I came up with a simple (i.e. very dumb, perhaps too much so) program to generate a histogram of a Y4MPEG2 frame. Using the program on Have you tried yuvcorrect -M STAT? It makes frame-by-frame histograms in YCbCr and RGB. I used it a little earlier to investigate the range of my camera; here is part of the histogram for a shot of the lens cap with exposure compensation turned down as much as I could (to try and keep the CCD noise to a minimum; as I might have mentioned 80 times by now, my camera is noisy):
INFO: [yuvcorrect] Histogramme i Y U V ... INFO: [yuvcorrect] 016 00000 00000 00000 INFO: [yuvcorrect] 017 00000 00000 00000 INFO: [yuvcorrect] 018 00000 00000 00000 INFO: [yuvcorrect] 019 00000 00000 00000 INFO: [yuvcorrect] 020 00041 00000 00000 INFO: [yuvcorrect] 021 00432 00000 00000 INFO: [yuvcorrect] 022 02900 00000 00000 INFO: [yuvcorrect] 023 09386 00000 00000 INFO: [yuvcorrect] 024 16027 00000 00000 INFO: [yuvcorrect] 025 16109 00000 00000 INFO: [yuvcorrect] 026 12281 00000 00000 INFO: [yuvcorrect] 027 09313 00000 00000 INFO: [yuvcorrect] 028 06954 00000 00000 INFO: [yuvcorrect] 029 04929 00000 00000 INFO: [yuvcorrect] 030 03300 00000 00000 INFO: [yuvcorrect] 031 02051 00000 00000 INFO: [yuvcorrect] 032 01248 00000 00000 INFO: [yuvcorrect] 033 00681 00000 00000 INFO: [yuvcorrect] 034 00384 00000 00000 INFO: [yuvcorrect] 035 00204 00000 00000 INFO: [yuvcorrect] 036 00091 00000 00000 INFO: [yuvcorrect] 037 00041 00000 00000 INFO: [yuvcorrect] 038 00014 00000 00000 INFO: [yuvcorrect] 039 00008 00000 00000 INFO: [yuvcorrect] 040 00005 00000 00000 ... INFO: [yuvcorrect] 124 00000 00000 00000 INFO: [yuvcorrect] 125 00000 00031 00000 INFO: [yuvcorrect] 126 00000 06528 00168 INFO: [yuvcorrect] 127 00000 63498 34962 INFO: [yuvcorrect] 128 00000 16180 49779 INFO: [yuvcorrect] 129 00000 00163 01486 INFO: [yuvcorrect] 130 00000 00000 00005 ... So it looks like I have less of a spread than you, especially in CbCr. Sounds like you want to apply a nonlinear mapping that squeezes your darker pixels closer together but leaves the rest alone. Perhaps a piecewise-linear extension to yuvcorrect? Have you tried adjusting the gamma (a power nonlinearity curve) via yuvcorrect? That might have a similar effect. Or, you could just clip below some "black" threshold, and then restretch what remains to the full range, something like: yuvcorrect -Y Y_1.0_28_235_16_235 or just clip: yuvcorrect -Y Y_1.0_28_235_28_235 or clip and shift down (makes it darker though): yuvcorrect -Y Y_1.0_28_235_16_223 I hope that the encoder doesn't waste a lot of bits encoding chroma for such low luma, as the eye can't distinguish dark colors so well. Dan ------------------------------------------------------- This SF.net email is sponsored by:Crypto Challenge is now open! Get cracking and register here for some mind boggling fun and the chance of winning an Apple iPod: http://ads.sourceforge.net/cgi-bin/redirect.pl?thaw0031en _______________________________________________ Mjpeg-users mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/mjpeg-users
