From c1e1b7104c60b406a09a4a5c0774e3922741f9a9 Mon Sep 17 00:00:00 2001
From: Mislav Bradac <mislavm@google.com>
Date: Fri, 18 Sep 2015 13:28:22 +0000
Subject: [PATCH] Changed delta palette to compress better

New palette compresses more than 20% better with minimum quality loss.
Tested on set of wikipedia images with command line:
cwebp -delta_palettization

Change-Id: I82ec7d513136599cd70386f607f634502eb9095d
---
 src/enc/delta_palettization.c | 468 ++++++++++++++++------------------
 src/enc/delta_palettization.h |   6 +-
 2 files changed, 225 insertions(+), 249 deletions(-)

diff --git a/src/enc/delta_palettization.c b/src/enc/delta_palettization.c
index a41baf9a..ebc6b3c3 100644
--- a/src/enc/delta_palettization.c
+++ b/src/enc/delta_palettization.c
@@ -5,262 +5,234 @@
 
 #define MK_COL(r, g, b) (((r) << 16) + ((g) << 8) + (b))
 
-// Palette used for delta_palettization.
+// Palette used for delta_palettization. Entries are roughly sorted by distance
+// of their signed equivalents from the origin.
 const uint32_t kDeltaPalette[DELTA_PALETTE_SIZE] = {
-  MK_COL(128u, 128u, 128u),
-  MK_COL(128u, 128u, 64u),
-  MK_COL(128u, 128u, 192u),
-  MK_COL(128u, 128u, 0u),
-  MK_COL(128u, 64u, 128u),
-  MK_COL(128u, 64u, 64u),
-  MK_COL(128u, 64u, 192u),
-  MK_COL(128u, 64u, 0u),
-  MK_COL(128u, 192u, 128u),
-  MK_COL(128u, 192u, 64u),
-  MK_COL(128u, 192u, 192u),
-  MK_COL(128u, 192u, 0u),
-  MK_COL(128u, 0u, 128u),
-  MK_COL(128u, 0u, 64u),
-  MK_COL(128u, 0u, 192u),
-  MK_COL(128u, 0u, 0u),
-  MK_COL(64u, 128u, 128u),
-  MK_COL(64u, 128u, 64u),
-  MK_COL(64u, 128u, 192u),
-  MK_COL(64u, 128u, 0u),
-  MK_COL(64u, 64u, 128u),
-  MK_COL(64u, 64u, 64u),
-  MK_COL(64u, 64u, 192u),
-  MK_COL(64u, 64u, 0u),
-  MK_COL(64u, 192u, 128u),
-  MK_COL(64u, 192u, 64u),
-  MK_COL(64u, 192u, 192u),
-  MK_COL(64u, 192u, 0u),
-  MK_COL(64u, 0u, 128u),
-  MK_COL(64u, 0u, 64u),
-  MK_COL(64u, 0u, 192u),
-  MK_COL(64u, 0u, 0u),
-  MK_COL(192u, 128u, 128u),
-  MK_COL(192u, 128u, 64u),
-  MK_COL(192u, 128u, 192u),
-  MK_COL(192u, 128u, 0u),
-  MK_COL(192u, 64u, 128u),
-  MK_COL(192u, 64u, 64u),
-  MK_COL(192u, 64u, 192u),
-  MK_COL(192u, 64u, 0u),
-  MK_COL(192u, 192u, 128u),
-  MK_COL(192u, 192u, 64u),
-  MK_COL(192u, 192u, 192u),
-  MK_COL(192u, 192u, 0u),
-  MK_COL(192u, 0u, 128u),
-  MK_COL(192u, 0u, 64u),
-  MK_COL(192u, 0u, 192u),
-  MK_COL(192u, 0u, 0u),
