shithub: libvpx

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Adjust q range

Skip Q values between the q.0 mode and a real q of
2.0 as these are not valuable from an RD perspective.

Change-Id: I110c4858c57f97315953f4d88a2596d4764360df

--- a/vp9/common/vp9_quant_common.c

+++ b/vp9/common/vp9_quant_common.c

@@ -15,7 +15,7 @@

 static int16_t dc_qlookup[QINDEX_RANGE];

 static int16_t ac_qlookup[QINDEX_RANGE];

-#define ACDC_MIN 4

+#define ACDC_MIN 8

 // TODO(dkovalev) move to common and reuse

 static double poly3(double a, double b, double c, double d, double x) {

@@ -25,10 +25,19 @@

 void vp9_init_quant_tables() {

   int i, val = 4;

-  for (i = 0; i < QINDEX_RANGE; i++) {

+  // A "real" q of 1.0 forces lossless mode.

+  // In practice non lossless Q's between 1.0 and 2.0 (represented here by

+  // integer values from 5-7 give poor rd results (lower psnr and often

+  // larger size than the lossless encode. To block out those "not very useful"

+  // values we increment the ac and dc q lookup values by 4 after position 0.

+  ac_qlookup[0] = val;

+  dc_qlookup[0] = val;

+  val += 4;

+

+  for (i = 1; i < QINDEX_RANGE; i++) {

     const int ac_val = val;

-    val = (int)(val * 1.02);

+    val = (int)(val * 1.01975);

     if (val == ac_val)

       ++val;

--- a/vp9/encoder/vp9_onyx_if.c

+++ b/vp9/encoder/vp9_onyx_if.c

@@ -161,6 +161,11 @@

   const double minqtarget = MIN(((x3 * maxq + x2) * maxq + x1) * maxq + c,

                                 maxq);

+  // Special case handling to deal with the step from q2.0

+  // down to lossless mode represented by q 1.0.

+  if (minqtarget <= 2.0)

+    return 0;

+

   for (i = 0; i < QINDEX_RANGE; i++) {

     if (minqtarget <= vp9_convert_qindex_to_q(i))

       return i;

--- a/vp9/encoder/vp9_quantize.c

+++ b/vp9/encoder/vp9_quantize.c

@@ -263,10 +263,6 @@

   cm->base_qindex = Q;

-  // Set lossless mode

-  if (cm->base_qindex <= 4)

-    cm->base_qindex = 0;

-

   // if any of the delta_q values are changing update flag will

   // have to be set.

   cm->y_dc_delta_q = 0;

-- 

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