[MEncoder-users] Codec-independant objective quality measurement

[Reimar Döffinger]

Hello,
On Sat, Aug 05, 2006 at 03:09:19PM +0200, Nicolas George wrote:
> I am not sure what the best is. On one hand, the downsampling of chrominance
> is an artifact of the exchange format, and should be compensated. On the
> other hand, if the codecs allows themselves to downsample chrominance, that
> must mean that it is visually less important, and thus should be counted
> with a lower weight. Did you give any thought to that question?

chroma downsampling is not really an artefact, it is part of the
compression that is based on the fact that the human eye is really bad
at seeing precise colour structures. Based on experience with my own
eyes, weighting chroma with 1/4 is still too much ;-) - though that's
not entirely correct, a general bias in chroma is usually easy to spot,
but even a heavy loss of details is hardly visible, whereas with luma a
bias (i.e. everthing's a bit too bright) is hardly visible whereas loss
of details is. So using different ways to measure quality might be worth
thinking about...

Greetings,
Reimar Döffinger

P.S.: nothing of this is of course based on scientific research, just
telling my impression ;-)