[FFmpeg-devel] [PATCH] lavfi: add colorlevels filter

[Lou Logan]

Nice. A user was asking for this recently (can't remember where).

On Wed, 10 Dec 2014 14:26:51 +0000, Paul B Mahol wrote:

> Signed-off-by: Paul B Mahol <onemda at gmail.com>
> ---
>  doc/filters.texi             |  41 +++++++
>  libavfilter/Makefile         |   1 +
>  libavfilter/allfilters.c     |   1 +
>  libavfilter/vf_colorlevels.c | 254 +++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 297 insertions(+)
>  create mode 100644 libavfilter/vf_colorlevels.c
> 
> diff --git a/doc/filters.texi b/doc/filters.texi
> index 0ea3955..444dfda 100644
> --- a/doc/filters.texi
> +++ b/doc/filters.texi
> @@ -2934,6 +2934,47 @@ colorbalance=rs=.3
>  @end example
>  @end itemize
>  
> + at section colorlevels
> +
> +Adjust video input frames using levels.
> +
> +The filter accepts the following options:
> +
> + at table @option
> + at item rimim

rimin

> + at item gimin
> + at item bimin
> + at item aimin
> +Adjust red, green, blue and alpha input black point.
> +Allowed ranges for options are @code{[-1.0, 1.0]}. Defaults are @code{0}.

How about a "master" point to control RGB all at once in case each value
is the same for each component?

> + at item rimax
> + at item gimax
> + at item bimax
> + at item aimax
> +Adjust red, green, blue and alpha input white point.
> +Allowed ranges for options are @code{[-1.0, 1.0]}. Defaults are @code{1}.
> +
> +Input levels are used to lighten highlights (bright tones), darken shadows
> +(dark tones), change the balance of bright and dark tones.
> +
> + at item romim

romin

> + at item gomin
> + at item bomin
> + at item aomin
> +Adjust red, green, blue and alpha output black point.
> +Allowed ranges for options are @code{[0, 1.0]}. Defaults are @code{0}.
> +
> + at item romax
> + at item gomax
> + at item bomax
> + at item aomax
> +Adjust red, green, blue and alpha output white point.
> +Allowed ranges for options are @code{[0, 1.0]}. Defaults are @code{1}.
> +
> +Output levels allows manual selection of a constrained output level range.
> + at end table
> +

I'd like to see an example or two in the docs.

Perhaps this filter could implement 'presets' and 'psfile' options for
Photoshop levels preset files such as in curves filter. Attached is an
example ALV file.

Here are some of the PS presets and their values.

Darker:
rimin=0.0588235294:gimin=0.0588235294:bimin=0.0588235294

Increase Contrast 1:
rimin=0.0392156863:gimin=0.0392156863:bimin=0.0392156863:rimax=0.9607843137:gimax=0.9607843137:bimax=0.9607843137

Increase Contrast 2:
rimin=0.0784313725:gimin=0.0784313725:bimin=0.0784313725:rimax=0.9215686275:gimax=0.9215686275:bimax=0.9215686275

Increase Contrast 3:
rimin=0.1176470588:gimin=0.1176470588:bimin=0.1176470588:rimax=0.8823529412:gimax=0.8823529412:bimax=0.8823529412

Lighter:
rimax=0.9019607843:gimax=0.9019607843:bimax=0.9019607843

I didn't figure out Lighten Shadows, Midtones Brighter, and Midtones
Darker. Maybe I'll look again later.
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