Abstract:
The present invention provides an image coding apparatus and method, which can achieve a low-cost, real time, and high-performance coding process by utilizing a line buffer and an auxiliary buffer to execute a typical prediction process in JBIG encoding, a ping-pong buffer and a window template, and an adaptive encoder/decoder. The image encoding apparatus includes a typical prediction unit for storing input image data and performing typical predication in JBIG encoding of the input image data, a ping-pong buffer unit which has a plural sets of line memories for sequentially updating and storing the image data into corresponding addresses of the plural sets of line memories, and generating a template, a encoding unit for reading out the image data stored in the ping-pong buffer, and performing adaptive arithmetic encoding, and a control unit for controlling access to the ping-pong buffer unit between the typical prediction unit and the encoding unit.

Description:
BACKGROUND OF THE PRESENT INVENTION 
   1. Field of Invention 
   The present invention relates to an image processing apparatus and method having compression/decompression function for image data, and more particularly to an image processing apparatus and method for high-performance and real time conversion of image data by the JBIG (Joint Bi-level Image Experts Group) standard utilizing the ping-pong buffer and line buffer to generate necessary context. 
   2. Description of Related Arts 
   Please refer to the prior art described in U.S. Pub. No. 20020024525. As shown in FIG. 1 of U.S. Pub. No. 20020024525, it illustrates a hardware block diagram of a typical sequential JBIG process. Referring to  FIG. 1 , reference numerals  101  to  104  denote line buffers which sequentially update and store image data for one line in synchronism with clocks (not shown), thus outputting image data for four lines including a line to be encoded and reference lines for template generation to a TP discriminator  105  and adaptive arithmetic encoder  107 . 
   Image data input from an input terminal  100  at a rate of one pixel/clock in synchronism with transfer clocks (not shown) is stored in the line buffer  101 . The line buffer  101  stores the data, and simultaneously reads out image data for the previous line and outputs it to the line buffer  102  in synchronism with the transfer clocks. The line buffer  102  stores the data output from the line buffer  101  in synchronism with the transfer clocks, and simultaneously reads out the stored data for the previous line and outputs it to the line buffer  103 , as in the line buffer  101 . In this manner, data are sequentially transferred to the line buffers  102 ,  103 , and  104  while being updated, thus simultaneously extracting delayed data for four lines from the memories. In this example, the data read out from the line buffer  102  corresponds to the line to be encoded. 
   Reference numeral  105  denotes a TP (typical prediction) discriminator for comparing data read out from the line buffer  101  and data of the immediately above line read out from the line buffer  102  for one line so as to check if data for one line, which is read out from the line buffer  101  and is stored in the line buffer  102 , allows typical prediction. A discrimination result indicating whether data allows typical prediction (LNTPy=0) or not (LNTPy=1) is output to a register  106  every time a process for one line is completed, and is held in the register to update the register value. Reference numeral  107  denotes an adaptive arithmetic encoder for receiving data for three lines, which are read out from the line buffers  102 ,  103 , and  104 , and generating template data corresponding to a pixel to be encoded using shift registers (not shown). The adaptive arithmetic encoder makes an adaptive arithmetic coding operation of the pixel to be encoded using this template data, thus generating and outputting encoded data. At the head of each line, a temporary pixel is computed using the register value held in the register  106 , and an adaptive arithmetic coding operation is made using a fixed template therefor so as to encode the typical prediction result by adaptive arithmetic coding, thus generating and outputting encoded data. 
   However, since the prior art implements the TP (typical prediction) process by hardware, as shown in FIG. 1 of U.S. Pub. No. 20020024525, four line buffer memories for reference lines are required for the TP process, thus increasing the hardware scale. Furthermore, in the example shown in FIG. 1 of U.S. Pub. No. 20020024525, since all the line buffer memory update process, TP discrimination process, and adaptive arithmetic coding operation are parallelly executed in synchronism with identical clocks, each line to be encoded requires a processing time given by the number of pixels for one line.times.clocks although the TP process that can reduce the number of pixels to be encoded if they allow typical prediction and that can achieve high-speed processing is used. 
