Quote:
Originally posted by Acaila
And since using too high values cause ringing as mentioned before, I believe the standard matrices are already quite well made. The only reason I could see anyone using a custom QM is for increasing the amount of detail/size of a video (since for higher compression you could just as well use a higher quant, no need for a custom matrix).[/B]
|
Well, let me bore you with my points in using custom matrices.
The standard matrix is well designed as an all-purpose-matrix. It delivers reasonable results with all quality ranges. But obviously, it is not at all optimized for either hi-quality or hi-compression scenarios. For both, a good custom one will fit better.
On the hi-quality side, we already had the discussion "better quality at max quality" (
here). Quant-2 doesn't deliver super-high quality, and quant-1 ... you know.
Moreover, I think that the bigger coeffs for the high frequencies are mostly there to deal with
noise, not with image detail. (Well, intended or not, it IS like that.) But if you have a well-denoised picture, then your interest in keeping high frequencies will raise quickly, proportional to the ratio of win/loss forced by keeping them. Hah, what a sentence
Furthermore, there is an additional benefit for 2-pass scenarios:
The codec can scale the bitrate much smoother.
Usually, for really good quality, we're still aiming for an average quantizer of '3' or better - at least for P-frames. Right?
Now, with the standard matrix we have that "big jump" in filesize, or bitrate, between quant-2 and quant-3. Therefore, when the codec is working with only q2 and q3, the bitrate is not distributed smoothly: one expensive q2 equals to many cheap q3's, and the quality improvement from those seldom q2's is hard to notice. There should be something between q2 and q3 ...
ATM, I use the following matrix almost all the time. Scales well with all high-bitrate to better-medium-bitrate scenarios - but only for well-denoised material. I always use PixieDust(2|3), seldom with a little caliming-down the noise beforehand by light Convolution3D or Fluxsmooth. Undot() of course.
Since attaching seems down again, I'll do a little more typing. Perhaps you will, too.
Code:
# "SixOfNine"
08 10 11 12 12 13 14 15 10 10 11 12 12 13 14 15
10 11 12 13 13 15 15 16 10 11 12 13 14 14 15 16
11 12 12 14 15 15 16 17 11 12 12 14 14 15 16 17
12 13 14 15 15 16 17 18 12 13 14 14 15 16 17 18
12 13 15 15 16 17 18 19 12 14 14 15 16 17 18 19
13 15 15 16 17 18 19 19 13 14 15 16 17 18 19 20
14 15 16 17 18 19 19 20 14 15 16 17 18 19 20 20
15 16 17 18 19 19 20 20 15 16 17 18 19 20 20 20
- This' matrix quantizer range q2-q8 eaquals about the standard matrix range 'q1.4'-'q4.5'
- q3 is a tad better as q2(standard)
- q4 is between q2 and q3 (std)
- q5 is a little weaker as q3 (std)
- ...
For the same bitrate range, the codec simply has more quantizers available for scaling.
Regards
Didée