WeBWorK Main Forum

2.4.1 images broken on MS Windows browser

2.4.1 images broken on MS Windows browser

by George Jennings -
Number of replies: 3

After we upgraded to webwork 2.4.1 one of our instructors complained that he can't read text displayed in webwork 'images' mode with his MS Internet Explorer browser on Windows. All that comes up is some random looking dots. This seems to affect the library browser and also problem sets.

He receives no error messages. When I look at the same pages with my linux browser the images look perfect, no problems at all. We have tried reloading the pages on his machine but this doesn't help.

Does anyone have any idea how to fix this? The images looked good on his browser when we used the old webwork version (2.3).

Thanks in advance.

George Jennings
Math Dept.
Calif. State University, Dominguez Hills

In reply to George Jennings

Re: 2.4.1 images broken on MS Windows browser

by Eddie Fuller -

Check the file webwork2/lib/WebWork/Constants.pm for the line that sets the dvipng parameters. It should read

$WeBWorK::PG::ImageGenerator::DvipngArgs = "-bgtransparent -D120 -q -depth";

if you are using a recent version of dvipng (and you likely have 1.7). The default copy coming with WW2.4.x has -bgTransparent which causes IE6.x and up to render incorrectly (due to a bug in the png file renderer in the browser).

You may have to clear out all the old images that have been generated from webwork2/htdocs/tmp/equations since all these will have the problematic png structure and will still be delivered to browsers.

In reply to Eddie Fuller

Re: 2.4.1 images broken on MS Windows browser

by Dennis Keeler -
I had the same issue. The solution Eddie suggests works, but as he says, you need to clear out the old images. A command to do that and more info about the bug is at