   Accordingly, according to the prior art described in U.S. Pub. No. 20020024525, there are at least one line buffer memory for processing TP, and three line buffer memories for processing context, wherein the TP memory and the context memory are sequentially assembled for later purposes. Therefore, there are at least four line buffers necessary for processing TP (typical predication) and combining the context, a rather larger memory will be required for accomplishing such tasks. Furthermore, when the high resolution image is processed, the SRAM will eaten up as octuple as much, that is to say, more SRAM would be occupied by such JBIG system. What is more, it is awesomely time-consuming for wait such TP (typical prediction), as well as the context are forwarded to the adaptive arithmetic encoder, which is intolerable for most of users. 
   SUMMARY OF THE PRESENT INVENTION 
   A primary object of the present invention is to provide a JBIG coding apparatus and method with ping-pong buffer arrangement for compressing/decompressing data by adaptive arithmetic operations using typical prediction as a pre-process to economize the use of memory and increase the performance, wherein the typical prediction operation and the ping-pong buffer operation could be are parallelly executed so as to increase the performance. 
   Another object of the present invention is to provide a buffer arrangement for a JBIG coding apparatus, wherein the buffer arrangement comprises two separate buffers for the JBIG encoder/decoder, namely, a line buffer and an auxiliary buffer, which could execute a typical prediction process just only use of the line buffer and the auxiliary buffer. 
   Another object of the present invention is to provide a buffer arrangement and a ping-pong buffer as well as a window unit for JBIG coding apparatus and method for performing coding by optimizing a coding efficiency in accordance with image data. 
   Another object of the invention is to provide a coding apparatus and method capable of efficiently performing task processes in units of a predetermined time in accordance with image data. 
   Another object of the present invention is to provide a ping-pong buffer as well as a window unit of processing the high resolution image, wherein a line buffer is further prolonged while other memory arrangement are intact, so that no more substantial memory body are necessary. 
   Another object of the present invention is to provide a buffer arrangement and a ping-pong buffer as well as a window unit for processing the high resolution image, wherein the size of the ping-pong buffer is adjustable based on the speed of the arithmetically encoding speed of the adaptive arithmetic encoder for achieving high efficiency operation of the JBIG coding process and reducing the use of the memory size. 
   Another object of the present invention is to utilize a buffer arrangement and ping-pong buffer to generate a necessary context in order to reduce the time consumption of generating a necessary context for achieving a low-cost, real time, and high efficiency operation of JBIG coding process. 
   Accordingly, in order to achieve above mentioned objects, the present invention provides an image encoding apparatus, comprising:
         a typical prediction unit for storing input image data, and performing typical predication in JBIG encoding of the input image data;   a ping-pong buffer unit which has a plural sets of line memories for sequentially updating and storing the image data into corresponding addresses of the plural sets of line memories, and generating a template;   a encoding unit for reading out the image data stored in the ping-pong buffer, and performing adaptive arithmetic encoding; and   a control unit for controlling access to the ping-pong buffer unit between the typical prediction unit and the encoding unit.       

   These and other objectives, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view showing a bi-level image. 
       FIG. 2  is a block diagram showing the arrangement of an encoding apparatus according to a preferred embodiment of the present invention. 
       FIG. 3  shows the ping pong buffer according to the above preferred embodiment of the present invention. 
       FIG. 4  illustrates a sequential Window-based JBIG compression according to the above preferred embodiment of the present invention. 
