Spatial Constant Quantization in JPEG XR is Nearly Optimal

Data Compression Conference (DCC), 2010, page 79-88. Snowbird, UT, IEEE, (March 2010)
DOI: 10.1109/DCC.2010.14


The JPEG XR image compression standard, originally developed under the name HD-Photo by Microsoft, offers the feature of spatial variably quantization; its codestream syntax allows to select one out of a limited set of possible quantizers per macro block and per frequency band. In this paper, an algorithm is presented that finds the rate-distortion optimal set of quantizers, and the optimal quantizer choice for each macro block. Even though it seems plausible that this feature may provide a huge improvement for images whose statistics is non-stationary, e.g. compound images, it is demonstrated that the PSNR improvement is not larger than 0.3dB for a two-step heuristics of feasible complexity, but improvements of up to 0.8dB for compound images are possible by a much more complex optimization strategy.



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