On Thu, 12 May 2005, Steven M. Schultz wrote:
Next, I tried to get rid of all the noise in the chroma data. The CCD
I think that is far too ambitious of a goal. Only way to get rid of _all_ the chroma noise is to create a black&white video. A more reasonable goal would be to reduce the noise to a less objectionable level.
I know, but I still wanted to try how far I could push it ;) As it turned out, using yuvdenoise can get you pretty close to that goal. It seems that you can treat the luma data quite agressively without degrading the appearance of the image.
induced chroma noise is quite heavy in the low-light scene I use for testing. First I tried spatial filtering only by using y4mspatialfilter and yuvmedianfilter. This approach failed, because the groups of
Hmmm, the report yesterday or so mentioned yuvmedianfilter as being effective.
I was using a less challenging recording then.
adjacent pixels that change color from one frame to the next are too large. Removing the noise would require using a filtering radius of > 15 pixels or so, which blurs the chroma channel too much.
Did you use the normal/default mode of yuvmedianfilter or the '-f' averaging mode? Something like "-t 0 -f -R 4" might do a reasonable job.
I didn't try -f, will try that next time.
But wow - 15 pixel groups of noise? Sounds like it's time for a
camcorder with a better CCD - either that or the CCD (or electronics)
have developed a fault of some kind.
That is only in low light conditions, and only in the shadows. The groups themselves are *at most* about 10 pixels wide, so I figured you need to average every chroma pixel with neighbouring pixels in a radius of 15 pixels or so, ot get rid of the noise.
Ah, but "-t 0 -z 0" doesn't disable the luma processing in y4mdenoise,
does it? I think those values cause the most exhaustive time
consuming processing y4mdenoise is capable of!
Ah, yes that would explain it all. Somehow I assumed that yuvdenoise would be so wise not to try denoising with an error threshold of zero.
But this also has a downside: It touches the luma data too because, AFAIK,
But with very mild settings. I think you might actually want that to help reduce the 'sandpaper' or "boiling sand" effect - something I have seen with lowlight footage shot with a Digital8 camcorder (1/6" CCD).
The boiling sand effect is there indeed. I just had not decided which tool I wanted to use to reduce that kind of noise, either yuvdenoise or y4mdenoise. I guess my choice has been made. :)
Could yuvdenoise be fixed to ignore the luma channel when the threshold is zero? It seems to me that it would be the ideal chroma noise filter.
Probably be fairly easy - perhaps Stefan will see the request and put that in along with the new algorithm he mentioned the other day.
Cheers, Steven Schultz
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