Abstract:
Provided are a graphic image data compressor that provides a complete image instead of an erroneous image when graphic image data fails to be compressed to satisfy its bandwidth and a method of compressing graphic image data using the same, where the graphic image data compressor includes a compression block for compressing received graphic image data using a loss compression algorithm and a lossless compression algorithm and controlling an amount of loss data in the loss and lossless compression algorithms, and a compressed data determination block for comparing a compression rate of data compressed according to the loss and lossless compression algorithms with an established compression rate, selecting optimum compressed data, and determining to output the selected compressed data or the graphic image data.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims foreign priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2005-0004488, filed on Jan. 18, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present disclosure relates to graphic image data compression, and more particularly, to graphic image data compressors using an effective loss compression algorithm in a system with a restricted bandwidth, and a method of compressing graphic image data. 
   2. Description of the Related Art 
   Digital broadcasting is distinguished from analog broadcasting in that relatively numerous types of services can be provided to users. Users expect the digital broadcasting to provide pictures with good quality. Since a receiver performs a variety of functions including a display of graphic image data, the graphic image data have restricted bandwidths. 
   Digital broadcasting data may be stored in a memory included in the receiver and transmitted to necessary function blocks by a controller using ground waves. Graphic image data included in the ground waves are stored in the memory and transmitted by the controller to a display device, such as a monitor. Among various service function blocks of the receiver, function blocks used to process graphic image data relevant to the present disclosure will now be described. 
     FIG. 1  is a block diagram illustrating a digital receiver for processing graphic image data. Referring to  FIG. 1 , the digital receiver  100  includes a CPU  110 , a graphic processor  120 , a memory  130 , a display processor  140 , and a monitor  150 . Graphic image data are transmitted to the function blocks of the digital receiver  100  through a bus embedded therein. 
   The graphic processor  120  transmits graphic image data to the memory  130  through the bus under the control of the CPU  110 . The display processor  140  transmits the graphic image data stored in the memory  130  to the monitor  150  through the bus. The monitor  150  displays the graphic image data. 
   Each data of various services performed by the digital receiver has a restricted bandwidth. Graphic image data also have restricted bandwidths. Since more graphic image data are processed than service data, graphic image data are compressed and stored in the memory. 
     FIG. 2  is a block diagram illustrating a conventional digital receiver for compressing and storing graphic image data. Referring to  FIG. 2 , the digital receiver  200  includes a CPU  210 , a graphic processor  220 , a compressor  230 , a memory  240 , a de-compressor  250 , a display processor  260 , and a monitor  270 . Since the digital receiver  200  additionally includes the compressor  230  and the de-compressor  250  as compared with the digital receiver  100  shown in  FIG. 1 , the compressor  230  and the de-compressor  250  will now be described. 
   The compressor  230  compresses graphic image data received from the graphic processor  220  to a smaller data stream using a predetermined algorithm and stores the compressed data in the memory  240  through a bus. The de-compressor  250  decompresses the compressed data read from the memory  240  and transmits the decompressed data to the monitor  270  to display the data. 
   A process of compressing and decompressing graphic image data may cause a loss of compressed data. To avoid such loss, lossless compression methods such as Run Length Encoding (RLE) and Differential Pulse Code Modulation (DPCM) are widely used. Here, a loss compression method can be used for a system capable of dealing with the data loss in order to equally process other data. 
   Graphic image data typically have different compression rates according to the kinds of graphic images. A graphic image with little change can have a very high compression rate, while a compressed graphic image with many changes may be larger than an uncompressed graphic image. 
   A data bandwidth between the memory  240  and the display processor  260  becomes much narrower due to a data bit width of the memory  240  and an operation frequency of the digital receiver providing various kinds of services. In this case, graphic image data must be compressed with a high compression rate to satisfy its bandwidth. If compression fails, conventional image pixel data may be repeatedly displayed or a current image may be skipped. 
   SUMMARY OF THE INVENTION 
   The present disclosure provides a graphic image data compressor providing a complete image instead of an erroneous image when graphic image data fails to be compressed according to its bandwidth. 
   The present disclosure also provides a method of compressing graphic image data that provides a complete image instead of an erroneous image when graphic image data fails to be compressed according to its bandwidth. 
   According to an aspect of the present disclosure, there is provided a graphic image data compressor, including a compression block compressing received graphic image data using a loss compression algorithm and a lossless compression algorithm and controlling an amount of loss data in the loss and lossless compression algorithms, and a compressed data determination block comparing a compression rate of data compressed according to the loss and lossless compression algorithms with an established compression rate, selecting optimum compressed data, and determining to output the selected compressed data or the graphic image data. 
   According to another aspect of the present disclosure, there is provided a graphic image data compressor including a compression block compressing received graphic image data using a loss compression algorithm and a lossless compression algorithm in response to a control signal and controlling an amount of loss data in the loss and lossless compression algorithms, and a compressed data determination block comparing a compression rate of data compressed according to the loss and lossless compression algorithms with an established compression rate, selecting optimum compressed data, determining to output the selected compressed data or the graphic image data, and outputting the control signal for instructing which algorithm is used to compress the graphic image data by the compression block and a loss rate of a loss compression algorithm. 
