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trying to make sense of png filter modes

db4
Doug Coleman 2009-09-26 18:46:27 -05:00
parent 117a0e2ac7
commit 71952f702a
1 changed files with 26 additions and 7 deletions
basis/images/png

33
basis/images/png/png.factor
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@ -14,6 +14,18 @@ TUPLE: loading-png
width height bit-depth color-type compression-method
filter-method interlace-method uncompressed ;
CONSTANT: filter-none 0
CONSTANT: filter-sub 1
CONSTANT: filter-up 2
CONSTANT: filter-average 3
CONSTANT: filter-paeth 4
CONSTANT: greyscale 0
CONSTANT: truecolor 2
CONSTANT: indexed-color 3
CONSTANT: greyscale-alpha 4
CONSTANT: truecolor-alpha 6
: <loading-png> ( -- image )
loading-png new
V{ } clone >>chunks ;
@ -66,6 +78,7 @@ ERROR: bad-checksum ;
ERROR: unknown-color-type n ;
ERROR: unimplemented-color-type image ;
ERROR: unknown-filter-method image ;
: inflate-data ( loading-png -- bytes )
find-compressed-bytes zlib-inflate ;
@ -77,9 +90,15 @@ ERROR: unimplemented-color-type image ;
[ unknown-color-type ]
} case ;
: filter-png ( groups loading-png -- byte-array )
filter-method>> {
{ filter-none [ reverse-png-filter ] }
[ unknown-filter-method ]
} case ;
: png-image-bytes ( loading-png -- byte-array )
[ inflate-data ] [ png-group-width ] bi group
reverse-png-filter ;
[ [ inflate-data ] [ png-group-width ] bi group ]
[ filter-png ] bi ;
: decode-greyscale ( loading-png -- loading-png )
unimplemented-color-type ;
@ -127,11 +146,11 @@ ERROR: invalid-color-type/bit-depth loading-png ;
: decode-png ( loading-png -- loading-png )
dup color-type>> {
{ 0 [ validate-greyscale decode-greyscale ] }
{ 2 [ validate-truecolor decode-truecolor ] }
{ 3 [ validate-indexed-color decode-indexed-color ] }
{ 4 [ validate-greyscale-alpha decode-greyscale-alpha ] }
{ 6 [ validate-truecolor-alpha decode-truecolor-alpha ] }
{ greyscale [ validate-greyscale decode-greyscale ] }
{ truecolor [ validate-truecolor decode-truecolor ] }
{ indexed-color [ validate-indexed-color decode-indexed-color ] }
{ greyscale-alpha [ validate-greyscale-alpha decode-greyscale-alpha ] }
{ truecolor-alpha [ validate-truecolor-alpha decode-truecolor-alpha ] }
[ unknown-color-type ]
} case ;