shithub: dav1d

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Use linear interpolation for high bit-depth pixel values

--- a/src/film_grain_tmpl.c

+++ b/src/film_grain_tmpl.c

@@ -172,6 +172,7 @@

 {

     const int shift_x = bitdepth - 8;

     const int scaling_size = 1 << bitdepth;

+    const int pad = 1 << shift_x;

     // Fill up the preceding entries with the initial value

     for (int i = 0; i < points[0][0] << shift_x; i++)

@@ -186,7 +187,7 @@

         const int dx = ex - bx;

         const int dy = ey - by;

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

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

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

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

             scaling[bx + x] = v;

         }

@@ -195,6 +196,21 @@

     // Fill up the remaining entries with the final value

     for (int i = points[num - 1][0] << shift_x; i < scaling_size; i++)

         scaling[i] = points[num - 1][1];

+

+    if (pad > 1) {

+        const int rnd = pad >> 1;

+        for (int i = 0; i < num - 1; i++) {

+            const int bx = points[i][0] << shift_x;

+            const int ex = points[i+1][0] << shift_x;

+            const int dx = ex - bx;

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

+                const int range = scaling[bx + x + pad] - scaling[bx + x];

+                for (int n = 1; n < pad; n++) {

+                    scaling[bx + x + n] = scaling[bx + x] + ((range * n + rnd) >> shift_x);

+                }

+            }

+        }

+    }

 }

 // samples from the correct block of a grain LUT, while taking into account the