new segmentation algorithm

fixes the 'blocky sky problem' (saturation problem: when luma was flat,
chroma noise was taking over, resulting in random segment id assigned.
When just using a common uniform segment was better).

+ side clean-up and readibility/experimentability MACRO'ization
+ added '-map 7' option

Change-Id: I35982a9e43c0fecbfdd7b05e4813e8ba8c121d71

src/enc/vp8enci.h

@@ -29,9 +29,6 @@ extern "C" {
 #define ENC_MIN_VERSION 2
 #define ENC_REV_VERSION 0
 
-// size of histogram used by CollectHistogram.
-#define MAX_COEFF_THRESH   64
-
 // intra prediction modes
 enum { B_DC_PRED = 0,   // 4x4 modes
        B_TM_PRED = 1,
@@ -162,6 +159,14 @@ static WEBP_INLINE int QUANTDIV(int n, int iQ, int B) {
 }
 extern const uint8_t VP8Zigzag[16];
 
+// size of histogram used by CollectHistogram.
+#define MAX_COEFF_THRESH   31
+typedef struct VP8Histogram VP8Histogram;
+struct VP8Histogram {
+  // TODO(skal): we only need to store the max_value and last_non_zero actually.
+  int distribution[MAX_COEFF_THRESH + 1];
+};
+
 //------------------------------------------------------------------------------
 // Headers