-  MK_COL(176u, 80u, 80u),
-  MK_COL(176u, 80u, 176u),
-  MK_COL(176u, 80u, 40u),
-  MK_COL(176u, 80u, 216u),
-  MK_COL(176u, 176u, 80u),
-  MK_COL(176u, 176u, 176u),
-  MK_COL(176u, 176u, 40u),
-  MK_COL(176u, 176u, 216u),
-  MK_COL(176u, 40u, 80u),
-  MK_COL(176u, 40u, 176u),
-  MK_COL(176u, 40u, 40u),
-  MK_COL(176u, 40u, 216u),
-  MK_COL(176u, 216u, 80u),
-  MK_COL(176u, 216u, 176u),
-  MK_COL(176u, 216u, 40u),
-  MK_COL(176u, 216u, 216u),
-  MK_COL(0u, 128u, 128u),
-  MK_COL(0u, 128u, 64u),
-  MK_COL(0u, 128u, 192u),
-  MK_COL(0u, 128u, 0u),
-  MK_COL(0u, 64u, 128u),
-  MK_COL(0u, 64u, 64u),
-  MK_COL(0u, 64u, 192u),
-  MK_COL(0u, 64u, 0u),
-  MK_COL(0u, 192u, 128u),
-  MK_COL(0u, 192u, 64u),
-  MK_COL(0u, 192u, 192u),
-  MK_COL(0u, 192u, 0u),
-  MK_COL(0u, 0u, 128u),
-  MK_COL(0u, 0u, 64u),
-  MK_COL(0u, 0u, 192u),
-  MK_COL(80u, 80u, 80u),
-  MK_COL(80u, 80u, 176u),
-  MK_COL(80u, 80u, 40u),
-  MK_COL(80u, 80u, 216u),
-  MK_COL(80u, 176u, 80u),
-  MK_COL(80u, 176u, 176u),
-  MK_COL(80u, 176u, 40u),
-  MK_COL(80u, 176u, 216u),
-  MK_COL(80u, 40u, 80u),
-  MK_COL(80u, 40u, 176u),
-  MK_COL(80u, 40u, 40u),
-  MK_COL(80u, 40u, 216u),
-  MK_COL(80u, 216u, 80u),
-  MK_COL(80u, 216u, 176u),
-  MK_COL(80u, 216u, 40u),
-  MK_COL(80u, 216u, 216u),
-  MK_COL(40u, 80u, 80u),
-  MK_COL(40u, 80u, 176u),
-  MK_COL(40u, 80u, 40u),
-  MK_COL(40u, 80u, 216u),
-  MK_COL(40u, 176u, 80u),
-  MK_COL(40u, 176u, 176u),
-  MK_COL(40u, 176u, 40u),
-  MK_COL(40u, 176u, 216u),
-  MK_COL(40u, 40u, 80u),
-  MK_COL(40u, 40u, 176u),
-  MK_COL(40u, 40u, 40u),
-  MK_COL(40u, 40u, 216u),
-  MK_COL(40u, 216u, 80u),
-  MK_COL(40u, 216u, 176u),
-  MK_COL(40u, 216u, 40u),
-  MK_COL(40u, 216u, 216u),
-  MK_COL(216u, 80u, 80u),
-  MK_COL(216u, 80u, 176u),
-  MK_COL(216u, 80u, 40u),
-  MK_COL(216u, 80u, 216u),
-  MK_COL(216u, 176u, 80u),
-  MK_COL(216u, 176u, 176u),
-  MK_COL(216u, 176u, 40u),
-  MK_COL(216u, 176u, 216u),
-  MK_COL(216u, 40u, 80u),
-  MK_COL(216u, 40u, 176u),
-  MK_COL(216u, 40u, 40u),
-  MK_COL(216u, 40u, 216u),
-  MK_COL(216u, 216u, 80u),
-  MK_COL(216u, 216u, 176u),
-  MK_COL(216u, 216u, 40u),
-  MK_COL(216u, 216u, 216u),
-  MK_COL(104u, 104u, 0u),
-  MK_COL(104u, 152u, 0u),
-  MK_COL(104u, 0u, 104u),
-  MK_COL(104u, 0u, 152u),
-  MK_COL(104u, 0u, 0u),
-  MK_COL(152u, 104u, 0u),
-  MK_COL(152u, 152u, 0u),
-  MK_COL(152u, 0u, 104u),
-  MK_COL(152u, 0u, 152u),
