hermite hava more light and more details for others
[image: 41662642193_.pic.jpg]


<mirsfang@gmail.com> 于2022年9月8日周四 20:42写道：

> From: mirs <fangpengcheng@bilibili.com>
>
> Signed-off-by: mirs <fangpengcheng@bilibili.com>
>
> add tonemapping hermite,this looks close real hdr display
>
> ---
>  libavfilter/vf_tonemap.c | 65 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 65 insertions(+)
>
> diff --git a/libavfilter/vf_tonemap.c b/libavfilter/vf_tonemap.c
> index d1087e6bd9..3fb2bdfa2c 100644
> --- a/libavfilter/vf_tonemap.c
> +++ b/libavfilter/vf_tonemap.c
> @@ -48,6 +48,7 @@ enum TonemapAlgorithm {
>      TONEMAP_REINHARD,
>      TONEMAP_HABLE,
>      TONEMAP_MOBIUS,
> +    TONEMAP_HERMITE,
>      TONEMAP_MAX,
>  };
>
> @@ -106,6 +107,66 @@ static float mobius(float in, float j, double peak)
>      return (b * b + 2.0f * b * j + j * j) / (b - a) * (in + a) / (in + b);
>  }
>
> +static float hermite(float in) {
> +    /*
> +     * in theory, max mastering lumi 、max content lumi frome packet side
> data,
> +     * display max lumi from Display system value,current value is
> R-REP-BT.2390 max value
> +     */
> +    float max_mastering_lumi = 1000.0f;
> +    float max_content_lumi = 1000.0f;
> +    float display_max_lumi = 400.0f; // Terminal domain 400NITS is the
> maximum lumen of a normal screen
> +
> +    float max_in_lumi = FFMAX(max_mastering_lumi,max_content_lumi);
> +    float max_out_lumi = display_max_lumi;
> +    float nits = in * (display_max_lumi / max_mastering_lumi);
> +
> +    // clamp
> +    if (nits < 0) {
> +        nits = 0.0;
> +    } else if (nits > max_in_lumi) {
> +        nits = max_in_lumi;
> +    }
> +
> +    if (max_in_lumi <= max_out_lumi) {
> +        nits *= max_out_lumi / max_in_lumi;
> +    } else {
> +        // three control points
> +        const float x0 = 10.0f;
> +        const float y0 = 17.0;
> +        float x1 = max_out_lumi * 0.75;
> +        float y1 = x1;
> +        float x2 = x1 + (max_in_lumi - x1) / 2.0;
> +        float y2 = y1 + (max_out_lumi - y1) * 0.75;
> +        // horizontal distances between the last three control points
> +        float h12 = x2 - x1;
> +        float h23 = max_in_lumi - x2;
> +        // tangents at the last three control points
> +        float m1 = (y2 - y1) / h12;
> +        float m3 = (max_out_lumi - y2) / h23;
> +        float m2 = (m1 + m3) / 2.0;
> +
> +        if (nits < x0) {
> +            // scale [0.0, x0] to [0.0, y0] linearly
> +            float slope = y0 / x0;
> +            nits *= slope;
> +        } else if (nits < x1) {
> +            // scale [x0, x1] to [y0, y1] linearly
> +            float slope = (y1 - y0) / (x1 - x0);
> +            nits = y0 + (nits - x0) * slope;
> +        } else if (nits < x2) {
> +            // scale [x1, x2] to [y1, y2] using Hermite interp
> +            float t = (nits - x1) / h12;
> +            nits = (y1 * (1.0 + 2.0 * t) + h12 * m1 * t) * (1.0 - t) *
> (1.0 - t) +(y2 * (3.0 - 2.0 * t) + h12 * m2 * (t - 1.0)) * t * t;
> +        } else {
> +            // scale [x2, maxInLumi] to [y2, maxOutLumi] using Hermite
> interp
> +            float t = (nits - x2) / h23;
> +            nits = (y2 * (1.0 + 2.0 * t) + h23 * m2 * t) * (1.0 - t) *
> (1.0 - t) +(max_out_lumi * (3.0 - 2.0 * t) + h23 * m3 * (t - 1.0)) * t * t;
> +        }
> +    }
> +
> +    return nits;
> +}
> +
>  #define MIX(x,y,a) (x) * (1 - (a)) + (y) * (a)
>  static void tonemap(TonemapContext *s, AVFrame *out, const AVFrame *in,
>                      const AVPixFmtDescriptor *desc, int x, int y, double
> peak)
> @@ -163,6 +224,9 @@ static void tonemap(TonemapContext *s, AVFrame *out,
> const AVFrame *in,
>      case TONEMAP_MOBIUS:
>          sig = mobius(sig, s->param, peak);
>          break;
> +    case TONEMAP_HERMITE:
> +        sig = hermite(sig);
> +        break;
>      }
>
>      /* apply the computed scale factor to the color,
> @@ -291,6 +355,7 @@ static const AVOption tonemap_options[] = {
>      {     "reinhard", 0, 0, AV_OPT_TYPE_CONST, {.i64 =
> TONEMAP_REINHARD},          0, 0, FLAGS, "tonemap" },
>      {     "hable",    0, 0, AV_OPT_TYPE_CONST, {.i64 = TONEMAP_HABLE},
>          0, 0, FLAGS, "tonemap" },
>      {     "mobius",   0, 0, AV_OPT_TYPE_CONST, {.i64 = TONEMAP_MOBIUS},
>           0, 0, FLAGS, "tonemap" },
> +    {     "hermite",  0, 0, AV_OPT_TYPE_CONST, {.i64 = TONEMAP_HERMITE},
>         0, 0, FLAGS, "tonemap" },
>      { "param",        "tonemap parameter", OFFSET(param),
> AV_OPT_TYPE_DOUBLE, {.dbl = NAN}, DBL_MIN, DBL_MAX, FLAGS },
>      { "desat",        "desaturation strength", OFFSET(desat),
> AV_OPT_TYPE_DOUBLE, {.dbl = 2}, 0, DBL_MAX, FLAGS },
>      { "peak",         "signal peak override", OFFSET(peak),
> AV_OPT_TYPE_DOUBLE, {.dbl = 0}, 0, DBL_MAX, FLAGS },
> --
> 2.32.1 (Apple Git-133)
>
>