[FFmpeg-user] fftfilt

[Paul B Mahol]

On Tue, Oct 12, 2021 at 10:55 AM Michael Koch <astroelectronic at t-online.de>
wrote:

> I have a question about the "fftfilt" filter. What's the default value
> of the weight_U and weight_V options? I'm asking because I get an
> unexpected result.
>
> This command line creates my input image for testing:
>
> ffmpeg -f lavfi -i color=black:s=300x50 -lavfi
> drawgrid=c=white:y=-1:w=2:h=51,split[a][b];[b]crop=iw/2:x=0,scale=2*iw:ih:flags=neighbor,split[b][c];[c]crop=iw/2:x=0,scale=2*iw:ih:flags=neighbor,split[c][d];[d]crop=iw/2:x=0,scale=2*iw:ih:flags=neighbor,split[d][e];[e]crop=iw/2:x=0,scale=2*iw:ih:flags=neighbor,split[e][f];[f]crop=iw/2:x=0,scale=2*iw:ih:flags=neighbor[f];[a][b][c][d][e][f]vstack=6,split[h][v];[v]transpose[v];[v][h]hstack
>
> -frames 1 -y test.png
>
> This is the fftfilt lowpass example from the official documentation:
>
> ffmpeg -i test.png -vf fftfilt=dc_Y=0:weight_Y='squish((Y+X)/100-1)' -y
> out1.png
>
> Problem: The output has a greenish tint.
>

Expressions by default for U and V are copied from Y if are unset.
filter works only in YUV or gray space thus in above combination one gets
green tint.

>
> If I set the weight_U and weight_V options to 1, then the greenish tint
> disappears:
>
> ffmpeg -i test.png -vf
> fftfilt=dc_Y=0:weight_Y='squish((Y+X)/100-1)':weight_U=1:weight_V=1 -y
> out2.png
>
> Michael
>
>
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