Is it ok "AQ" for a dark movie?

[Episodio1]

Hi! For full-res DVD XviD@1000-1500Kbps:

Is it ok to encode a dark movie with "AQ"?

Is it ok to encode all movies with "AQ"?

Is AQ the same as "lumi_mask" ?


Thanks in advance.

[Kopernikus]

AQ = adaptive quantisation. That means that individual macroblocks in one frame can get different quantization.

Lumimasking is a property of HVS to notice stimuli dependant of the background luminance.

In XviD a sort of Lumimasking is implemented which uses AQ. But this will change soon.

I would not recommend to AQ in XviD for a dark movie, because sometimes visible quality degredations are possible.

[Didée]

It should be okay, but I'm not sure if it actually *is*. From my last point of knowledge, XviD's way of controlling AQ is (shortly):

- use AQ only for some outmost few percent of a frame's actual luminance range (so i.e. for a very dark frame covering only Y= [16,32], not very much should be left over where AQ could kick in)

- don't use AQ for small quants (i.e. only use AQ for quants >= 5 ... so AQ were rather unlikely to kick in for very dark frames, since these tend to get smaller quantizers anyways.


However it [i]could be that AQ is not working correctly in the latest beta2 builds of XviD. I smell something from here (http://forum.doom9.org/showthread.php?p=742455#post742455).


@ Kopernikus: you remember I said >> *that* impossibly can be the way it's actually handled" << ? :D
AQ within XviD was laid out to be rather failsafe, i.e. better do too less than too much ... which does not comply at all with those relations you dug from the source ...

[JarrettH]

Have a look at what you're going to encode before you do it and base it on that. If it's nice quality then you can use AQ, and at your high bitrate, it should have little effect on darker areas. If you have a noisey source like Aliens, disabling AQ might degrade the not-so-black dark areas making them even more visible.