http://www.perlmonks.org?node_id=11105858

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks,

I read a png file and want to work with the image data, A set of colors I consider as foreground all others as background. I convert the png data into a string of 0/1s and store them as one string per line (@sw)

I have two slow working versions ....

My first try was to read out every pixel-color:

use GD::Simple; my $png = GD::Image->newFromPng('test.png'); my @sw; my ($width, $height) = $png->getBounds; for my $x ( 0 .. $width-1 ) { for my $y ( 0 .. $height-1 ) { $sw[$y].=getPixel($x,$y); } } sub getPixel { my $p; my ($index) = $png->getPixel($_[0],$_[1]); my ($r,$g,$b) = $png->rgb($index); if ($b>128 || $r>128) {$p=0;} else {$p=1;} return $p; }
But this was really, really slow.

The next try was to use GD::wbmp. It is much faster, but for several foreground-colors this seems far away from optimum.

use GD::Simple; my $png = GD::Image->newFromPng('test.png'); my @sw; my $pdata=''; my ($bx, $by) = $png->getBounds; my @col; # foreground colo +rs for (0..$png->colorsTotal) { my ($r,$g,$b) = $png->rgb($_); push (@col,$_) unless ($b>128 || $r>128); } $pdata |= ~$png->wbmp($_) foreach (@col); our $zlen=int(($bx+7)/8); # number of Bytes + per line my $pos=6; my $y=0; # position after +Header of WBMP while ($pos<length($pdata)) { $sw[$y]=''; for (1..$zlen) {$sw[$y].=sprintf("%08b",ord(substr($pdata,$pos++,1 +))); } # convert binary data into string $y++; }
Do you have a better(faster) idea, to convert the png data to a 0/1 bit stream by using the color definition in @col ?

Thanks for your help !!!