[FFmpeg-devel] [PATCH v1 1/1] avfilter/vf_tonemap: add herimte tone mapping

[mirsfang@gmail.com]

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)

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