Right, I probably came across not quite as intended; sorry about that. I didn't mean to say the study is hosed (which I can't say because I didn't read it!), t

Right, I probably came across not quite as intended; sorry about that. I didn't mean to say the study is hosed (which I can't say because I didn't read it!), the remark about objective metrics was a more general one. Yes, SSIM is one of the better metrics available, and obviously it's useful for certain things. However it still doesn't accurately represent preceived quality; time and time again certain psy optimizations for instance are shown to reduce SSIM while perceived quality goes up. Conversely, a codec can optimize for SSIM alone and score well on a test that ranks by SSIM; but the perceived quality could be better. For this reason e.g. x264 has an option to disable psy optimizations that hurt the objective metrics. There are other things that can hurt metrics a lot while doing nothing perceptible, though these are rather like bugs or errors in testing methodology, and as such would likely be noticed in a well conducted study. See also: https://wiki.xiph.org/Notes_on_testing_theora#General_points_on_.22objective.22_measures_like_PSNR_and_SSIM https://wiki.xiph.org/Notes_on_testing_theora#General_points...