Research On Real-time Image Encoding Chip Based On Vector Quantization Technology

Because of the immense values of image compression, relevant research has always been the hot topic of image field. But the prevalent image coding standard is limited out of some place requisite of real time and low cost, due to its high patent fee and high system configuration.As an effective technology for data compression, vector quantization (VQ) is widely used in the field of image coding because of its simple algorithm and high compression rate.According to analyzing the basic technique of VQ, three improved algorithms are presented and simulated in this paper, which are partition dynamically VQ, EBNNS and category codebook based on direction. Integrating the merits of these three algorithms, the PDVQ encoding system is established, and it can improve the compression rate and coding speed in contrast with the common VQ. While implementing the PDVQ encoding system using VLSI technology, the circuit design techniques such as time-sharing, distribution-computing and pipe-line, were used to increase the process speed. According to mainstream ASIC design flow, the PDVQ chip was designed and fabricated with 0.35μm CMOS process.The chip area is 2.08mm×2.08mm, it can operate up to 100MHz at 3.3V power supply, and its power dissipation is 343mW at this operation. To encode medium complexity standard test gray image'Airplane' of 512x512 piexls using PDVQ chip, its compression ratio can achieve 21.51, and PSNR of its reconstructive image is 26.95. Under 100MHz work frequency, it is less than 20ms to encoding this image using PDVQ chip, this processing speed can prove that the PDVQ chip can compress about 50 frame such image within 1 second.Aim at improving performance of the PDVQ chip, three novel algorithms are presented in this paper, which are 2R codebook compression algorithm, Mean-value and VQ category algorithm, and Left-correlation coding algorithm. And a novel Left-correlation and category VQ (LCCVQ) image coding system is combined with these three algorithms and EBNNS algorithm. This novel system has better image quality than PDVQ encoding system, while its codebook size is only a half of the PDVQ system.The VLSI architecture of the LCCVQ encoding system was designed with the FPGA chip of Altera FPGA cycloneⅡEP2C35F672C6, and the experimental results show that the LCCVQ encoding system implemented by this FPGA chip can operate up to 100MHz. Under this work frequency, only about 8.27ms is needed to encode a same standard test gray image'Airplane'of 512×512 pixels with medium complexity using the LCCVQ encoding system, this encoding time is about 11ms faster than that of PDVQ encoding system, so that it is enough to transmission such image in real time at this speed, and using LCCVQ system to encode this image,its compression ratio is 18.15, PSNR of its reconstructive image is 28.15. Therefore, both of the PDVQ encoding system and LCCVQ encoding system implemented using VLSI technology can meet the requirement of image transmission in real time.