-  MK_COL(152u, 0u, 0u),
-  MK_COL(0u, 104u, 104u),
-  MK_COL(0u, 104u, 152u),
-  MK_COL(0u, 104u, 0u),
-  MK_COL(0u, 152u, 104u),
-  MK_COL(0u, 152u, 152u),
-  MK_COL(0u, 152u, 0u),
-  MK_COL(0u, 0u, 104u),
-  MK_COL(0u, 0u, 152u),
-  MK_COL(80u, 80u, 0u),
-  MK_COL(80u, 176u, 0u),
-  MK_COL(80u, 0u, 80u),
-  MK_COL(80u, 0u, 176u),
-  MK_COL(80u, 0u, 0u),
-  MK_COL(176u, 80u, 0u),
-  MK_COL(176u, 176u, 0u),
-  MK_COL(176u, 0u, 80u),
-  MK_COL(176u, 0u, 176u),
-  MK_COL(176u, 0u, 0u),
-  MK_COL(0u, 80u, 80u),
-  MK_COL(0u, 80u, 176u),
-  MK_COL(0u, 80u, 0u),
-  MK_COL(0u, 176u, 80u),
-  MK_COL(0u, 176u, 176u),
-  MK_COL(0u, 176u, 0u),
-  MK_COL(0u, 0u, 80u),
-  MK_COL(0u, 0u, 176u),
-  MK_COL(224u, 224u, 224u),
-  MK_COL(32u, 224u, 224u),
-  MK_COL(224u, 32u, 224u),
-  MK_COL(32u, 32u, 224u),
-  MK_COL(224u, 224u, 32u),
-  MK_COL(32u, 224u, 32u),
-  MK_COL(224u, 32u, 32u),
-  MK_COL(32u, 32u, 32u),
-  MK_COL(24u, 0u, 0u),
-  MK_COL(0u, 24u, 0u),
-  MK_COL(0u, 0u, 24u),
-  MK_COL(232u, 0u, 0u),
-  MK_COL(0u, 232u, 0u),
-  MK_COL(0u, 0u, 232u),
-  MK_COL(240u, 240u, 240u),
-  MK_COL(16u, 240u, 240u),
-  MK_COL(240u, 16u, 240u),
-  MK_COL(16u, 16u, 240u),
-  MK_COL(240u, 240u, 16u),
-  MK_COL(16u, 240u, 16u),
-  MK_COL(240u, 16u, 16u),
-  MK_COL(16u, 16u, 16u),
-  MK_COL(8u, 8u, 0u),
-  MK_COL(8u, 248u, 0u),
-  MK_COL(8u, 0u, 8u),
-  MK_COL(8u, 0u, 248u),
-  MK_COL(8u, 0u, 0u),
-  MK_COL(248u, 8u, 0u),
-  MK_COL(248u, 248u, 0u),
-  MK_COL(248u, 0u, 8u),
-  MK_COL(248u, 0u, 248u),
-  MK_COL(248u, 0u, 0u),
-  MK_COL(0u, 8u, 8u),
-  MK_COL(0u, 8u, 248u),
-  MK_COL(0u, 8u, 0u),
-  MK_COL(0u, 248u, 8u),
-  MK_COL(0u, 248u, 248u),
-  MK_COL(0u, 248u, 0u),
-  MK_COL(0u, 0u, 8u),
-  MK_COL(0u, 0u, 248u),
   MK_COL(0u, 0u, 0u),
   MK_COL(255u, 255u, 255u),
   MK_COL(1u, 1u, 1u),
-  MK_COL(254u, 254u, 2u),
-  MK_COL(248u, 249u, 248u),
-  MK_COL(255u, 0u, 255u),
-//  MK_COL(0u, 255u, 255u),
-  MK_COL(1u, 2u, 255u),
-  MK_COL(50u, 50u, 50u),
-  MK_COL(1u, 254u, 1u),
-  MK_COL(5u, 5u, 5u),
-  MK_COL(255u, 2u, 1u),
-  MK_COL(9u, 9u, 9u),
-  MK_COL(3u, 3u, 3u),
-  MK_COL(253u, 253u, 253u),
-//  MK_COL(0u, 0u, 1u),
-//  MK_COL(0u, 0u, 255u),
-  MK_COL(2u, 2u, 2u),
   MK_COL(254u, 254u, 254u),
-  MK_COL(244u, 244u, 244u),
-  MK_COL(255u, 0u, 0u),
-  MK_COL(232u, 232u, 232u),
-//  MK_COL(1u, 1u, 2u),
-//  MK_COL(1u, 0u, 0u),
-//  MK_COL(0u, 0u, 2u),