   According to yet another aspect of the present disclosure, there is provided a method of compressing graphic image data, including compressing received graphic image data using a loss compression algorithm and/or a lossless compression algorithm, and selecting optimum compressed data by comparing a compression rate of the compressed data with an established compression rate wherein an amount of loss data in the loss compression algorithm and/or the lossless compression algorithm is adjusted. 
   According to still another aspect of the present disclosure, there is provided a method of compressing graphic image data, including RLE compressing received graphic image data using an RLE compression algorithm, first comparing a compression rate of the compressed data with an established compression rate and, when the compression rate of the compressed data is higher than the established compression rate, outputting the compressed data, comparing the compression rate of the compressed data as a result of the first comparing operation with the established compression rate and, when the compression rate of the compressed data is lower than the established compression rate, RLEL compressing the compressed data using an RLEL compression algorithm, second comparing a compression rate of the data compressed using the RLEL compression algorithm with the established compression rate and, when the compression rate of the compressed data is higher than the established compression rate, outputting the compressed data, and comparing the compression rate of the data compressed using the RLEL compression algorithm with the established compression rate as a result of the second comparing operation and, when the compression rate of the compressed data is lower than the established compression rate, compressing and outputting the compressed data using a TRUNC compression algorithm, wherein an amount of loss data in the RLEL compression algorithm and the TRUNC compression algorithm is adjusted. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present disclosure will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which: 
       FIG. 1  is a block diagram illustrating a digital receiver for processing graphic image data; 
       FIG. 2  is a block diagram illustrating a conventional digital receiver for compressing and storing graphic image data; 
       FIG. 3  illustrates graphic image data used to explain basic principles of a graphic image data compressor according to an embodiment of the present disclosure; 
       FIG. 4  is a block diagram illustrating a graphic image data compressor according to an embodiment of the present disclosure; 
       FIG. 5  illustrates an amount of loss data determined by the mode selection signal M/S of  FIG. 4 ; 
       FIG. 6  is a flowchart illustrating a method of compressing graphic image data according to an embodiment of the present disclosure; and 
       FIG. 7  is a flowchart illustrating a method of compressing graphic image data according to another embodiment of the present disclosure. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The present disclosure will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the disclosure are shown. Like reference numerals in the drawings may be used to denote like elements. 
     FIG. 3  illustrates graphic image data, indicated generally by the reference numeral  300 , used to illustrate basic principles of a graphic image data compressor according to an embodiment of the present disclosure. Referring to  FIG. 3 , when graphic image data having eight blocks  128 ,  129 ,  128 ,  129 ,  130 ,  131 ,  130 , and  131 , respectively, are input, a Run Length Encoding (RLE) compression algorithm needs eight Runs and eight Lengths, while a Run Length Encoding Lossy (RLEL) compression algorithm needs one Run and one Length. 
   The RLE compression algorithm replaces sequences of the same data (Run) by a count number (Length). Since a first block has data  128  and an adjacent block has data  129 , two blocks are determined to have different data, and Run  128  is replaced by one Length. As such, when the same data are repeating by comparing data of adjacent blocks, the count number (Length) of the repetitive data blocks is encoded. 
   The RLEL compression algorithm compresses graphic image data regardless of a Least Significant Bit (LSB) of the graphic image data. Regardless of a differential value of 1 between a reference first block value  128  and an adjacent block value  129 , the adjacent block value  129  is recognized to be substantially equal to the reference first block value  128 . Regardless of a differential value of 1 between a reference fifth block value  130  and an adjacent block value  131 , the adjacent block value  131  is recognized to be substantially equal to the reference fifth block value  130 . Four block values  128  are determined to be repeating and four block values  130  are determined to be repeating to encode data. In this case, if data is compressed regardless of a differential value of 1 between blocks, an image quality of the compressed data deteriorates by the differential value of 1. If a differential value is more than 2, the image quality of the compressed data may be considered to deteriorate considerably. 
   While a low compression rate causes conventional image pixel data to be repeatedly displayed or a current image to be skipped, it is more effective to display a repetitive picture even though an image quality of the picture deteriorates. 
     FIG. 4  is a block diagram illustrating a graphic image data compressor, indicated generally by the reference numeral  400 , according to an embodiment of the present disclosure. Referring to  FIG. 4 , the graphic image data compressor includes a buffer  410 , a compression block  420 , a compressed data determination block  430 , and a memory controller  440 . 
   The buffer  410  receives and stores graphic image data. The compression block  420 , which includes an RLE block  421 , a TRUNC block  422 , an RLEL block  423 , and a mode selector  424 , compresses the received graphic image data using a loss compression algorithm and a lossless compression algorithm and controls an amount of loss data in the loss and lossless compression algorithms. 
   The RLE block  421  performs the lossless compression algorithm for the graphic image data (GID) stored in the buffer  410  and outputs compressed data CD1. The TRUNC block  422  performs the loss compression algorithm for the GID stored in the buffer  410  in response to a mode selection signal M/S and outputs compressed data CD2. 
