[FFmpeg-devel] [PATCH v2 15/17] swscale/graph: add color mapping pass

[Niklas Haas]

From: Niklas Haas <git at haasn.dev>

This leverages the previously introduced color management subsystem in order
to adapt between transfer functions and color spaces, as well as for HDR tone
mapping.

Take special care to handle grayscale formats without a colorspace
gracefully.
---
 libswscale/graph.c | 95 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 93 insertions(+), 2 deletions(-)

diff --git a/libswscale/graph.c b/libswscale/graph.c
index bf2f54b979..7160458a5f 100644
--- a/libswscale/graph.c
+++ b/libswscale/graph.c
@@ -30,6 +30,8 @@
 #include "libswscale/swscale.h"
 #include "libswscale/utils.h"
 
+#include "cms.h"
+#include "lut3d.h"
 #include "swscale_internal.h"
 #include "graph.h"
 
@@ -463,6 +465,89 @@ static int add_legacy_sws_pass(SwsGraph *graph, SwsFormat src, SwsFormat dst,
     return 0;
 }
 
+/**************************
+ * Gamut and tone mapping *
+ **************************/
+
+static void free_lut3d(void *priv)
+{
+    SwsLut3D *lut = priv;
+    sws_lut3d_free(&lut);
+}
+
+static void run_lut3d(const SwsImg *out_base, const SwsImg *in_base,
+                      int y, int h, const SwsPass *pass)
+{
+    SwsLut3D *lut = pass->priv;
+    const SwsImg in  = shift_img(in_base,  y);
+    const SwsImg out = shift_img(out_base, y);
+
+    sws_lut3d_apply(lut, in.data[0], in.linesize[0], out.data[0],
+                    out.linesize[0], pass->width, h);
+}
+
+static int adapt_colors(SwsGraph *graph, SwsFormat src, SwsFormat dst,
+                        SwsPass *input, SwsPass **output)
+{
+    enum AVPixelFormat fmt_in, fmt_out;
+    SwsColorMap map = {0};
+    SwsLut3D *lut;
+    SwsPass *pass;
+    int ret;
+
+    /**
+     * Grayspace does not really have primaries, so just force the use of
+     * the equivalent other primary set to avoid a conversion. Technically,
+     * this does affect the weights used for the Grayscale conversion, but
+     * in practise, that should give the expected results more often than not.
+     */
+    if (isGray(dst.format)) {
+        dst.color = src.color;
+    } else if (isGray(src.format)) {
+        src.color = dst.color;
+    }
+
+    /* Fully infer color spaces before color mapping logic */
+    graph->incomplete |= ff_infer_colors(&src.color, &dst.color);
+
+    map.intent = graph->ctx->intent;
+    map.src    = src.color;
+    map.dst    = dst.color;
+
+    if (sws_color_map_noop(&map))
+        return 0;
+
+    lut = sws_lut3d_alloc();
+    if (!lut)
+        return AVERROR(ENOMEM);
+
+    fmt_in  = sws_lut3d_pick_pixfmt(src, 0);
+    fmt_out = sws_lut3d_pick_pixfmt(dst, 1);
+    if (fmt_in != src.format) {
+        SwsFormat tmp = src;
+        tmp.format = fmt_in;
+        ret = add_legacy_sws_pass(graph, src, tmp, input, &input);
+        if (ret < 0)
+            return ret;
+    }
+
+    ret = sws_lut3d_generate(lut, fmt_in, fmt_out, &map);
+    if (ret < 0) {
+        sws_lut3d_free(&lut);
+        return ret;
+    }
+
+    pass = pass_add(graph, lut, fmt_out, src.width, src.height,
+                    input, 1, run_lut3d);
+    if (!pass) {
+        sws_lut3d_free(&lut);
+        return AVERROR(ENOMEM);
+    }
+    pass->free = free_lut3d;
+
+    *output = pass;
+    return 0;
+}
 
 /***************************************
  * Main filter graph construction code *
@@ -470,11 +555,17 @@ static int add_legacy_sws_pass(SwsGraph *graph, SwsFormat src, SwsFormat dst,
 
 static int init_passes(SwsGraph *graph)
 {
-    const SwsFormat src = graph->src;
-    const SwsFormat dst = graph->dst;
+    SwsFormat src = graph->src;
+    SwsFormat dst = graph->dst;
     SwsPass *pass = NULL; /* read from main input image */
     int ret;
 
+    ret = adapt_colors(graph, src, dst, pass, &pass);
+    if (ret < 0)
+        return ret;
+    src.format = pass ? pass->format : src.format;
+    src.color  = dst.color;
+
     if (!ff_fmt_equal(&src, &dst)) {
         ret = add_legacy_sws_pass(graph, src, dst, pass, &pass);
         if (ret < 0)
-- 
2.47.0