-  MK_COL(13u, 13u, 13u),
-//  MK_COL(255u, 255u, 0u),
-  MK_COL(23u, 23u, 23u),
-  MK_COL(0u, 255u, 0u),
-  MK_COL(250u, 249u, 253u),
-  MK_COL(2u, 1u, 1u),
-  MK_COL(254u, 254u, 255u),
-  MK_COL(255u, 254u, 254u),
-  MK_COL(254u, 249u, 249u),
-  MK_COL(1u, 2u, 1u),
-//  MK_COL(0u, 1u, 0u),
-  MK_COL(254u, 255u, 254u),
-  MK_COL(2u, 2u, 3u),
-  MK_COL(3u, 2u, 2u),
-  MK_COL(249u, 254u, 249u),
-  MK_COL(251u, 251u, 251u),
+  MK_COL(2u, 2u, 2u),
   MK_COL(4u, 4u, 4u),
-  MK_COL(2u, 3u, 2u),
-//  MK_COL(0u, 1u, 255u),
-  MK_COL(0u, 0u, 253u),
   MK_COL(252u, 252u, 252u),
-  MK_COL(236u, 236u, 236u),
-  MK_COL(255u, 1u, 0u),
-  MK_COL(204u, 204u, 204u),
+  MK_COL(250u, 0u, 0u),
+  MK_COL(0u, 250u, 0u),
+  MK_COL(0u, 0u, 250u),
+  MK_COL(6u, 0u, 0u),
+  MK_COL(0u, 6u, 0u),
+  MK_COL(0u, 0u, 6u),
+  MK_COL(0u, 0u, 248u),
+  MK_COL(0u, 0u, 8u),
+  MK_COL(0u, 248u, 0u),
+  MK_COL(0u, 248u, 248u),
+  MK_COL(0u, 248u, 8u),
+  MK_COL(0u, 8u, 0u),
+  MK_COL(0u, 8u, 248u),
+  MK_COL(0u, 8u, 8u),
+  MK_COL(8u, 8u, 8u),
+  MK_COL(248u, 0u, 0u),
+  MK_COL(248u, 0u, 248u),
+  MK_COL(248u, 0u, 8u),
+  MK_COL(248u, 248u, 0u),
+  MK_COL(248u, 8u, 0u),
+  MK_COL(8u, 0u, 0u),
+  MK_COL(8u, 0u, 248u),
+  MK_COL(8u, 0u, 8u),
+  MK_COL(8u, 248u, 0u),
+  MK_COL(8u, 8u, 0u),
+  MK_COL(23u, 23u, 23u),
+  MK_COL(13u, 13u, 13u),
+  MK_COL(232u, 232u, 232u),
+  MK_COL(244u, 244u, 244u),
   MK_COL(245u, 245u, 250u),
-//  MK_COL(0u, 255u, 1u)
+  MK_COL(50u, 50u, 50u),
+  MK_COL(204u, 204u, 204u),
+  MK_COL(236u, 236u, 236u),
+  MK_COL(16u, 16u, 16u),
+  MK_COL(240u, 16u, 16u),
+  MK_COL(16u, 240u, 16u),
+  MK_COL(240u, 240u, 16u),
+  MK_COL(16u, 16u, 240u),
+  MK_COL(240u, 16u, 240u),
+  MK_COL(16u, 240u, 240u),
+  MK_COL(240u, 240u, 240u),
+  MK_COL(0u, 0u, 232u),
+  MK_COL(0u, 232u, 0u),
+  MK_COL(232u, 0u, 0u),
+  MK_COL(0u, 0u, 24u),
+  MK_COL(0u, 24u, 0u),
+  MK_COL(24u, 0u, 0u),
+  MK_COL(32u, 32u, 32u),
+  MK_COL(224u, 32u, 32u),
+  MK_COL(32u, 224u, 32u),
+  MK_COL(224u, 224u, 32u),
+  MK_COL(32u, 32u, 224u),
+  MK_COL(224u, 32u, 224u),
+  MK_COL(32u, 224u, 224u),
+  MK_COL(224u, 224u, 224u),
+  MK_COL(0u, 0u, 176u),
+  MK_COL(0u, 0u, 80u),
+  MK_COL(0u, 176u, 0u),
+  MK_COL(0u, 176u, 176u),
+  MK_COL(0u, 176u, 80u),
+  MK_COL(0u, 80u, 0u),
+  MK_COL(0u, 80u, 176u),
+  MK_COL(0u, 80u, 80u),
+  MK_COL(176u, 0u, 0u),
+  MK_COL(176u, 0u, 176u),
