linear conversion

gopro_8:7/unfish_gopro_8:7.glsl

@@ -17,7 +17,8 @@
 
 #extension GL_ARB_texture_rectangle: enable
 
-#define rotate_180
+#define non_linear_decoding
+//#define rotate_180
 //#define debug_borders
 
 #undef highp // defined by Qt-OpenGl
@@ -62,34 +63,63 @@ vec2 equidistant_to_rectilinear(const in vec2 coord) {
     return coord * (equidistant_radius / rectilinear_radius);
 }
 
-vec4 sample_texture(const in vec2 coord) {
+vec3 sample_texture(const in vec2 coord) {
     vec2 rectilinear = equidistant_to_rectilinear((coord - texture_center) * texture_to_sensor);
     vec2 y_coord = texture_center + rectilinear * sensor_to_texture;
 #ifdef debug_borders
     if (y_coord.x < 0.0 || y_coord.y < 0.0 || y_coord.x > myResolution.x || y_coord.y > myResolution.y) {
-        return vec4(1.0);
+        return vec3(1.0);
     }
 #endif
     vec2 uv_coord = y_coord * 0.5;
-    return vec4(
+    return vec3(
         texture2DRect(myTextureY, y_coord).x,
         texture2DRect(myTextureU, uv_coord).x,
-        texture2DRect(myTextureV, uv_coord).x,
-        1.0);
+        texture2DRect(myTextureV, uv_coord).x);
 }
 
+#ifdef non_linear_decoding
+
+// https://en.wikipedia.org/wiki/Rec._709
+
+#define y_min    ( 16.0 / 255.0)
+#define y_max    (235.0 / 255.0)
+#define uv_min   ( 16.0 / 255.0)
+#define uv_max   (240.0 / 255.0)
+#define y_range  (y_max - y_min)
+#define uv_range (uv_max - uv_min)
+
+const vec3 yuv_min = vec3(y_min, uv_min, uv_min);
+const vec3 yuv_range = vec3(y_range, uv_range, uv_range);
+const vec3 yuv_center = vec3(0.0, 0.5, 0.5);
+
+vec3 decode_pixel(const in vec3 pixel) {
+    vec3 color = (pixel - yuv_min) / yuv_range - yuv_center;
+    float l = (color.x < 0.081) ? (color.x / 4.5) : pow((color.x + 0.099) / 1.099, 1.0 / 0.45);
+    return vec3(l, color.yz);
+}
+
+vec3 encode_pixel(const in vec3 color) {
+    float y = (color.x < 0.018) ? (color.x * 4.5) : (pow(color.x, 0.45) * 1.099 - 0.099);
+    return (vec3(y, color.yz) + yuv_center) * yuv_range + yuv_min;
+}
+
+#else
+
+#define decode_pixel(_color) _color
+#define encode_pixel(_color) _color
+
+#endif // non_linear_decoding
+
 void main() {
     initialize();
-
     vec2 coord = gl_TexCoord[0].xy;
-    vec4 pixel = vec4(0.0);
-
+    vec3 color = vec3(0.0);
     for (int y = 0; y < subsampling; y++) {
         for (int x = 0; x < subsampling; x++) {
             vec2 offset = subsampling_start + subsampling_step * vec2(x, y);
-            pixel += sample_texture(coord + offset);
+            color += decode_pixel(sample_texture(coord + offset));
         }
     }
-
-    gl_FragColor = pixel * subsampling_scale;
+    gl_FragColor = vec4(encode_pixel(color * subsampling_scale), 1.0);
 }