       FIG. 5  illustrates a sequential JBIG decompression according to the preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , a bi-level image is illustrated, the edge area of such image could be deemed pixel with a background color (white=0), for facilitating the compression of the image, according to the present invention, the pixel value of each of the line buffer is identical with the previous line buffer. If the pixel value is the same, the Typical prediction value (LNTP) is 0, however, if any of pixel is showing different value, the LNTP is 1, so each of the line has a corresponding Typical prediction value (LNTP). In other words, in sequential JBIG, if the line to be encoded matches the immediately above line, it is determined that the line of interest is typical, and LNTP y =0 is set. If the line to be encoded is different from the immediately above line even by one pixel, it is determined that the line of interest is not typical, and LNTP y =1 is set. Upon encoding a head line of an image, the immediately above line is assumed to be background color (white=0), thus making comparison for typical prediction. 
   If the previous line&#39;s Typical prediction value is LNTP y-1 , and the current scan line&#39;s Typical prediction value is LNTP y , so in the very beginning, the Typical prediction value of such line as well as a fixed set of context will be send into the adaptive arithmetic encoding to be compressed, wherein SLNTP y =!(LNTP y  XOR LNTP y-1 ), if the value is the same, a following procedure will be followed to compare pixel value of the line buffer, no data would be send into the adaptive arithmetic encoder, this is due to the fact that each line has to be processed by the adaptive arithmetic encoder first. 
     FIG. 2  is a block diagram showing the arrangement of an encoding apparatus according to a preferred embodiment of the present invention. Traditionally, as described in U.S. Pub. No. 2002/0024525, the JBIG is compressed by two line buffers to process TP prediction of the JBIG, and data of the previous line buffer will be maintained for later comparison with data of the current line buffer so as to decide the TP value. However, if a high resolution image is processed, a relatively larger memory would be needed for processing such JBIG compression. According to the present invention, the memory element is embodied as two separated line memory, namely, a line buffer  201  and an auxiliary line buffer  202 . The auxiliary line buffer  202  could be 32 bytes or 64 bytes so that 32 bytes or 64 bytes of data could be retrieved from an image memory (not shown) through DMA (Direct Memory Access) via a first DMA channel  501 , and stored into such auxiliary line buffer  202 . In the beginning, the line buffer  210  is set to zero. The auxiliary line buffer  202  could be retrieved from an image memory (not shown) through DMA (Direct Memory Access) via the first DMA channel  501 , and stored into such auxiliary line buffer  202 . Afterwards, the image data stored in such auxiliary line buffer  202  could be read out via a signal line  206  and compared with the data of the line buffer  201  via a signal line  207  through a comparator  203 . If the comparison result is different, the current line&#39;s LNTP value will be reset. The comparator  203  outputs the LNTP value of the current line, wherein such value should be stored into a register  204 . Once the comparator  203  outputs the LNTP value of the current line, the data of the auxiliary buffer  202  update and store image data into corresponding address of the line buffer  201  in synchronism with clocks (not shown) via a signal line  210 . Afterwards, the auxiliary line buffer  202  could be retrieved from the image memory through DMA (Direct Memory Access) via the first DMA channel  501 , and stored into such auxiliary line buffer  202  again. Likewise, the image data stored in such auxiliary line buffer  202  could be read out via a signal line  206  and compared with the data of the line buffer  201  via a signal line  207  through a comparator  203 . If the comparison result is different, the current line&#39;s LNTP value will be reset. The comparator  203  outputs the LNTP value of the current line, wherein such value should be stored into a register  204 . The data of the auxiliary buffer  202  sequentially update and store image data into corresponding address of the line buffer  201  in synchronism with clocks (not shown) via the signal line  210 , such repetition would not ceased until the current line buffer  201  is ended so as to obtain the LNTP values of the current line, such values should be stored into the register  204 , meanwhile, data stored in the line buffer  201  will be rewritten into the current line for later reference. 
