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Change the rule of picking UV mode in MBAnalyzeBestUVMode()

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Pick the mode with the smallest alpha.
It only affects m0, in which case the mode decision is not re-examined
later in VP8Decimate(). Tests on some natural content png images show
PSNR increase as well as visual quality improvement.

Change-Id: Iea997e718cd7477160fa05eb7cfb35f4cec2fa9a
(cherry picked from commit 1377ac2ec1cb81e4a74fa6294ff30a9e4cc584aa)
This commit is contained in:
hui su 2016-09-14 10:34:25 -07:00 committed by James Zern
parent 9c75dbd39c
commit 532215dd29
1 changed files with 5 additions and 0 deletions
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5
src/enc/analysis.c
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@ -307,6 +307,7 @@ static int MBAnalyzeBestIntra4Mode(VP8EncIterator* const it,
static int MBAnalyzeBestUVMode(VP8EncIterator* const it) {
int best_alpha = DEFAULT_ALPHA;
int smallest_alpha = 0;
int best_mode = 0;
const int max_mode = MAX_UV_MODE;
int mode;
@ -322,6 +323,10 @@ static int MBAnalyzeBestUVMode(VP8EncIterator* const it) {
alpha = GetAlpha(&histo);
if (IS_BETTER_ALPHA(alpha, best_alpha)) {
best_alpha = alpha;
}
// The best prediction mode tends to be the one with the smallest alpha.
if (mode == 0 || alpha < smallest_alpha) {
smallest_alpha = alpha;
best_mode = mode;
}
}