Optimized run length coding for jpeg image compression used in space research program of IST

This work aims to present an optimized scheme for entropy encoding part of JPEG image compression by modifying the run length encoding method. In JPEG (Joint Photographic Experts Group) image compression algorithm run length coding performs the actual compression by removing the redundancy from transformed and quantized image data. Using the fact that the preceding processes of run length coding, in JPEG compression algorithm, produces a large number of zeros, the original run length coding uses an ordered pair (a,b), where `a´ is the length of consecutive zeros preceding the ASCII character `b´. It has been observed the occurrence of consecutive ASCII characters at the input introduce another redundancy to the encoded data, i.e. `a = 0´ before each consecutive ASCII character `b´. The proposed run length encoding scheme removes the unintended redundancy by using an ordered pair only when a zero occurs and using the same EOB (End of Block) parameter at the end of each block. The proposed encoding scheme does not alter the PSNR value for the algorithm. Using Matlab simulation, the proposed scheme has been tested on various images over a range of quantization (quality) factor and the results confirmed the effectiveness of the new run length encoding scheme in reducing the run length encoded data.