How do I get rid of blotchy effect?

[rakan]

Hi guys,

I have a quesiton about the x264 codec, I was using Gordian Knot to convert a VOB to an avi (compressed with the x264 codec) and I noticed that whenever the compressed video comes to a lighter color that dominates the background I get what I can best describe as a blotchy sections of discolored blocks, they are subtle but annoying. I get this effect with XviD also.




You can see them in this screenshot in the upper left corner (they are much more pronounced while the video is playing). You can barely see them but when the video is playing they move around (even though the camera is perfectly still) and look annoying. My resizeing filter is set on Lanczos (sharp). If I try a softer resize filter it slightly reduces it. Any other suggestions. I can also post a sample of the video clip in XviD or x264 if it will help someone diagnose my problem. Thanks

[guns1inger]

Try using a higher bitrate. This effect is a common issue with Xvid/Divx encoding as well. Even with a higher bitrate you may not be able to get rid of it. The encoder seems to allocate too low a bitrate to large areas that have a low tonal range - like plaster walls - and produces this effect. The sad thing is that if the wall had a big patterned rug on it you would not have this problem at all.

[rakan]

thx guns1inger

I tried to use a higher bitrate but got the same result. I was hoping there was some type of filter to get rid of it. Is there anyway particular setting in MPC that can filter this out during playback? Thanks again.

[guns1inger]

ffdshow filters might. I haven't played enough with MPC filters to be able to suggest anything off the top of my head. Unfortuantely, because this happens during encoding, there are no filters you can use to stop it happening in the first place.

[rakan]

I just noticed, when I use my LCD monitor at work the blotchy is significantly reduced.

At home on my CRT monitor at 1024X768 at 75hz this blotchyness in the above mentioned areas is apparent. The same video on my LCD monitor at 1280X1024 at 60hz (I think) significantly reduces the blotchyness. I don't think the resolution is the problem, could the lower refresh (75 hz ) be the source of this blothchyness?

[TBoneit]

if it were the monitor it would not show up in the screen capture you did.

It is nothing to do with the display except that CRT monitors vs LCDs
display things differently. There are some message threads here abut LCD vs CRTs.

The blotchness is due to the encoding. It can also become apparent in MPEG2 with to low a bitrate.

Even if you can filter it out in playback it will still be in the file. It is a highly compressed file. Live with it or switch to a less compressed format. IOWs leave it as a DVD.

What you are doing is taking a compressed format and recompressing it which will result in a loss of quality.

[jagabo]

Add noise while converting:

http://www.compression.ru/video/noise_generation/index_en.html