shithub: dav1d

Info  •  Files  •  Log  •  Branches

Fix bugs in film grain generation

- calculate chroma grain based on src (not dst) luma pixels;
- division should precede multiplication in delta calculation.

Together, these fix differences in film grain reconstruction between
libaom and dav1d for various generated samples.

--- a/src/film_grain_tmpl.c

+++ b/src/film_grain_tmpl.c

@@ -185,7 +185,7 @@

         const int ey = points[i+1][1];

         const int dx = ex - bx;

         const int dy = ey - by;

-        const int delta = dy * ((0xFFFF + (dx >> 1))) / dx;

+        const int delta = dy * ((0x10000 + (dx >> 1)) / dx);

         for (int x = 0; x < dx; x++) {

             const int v = by + ((x * delta + 0x8000) >> 16);

             scaling[bx + x] = v;

@@ -364,7 +364,7 @@

     const int by = row_num * (BLOCK_SIZE >> sy);

     pixel *const dst_row = (pixel *) out->data[1 + uv] + PXSTRIDE(stride) * by;

     pixel *const src_row = (pixel *)  in->data[1 + uv] + PXSTRIDE(stride) * by;

-    pixel *const luma_row = (pixel *) out->data[0] + PXSTRIDE(out->stride[0]) * row_num * BLOCK_SIZE;

+    pixel *const luma_row = (pixel *) in->data[0] + PXSTRIDE(in->stride[0]) * row_num * BLOCK_SIZE;

     int offsets[2 /* col offset */][2 /* row offset */];

@@ -394,7 +394,7 @@

 #define add_noise_uv(x, y, grain)                                               \

             const int lx = (bx + x) << sx;                                      \

             const int ly = y << sy;                                             \

-            pixel *luma = luma_row + ly * PXSTRIDE(out->stride[0]) + lx;        \

+            pixel *luma = luma_row + ly * PXSTRIDE(in->stride[0]) + lx;         \

             pixel avg = luma[0];                                                \

             if (sx && lx + 1 < out->p.w)                                        \

                 avg = (avg + luma[1] + 1) >> 1;                                 \