Rd optimized progressive image coding using JPEG

• Main Author: In, Jaehan
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/7921

The JPEG standard allows four modes of operation. They are the hierarchical (HJPEG), progressive (PJPEG), sequential (SJPEG), and lossless modes1: The HJPEG and PJPEG modes inherently support progressive image coding. In HJPEG, an image is decomposed into subimages of different resolution, each of which is then coded using one of the other three modes of JPEG. Progressiveness within a resolution in HJPEG can be achieved when each subimage is coded using PJPEG. An image coded using PJPEG consists of scans, each of which contributes to a portion of the reconstructed image quality. While SJPEG yields essentially the same level of compression performance for most encoder implementations, the performance of PJPEG depends highly upon the designed encoder structure. This is due to the flexibility the standard leaves open in designing PJPEG encoders. In this thesis, an efficient progressive image, coding algorithm is developed that is compliant with the JPEG still image compression standard. The JPEG-compliant progressive image encoder is a HJPEG encoder that employs a rate-distortion optimized PJPEG encoding algorithm for each image resolution. Our encoder outperforms an op- timized SJPEG encoder in terms of compression efficiency, substantially at low and high bit rates. Moreover, unlike existing J P EG compliant encoders, our encoder can achieve precise rate control for each fixed resolution. Such good compression performance at low bit rates and precise rate control are two highly desired features currently sought for the emerging JPEG-2000 standard. 1 Lossless JPEG algorithms are rarely used since their performance levels are significantly lower than those of other lossless image compression algorithms, and are therefore not widely used.