On 25-Jan-2003 [EMAIL PROTECTED] wrote:
|
| (Lets see if my mail gets through this time...)
|
| I'm using the mjpegtools to convert DV to DVD, generally using the
| chain lav2yuv->mpeg2enc directly for low-noise (bright) scenes and
| lav2yuv->yuvdenoise->mpeg2enc for noisier scenes (low light). I also
| use it to convert VHS to DVD via
| (lav2yuv->yuvscaler->yuvdenoise->yuvmedianfilter->mpeg2enc). I can't
| help noticing that yuvdenoise, and to a lesser extent
| yuvmedianfilter,
| give their output a distinct greenish tint. You can do a direct
| comparison like this:
|
| lav2yuv myDV.avi | tee >(yuvplay) | yuvdenoise | yuvplay
|
| which plays both denoised and non-denoised versions at once. I wind
| up doing something like "yuvcorrect -R G_1.0_0_255_0_245" to try to
| fix the color. I had thought this was related to the pixel layout of
| my DV camera, since the noise is mostly red and blue, but I get the
| same green tint if I use a commercial DVD as my movie source instead.
|
| So, what's the deal? Is this an actual error in
| yuvdenoise/medianfilter, or an expected artifact from denoising the
There are definitively errors/inaccuracies in the lav-tools concerning the
range of YUV-values. yuvdenoise tends to broaden the [16-235]-range of Y.
Maybe there are other yuvxxx-tools that do this, too. Maybe it's rounding
errors, maybe it's just a design error. There is much code around that
assumes [0-255]-ranges! At least mpeg2enc needs the correct
(small) range to encode. It clips out-of-range values. For me this results
in a slight increase of contrast with a unwanted loss of color resolution
in the dark/light areas. This is really painfull, as these image areas are
sometimes essencial. Currently, I workaround this problem by inserting a
self made yuv-filter which compresses the values into the needed range.
When someone looks at this code to fix the "greenish-problen", he should
look for the "range-problem", too.
Regards,
Ralf
| color info? Am I the only one who sees this? I see it both in 1.6.x
| and in CVS.
|
| --
| Dan Scholnik
| [EMAIL PROTECTED]
|
|
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