Adaptive CDEF: feedback follow-up
Following up on CL feedback from:
https://aomedia-review.googlesource.com/c/aom/+/195781
Bug: aomedia:375221136
Change-Id: Ia4755f4b4eed412b75392276462fee13bd3d4ef1
diff --git a/av1/encoder/pickcdef.c b/av1/encoder/pickcdef.c
index 1e5701a..b0c1e58 100644
--- a/av1/encoder/pickcdef.c
+++ b/av1/encoder/pickcdef.c
@@ -960,10 +960,18 @@
// For CDEF_ADAPTIVE, set primary and secondary CDEF at reduced strength for
// qindexes 33 through 220.
- // Please note that the ">> 1" often reduces strengths by more than a half in
- // practice, due to how few strength levels there are (0-15 pri, 0-3 sec).
- // For example: a pri strength of 3 becomes 1, and a sec strength of 1 becomes
- // 0.
+ // Note 1: for odd strengths, the 0.5 discarded by ">> 1" is a significant
+ // part of the strength when the strength is small, and because there are
+ // few strength levels, odd strengths are reduced significantly more than a
+ // half. This is intended behavior for reduced strength.
+ // For example: a pri strength of 3 becomes 1, and a sec strength of 1
+ // becomes 0.
+ // Note 2: a (signaled) sec strength value of 3 is special as it results in an
+ // actual sec strength of 4. We tried adding +1 to the sec strength 3 so it
+ // maps to a reduced sec strength of 2. However, on Daala's subset1, the
+ // resulting SSIMULACRA 2 scores were either exactly the same (at cpu-used 6),
+ // or within noise level (at cpu-used 3). Given that there were no discernable
+ // improvements, this special mapping was left out for reduced strength.
if (cdef_control == CDEF_ADAPTIVE && cpi->oxcf.mode == ALLINTRA &&
(cpi->oxcf.rc_cfg.mode == AOM_Q || cpi->oxcf.rc_cfg.mode == AOM_CQ) &&
cpi->oxcf.rc_cfg.cq_level <= 220) {
