# [FFmpeg-user] In and out-range Scale option able to correct 0-255 video to 0-235?

Dave Rice dave at dericed.com
Fri May 22 05:59:08 CEST 2015

Hi Christoph,

> On May 20, 2015, at 1:59 AM, Christoph Gerstbauer <christophgerstbauer at gmail.com> wrote:
>
> Am 19.05.15 um 23:06 schrieb Carl Eugen Hoyos:
>> Christoph Gerstbauer <christoph.gerstbauer <at> gmail.com> writes:
>>
>>> C:\Windows\System32>ffmpeg -i
>>> "scale=in_range=full:out_range=tv" -vcodec ffvhuff
>> It seems to me that the scale filter is so smart
>> that it doesn't scale if the input and output
>> resolution and input and output colourspace
>> are identical.
>>
>> Even worse, both the filter and the software
>> scaler are smart enough to skip actual scaling,
>> so fixing the issue in the scale filter is not
>> sufficient...
>>
>> I am not 100% sure if this is a bug, but it
>> seems so;-)
>>
>> (Please try to understand that I had no idea
>> what you are talking about until seeing your
>> - imo sensible - command line.)
>>
>> I hope you mean "to correct 0-255 to 16-235".
>>
> YES. thats what I want to do: correction to 16-235 levels.
> I am checking different files with QCtools. It shows me optical if the values are above 235 or under 16. A numerical way would be much better, of course. But that is another issue.

QCTools quantifies samples out of the 16-235 range with the BRNG value from the signalstats filter. You can get the same numbers (range of 0-1) via:
ffprobe -f lavfi movie=input.mov,signalstats=stat=brng -show_entries frame_tags=lavfi.signalstats.BRNG -of flat
Dave Rice