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jkwarras
29th November 2003, 14:22
Hi,

I always denoise my Dv footage, and all DV users know how DV is noisy. But noise isn't constant, in low lights shots noise is MUCH more visible. I use Mipsmooth, or Fluxsmooth or C3d with Cnr2, depending on the source. But the problem is that: what amount of denoising do you set? What i do is look at low lights and worst parts first, set the denosing filters and then go to best parts and adapt it until i have a compormise between denoise in worst parts and detail in best parts (i hope i'm clear :D). BUt you can get to a point where worst parts are well denoised and best parts are too washed. At the end, worst parts are not well denoised so best parts can look better.

Of course, we can set differents denoisers in differents parts of the movie, but since i've discovered the QMF script here
http://forum.doom9.org/showthread.php?s=&threadid=56051&highlight=QMF

i was thinking if there's a way to apply it for adaptative noise filter? So in parts with mor enoise you can denoise more and in parts with less noise you denoise less.

Maybe QMF as it is, can be use for that purpose, since noise can be in some ways considered as "motion" in the image. MOre noise, more motion. But i'm not sure. And this script is more focused in improving compresibility of MPEG-4 encodes so you "blur" more in high motion scenes qhere you don't see details and so use less bitrate. bu tin DV encoding the point is JUSt denoise to look better, bitrate is not the point because is constant.

I hope my statements makes some sens :rolleyes:

Regards

ronnylov
1st December 2003, 16:57
In the SSIM thread http://forum.doom9.org/showthread.php?s=&threadid=61128 there is a post by Sh0dan suggesting using SSIM to compare the original frame to a blurred version and use the difference as a threshold for a filter.

jkwarras
2nd December 2003, 13:48
Originally posted by ronnylov
In the SSIM thread http://forum.doom9.org/showthread.php?s=&threadid=61128 there is a post by Sh0dan suggesting using SSIM to compare the original frame to a blurred version and use the difference as a threshold for a filter.

Wow, this is really a good idea. Quite complicated to me, but i will try it. Changing filter in a frame-based SSIM quality basis seems just very right in order to get the best quality when removing noise in DV footage. Keeping in mind that i'm not trying to lower the bitrate (DV is CBR) just make it denoise more intelegly. QMF is good for DV (or DVD) to MPEG-4 encoding (really very good), but i don't really know what to think for DV to DV footage. I still think that this filter check motion in the image (and noise can then assume as a value) but also "real"motion, so if there's a car race, QMF will apply a strong denoise even if image look gorgeous without grain at all.