From b39e7487a7c1596532549bea8ae92b1905cec411 Mon Sep 17 00:00:00 2001
From: Vikas Arora <vikasa@google.com>
Date: Thu, 26 Apr 2012 10:25:49 +0000
Subject: [PATCH] Reducing emerging palette size from 11 to 9 bits.

This is required to reduce memory used to construct histo_image.

Change-Id: I491a06e10a3e3f3d8a00ecec286394378283ffea
---
 src/enc/backward_references.c | 2 +-
 src/enc/backward_references.h | 6 ++++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/enc/backward_references.c b/src/enc/backward_references.c
index 6b948871..d6f6183f 100644
--- a/src/enc/backward_references.c
+++ b/src/enc/backward_references.c
@@ -751,7 +751,7 @@ int VP8LCalculateEstimateForCacheSize(
                                        stream, &stream_size)) {
     goto Error;
   }
-  for (cache_bits = 0; cache_bits < 12; ++cache_bits) {
+  for (cache_bits = 0; cache_bits <= kColorCacheBitsMax; ++cache_bits) {
     double cur_entropy;
     VP8LHistogram histo;
     VP8LHistogramInit(&histo, cache_bits);
diff --git a/src/enc/backward_references.h b/src/enc/backward_references.h
index 7bcc3313..d5e1de8b 100644
--- a/src/enc/backward_references.h
+++ b/src/enc/backward_references.h
@@ -27,8 +27,10 @@ extern "C" {
 // Compression constants
 #define CODE_LENGTH_CODES 19
 static const int kLengthCodes = 24;
-static const int kColorCacheBitsMax = 11;
-#define PIX_OR_COPY_CODES_MAX (256 + 24 + (1 << 11))
+// The spec allows 11, we use 9 bits to reduce memory consumption in encoding.
+// Having 9 instead of 11 removes about 0.25 % of compression density.
+static const int kColorCacheBitsMax = 9;
+#define PIX_OR_COPY_CODES_MAX (256 + 24 + (1 << 9))
 static const int kMaxLength = 4096;
 
 // use GNU builtins where available.