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

[Michael Koch]

Am 20.09.2020 um 15:19 schrieb Michael Koch:
> 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?

I've solved the problem. If "-color_range pc" is added to the command 
line, the video plays fine in FFplay and also in VLC.

Michael