   Referring back to  FIG. 2 , a schematic view of the buffer arrangement of the preferred embodiment of the present invention is illustrated. The encoding buffer arrangement comprises an adaptive arithmetic encoder  300 , a TP (typical prediction) unit  200  which includes the line buffer  201 , the auxiliary line buffer  202 , the comparator  203 , and the set of register  204 , a ping-pong buffer  100  which includes a 3-line memory  101  and a 3-line memory  102 , a set of encode controller  400 , and three set of DMA channel, namely a first DMA channel  501 , a second DMA channel  502 , and a third DMA channel  503 . Data are sent into the auxiliary line buffer  202  via the first DMA channel  501  and to be compared with pixel value of line buffer  201  at corresponding position. If the data information is different, a LNTP value of the line buffer  201  is determined and then send into the register  204 . Furthermore, after the comparing process, the pixel information stored in the auxiliary line buffer  202  will be written into a corresponding position in the line buffer  201  until the pixel line is fully scanned. In this example, the auxiliary line buffer  202  is a 128 byte SRAM. Nevertheless, the auxiliary line buffer  202  of this invention is not limited to a 128 byte SRAM. 
   The LNTP value will determine whether the current line is forwarded to the adaptive arithmetic encoder  300  or not. The second DMA channel  502  is adapted to grab necessary information and to send such information into the ping-pong buffer  100 . Upon receiving the LNTP values, the encoder controller  400  communicates with the ping-pong buffer  100  via the signal lines  504  and  505  so that the encoder controller  400  determines whether data of the 3-line memory  101  or the 3-line memory  102  are forwarded to the adaptive arithmetic encoder  300  or not by the TP (Typical prediction) value, and the ping-pong buffer  100  sequentially update and store image data into corresponding address of the 3-line memory  101  or the 3-line memory  102  via the second DMA channel  502 . In this manner, data are sequentially transferred to the line memories  0  to  3  to read out/write data from/in line memories  0  to  3  of the 3-line memory  101  or the line memories  0  to  3  to read out/write data from/in line memories  0  to  3  of the 3-line memory  102 . Every time for one line is processed, image data are sequentially read out from line memories  0 ,  1 , and  2  of the 3-line memory  101  or the 3-line memory  102  in response to an access request from the encoder controller  400 . Likewise, when image data input from the second DMA channel  502  is written in the 3-line memory  101  in response to an access request from the encoder controller  400 , image data are read out from the 3-line memory  102  and output to the adaptive arithmetic encoder  300 . The adaptive arithmetic encoder  300  outputs an update due to line end to the encoder controller  400  via signals lines  508  and  509 . In this example, the 3-line memory  101  or the 3-line memory  102  is a 384 byte SRAM. Nevertheless, the 3-line memory  101  or the 3-line memory  102  of this invention is not limited to a 384 byte SRAM. However, the size of the 3-line memory  101  or the 3-line memory  102  could be adjustable based on the speed of the arithmetically encoding speed of the adaptive arithmetic encoder. Hence the size of the ping-pong buffer could be adjustable based on the speed of the arithmetically encoding speed of the adaptive arithmetic encoder so that the present invention could utilize different size of the ping-pong buffer  100  to satisfy real conditions. In addition, the third DMA channel  503  is adapted to sending out the compressed data. 
   What is more, pertaining to the compression process in the adaptive arithmetic encoder  300 , each line is started with a SLNTP value, representing the current line differing with the previous line, so that the current SLNTP value is associated with a fixed set of context so as to be send to the adaptive arithmetic encoder  300 . In case the data of the current line is identical with the previous line, the adaptive arithmetic encoder  300  would not perform the compression process. If the comparison result is differed, the data of the current line should be forwarded to the adaptive arithmetic encoder  300  to be compressed. 
   According to the JBIG three-line template, the current line, the previous line and the next line should be referenced. The conventional method utilized three-line buffer to store pixels for combing to form the context. However, in case of a high resolution image is applied, such three-line buffer would eaten up a huge fraction of the memory. According to the above description, furthermore, when the high-resolution image is processed, the present invention could not consume a large amount of memory to perform JBIG compression process because of the ping-pong arrangement. 
