IEPngFix plugin

This plugin automatically redirects PNG file requests from Internet Explorer 6 and below to GIF versions of the images. For best results, use with the PrettyGifs plugin, as the default .NET GIF encoding is very poor.

Does not work well with Amazon CloudFront, CDNs, or caching proxies.

Introduced in V3.1.3


  1. Add <add name="IEPngFix" /> to the <plugins /> section.


To enable 'catchall' mode, add catchAll="true"

Ex. <add name="IEPngFix" catchAll="true" />

Note: If you have to use the '.ashx' syntax due to your server configuration, catchAll will not be able to intercept static PNG requests; only those using the .ashx syntax.

To use rewriting instead of redirects, add redirect="false". Ex. <add name="IEPngFix" redirect="false" />

If redirect="true" (the default), the requests from IE will be HTTP redirected to new URLs. If false, the GIF will be silently served instead of the PNG, without any redirection. A CDN or caching proxy will mess things up regardless, but using redirection ensures that the CDN/proxy never caches the GIF version instead of the PNG.


  • When catchAll=false, the behavior is opt-in. You must add &iefix=true to enable the browser detection and redirection behavior for the URL.
  • When catchAll=true, the behavior is opt-out. You must add &iefix=false to disable the browser detection and redirection behavior for the URL.


image.png?iefix=true will redirect to image.png?format=gif&iefix=true under IE6 or earlier.

The plugin works even if PNG is not the original format. For example,

image.jpg?format=png&iefix=true will redirect to image.jpg?format=gif&iefix=true under IE6.

This plugin (IEPngFix plugin) is part of the Essential edition

Where is the plugins section?

The <plugins> section is located in Web.config, and is nested inside the <resizer> element, which is nested inside <configuration>. For examples, see this sample Web.config file.

Where can I find the dll?

We prefer that you install via NuGet, but you can also find the plugin DLL files in the /dlls/release folder of your download.

How do I typically install a plugin via Web.Config?

  1. In Visual Studio, right click on your project and choose "Add reference". Browse to the plugin DLL and click "OK".
  2. In the <plugins> section of Web.config, insert <add name="PluginName" />
  3. Look at the plugin documentation to see what configuration options (if any) are available.

How do I typically install a plugin via code?