Re: [FFmpeg-devel] [PATCH v2 01/32] avfilter/palettegen: allow a minimum of 2 colors

From: "Tomas Härdin" <git@haerdin.se>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Cc: "Clément Bœsch" <u@pkh.me>
Subject: Re: [FFmpeg-devel] [PATCH v2 01/32] avfilter/palettegen: allow a minimum of 2 colors
Date: Wed, 28 Dec 2022 22:04:26 +0100
Message-ID: <07febd751d473db875267afb20fbd7ec0891e45c.camel@haerdin.se> (raw)
In-Reply-To: <20221227231814.2520181-2-u@pkh.me>

ons 2022-12-28 klockan 00:17 +0100 skrev Clément Bœsch:
> ---
>  libavfilter/vf_palettegen.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/libavfilter/vf_palettegen.c
> b/libavfilter/vf_palettegen.c
> index 27f74fd147..c03f62b942 100644
> --- a/libavfilter/vf_palettegen.c
> +++ b/libavfilter/vf_palettegen.c
> @@ -82,7 +82,7 @@ typedef struct PaletteGenContext {
>  #define OFFSET(x) offsetof(PaletteGenContext, x)
>  #define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM
>  static const AVOption palettegen_options[] = {
> -    { "max_colors", "set the maximum number of colors to use in the
> palette", OFFSET(max_colors), AV_OPT_TYPE_INT, {.i64=256}, 4, 256,
> FLAGS },
> +    { "max_colors", "set the maximum number of colors to use in the
> palette", OFFSET(max_colors), AV_OPT_TYPE_INT, {.i64=256}, 2, 256,
> FLAGS },
>      { "reserve_transparent", "reserve a palette entry for
> transparency", OFFSET(reserve_transparent), AV_OPT_TYPE_BOOL,
> {.i64=1}, 0, 1, FLAGS },
>      { "transparency_color", "set a background color for
> transparency", OFFSET(transparency_color), AV_OPT_TYPE_COLOR,
> {.str="lime"}, 0, 0, FLAGS },
>      { "stats_mode", "set statistics mode", OFFSET(stats_mode),
> AV_OPT_TYPE_INT, {.i64=STATS_MODE_ALL_FRAMES}, 0, NB_STATS_MODE-1,
> FLAGS, "mode" },
> @@ -586,6 +586,11 @@ static int init(AVFilterContext *ctx)
>      if (s->use_alpha && s->reserve_transparent)
>          s->reserve_transparent = 0;
>  
> +    if (s->max_colors - s->reserve_transparent < 2) {
> +        av_log(ctx, AV_LOG_ERROR, "max_colors=2 is only allowed
> without reserving a transparent color slot\n");

Does this mean all-black with transparent is disallowed? Shouldn't it
be max_colors + reserve < 2?

/Tomas

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