Re: PNG offset problem (Jonathan Jeffus)

Hey Jonathan,

I ran into this same problem a few years ago, and the fix is to reset
the origin to 0x0 after a crop.  Here is how I do this in
Image::Magick:

#!/usr/bin/perl
use strict;
use Image::Magick;
my $img = new Image::Magick;
$img->Read("browse4.png");
my $copy = $img->Clone();
$copy->Crop(geometry=>'33x1960+1267+0');

$copy->Set(
     page => $copy->Get('width') . 'x' .  $copy->Get('height') . '+0+0'
);

$copy->Write("out.png");

# Hope this helps!

- Joe




On Mon, May 12, 2008 at 12:00 PM, <[email protected]> wrote:
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>   1. Re: PNG offset problem (Jonathan Jeffus)
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> ---------- Forwarded message ----------
> From: "Jonathan Jeffus" <[email protected]>
> To: [email protected]
> Date: Mon, 12 May 2008 08:45:25 -0400
> Subject: Re: [Magick-bugs] PNG offset problem
> Hi,
>
> I hope I'm reporting this in the right place (and it's not a long squashed
> bug, I couldn't find anything on it.) I tried at the Magick++ support forum
> referenced here <http://www.imagemagick.org/Magick++/> but it does not seem
> to be working.
>
> The bug ocurrs when you use image.crop() on an image and then save a PNG.  I
> first verified it on 6.2.4 (standard for Debian Gutsy). Then I installed
> 6.4.1-1 from source hoping it would go away, to no avail. I just hope I'm
> not doing something dumb.
>
> // This is a simplified version that reproduces the bug.
> // I reproduced it with several images my program works on
> // The image in question is a 1300x2004 image, I'm trying to
> // crop out a region on the right side of it.
>
> #include <cstdio>
> #include <Magick++.h>
> #include <iostream>
> using namespace std;
> using namespace Magick;
> int main(int argc,char **argv) {
>  Image image, cur;
>  image.read( "browse4.png" );
>  cur = image;
>  cur.crop( Geometry(30,1960,1267, 0) );
>  cur.modifyImage(); // Added this hoping the bug would go away by using it.
>  cur.quality(100);
>  cur.write( "out.png" );
>  return 0;
> }
>
> In this case, in.png is a 24bit png file with an alpha layer (an image
> created by Inkscape 0.45, which seems to be using gtk_pixbuf for writing the
> PNG.) Everything works great if I try to open out.png with a program that
> uses libpng (like XV.) When I try to open it in GIMP 2.4.2 I get the message
> "The PNG file specifies an offset that caused the layer to be positioned
> outside the image."  The image which is then displayed is the correct width
> and height but is otherwise blank. The bug also appears in PerlMagick.
>
> #!/usr/bin/perl
> use strict;
> use Image::Magick;
> my $img = new Image::Magick;
> $img->Read("browse4.png");
> my $copy = $img->Clone();
> $copy->Crop(geometry=>'33x1960+1267+0');
> $copy->Write("out.png");
>
> Same thing in RMagick as well:
> #!/usr/local/bin/ruby
> require 'RMagick'
> include Magick
> img = Magick::Image::read("browse4.png").first
> # 33x1960+1267+0
> cur = img.crop(1267, 0, 33, 1960)
> cur.write "out.png"
>
> Which means it's probably an ImageMagick bug? Is this a problem with the PNG
> encoder? How do I remove the offset? I'd gladly provide the PNG in question,
> although it ocurrs on any PNG I tried.
>
> Peace,
> Jonathan Jeffus
>
> Psylus Development, LLC.
>
>
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