+  MK_COL(176u, 0u, 80u),
+  MK_COL(176u, 176u, 0u),
+  MK_COL(176u, 80u, 0u),
+  MK_COL(80u, 0u, 0u),
+  MK_COL(80u, 0u, 176u),
+  MK_COL(80u, 0u, 80u),
+  MK_COL(80u, 176u, 0u),
+  MK_COL(80u, 80u, 0u),
+  MK_COL(0u, 0u, 152u),
+  MK_COL(0u, 0u, 104u),
+  MK_COL(0u, 152u, 0u),
+  MK_COL(0u, 152u, 152u),
+  MK_COL(0u, 152u, 104u),
+  MK_COL(0u, 104u, 0u),
+  MK_COL(0u, 104u, 152u),
+  MK_COL(0u, 104u, 104u),
+  MK_COL(152u, 0u, 0u),
+  MK_COL(152u, 0u, 152u),
+  MK_COL(152u, 0u, 104u),
+  MK_COL(152u, 152u, 0u),
+  MK_COL(152u, 104u, 0u),
+  MK_COL(104u, 0u, 0u),
+  MK_COL(104u, 0u, 152u),
+  MK_COL(104u, 0u, 104u),
+  MK_COL(104u, 152u, 0u),
+  MK_COL(104u, 104u, 0u),
+  MK_COL(216u, 216u, 216u),
+  MK_COL(216u, 216u, 40u),
+  MK_COL(216u, 216u, 176u),
+  MK_COL(216u, 216u, 80u),
+  MK_COL(216u, 40u, 216u),
+  MK_COL(216u, 40u, 40u),
+  MK_COL(216u, 40u, 176u),
+  MK_COL(216u, 40u, 80u),
+  MK_COL(216u, 176u, 216u),
+  MK_COL(216u, 176u, 40u),
+  MK_COL(216u, 176u, 176u),
+  MK_COL(216u, 176u, 80u),
+  MK_COL(216u, 80u, 216u),
+  MK_COL(216u, 80u, 40u),
+  MK_COL(216u, 80u, 176u),
+  MK_COL(216u, 80u, 80u),
+  MK_COL(40u, 216u, 216u),
+  MK_COL(40u, 216u, 40u),
+  MK_COL(40u, 216u, 176u),
+  MK_COL(40u, 216u, 80u),
+  MK_COL(40u, 40u, 216u),
+  MK_COL(40u, 40u, 40u),
+  MK_COL(40u, 40u, 176u),
+  MK_COL(40u, 40u, 80u),
+  MK_COL(40u, 176u, 216u),
+  MK_COL(40u, 176u, 40u),
+  MK_COL(40u, 176u, 176u),
+  MK_COL(40u, 176u, 80u),
+  MK_COL(40u, 80u, 216u),
+  MK_COL(40u, 80u, 40u),
+  MK_COL(40u, 80u, 176u),
+  MK_COL(40u, 80u, 80u),
+  MK_COL(80u, 216u, 216u),
+  MK_COL(80u, 216u, 40u),
+  MK_COL(80u, 216u, 176u),
+  MK_COL(80u, 216u, 80u),
+  MK_COL(80u, 40u, 216u),
+  MK_COL(80u, 40u, 40u),
+  MK_COL(80u, 40u, 176u),
+  MK_COL(80u, 40u, 80u),
+  MK_COL(80u, 176u, 216u),
+  MK_COL(80u, 176u, 40u),
+  MK_COL(80u, 176u, 176u),
+  MK_COL(80u, 176u, 80u),
+  MK_COL(80u, 80u, 216u),
+  MK_COL(80u, 80u, 40u),
+  MK_COL(80u, 80u, 176u),
+  MK_COL(80u, 80u, 80u),
+  MK_COL(0u, 0u, 192u),
+  MK_COL(0u, 0u, 64u),
+  MK_COL(0u, 0u, 128u),
+  MK_COL(0u, 192u, 0u),
+  MK_COL(0u, 192u, 192u),
+  MK_COL(0u, 192u, 64u),
+  MK_COL(0u, 192u, 128u),
+  MK_COL(0u, 64u, 0u),
+  MK_COL(0u, 64u, 192u),
+  MK_COL(0u, 64u, 64u),
+  MK_COL(0u, 64u, 128u),
+  MK_COL(0u, 128u, 0u),
+  MK_COL(0u, 128u, 192u),
+  MK_COL(0u, 128u, 64u),
+  MK_COL(0u, 128u, 128u),
