Decoded image appears pixelated

[Shnatsel]

Found in image-webp v0.2.0

Input: bsk.webp.gz

imagemagick result:

image-webp result:

Same versions and reproduction code as in https://github.com/image-rs/image-webp/issues/117

This happens on vibrant reds so might be related to image-rs/image#115

[fintelia]

Seems this is a bug in the lossy decoding:

$ webpinfo bsk.webp
File: bsk.webp
RIFF HEADER:
  File size:   3712
Chunk VP8X at offset     12, length     18
  ICCP: 0
  Alpha: 1
  EXIF: 0
  XMP: 0
  Animation: 0
  Canvas size 89 x 90
Chunk ALPH at offset     30, length    652
Chunk VP8  at offset    682, length   3030
  Width: 89
  Height: 90
  Alpha: 0
  Animation: 0
  Format: Lossy (1)
No error detected.

[Shnatsel]

Since it's pixelated I thought the loop filter might be to blame. But dwebp -nofilter does not produce output that's anywhere near this pixelated, so it's not a bug in the loop filter.

[Shnatsel]

Duplicate of #142