T. Richter. Applications of Digital Image Processing XXXIII, 7798, San Diego, CA, SPIE, SPIE, (September 2010)
In a recent work, the author proposed to study the performance of still image quality indices such as the SSIM by using it as objective function of a rate allocation algorithm. The outcome of that work was not only a multi-scale SSIM optimal JPEG 2000 implementation, but also a first-order approximation of the MS-SSIM that is surprisingly similar to more traditional contrast-sensitivity and visual masking based approaches. It will be seen in this work that the only difference between the latter works and the MS-SSIM index is the choice of the exponent of the masking term, and furthermore, that a slight modification of the SSIM definition that reproduces more traditional exponents is able to improve the correlation with subjective tests and also improves the performance of the SSIM optimized JPEG 2000 code. That is, understanding the duality of quality indices and rate allocation helps to improve both the visual performance and the performance of the index.