+  MK_COL(176u, 216u, 216u),
+  MK_COL(176u, 216u, 40u),
+  MK_COL(176u, 216u, 176u),
+  MK_COL(176u, 216u, 80u),
+  MK_COL(176u, 40u, 216u),
+  MK_COL(176u, 40u, 40u),
+  MK_COL(176u, 40u, 176u),
+  MK_COL(176u, 40u, 80u),
+  MK_COL(176u, 176u, 216u),
+  MK_COL(176u, 176u, 40u),
+  MK_COL(176u, 176u, 176u),
+  MK_COL(176u, 176u, 80u),
+  MK_COL(176u, 80u, 216u),
+  MK_COL(176u, 80u, 40u),
+  MK_COL(176u, 80u, 176u),
+  MK_COL(176u, 80u, 80u),
+  MK_COL(192u, 0u, 0u),
+  MK_COL(192u, 0u, 192u),
+  MK_COL(192u, 0u, 64u),
+  MK_COL(192u, 0u, 128u),
+  MK_COL(192u, 192u, 0u),
+  MK_COL(192u, 192u, 192u),
+  MK_COL(192u, 192u, 64u),
+  MK_COL(192u, 192u, 128u),
+  MK_COL(192u, 64u, 0u),
+  MK_COL(192u, 64u, 192u),
+  MK_COL(192u, 64u, 64u),
+  MK_COL(192u, 64u, 128u),
+  MK_COL(192u, 128u, 0u),
+  MK_COL(192u, 128u, 192u),
+  MK_COL(192u, 128u, 64u),
+  MK_COL(192u, 128u, 128u),
+  MK_COL(64u, 0u, 0u),
+  MK_COL(64u, 0u, 192u),
+  MK_COL(64u, 0u, 64u),
+  MK_COL(64u, 0u, 128u),
+  MK_COL(64u, 192u, 0u),
+  MK_COL(64u, 192u, 192u),
+  MK_COL(64u, 192u, 64u),
+  MK_COL(64u, 192u, 128u),
+  MK_COL(64u, 64u, 0u),
+  MK_COL(64u, 64u, 192u),
+  MK_COL(64u, 64u, 64u),
+  MK_COL(64u, 64u, 128u),
+  MK_COL(64u, 128u, 0u),
+  MK_COL(64u, 128u, 192u),
+  MK_COL(64u, 128u, 64u),
+  MK_COL(64u, 128u, 128u),
+  MK_COL(128u, 0u, 0u),
+  MK_COL(128u, 0u, 192u),
+  MK_COL(128u, 0u, 64u),
+  MK_COL(128u, 0u, 128u),
+  MK_COL(128u, 192u, 0u),
+  MK_COL(128u, 192u, 192u),
+  MK_COL(128u, 192u, 64u),
+  MK_COL(128u, 192u, 128u),
+  MK_COL(128u, 64u, 0u),
+  MK_COL(128u, 64u, 192u),
+  MK_COL(128u, 64u, 64u),
+  MK_COL(128u, 64u, 128u),
+  MK_COL(128u, 128u, 0u),
+  MK_COL(128u, 128u, 192u),
+  MK_COL(128u, 128u, 64u),
+  MK_COL(128u, 128u, 128u),
 };
 
 #undef MK_COL
diff --git a/src/enc/delta_palettization.h b/src/enc/delta_palettization.h
index e8f2e6de..78a2a6bd 100644
--- a/src/enc/delta_palettization.h
+++ b/src/enc/delta_palettization.h
@@ -5,7 +5,11 @@
 
 #include "../webp/types.h"
 
-#define DELTA_PALETTE_SIZE (256 - 10)
+// Format allows palette up to 256 entries, but more palette entries produce
+// bigger entropy. In the future it will probably be useful to add more entries
+// that are far from the origin of the palette or choose remaining entries
+// dynamically.
+#define DELTA_PALETTE_SIZE 226
 
 extern const uint32_t kDeltaPalette[DELTA_PALETTE_SIZE];