layering/gradient in divx rips

[fordprefect]

Hi all,

I'm new to the forums, and fairly new to DiVX encoding. I've noticed on some of my rips that I do using DiVX 3.11 and Nandub that often times, there's a layering/gradient effect that happens in dark scenes.

For example, when it's night time and you see a light bulb (or some source of light), there are distinct "layers" of light that form the surrounding glow/halo (as opposed to a subtle blending between the layers). This also happens sometimes with skin in dark scenes, where the flesh tones are almost quantized according to gradient. It doesn't look blocky, just really ugly and unnatural.

Is this a limitation of the codec, or is there something I'm not doing right in my encoding? Any insight would be a great help. Thanks!

[Cradle22]

Hi!

This is normal behaviour for any mpeg (be it mpeg2 or mpeg4) codec. It can only be avoided by giving the frame a higher bitrate.

But often I have observed this effect being stronger in the original DVD mpeg2 stream, than in the DivX-encoded mpeg4 stream...

And often you will only notice those artifacts on a computer screen, whereas on TV everything looks normal again (most often your distance to the TV is higher than to your monitor, and the overall visual quality of the TV is poorer, thus producing a more "natural" image than the monitor)...

Some high end DVD players use (very expensive) filters to supress those artifacts in dark scenes...

Bye,

Cradle22

[fordprefect]

Thanks for the response. I will try to encode at a higher bitrate, though it is probably already pushing it close to my 1- or 2- CD file size limit.

Sometimes, but not always, when I turn up the quality slider setting on the DivX settings in Windows Media Player, it gets rid of the problem, so I suspect half the problem might be the actual encoding, and half might be the quality of the decoding.

[Cradle22]

Yeah, it is the post-processing which eats up most of the cpu power while decoding DivX, so better post-processing settings = better picture = higher CPU usage.

Even on my Athlon 1800 XP, the CPU usage tends to be about 60% while DivX playback at highest post-processing settings, with a 704*XXX movie, and 128 kbit ABR mp3.

This is actually the same effect that highend DVD players produce with hadrware filters...

Tuning the brightness slider to the actual movie can help a lot, as well...

Bye,

Cradle

[clodomiro]

Are you sure you can get rid of this through higher bitrate? I'm encoding Road to Perdition and the max I get is 980mb, even maxed out I still have lots of blocks on dark scenes.

Any ideas?(I'm using Gknot and 3.11)

[esby]

Try to add a little random noise before encoding.
(using sangrip avs plugin blockbuster)

You could try to do:

Blockbuster
then
Deen with lower settings, ( maybe something like ("a2d",3,8,4) )
In order to clean most of the random noise,
while keeping some of them for a granulous non blocky display.

Of course the counterpart is that you must watch the result
using divx3.11 codec with max post processing.
(ffdshow is to exclude as far i tested for this kind of situation...
while divx5 might be ok if we forget the evil decoding bug)

The post processing will clean up the rest of the noise,
and will not show the blocking normally.

esby