   The RLEL block  423  performs the loss compression algorithm for the GID stored in the buffer  410  in response to the mode selection signal M/S and outputs compressed data CD3. The loss compression algorithm performed by the RLEL block  423  compresses graphic image data by truncating the LSB of the graphic image data. The mode selector  424  outputs the mode selection signal M/S for determining an amount of loss data in the lossless and loss compression algorithms, which will be described with reference to  FIG. 5 . 
   The compressed data determination block  430  compares compression rates of the CD1 to CD3 output by the compression block  420  with an established compression rate, selects optimum compressed data, and outputs the selected compressed data SCD or GID. Uncompressed GID are stored in a memory in order to use the present embodiment when a system does not require to compress the GID due to a quite wide bandwidth. 
   The compressed data determination block  430  includes a comparator/selector  431  and a multiplexer  432 . The comparator/selector  431  compares compression rates of the CD1 to CD3 output by the compression block  420  with an established compression rate, selects optimum compressed data, and outputs a selection signal CON 1  for instructing to output the SCD or the GID. 
   The comparator/selector  431  enables to generate a control signal CON 2  for controlling blocks including the compression block  420  and determining operations of necessary blocks. To be more specific, after the comparator/selector  431  compares compression rates of the CD1 to CD3obtained by first operating the RLE block  421  and the RLEL block  423  and, the comparison result does not satisfy a desired condition, it compares a compression rate of the CD2 obtained by operating the TRUNC block  422 . Such a process reduces power consumption since multiple blocks including the compression block  420  do not simultaneously perform operations. The multiplexer  432  outputs the SCD or the GID in response to the selection signal CON  1 . The memory controller  440  stores the data received through the multiplexer  432  in a memory (not shown). 
     FIG. 5  illustrates an amount of loss data determined by the mode selection signal M/S and indicated generally by the reference numeral  500 . Referring to  FIG. 5 , each amount of loss data representing three colors of Red (R), Green (G), and Blue (B) is adjusted. Such an adjustment can be made by a receiver manufacturer based on user&#39;s requirements and conditions, or by a user. N R , N G , and N B  denote actual data lengths, and n R , n G , and n B  denote discarded or deleted data lengths. 
   A mode signal  0  designates data coding without loss and a mode signal  1  designates data coding with a loss of one bit. A mode signal  3  designates data coding with losses of one bit in the R data, one bit in the G data, and two bits in the B data in that such a designation differs according to a data color. A mode signal N is considered to have a loss by each bit R N , G N , and B N . 
     FIG. 6  is a flowchart illustrating a method of compressing graphic image data according to an embodiment of the present disclosure and indicated generally by the reference numeral  600 . Referring to  FIG. 6 , graphic image data is compressed (Operation  610 ) and the compressed data is selected (Operation  620 ). 
   In Operation  610 , received graphic image data is RLE compressed (Operation  611 ) using a lossless compression algorithm, TRUNC compressed (Operation  612 ), and RLEL compressed (Operation  613 ) using a loss compression algorithm. In Operation  612 , received graphic image data are compressed by truncating the LSB of the graphic image data. In Operation  613 , received graphic image data are compressed regardless of an LSB of the graphic image data. An amount of loss data in the loss and lossless compression algorithms can be adjusted, which is described with reference to  FIG. 5 . In Operation  620 , a compression rate of the data compressed in Operation  610  is compared with an established compression rate and optimum compressed data are selected. 
     FIG. 7  is a flowchart illustrating a method of compressing graphic image data according to another embodiment of the present disclosure and indicated generally by the reference numeral  700 . Referring to  FIG. 7 , graphic image data is RLE compressed (Operation  710 ), first compared (Operation  711 ), RLEL compressed (Operation  720 ), second compared (Operation  721 ), and TRUNC compressed (Operation  730 ). 
   In Operation  710 , received graphic image data are RLE compressed using an RLE compression algorithm. In Operation  711 , a compression rate of the data compressed in Operation  710  is compared with an established compression rate and, when the compression rate of the compressed data is higher than the established compression rate, the compressed data  740  are output. 
   In Operation  720 , the compression rate of the compressed data according to a result of Operation  711  is compared with the established compression rate and, when the compression rate of the compressed data is lower than the established compression rate, the graphic image data are compressed using an RLEL compression algorithm. In Operation  721 , when a compression rate of the data compressed in Operation  720  is higher than the established compression rate, the compressed data  740  are output. 
   In Operation  730 , when a compression rate of the data compressed in Operation  720  is lower than the established compression rate according to the result of Operation  721 , the graphic image data are compressed using a TRUNC compression algorithm. An amount of loss data in the RLEL and TRUNC compression algorithms can be adjusted, which is described with reference to  FIG. 5 . 
   The RLEL compression algorithm compresses graphic image data regardless of an LSB of the graphic image data, and the TRUNC compression algorithms compresses graphic image data by truncating the LSB of the graphic image data. The graphic image data compressor and the method of compressing graphic image data can be applied to a system with a variable compression rate and a narrow data bandwidth, and select a simple and effective compression rate. 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the pertinent art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the following claims.