commit 904a1f18390ed2fea91d0199e99374af744aacf1
author Cheng Chen <chengchen@google.com> Tue Oct 27 09:40:48 2020 -0700
committer Debargha Mukherjee <debargha@google.com> Thu Oct 29 09:03:55 2020 -0700
tree 95f1ba09f64a3dcc46e9d0d15b5ed2817129aeb6
parent ebf1107dc288723c6e12743c528d1b0b42e821c1

Adjust threshold in palette color cache clustering

Use a higher threshold to bias towards using cached colors.

On speed 0, key frame only, screen content set:
        ovr_psnr    ssim    vmaf_neg
 8-bit    -0.37%    -0.57%    -0.27%
10-bit    -1.18%    -0.97%    -0.65%
12-bit    -0.53%    -0.99%    -0.71%

BUG=aomedia:2847

STATS_CHANGED

Change-Id: Ibc6018ff6a39823547faff8ab6a1625beed9ffbc
(cherry picked from commit 35d1af3053a03b9d963802ac77f458e8f520fc73)

av1/encoder/palette.c

diff --git a/av1/encoder/palette.c b/av1/encoder/palette.c
index 9eedd6f..d608a23 100644
--- a/av1/encoder/palette.c
+++ b/av1/encoder/palette.c
@@ -187,6 +187,7 @@
 
 // Bias toward using colors in the cache.
 // TODO(huisu): Try other schemes to improve compression.
+#define PALETTE_CACHE_BIAS_THRESH 4
 static AOM_INLINE void optimize_palette_colors(uint16_t *color_cache,
                                                int n_cache, int n_colors,
                                                int stride, int *centroids,
@@ -202,7 +203,7 @@
         idx = j;
       }
     }
-    int min_threshold = (1 << (bit_depth - 8));
+    const int min_threshold = (PALETTE_CACHE_BIAS_THRESH) << (bit_depth - 8);
     if (min_diff <= min_threshold) centroids[i] = color_cache[idx];
   }
 }