package Image::Leptonica::Func::binreduce;
$Image::Leptonica::Func::binreduce::VERSION = '0.04';
1;
__END__
=pod
=encoding UTF-8
=head1 NAME
Image::Leptonica::Func::binreduce
=head1 VERSION
version 0.04
=head1 C<binreduce.c>
binreduce.c
Subsampled 2x reduction
PIX *pixReduceBinary2()
Rank filtered 2x reductions
PIX *pixReduceRankBinaryCascade()
PIX *pixReduceRankBinary2()
Permutation table for 2x rank binary reduction
l_uint8 *makeSubsampleTab2x(void)
=head1 FUNCTIONS
=head2 makeSubsampleTab2x
l_uint8 * makeSubsampleTab2x ( void )
makeSubsampleTab2x()
This table permutes the bits in a byte, from
0 4 1 5 2 6 3 7
to
0 1 2 3 4 5 6 7
=head2 pixReduceBinary2
PIX * pixReduceBinary2 ( PIX *pixs, l_uint8 *intab )
pixReduceBinary2()
Input: pixs
tab (<optional>; if null, a table is made here
and destroyed before exit)
Return: pixd (2x subsampled), or null on error
Notes:
(1) After folding, the data is in bytes 0 and 2 of the word,
and the bits in each byte are in the following order
(with 0 being the leftmost originating pair and 7 being
the rightmost originating pair):
0 4 1 5 2 6 3 7
These need to be permuted to
0 1 2 3 4 5 6 7
which is done with an 8-bit table generated by makeSubsampleTab2x().
=head2 pixReduceRankBinary2
PIX * pixReduceRankBinary2 ( PIX *pixs, l_int32 level, l_uint8 *intab )
pixReduceRankBinary2()
Input: pixs (1 bpp)
level (rank threshold: 1, 2, 3, 4)
intab (<optional>; if null, a table is made here
and destroyed before exit)
Return: pixd (1 bpp, 2x rank threshold reduced), or null on error
Notes:
(1) pixd is downscaled by 2x from pixs.
(2) The rank threshold specifies the minimum number of ON
pixels in each 2x2 region of pixs that are required to
set the corresponding pixel ON in pixd.
(3) Rank filtering is done to the UL corner of each 2x2 pixel block,
using only logical operations. Then these pixels are chosen
in the 2x subsampling process, subsampled, as described
above in pixReduceBinary2().
=head2 pixReduceRankBinaryCascade
PIX * pixReduceRankBinaryCascade ( PIX *pixs, l_int32 level1, l_int32 level2, l_int32 level3, l_int32 level4 )
pixReduceRankBinaryCascade()
Input: pixs (1 bpp)
level1, ... level 4 (thresholds, in the set {0, 1, 2, 3, 4})
Return: pixd, or null on error
Notes:
(1) This performs up to four cascaded 2x rank reductions.
(2) Use level = 0 to truncate the cascade.
=head1 AUTHOR
Zakariyya Mughal <zmughal@cpan.org>
=head1 COPYRIGHT AND LICENSE
This software is copyright (c) 2014 by Zakariyya Mughal.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
=cut