Pascal Massimino 31b1e34342 fix SSIM metric ... by ignoring too-dark area
Roughly, if both the source and the reference areas are
darker too dark (R/G/B <= ~6), they are ignored.

One caveat: SSIM calculation won't work for U/V planes,
which are 128-centered and not related to luminance.
But WebPPlaneDistortion() enforces the conversion to RGB,
if needed.

Change-Id: I586c2579c475583b8c90c5baefd766b1d5aea591
2016-10-20 15:17:55 +02:00
..