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Reduce loop filter in cyclic refresh.

Reduce the delta loop filter for blocks that are cyclicly refreshed.
This helps to reduce the dot artifacts that may happen
when zero_mv blocks are repeatedly loop-filtered.

This change, along with the fix in:
https://gerrit.chromium.org/gerrit/#/c/40409/
helps to reduce this artifact, but cannot remove the dot artifacts completely.

Change-Id: I44675e7a0f59295b648a3b7d4956fb301231a97f

--- a/vp8/encoder/onyx_if.c

+++ b/vp8/encoder/onyx_if.c

@@ -3732,11 +3732,22 @@

     /* Setup background Q adjustment for error resilient mode.

      * For multi-layer encodes only enable this for the base layer.

-     */

+     * Reduce loop filter to reduce "dot" artifacts that can occur for repeated

+     * loop filtering on ZEROMV_LASTREF blocks.

+     * For now reducing it to -32, only for resolutions above CIF and

+     * #temporal_layers < 3 (artifact is hard to see at low spatial resolution

+     * and/or high #temporal layers).

+    */

     if (cpi->cyclic_refresh_mode_enabled)

     {

+      int delta_loop_filter = 0;

+      if (cm->Width > 352 && cm->Height > 288 &&

+          cpi->oxcf.number_of_layers < 3)

+      {

+        delta_loop_filter = -32;

+      }

       if (cpi->current_layer==0)

-        cyclic_background_refresh(cpi, Q, 0);

+        cyclic_background_refresh(cpi, Q, delta_loop_filter);

       else

         disable_segmentation(cpi);

     }