Hey guys, I am working with an exr image sequence (colorspace: linear) I have a lut file to go from AlexaV3LogC to rec709. Obviously to do the encoding i need to change the colorspace first. I can't use apply_trc flag as AlexaV3LogC is different from ffmpeg logC colorspace.
To counter that in Nuke i used a Expression node with this value in every channels (channel r example): *r>0.0106232?(log10((r + 0.00937677) / 0.18)*0.2471896) + 0.385537:(((r+0.00937677) / 0.18) + 0.04378604) * 0.9661776* Which is the same than using a OCIOColorSpace node with in=linear and out=AlexaV3LogC As i want to do that with ffmpeg, i updated those expressions with ffmpeg convention: *"lutrgb=r='if(gt(val, 0.0106232), log((val + 0.00937677) / 0.18)/log(10)*0.2471896 + 0.385537, (((val + 0.00937677) / 0.18) + 0.04378604) * 0.9661776)':g='if(gt(val, 0.0106232), log((val + 0.00937677) / 0.18)/log(10)*0.2471896 + 0.385537, (((val + 0.00937677) / 0.18) + 0.04378604) * 0.9661776)':b='if(gt(val, 0.0106232), log((val + 0.00937677) / 0.18)/log(10)*0.2471896 + 0.385537, (((val + 0.00937677) / 0.18) + 0.04378604) * 0.9661776)'"* Theoretically, and double checked in a python shell: for a val=0.2 val will be 0.40.. for a val=0.01 val will be 0.14.. But it seems that I can't use the log(x) function in lutrgb. I get black frames with no data: every pixel [0,0,0] By removing all log(x) functions, obviously the values are wrong, but I can see my images.. And I don't have any error message. Did someone already use log(x) function in lutrgb? Is there a clever way to do it? Any help is welcome. Thank you. Clement _______________________________________________ ffmpeg-user mailing list [email protected] https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email [email protected] with subject "unsubscribe".
