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Add GF group noise weighting in rd_variance_adjustment()

For film mode add a weighting to the thresholds used
in rd_variance_adjustment() based on noise measured in the
first pass.

Change-Id: I83ca669bb55aa52f1d34f03a2268b79fba890770

--- a/vp9/encoder/vp9_rdopt.c

+++ b/vp9/encoder/vp9_rdopt.c

@@ -3140,6 +3140,7 @@

   unsigned int absvar_diff = 0;

   unsigned int var_factor = 0;

   unsigned int adj_max;

+  unsigned int low_var_thresh = LOW_VAR_THRESH;

   const int bw = num_8x8_blocks_wide_lookup[bsize];

   const int bh = num_8x8_blocks_high_lookup[bsize];

   vp9e_tune_content content_type = cpi->oxcf.content;

@@ -3164,12 +3165,23 @@

   rec_variance /= (bw * bh);

   src_variance /= (bw * bh);

+  if (content_type == VP9E_CONTENT_FILM) {

+    if (cpi->oxcf.pass == 2) {

+      // Adjust low variance threshold based on estimated group noise enegry.

+      double noise_factor =

+          (double)cpi->twopass.gf_group.group_noise_energy / SECTION_NOISE_DEF;

+      low_var_thresh = (unsigned int)(low_var_thresh * noise_factor);

+    }

+  } else {

+    low_var_thresh = LOW_VAR_THRESH / 2;

+  }

+

   // Lower of source (raw per pixel value) and recon variance. Note that

   // if the source per pixel is 0 then the recon value here will not be per

   // pixel (see above) so will likely be much larger.

   src_rec_min = VPXMIN(src_variance, rec_variance);

-  if (src_rec_min > LOW_VAR_THRESH) return;

+  if (src_rec_min > low_var_thresh) return;

   absvar_diff = (src_variance > rec_variance) ? (src_variance - rec_variance)

                                               : (rec_variance - src_variance);

@@ -3183,7 +3195,7 @@

   *this_rd += (*this_rd * var_factor) / 100;

   if (content_type == VP9E_CONTENT_FILM) {

-    if (src_rec_min <= LOW_VAR_THRESH / 2) {

+    if (src_rec_min <= low_var_thresh / 2) {

       if (ref_frame == INTRA_FRAME) {

         if (this_mode == DC_PRED)

           *this_rd *= 2;