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Old 2nd July 2019, 18:17   #1769  |  Link
benwaggoner
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Join Date: Jan 2006
Location: Portland, OR
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Quote:
Originally Posted by dapperdan View Post
My theory is that the people hired for the subjective tests that underly the objective stats or that vote VP9 as very slightly better than x265 in the MSU tests on subjectify.us have a different notion of quality than the kind of person who is interested in codecs for their own sake.
These are double-blind tests; the people doing it just compare two encodes.

That said, I've not seen any study demonstrating better subjective quality from a well-tuned libpvx encode versus a well-tuned x265 encode, using the same bitrate @ time.

Quote:
Like, I read a paper recently where someone was applying their grain synthesis approach to HEVC and the subjective tests they did to prove it worked showed they could get basically all the subjective benefit by just doing the noise removal step and not bothering to add the grain back in, something that could be done by any encoder, for any codec (and I'm guessing this makes up part of the secret sauce of some encoders).
This opens up the interesting question of no-reference quality versus creative intent. Someone just looking at a clip without grain might think it looks great. But if the creators meant there to be grain, than the output isn't accurate. That's something that some studies might not rate. And if customers dislike grain, they might rate the encoded version higher than the source!

Quote:
But I guess someone who said they could get a massive increase in subjective quality via the Psy optimisation of basically blurring the input would get some pushback on that view in some quarters, even with subjective tests to back it up.
Well, that is what adaptive quantization is all about, really. Put the artifacts where they are less painful, and used the saved bits where they'll provide the most visible improvements.

There are similar debates about TV's default "vivid" mode. Some people claim to like it, even though what's displayed in manifestly wrong on many axes.
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