I'm trying to use GD to make some composite images. However, when I try to print the pictures out, the resultant image loses some sharpness that existed in the originals. I've isolated it down to the following test case: 
use GD;

my $x = GD::Image->new('start.png');
open OUT, '>end.png';
print OUT $x->png(0); # Use least compression

# Or ...

use GD;

my $x = GD::Image->new('start.jpeg');
open OUT, '>end.jpeg';
print OUT $x->jpeg(100); # Use best quality

[download]

When I use a program to view the images on Windows and zoom in, the background is mottled. (Neighboring pixels are different shades of the same color.) This also causes previously sharp borders between a picture and the background to be ... well ... merged (in terms of colors).

It seems to be that GD (and libgd) seem to be changing the image. I've used GD's compare() method and it says the images are the same. But, zooming in shows they're different.

Does anyone have any suggestions for this?

------
We are the carpenters and bricklayers of the Information Age.

The idea is a little like C++ templates, except not quite so brain-meltingly complicated. -- TheDamian, Exegesis 6

... strings and arrays will suffice. As they are easily available as native data types in any sane language, ... - blokhead, speaking on evolutionary algorithms

Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.

In reply to GD question by dragonchild

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