It seems that many people don't approve of PSNR as a measure of quality, because it has no HVS modelling of any sort. However, it would clearly be useful to have a metric for comparing quality, partly just because of the time savings involved. My question is this: does it make sense to use PSNR as an indication of quality when tweaking settings in x264 which are not HVS-based, namely reference frames, mixed references, RDO, and ME method?
--------------------- M.Wong E38 2000 740iL Orient Blue E91 2012 328xiT Alpine White Passed on to a new families: E30 1987 325i Royal Blue E39 2003 540i/6 Sterling Gray R56 2010 Mini Cooper S British Racing Green
b-frames were "invented" as a HVS method: lowering quality on certain frames coz the human eye cant spot the difference. so the answare is "no" unless you disable b-frames too. at least that is my POV.
Yes, PSNR is less applicable to comparing an encode with B-frames against an encode without B-frames. But that doesn't mean you can't use PSNR to compare variations in other options just because B-frames are present.
well, that's for sure, but PSNR as a measure of quality (as stated in the first post) is only relative to encodes without HVS tuning, while it's pretty usefull to compare quality of 2 or more encodes for tweaking settings (supposing those encodes are made with comparable HVS tunings).
or to put it another way, metrics such as PSNR and SSIM are more useful for development purposes rather than for telling people what they are actually going to like.
BTW, another myth should be forgotten : bframes don't necessary work by decreasing quality. BFrames by themself are more efficient than PFrames, even (and especially) when their quantizers are the same. Just set the pbratio to 1, and do a constant quantizer encode with and without adaptive bframes, you'll see.
ok, maybe the divx vs xvid thing should not be taken into consideration (too much fans from both sides...). However h.263 quantization gets highly PSNR metrics results than almost any custom matrix and the visual result is clearly in favour of the custom matrices... Also, talking about myths and b-frames, most codec default options are set to rise the quantizers of b-frames. Ok, they're more efficient but not enaugh to compensate for the higher quantizer usually applied. The question is: why those codecs use higher quantizers for b-frames? The answer is: coz it's a measure to rise compression/efficiency/perceived quality by reducing quality/frame size on some frames without having the human eye spotting the difference: HVS tuning.
Search
Users
Entrance
RE: When is PSNR applicable?
