After getting excellent monk advice in another thread concerning the best options for scientific graphing (thanks again for that), I settled on using the external package gnuplot. For patent reasons, it generates images in PNG format instead of GIF, which I think should work fine with all the more recent browsers.

The start of my cgi puts up an h2 header and a scrolling menu where the user selects a dataset file, then clicks a "show me" button and then I want a graph to appear, either in the same window below the menu or in a new window - I don't care which.

I use open3 to launch gnuplot in a mode where it accepts commands and data in stdin, sends errors to stderr, and sends the image to stdout. (Please no warnings about deadlocks with open3, I know all about that.) So my PNG image ends up in a file handle returned by open3, which I'll call $png_image_fh. This all works fine and an examination of the PNG data looks apparantly correct, though we won't know until I can actually display it as an image.

Now, I need to read the data from the $png_image_fh and print it out as a PNG image. Looking around in the perlmonk faq, I found this thread: http://www.perlmonks.com/index.pl?node_id=18565 from which I generated the following code: 

my ($image_buf,$chunk);
while ( read( $png_image_fh , $chunk , 1024 ) ) {
    $image_buf .= $chunk;
}
print "Content-type: image/png\n\n";
# binmode included in case we run on Windoze
binmode STDOUT;
print $image_buf;

[download]
Instead of an image, what I get is the PNG data printed in text mode. Any ideas why this might be? The server is Linux, the browser is IE 6.

Thanks
Bret

In reply to Getting the picture by bret.foreman

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