Acme-Steganography-Image-Png

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Changes  view on Meta::CPAN

0.02  Sat Mar 12 13:33:13 GMT 2005
	- Added RGB classes.

0.03  Mon Mar 14 21:19:05 GMT 2005
	- Use string & and | operators for about 30% speedup
	  Ops are bad, m'kay.

0.04  Mon Mar 14 22:59:27 GMT 2005
	- Acme::Steganography::Image::Png::556FS uses Floyd-Steinberg dithering
	  to spread around the errors caused by stuffing way too much data in.

0.05  Mon Apr  3 15:20:09 BST 2006
	- Actually give the error message on file open failure
	- Patch from Simon Wistow to allow write_images to use an existing
	  Imager object, which allowed support for inlining images within
	  files.

0.06  Mon Oct  2 00:33:16 BST 2006
	- Wrap the arguments to calls to croak in (), to avoid problems with
	  croak being misinterpreted as a method to call on an object.

Png.pm  view on Meta::CPAN

  my $self = shift;
  $self->x * $self->y * 2;
}

package Acme::Steganography::Image::Png::RGB::556FS;

use vars '@ISA';
@ISA = 'Acme::Steganography::Image::Png::RGB::556';

# Raw data in the low bits of a colour image, with Floyd-Steinberg dithering
# to spread the errors around. Share and enjoy, share and enjoy.

sub make_image {
  my $self = shift;
  # We get a copy to play with
  my $raw = $self->raw;
  my $img = new Imager;
  my $next_row;

  my $xsize = $self->x;
  my $ysize = $self->y;

Png.pm  view on Meta::CPAN

    for (my $x = $xsize; $x-- > 0; ) {
      my $offset = $y * $xsize + $x;

      # I'm not sure if I've got the algorithm correct.
      my $datum = unpack 'x' . ($offset * 2) . 'n', $_[0];

      my @rgb = unpack 'x' . ($offset * 3) . 'C3', $raw;
      foreach (0..2) {
	$rgb[$_] += $this_row->[$x + 1][$_] || 0;
	# And this is most definitely an empirical hack, as there seem to be
	# big systematic problems if the errors drive things outside the range
	# 0-255
	if ($rgb[$_] > 255) {
	  $rgb[$_] = 255;
	} elsif ($rgb[$_] < 0) {
	  $rgb[$_] = 0;
	}
      }
      # What we'd ideally have liked to output
      my @rgb_ideal = @rgb;
      # Pack 16 bits into the low bits of R G and B
      $rgb[0] = ($rgb[0] & 0xE0) | $datum >> 11;
      $rgb[1] = ($rgb[1] & 0xE0) | (($datum >> 6) & 0x1F);
      $rgb[2] = ($rgb[2] & 0xC0) | ($datum & 0x3F);
      substr($raw, $offset * 3, 3, pack 'C3', @rgb);

      # Calculate the error and dither it
      # 7 x
      # 1 5 3
      # Note that the backwards dithering is why we need the +1 on the co-ords.
      foreach (0..2) {
	my $error = ($rgb_ideal[$_] - $rgb[$_]) / 16;
	$this_row->[$x][$_] += $error * 7;
	$next_row->[$x + 2][$_] += $error * 3;
	$next_row->[$x + 1][$_] += $error * 5;
	$next_row->[$x][$_] += $error;
      }
    }
  }

  $img->read(data=>$raw, type => 'raw', xsize => $xsize,
	     ysize => $ysize, datachannels => 3,interleave => 0);
  $img;
}

package Acme::Steganography::Image::Png::RGB::323;

Png.pm  view on Meta::CPAN

Also stuffs your data into a sample image, using the low order bits of each
colour. Only 1 byte of your data is stored in each pixel, 3 bits in Red and
Blue, 2 in Green. To the untrained eye the image looks good. But the fact
that it's PNG will make anyone suspicious about the contents.

=item Acme::Steganography::Image::Png::RGB::556FS

Stuffs your data into a sample image, using the low order bits of each colour.
2 bytes of your data are stored in each pixel, 5 bits in Red and Green, 6 in
Blue. Changing the value of pixels to store data is adding error to the image,
in this case rather a lot of error. To attempt to conceal some of the
graininess Floyd-Steinberg dithering is used to spread the errors around. It's
not perfect, but effects are quite interesting, producing a reasonably nice
dithered image.

=back

Write your data out by calling C<write_images>

Read your data back in by calling C<read_files>

You don't have to return the filenames in the correct order.