   Accordingly, the present invention utilizes the TP (typical prediction) unit to determine whether the current line should be forwarded to the adaptive arithmetic encoder or not, and the ping-pong arrangement to economize the use of memory. Therefore, the present invention could provide a low cost and high performance JBIG coding apparatus and method with ping-pong arrangement. 
   Referring to  FIG. 3 , the ping pong buffer  100  according to the preferred embodiment of the present invention is illustrated. The image context is processed by window template  105 , and processed by window shift mode. After such context is combined, the next patch of data will be processed. Therefore, the build-up context and the procedure of the arithmetic encoding process could be divided into two separate steps to speed up the processing speed. The window shift mode is applied to frame-by-frame outputting pixel value as well as corresponding context value, and then send such information into the adaptive arithmetic encoder. 
   Referring to  FIG. 4 , a sequential Window-based JBIG compression is illustrated, wherein a neighborhood, surrounding pixels, around a pixel PX for each pixel to be coded defines a context CX so as to make arithmetic operations for dividing several straight lines from the result of the template, and update a learning table. The context CX is used to establish probability table. The context CX could be 2-line template or 3-line template. In this example, a 3-line template is done to generate a template for the adaptive arithmetic coding operation. The template is a 3*1 byte window unit as shown in  FIG. 4 . 
   The context CX is shown as below.
 
CX={bit9, bit8, bit7, bit6, bit5, bit4, bit3, bit2, bit1, bit0}
 
   In this present invention, the pixel PX and the context CX are read out from the 3-line memory  101  or the 3-line memory  102  and output to the adaptive arithmetic encoder  300  via signal lines  506  and  507 . Every time image data are read out from the 3-line memory  101  or the 3-line memory  102 , the pixel PX and the context CX per time is sequentially shifted and output to the adaptive arithmetic encoder  300  by one bit. In other words, the pixel PX and the context CX from signal lines  506  and  507  at a rate of one pixel per time is output to the adaptive arithmetic encoder  300 . The adaptive arithmetic encoding operation is made using this template and data of the pixel to be encoded, thus outputting encoded data onto the third DMA channel  503 . 
   Referring to  FIG. 5 , a sequential JBIG decompression is illustrated, wherein the decoding arrangement comprises an adaptive arithmetic decoder  800 , a line buffer  701 , an auxiliary buffer  702 , a ping-pong buffer  600 , a set of register  703 , a set of decoder controller  900  and three set of DMA channel  901 ,  902 , and  903 , wherein data is send into the adaptive arithmetic decoder  800  via the third DMA channel  903  to obtain a SLNTP value. The SLNTP value is sent to the decoder controller  900  and then decoded to a LNTP value of the present line based on the SLNTP value and the LNTP value of the previous line. Afterwards, the LNTP value of the present line will be stored into the register  703  via the decoder controller  900 . If the LNTP value shows that the line is not needed to be decoded, a previous line data stored in the line buffer  701  will be outputted. If the LNTP value shows that the current line is to be decoded, the previous two line data will be send into the ping-pong buffer  600  through the second DMA channel  902 . Afterwards, the context CX are read out from the ping-pong buffer  600  and output to the adaptive arithmetic decoder  800  via signal lines  906  and  907 . A window shift mode is applied to frame-by-frame scanning each pixel-combining context within the decode controller  900 , to be send into the adaptive arithmetic decoder  800 . Every time image data are read out from the ping-pong buffer  600 , the context CX per time is sequentially shifted and output to the adaptive arithmetic decoder  800  by one bit. Each pixel value to be decoded is sent into the auxiliary buffer  702 . The data of the auxiliary buffer  702  update and store image data into corresponding address of the line buffer  701  in synchronism with clocks (not shown), such repetition would not ceased until all one line has been completed, meanwhile, data stored in the line buffer  701  will be rewritten into an image memory (not shown) through DMA (Direct Memory Access) via the first DMA channel  901 . 
   One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting. 
   It will thus be seen that the objects of the present invention have been fully and effectively accomplished. Its embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure form such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.