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vp8: Suppress denoising with respect to old reference frames.

If the GOLDEN or ALTREF frame was last updated > x frames in the past,
don't use them for denoising (only consider LAST). Using an old reference
frame for denoising, e.g., if it is a long-term reference or the last key frame,
can cause some visible artifacts, in particular in the aggressive denoising mode.

Change-Id: I239c9fbb092c36cba7e95328f1fa67a58d6a7ed9

--- a/vp8/encoder/denoising.h

+++ b/vp8/encoder/denoising.h

@@ -27,6 +27,8 @@

 #define SUM_DIFF_FROM_AVG_THRESH_UV (8 * 8 * 8)

 #define MOTION_MAGNITUDE_THRESHOLD_UV (8*3)

+#define MAX_GF_ARF_DENOISE_RANGE (16)

+

 enum vp8_denoiser_decision

 {

   COPY_BLOCK,

--- a/vp8/encoder/pickinter.c

+++ b/vp8/encoder/pickinter.c

@@ -1083,7 +1083,14 @@

         {

             /* Store for later use by denoiser. */

-            if (this_mode == ZEROMV && sse < zero_mv_sse )

+            // Dont' denoise with GOLDEN OR ALTREF is they are old reference

+            // frames (greater than MAX_GF_ARF_DENOISE_RANGE frames in past).

+            int skip_old_reference = ((this_ref_frame != LAST_FRAME) &&

+                (cpi->common.current_video_frame -

+                 cpi->current_ref_frames[this_ref_frame] >

+                 MAX_GF_ARF_DENOISE_RANGE)) ? 1 : 0;

+            if (this_mode == ZEROMV && sse < zero_mv_sse &&

+                !skip_old_reference)

             {

                 zero_mv_sse = sse;

                 x->best_zeromv_reference_frame =

@@ -1092,7 +1099,7 @@

             /* Store the best NEWMV in x for later use in the denoiser. */

             if (x->e_mbd.mode_info_context->mbmi.mode == NEWMV &&

-                    sse < best_sse)

+                sse < best_sse && !skip_old_reference)

             {

                 best_sse = sse;

                 x->best_sse_inter_mode = NEWMV;