Cause of mosquito noise

[ChannelK]

Just wondering if anyone can shed some light on the the primary causes of mosquito noise when veiwing a divx at full screen. Is it a result of enlarging a smaller eg. 5xx * xxx or 6xx * xxx res. divx to 1024 * 768 for full screen on the crt with the divx having only around 50% compressibily before encoding and a low bitrate, or does it have more to do with the resizing filter used based on the compressibility before encoding.

(Hope this makes sense:rolleyes: )

[manono]

Hi-

Sometimes it's already on the DVD, and sometimes it's created by the MPEG4 compression, particularly when encoding at relatively low bit rates (such as the 50% compressibility you mentioned). Or both. Since a sharper resizer decreases compressibility, you'll get more with a sharper resizer. My impression is that downsizing also seems to magnify it somewhat, but that's based mostly on studying the results. I've never seen anything to back up my belief. Maybe others have an opinion, because I've spent a lot of time trying to get rid of the stuff. I've pretty much given up, as any method I use makes the video too soft for my tastes and doesn't do too good a job anyway.

If you want to read a pretty technical paper on it, then Check This Out (http://www.itl.nist.gov/div895/docs/MosquitoNoise2000.pdf).

[DJ Bobo]

I confirm, it's due to lower bitrates (= higher quantizers). Resolution plays only a secondary negligeable role.
But I want to point out, that divx5 makes more mosquito noise than divx3 by the same bitrate. So if you dislike mosquito noise, you better switch to divx3 sbc encoding, which is of course more complicated :D
Notice that on the other hand, divx3 tends to be more blocky than divx5 by the same bitrate.

[Tommy Carrot]

The qpel option can amplify the noise badly. Disabling it (if it was enabled) may solve your problem, at the cost of some details.

[ChannelK]

@All, Thanks.

From my encodes I had sort of figured it was due to lower bitrates but not entirely sure. Dont use Qpel (isnt that for downsizing to 1/4 of the original res.) and as I watch all my films on my 17" CRT from usually 2m away or so the mosiquito noise doesnt bother me. so I only try to eliminate it for 'archive' qaulity backups (eg. LoTRE) using higher bitrates over 2 cds and c3d etc. Just wondered what other people thought about it.:D

[theReal]

Mosquito noise has something to do with very sharp edges as well. If you're leaving one or two black lines at the top or bottom of a video, you'll have mosquito noise all over these mpeg4 blocks.
I don't know the technical reason, but avoiding sharp edges helps reducing mosquito noise. I also found that using convolution3d reduces mosquito noise in Divx5 movies (and you can still keep a good amount of sharpness with c3d)

[theReal]

*double post, sorry*

[TheXung]

Try setting your monitor to 640x480 and playing it. Some of the noise should be less noticeable.