Context for discussion, section 6.6 of this png rfc
* http://tools.ietf.org/html/rfc2083
The forward filter seems trivial, but the backward filter seems
tricky to me if not using loop. Any idea on a loop free
solution?
NB. Paeth Predictor
paeth=: 3 : 0
p=. +/ 1 1 _1 * y
y{~ (i.<./) |p-y
)
forward=: 4 : 0
prev=. 10$ 3 5 8
iy=. i.10
pae=. 256&| iy - paeth"1 ((-x)}.(x#0),iy),.prev,.((-x)}.(x#0),prev)
)
3 forward''
253 252 250 3 3 3 3 3 3 3
4 forward''
253 252 250 0 1 0 4 2 0 6
NB. backward ??
NB. 4 backward 4 forward ''
--
regards,
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