GD graphs and CGI

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Dear monks, I'm having problems printing graphs to a web-page from my cgi script. I'm creating the graphs with GD::Graph but when they are displayed on the web I get a load of gibberish like this:

KH*±Õšª@äfr'Hxþ¡A˜¢©‚&%Ž·4Úƒp!7)*R9Ïa
Can anyone tell me whats wrong with the script? The graph is created and printed to file.gif, but is not displayed on my cgi webpage.
Thanks!

@data = (
    ["1st","2nd","3rd","4th","5th","6th","7th", "8th", "9th"],
    [    1,    2,    5,    6,    3,  1.5,    1,     3,     4]
  );
                                                                      
+                                                           
my $graph = GD::Graph::points->new(400, 300);
                                                                      
+                                                           
  $graph->set(
      x_label           => 'X Label',
      y_label           => 'Y label',
      title             => 'Some simple graph',
      y_max_value       => 8,
      y_tick_number     => 8,
      y_label_skip      => 2
  ) or die $my_graph->error;
                                                                      
+                                                           
                                                                      
+                                                           
  my $gd = $graph->plot(\@data) or die $my_graph->error;
  open(IMG, '>file.gif') or die $!;
  binmode IMG;
  print IMG $gd->png;
  close IMG;
  binmode STDOUT;
  print $gd->png;
[download]

Comment on GD graphs and CGI Download Code

Replies are listed 'Best First'.
Re: GD graphs and CGI by borisz (Canon) on Jan 19, 2005 at 13:32 UTC
Look s like your content-type is wrong. Add `content-type: image/png` to your headers. Boris	[reply]
Re: GD graphs and CGI by friedo (Prior) on Jan 19, 2005 at 15:13 UTC
You are saving your PNG both to an image file (file.gif, which has the wrong extension, it should be file.png) and printing it to STDOUT, where it gets sent to the browser. If you want to send your image directly to the browser, then you'll need to send it to STDOUT with a proper content-type header: `print "Content-type: image/png\n\n"; print $gd->png;` [download] If you want to save the image on your server and tell the browser to display it, then use: `open IMG, '>file.png'; print IMG $gd->png; close IMG; print "Content-type: text/html\n\n"; print '<img src="http://yourserver.com/file.png">';` [download] UpdateFixed typo in content-type.	[reply] [d/l] [select]
Re: GD graphs and CGI by r34d0nl1 (Pilgrim) on Jan 20, 2005 at 12:53 UTC
It is also important to change you output type to `# make sure we are writing to a binary stream binmode STDOUT;` [download] So, when sending the correct header to the browser it will look like an image. I had the same problem when dealing with images for the web. I found easier to put the script that generates the graphic in a diferent page, staying like this `<img src='/perl/mygraph.pl'>` [download]	[reply] [d/l] [select]