[FFmpeg-user] Create a 10-bit VLog test video

Michael Koch astroelectronic at t-online.de
Sun Sep 20 16:19:54 EEST 2020

Am 19.09.2020 um 17:01 schrieb Paul B Mahol:
> On Sat, Sep 19, 2020 at 12:10 PM Michael Koch <astroelectronic at t-online.de>
> wrote:
>> Hello all,
>> I want to create a 10-bit VLog test video which contains 18 levels of
>> gray, according to Panasonic's VLog curve.
>> The curve is documented here:
>> https://pro-av.panasonic.net/en/cinema_camera_varicam_eva/support/pdf/VARICAM_V-Log_V-Gamut.pdf
>> I want the leftmost bar to be black (128) and the other 17 bars are for
>> -8 to +8 stops, so that the rightmost bar is at level 1023. I'm using
>> this command line and the console output is copied below:
>> ffmpeg -f lavfi -i nullsrc=s=svga,format=gray16 -lavfi
>> geq=lum='st(0,trunc(18*X/W));64*(128*eq(ld(0),0)+132*eq(ld(0),1)+136*eq(ld(0),2)+144*eq(ld(0),3)+160*eq(ld(0),4)+192*eq(ld(0),5)+240*eq(ld(0),6)+298*eq(ld(0),7)+363*eq(ld(0),8)+433*eq(ld(0),9)+505*eq(ld(0),10)+578*eq(ld(0),11)+652*eq(ld(0),12)+726*eq(ld(0),13)+800*eq(ld(0),14)+874*eq(ld(0),15)+949*eq(ld(0),16)+1023*eq(ld(0),17))'
>> -pix_fmt yuv444p10le -crf 10 -c:v h264 -t 5 -y VLog_10bit.mov
>> The video looks perfect when played with FFplay. The leftmost bars are
>> indistinguishable on a 8-bit monitor because the levels are too close
>> together, but the rightmost bars look as expected.
>> However when I play the same video with VLC, the two brightest bars at
>> the right side have the same shade of gray. I don't understand why. Is
>> this a problem in my video, or is it a problem in VLC?
>> When I extraxt a 16-bit PNG image from the video, this looks as expected
>> with 18 levels of gray.
>> ffmpeg -i VLog_10bit.mov -frames 1 -y out.png
>> Unrelated: I did try to add the oscilloscope filter at the end of the
>> filter chain, but it seems it doesn't work with 16-bit data. There
>> should be a warning or an error message. oscilloscope=tw=1:s=1
> That happened only with gray>8 formats and have been fixed already.

Thanks, oscilloscope works fine now.
Do you have any idea why the brightest bar looks correct in FFplay and 
wrong in VLC?
Is the problem reproducible on other computers?


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