[x264-devel] Re: [PATCH] PSNR averages

[Måns Rullgård]

Loren Merritt <lorenm at u.washington.edu> writes:

> On Sun, 8 Aug 2004, Laurent Aimar wrote:
>
>> On Sat, Aug 07, 2004, Loren Merritt wrote:
>> > x264 takes the arithmetic mean of frame-wise PSNRs to produce an
>> > overall PSNR. This is meaningless. (Extreme case: what do you do with a
>> > frame with no error? (infinite PSNR))
>> > This patch corrects it to calculate PSNR from the mean squared error.
>> >
>> > I also replace "PSNR/Size" (which is similarly meaningless) with
>> > "MSE*Size". This quantity is probably closer to what someone wants to
>> > measure when they think of "PSNR/Size". It also tends to be relatively
>> > constant for a given video over a wide range of QPs.)
>>  You are right mean PSNR is a bit meaningless, thanks for your patch :))
>>
>>  Now x264 will compute mean PSNR (as before, used by the JM), average
>> and global PSNR.
>>
>>  Average/global are computed over the whole picture (ie YUV), I hope
>> it's ok, if not I will change it to do it over each plane too.
>
> I still think that mean psnr is misleading and useless (it's greatly
> skewed by a few pure black frames with psnr=100), but I'm willing to
> ignore it and just look at global psnr.
> Yes, a sum over all 3 planes at once is ok.

BTW, why is it that the PSNR for the U and V planes is considerably
higher than the Y plane?

-- 
Måns Rullgård
mru at mru.ath.cx

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