternative selector; The code stream that original image frame header that transmits via inner buffer FIFO1 and code stream concatenation module obtain enters inner buffer FIFO2 output by the alternative selector; Wherein, described alternative selector is controlled by control module.
8. image compression processing system according to claim 1 is characterized in that, described code stream concatenation module is added digit counter in the link of code word splicing and output, if counter has satisfied compression ratio, then stops coding at once.
9. spaceborne image compress processing method of low bit rate may further comprise the steps:
(1) control module is sent view data into the wavelet transformation module by the sequence ground of original image;
(2) the wavelet transformation module is carried out band decomposition to the view data of input, does the processing of decorrelation, obtains the coefficient of wavelet decomposition of this view data, and this coefficient of wavelet decomposition is sent into CCSDS scanning encoding module;
(3) CCSDS scanning encoding module scans coefficient of wavelet decomposition and encodes, and coding is sent into the code stream concatenation module;
(4) to be spliced into the word be the code stream of unit to the coding that will import of code stream concatenation module;
It is characterized in that described control module is divided into view data the small images of 32*32 or 64*64,128*128 earlier, then this small images is sent into the wavelet transformation module and carries out wavelet transformation.
10. image compress processing method according to claim 9 is characterized in that, described step (1) further comprises: control module is at first by judging the synchronous head and the length and width of image, the frame head information of compression multiple, the position No. of computing block head; Row by pixel in the piece is set number and row number are judged the progress that image reads then; By position No., image first address, ram numbering in the piece, export the step of 1024,4096 or 16384 data continuously at last to the wavelet transformation module.
11. image compress processing method according to claim 9, it is characterized in that, described step (2) further comprises: the wavelet transformation module adopts foldable structure, utilize two one-dimensional wavelet transform nuclears successively the data of input to be carried out the row, column conversion, finally obtain the step of 2-d wavelet decomposition coefficient.
12. image compress processing method according to claim 9 is characterized in that, described step (3) further comprises: the step of DC coefficient coding and the parallel processing of ac coefficient coding in the CCSDS scanning encoding module.
13. image compress processing method according to claim 9, it is characterized in that, described step (3) further comprises: by first grandson's coefficient, the day after tomorrow subsystem number, last father's coefficient, single pass obtains the ac coefficient degree of depth of 16 " j-trees " to the scanning sequency of coefficient of wavelet decomposition; The escape word of 16 j-trees of parallel computation; Wherein, the memory space buffer memory opened up in addition in the escape word greater than 1 bit; The parallel processing of calculation code option time-division two parts, first finishes the reading of the escape word copy of 0～7 j-tree, and second portion is finished the step that reads to the escape word copy of 8～15 j-trees.
14. image compress processing method according to claim 13 is characterized in that, described step (3) further comprises: to 16 j-trees and the line scanning of coefficient of wavelet decomposition; In the process of coding, the option that the code word size that travels through all the encoding options is selected the code length minimum is the optimum code option, then according to the table look-up step of coding of option.
15. image compress processing method according to claim 13 is characterized in that, described step (2) and (3) further comprise: the data among wavelet transformation module and the block scan module reuse buffer memory Dwt_ram; DC coefficient code stream and ac coefficient encoding code stream that CCSDS scanning encoding module produces enter the code stream concatenation module by the alternative selector; The code stream that original image frame header that transmits via inner buffer FIFO1 and code stream concatenation module obtain enters the step of inner buffer FIFO2 output by the alternative selector; Wherein, described alternative selector is controlled by control module.
16. image compress processing method according to claim 9, it is characterized in that, described step (4) further comprises: the code stream concatenation module is added digit counter in the link of code word splicing and output, if counter has satisfied compression ratio, then stops the step of encoding at once.
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