Beefy Boxes and Bandwidth Generously Provided by pair Networks
Do you know where your variables are?

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

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 !!!

In reply to working with png data by Anonymous Monk

Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?

    What's my password?
    Create A New User
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others lurking in the Monastery: (6)
    As of 2019-11-22 20:33 GMT
    Find Nodes?
      Voting Booth?
      Strict and warnings: which comes first?

      Results (113 votes). Check out past polls.