Convergence of an iterative design algorithm for JPEG quantization tables

Discusses the convergence properties of an iterative design algorithm for JPEG quantization tables. The algorithm is useful for generating tables that control, to a specified amount, the proportion of quantization error produced (on average) by the JPEG encoder in each of the 64 DCT frequency bins. An initial table is iteratively improved in such a way that the achieved quantization error profile more closely approximates the desired profile, which might be based on a human vision model or various other criteria. The convergence of the design algorithm is relatively easy to ensure if the desired error profile is modified at each iteration to account for changes in the achieved error values. Adjustments to the quantization table entries may be made according to several different schemes. We propose a successive approximation method that is guaranteed to converge after no more than eight iterations, and also discuss some alternative strategies