poor dark scene quality... again...

[chrome]

hope noones thinking "oh, thiiiss question again", because ive done a search, and i haven't found any satisfactory answers to this question.

anyway, whenever i encode a movie with xvid, i notice that the quality in the dark scenes is poor in comparison to the brighter scenes, which look perfect. why is this? is there a way to take some of the quality away from the brighter scenes and use it for dark scenes? the quality in bright scenes in very sharp and clear, while in dark scenes, the image is "messy". someone said that xvid doesn't handle dark scenes very well - is that true?

i dont have this problem too badly when i encode 2 cd films, but as i said before, on single cd encodes, the bright scenes are perfect (so plz dont tell me to just encode for 2cds rather than 1!), and i wouldn't mind losing some quality on those if it'll help my dark scenes. any help, greatly appreciated. thanx.

[Teegedeck]

As you encode at a relatively high bitrate, I'd make sure whether the dark scenes do look good in the video-source. Seems like a cheapish piece of advice but for the last months, whenever I'd thought to have found an artifact that could be attributed to adaptive quantization, it became clear upon closer examination that the artifacts was present in the source already.

Part of the problem could also be that dark scenes or parts of the picture tend to contain more grain than brighter parts. So adding special filters in your AVS for those scenes could be an idea.

[Didée]

(From here (http://forum.doom9.org/showthread.php?s=&postid=440451#post440451))
Originally posted by sysKin
Okay imagine a scene. Think about watching the scene with two different brighness/contrast settings. Unless you set the brighness or contrast horribly high or horribly low, you notice the same amount of details - it's just a picture, the same edges and the same objects which move the same way.

For xvid however, the dark scene has less energy to code. It has less picture, because the dynamic range of the whole picture (the difference between darkest and brightest pixel) is smaller. As a result, the dark scene will have smaller bitrate and will look worse...

This is a HVS theory, which should be implemented as a HVS model. This is part of what I'm planning to do as soon as I'm allowed to - after 1.0 is out.