[FFmpeg-devel] [PATCH] avfilter/delogo: Set default band to 1

[Stefano Sabatini]

On date Wednesday 2015-10-07 08:54:59 +0200, Jean Delvare encoded:
> The original interpolation algorithm behaved poorly on the borders and
> did not even guarantee continuity at the borders. For this reason, a
> second interpolation/blending pass was required on the borders to make
> them seamless.
> 
> However, since the interpolation algorithm was improved in June 2013,
> the border issues no longer exist. The new algorithm does guarantee
> continuity at the borders, making the second pass useless. A larger
> band always increases the cumulated interpolation error. In most cases
> it also increases the average interpolation error, even though the
> samples in the band are only partially interpolated.
> 
> For this reason I would like to get rid of the "band" parameter. As a
> first step, let's change its default value from 4 to 1 and document it
> as deprecated.
> 
> I have benchmarked this change on a combination of input sources and
> realistic logo areas. Lowering the band value from 4 to 1 resulted in
> 8 to 39 % less interpolation error per frame (or 1 to 34 % less
> interpolation error per luma sample.)
> 
> Signed-off-by: Jean Delvare <jdelvare at suse.de>
> ---
>  doc/filters.texi        |    4 +++-
>  libavfilter/vf_delogo.c |   11 +++++++++--
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> --- ffmpeg.orig/doc/filters.texi	2015-10-02 11:41:24.035943770 +0200
> +++ ffmpeg/doc/filters.texi	2015-10-02 12:02:08.231484828 +0200
> @@ -4590,7 +4590,9 @@ specified.
>  
>  @item band, t
>  Specify the thickness of the fuzzy edge of the rectangle (added to
> - at var{w} and @var{h}). The default value is 4.
> + at var{w} and @var{h}). The default value is 1. This option is
> +deprecated, setting higher values should no longer be necessary and
> +is not recommended.
>  
>  @item show
>  When set to 1, a green rectangle is drawn on the screen to simplify
> --- ffmpeg.orig/libavfilter/vf_delogo.c	2015-10-02 11:41:24.035943770 +0200
> +++ ffmpeg/libavfilter/vf_delogo.c	2015-10-07 08:45:39.037203764 +0200
> @@ -165,8 +165,9 @@ static const AVOption delogo_options[]=
>      { "y",    "set logo y position",       OFFSET(y),    AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, FLAGS },
>      { "w",    "set logo width",            OFFSET(w),    AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, FLAGS },
>      { "h",    "set logo height",           OFFSET(h),    AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, FLAGS },
> -    { "band", "set delogo area band size", OFFSET(band), AV_OPT_TYPE_INT, { .i64 =  4 },  1, INT_MAX, FLAGS },
> -    { "t",    "set delogo area band size", OFFSET(band), AV_OPT_TYPE_INT, { .i64 =  4 },  1, INT_MAX, FLAGS },
> +    /* Actual default value for band/t is 1, set in init */
> +    { "band", "set delogo area band size", OFFSET(band), AV_OPT_TYPE_INT, { .i64 =  0 },  0, INT_MAX, FLAGS },
> +    { "t",    "set delogo area band size", OFFSET(band), AV_OPT_TYPE_INT, { .i64 =  0 },  0, INT_MAX, FLAGS },
>      { "show", "show delogo area",          OFFSET(show), AV_OPT_TYPE_BOOL,{ .i64 =  0 },  0, 1,       FLAGS },
>      { NULL }
>  };
> @@ -201,6 +202,12 @@ static av_cold int init(AVFilterContext
>      CHECK_UNSET_OPT(w);
>      CHECK_UNSET_OPT(h);
>  
> +    if (s->band == 0) { /* Unset, use default */
> +        av_log(ctx, AV_LOG_WARNING, "Note: default band value was changed from 4 to 1.\n");
> +        s->band = 1;
> +    } else if (s->band != 1) {
> +        av_log(ctx, AV_LOG_WARNING, "Option band is deprecated.\n");
> +    }
>      av_log(ctx, AV_LOG_VERBOSE, "x:%d y:%d, w:%d h:%d band:%d show:%d\n",
>             s->x, s->y, s->w, s->h, s->band, s->show);

LGTM. BTW, if you want to drop the band option, you could ifdef it so
that it will be dropt at the next lavfi major bump.
-- 
FFmpeg = Friendly and Fundamental Meaningless Programmable Enlightened God