# note: An uncompressed alpha plane under the horizontal filter.
# expect: ok
# exercises: WebPUnfilters[1], each byte a difference from the one to its
#   left.
chunks VP8X ALPH VP8
alpha 1
alph_filtering 1
width 16
height 16
yac_qi 30
macroblock
coeffs y2 -20
coeffs y[2] 1:5 -3