[MEncoder-users] New quality problem with low contrast images

[Michael Niedermayer]

Hi

On Sat, Sep 30, 2006 at 07:44:41PM +0200, Pepe wrote:
> Hi.
> 
> I'm having again a problem to get a quality image. I recorded a movie with my 
> dvd-recorder from a satellite channel. 
> 
> Now I'm trying to pass to divx. I'm having problems with some scenes. Scenes 
> well illuminated (outside, with sun) look very good. But the movie has a lot 
> of scenes with very low light. They are dark but not very dark, maybe they 
> have low contrast.
> 
> The problem is that those scenes look very bad in my xvid, a lot of blocks, 
> very annoying. In the original video, image looks much better. 
> 
> This is the command I used:
> 
> mencoder -noodml -o temp/video2.avi \
>   -oac mp3lame -lameopts vol=0:mode=3:cbr:br=64 \
>   -ovc xvid \
>   -xvidencopts 
> bitrate=1200:nointerlacing:nopacked:pass=2:max_iquant=15:max_pquant=15:max_bquant=15:max_bframes=0 
> \
>   -vf-add crop=688:560:20:8 \
>   -vf-add pp=l5 \
>   -vf-add scale=576:432 -zoom \
>   -vf-add harddup \
>   -force-avi-aspect 4:3 \
>   -sws 9   \
>   temp/video.avi
> 
> I tried everything. I used max_iquant=4:max_pquant=4. I tried different values 
> for -sws, also tried yadif instead of l5. I raised the bitrate up to 4000. I 
> used b-frames. I used libavcodec instead of xvid. But nothing improved the 
> quality, it always remained the same. Removing the filters (crop, 
> deinterlace, scale) may improve a little bit, but there's still very visible 
> blocks. And anyway I don't want to make a video with such a high resolution 
> (720x576) because I would need a bigger bitrate.
> 
> I also tried quant_type=mpeg. With that option the image is very different, 
> the blocks are smaller but there are even more, all over the whole image 
> and are even more annoying.
> 
> If I use hqdn3d after the other filters, yes it removes most of the blocks, 
> but image loses a lot of details.
> 
> Any idea of how to improve the image?

with libavcodec vqmin=1 lmin=1 and a sufficiently high bitrate should make
all blocks dissapear
alternatively cmp=10 subcmp=10 mbcmp=10 might also help (try various values 
for nssew)

and of course dont forget v4mv mbd=2 trell ...

and using -vf spp or -vf noise when viewing the final video will also 
remove all blocks pretty effectively or change the gamma of your 
monitor/grafix card
(and dont use a TFT based one if you can, TFTs suck for displaying 
dark colors correctly)

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In the past you could go to a library and read, borrow or copy any book
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