[FFmpeg-user] Documentation and feature request

[Michael Koch]

Hi Gyan,

> Contrast can go from -1000 to 1000. The range was expanded a few years 
> ago; the doc wasn't updated.
>
> Do note that what contrast does is scale the distance of a pixel's 
> value from the median value i.e. 128 for a 8-bit input. So, if a pixel 
> channel has a value of 100, then a contrast of 3 results in a value of 
>   128 + 3*(100-128) = 44.
>
> The order is contrast -> brightness -> gamma.
>

thank you very much for this information. Some time ago I tested the eq 
filter with high contrast values and had some problems, and then I 
thought that's because the allowed range is [-2..+2]. Now I tested it 
again and couldn't reproduce these problems. I just verified that two 
cascaded eq=contrast=2 filters give exactly the same result as one 
eq=contrast=4 filter. That's very good news!

I have one more question. Can you please explain the unit of the 
brightness value?
What does brightness=1 mean? Does it mean add 256 to a 8-bit video, or 
add 1024 to a 10-bit video?

Thanks,
Michael