Hi - On Sat, 19 Mar 2005, Dik Takken wrote:
> Two questions about making video streams better suited for encoding with > mpeg2enc: You've come to the right place :) > Question 1: > > negative impact on image detail (Does it?). Is it always a Good Thing to > use yuvdenoise as some sort of numerical conditioner before feeding the > stream to mpeg2enc, no matter the image cleanness? Are there For conditioning like that I use either 'y4mspatialfilter' (with relatively high thresholds) or 'yuvmedianfilter' (in its 'fast' mode with a high weight on the center pixel). > any cases where using 'yuvdenoise -f' is not advisable? Which is 'now'. The new yuvdenoise that was checked in yesterday (Stefan rewrote it completely) does not have '-f'. As a last step before the encoder perhaps 'y4mdenoise -t 1' would be a good choice. > Question 2: > > Is there any way to denoise the chroma channel, and have the denoise > strength depend on the luma channel? It seems that humans are unsensitive Not at the moment. What can be done is run 'yuvmedianfilter' on the chroma channels only. Use 'yuvmedianfilter -t 0' to disable luma processing. > to subtle chroma changes when the luma is very low (maybe also when it > is very high?), so you could perform more aggressive filtering in those > area's, saving bits for encoding. Which is very close (or identical) to the comment I made the other day about "desaturating the lows". In dark(er) areas removing some of the color info does a lot to improve the encoded image. I've found that desaturating the color info about 50% below 16 IRE (which roughly corresponds to a Y' of 32 if I've interpreted things correctly) works well. Actually the eye is relatively insensitive to color in the first place - that's why subsampling the chroma so drastically (from 4:4:4 to 4:1:1 or 4:2:0) works and we still get color pictures :) It's possible with 'y4mspatialfilter' and 'yuvmedianfilter' and now the new 'yuvdenoise' to specify different thresholds/amounts/etc for chroma and luma. In the Canopus ADVC300 (if you're using or thinking of using DV) there are luma and chroma filtering settings available - I've found that using weak/mild settings for the luma but strong/aggressive settings for the chroma to work well. I still filter thru y4mdenoise and others but doing the initial preprocessing in the hardware at capture time has resulted in quality I never thought I'd get from junky/old VHS tapes. Cheers, Steven Schultz ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click _______________________________________________ Mjpeg-users mailing list Mjpeg-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mjpeg-users