For some exact resonance the over-quantization was exactly
compensating the under-quantization, leading to resonance
and strange patterns.
-> we special-handle the very flat blocks, hopefully for the
greater good (and not just the bad-resonance case).
For 'fast mode' (-m 3 or less), we just pay special attention
to the border of the image, where the oscillation / instability
usually starts. For the inner part of the image, since we're not
doing rd-opt, it's harder to fix anything.
Overall, on 'regular' images, the change is written the noise,
often leading to overall faster encoding (because of the short-cut).
BUG=webp:432
Change-Id: Ifaa8286499add80fd77daecf8e347abbff7c3a15
Move IsFlat to its own header. This allows it to continue to be
inlined. Using the RTCD and creating a distinct function slows down arm
builds.
flower mug
C 3.59 2.12
NEON 3.47 2.01
BUG=b/118740850
Change-Id: Id77e8f76d9e9790c498806e7070bbe37c10bc2e9
