luma correction

[iago]

Since this is my first message here, first of all, I would like to say hello to everybody in the forum, the invaluable contributions of whom have helped me a great deal to find my way along the process of ripping and encoding movies.

Also, especially, I'd like to thank Doom9 for his Nandub Guide and Koepi for his Nandub Options Explained document.

However, though I've been searching almost all the threads in the nandub forum for a long time, I've been able to reach only very limited explanations regarding the luma correction algo in nandub, which imho can be effectively used (?) to get rid of -or at least to make less visible- the ugly blocks in certain scenes.

Does the "uniformly bright areas" mentioned in Koepi's document (citing Demi9OD) refer to a lack of contrast and a lack of brightness difference both in "dark" and "bright" scenes, or does it refer to only "bright" scenes with lack of contrast?

I would be very glad to hear from those who can provide some more explanation about this algo and who have been experimenting with the luma correction values in nandub.

Thanks a lot in advance...

( btw, I always make double rips, one with "sbc" and one with "xvid", and I'm very pleased with the quality I get with xvid. However, I still love to encode movies with nandub sbc as well :) )
mosuner@e-kolay.net

[iago]

Hello again everybody,

Guess it's pointless to wait any more for comments about this algorithm. It seems that the issue I referred to is either regarded of no importance or considered as an effort in vain :). Who knows? Or perhaps I was referring to sth. that is already perfectly grasped by everybody except me (That's possible!) :).

Still, in my own experience, I see that the luminance correction is an algo based on the lack of brightness difference in scenes with little contrast (which are harder to compress) and helps add some more bits to such scenes that fall under the threshold of a certain value of contrast (called luma noise).

I haven't noticed much visible gain in quality in my tries actually, but I think setting the threshold a little bit higher than 10 (maybe 12) and increasing the gain value (to somewhere between 40-50) helps those scenes with little contrast (eg. some dark scenes) look a little bit better (with less visible ugly blocks).

Seems to be useful to apply together with an antishit setting of 16/1/0 or 20-21/1/0 (at least in my tries).

@ everybody and masters of nandub
Please correct me if I've got the whole concept wrong so that the comments I make here would not be misleading for people trying to encode movies in sbc :).

Thanks a lot.

Best regards.