[FFmpeg-devel] [PATCH] avfilter/vf_zscale: add support for setting scaling filter parameters

[Jan Ekström]

On Tue, Feb 9, 2021 at 11:07 PM Jan Ekström <jeebjp at gmail.com> wrote:
>
> param_a/b are utilized for this.
> ---
>  libavfilter/vf_zscale.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/libavfilter/vf_zscale.c b/libavfilter/vf_zscale.c
> index 57199a0878..c195cf0591 100644
> --- a/libavfilter/vf_zscale.c
> +++ b/libavfilter/vf_zscale.c
> @@ -101,6 +101,8 @@ typedef struct ZScaleContext {
>      char *size_str;
>      double nominal_peak_luminance;
>      int approximate_gamma;
> +    double param_a;
> +    double param_b;
>
>      char *w_expr;               ///< width  expression string
>      char *h_expr;               ///< height expression string
> @@ -601,6 +603,8 @@ static int filter_frame(AVFilterLink *link, AVFrame *in)
>          s->params.resample_filter_uv = s->filter;
>          s->params.nominal_peak_luminance = s->nominal_peak_luminance;
>          s->params.allow_approximate_gamma = s->approximate_gamma;
> +        s->params.filter_param_a = s->params.filter_param_a_uv = s->param_a;
> +        s->params.filter_param_b = s->params.filter_param_b_uv = s->param_b;
>
>          format_init(&s->src_format, in, desc, s->colorspace_in,
>                      s->primaries_in, s->trc_in, s->range_in, s->chromal_in);
> @@ -897,6 +901,9 @@ static const AVOption zscale_options[] = {
>      { "cin",        "set input chroma location", OFFSET(chromal_in), AV_OPT_TYPE_INT, {.i64 = -1}, -1, ZIMG_CHROMA_BOTTOM, FLAGS, "chroma" },
>      { "npl",       "set nominal peak luminance", OFFSET(nominal_peak_luminance), AV_OPT_TYPE_DOUBLE, {.dbl = NAN}, 0, DBL_MAX, FLAGS },
>      { "agamma",       "allow approximate gamma", OFFSET(approximate_gamma),      AV_OPT_TYPE_BOOL,   {.i64 = 1},   0, 1,       FLAGS },
> +    { "param_a", "parameter A, which is parameter \"b\" for bicubic, "
> +                 "and the number of filter taps for lanczos", OFFSET(param_a), AV_OPT_TYPE_DOUBLE, {.dbl = NAN}, 0, DBL_MAX, FLAGS },

Basically the author of zimg was lamenting that he couldn't set the
taps for lanczos to 4, which is apparently the most optimized version.
Thus, added support for being able to set both of the scaling filter
parameters :) .

Jan