tree c377345a62ddcd22c31af36a95fc86ee8c7845a2
parent 6376ce80ad94ee797a360d3d98727b0786286e26
author Paul Wilkins <paulwilkins@google.com> 1644331599 +0000
committer Paul Wilkins <paulwilkins@google.com> 1644853130 +0000

Per SB Rd adjustment for ALLINTRA mode.

This patch adjusts the rd value for each SB in ALLINTRA mode.

Experiments showed that lowering the RD value a little at the frame
level improved metrics slightly on most images in our png-crush
tests set and also helped visual quality somewhat.

This patch is the result of extensive experiments  where the
adjustment was applied instead at the per SB level.

At the moment the choice is based on the relative min and max
variance of 4x4 sub blocks within each SB though various other
possible measures were considered and further gains may be
possible.

Having tuned using the png crush data set the behavior was then
validated using the larger Tecnick data set.

Metrics results (PSNR, SSIM, Butteraugli) were as follows.

Png Crush -1.37, 0.25, -3.59
Tecnick -2.60, -0.46, -4.42

Change-Id: I0a5342e1d74a3e64f3768f07686b58eb755c60d7