FreeImage Plugins

ImageResizer.Plugins.FreeImage.dll contains several plugins, all based around the abilities offered by the C/C++ FreeImage library. These plugins are alpha-level.

Required files

3 dlls must be placed in the /bin folder of the application for the plugins to work.

  • ImageResizer.Plugins.FreeImage.dll (dlls\release)
  • FreeImageNET.dll (dlls\release)
  • FreeImage.dll (download x86 here or the 64-bit version here) NOTE - you must copy the right bitness for your application pool! In V3.2 and higher, you can use the downloadNativeDependencies="true" attribute on any of the FreeImage plugins instead of manually downloading those images.


Introduces support for RAW & HDR image formats, such as CRW/CR2, NEF, RAF, DNG, MOS, KDC, DCR, etc. Also introduced support for XBM, XPM, TARGA, SGI, Sun RAS, PSD, PICT, PNG, PFM, PBM, PGM, PPM, PCX, MNG, Kodak PhotoCD, KOALA, JPEG-2000, JIF, JNG, IFF, ICO, Raw Fax G3, EXR, DDS, and Dr. Halo CUT files.

Install by adding <add name="FreeImageDecoder" /> to the plugins section of Web.config. And make sure you've added the 3 required dlls.

FreeImageDecoder shows a 50%-400% increase in performance over GDI when loading TIFF files. By default, FreeImageDecoder is a fallback, so if you want it to load TIFF files, add &decoder=freeimage to the querystring (v3.1+). It does not support &page= at the moment.


FreeImageEncoder can encode jpegs 2-3x as fast as GDI can, and offers more encoding options.

Install by adding <add name="FreeImageEncoder" /> to the plugins section of Web.config. And make sure you've added the 3 required dlls.

Use by adding &encoder=freeimage to the URL.

No support for transparency - so only use it on PNG and GIF files that don't need it.


Provides an alternate resizing pipeline that never touches GDI. Only supports width/maxwidth/height/maxheight/scale/marginWidth/paddingWidth/fi.scale settings. Only operates on requests specifying builder=freeimage

Install by adding <add name="FreeImageBuilder" /> to the plugins section of Web.config. And make sure you've added the 3 required dlls.

Not always faster, as FreeImage is slower at scaling images than GDI, even if it has faster encoding/decoding.

Defaults to box scaling


Adds support for FreeImage resizing algorithms, which include CatmullRom, Lanczos3, bspline, box, bicubic, and bilinear filters.

Installed by adding <add name="FreeImageResizer" />

Activated by adding &fi.scale=bicubic|bilinear|box|bspline|catmullrom|lanczos command


This set of plugins is part of the Design bundle, and licensed accordingly. The underlying native FreeImage dlls are licensed under the FreeImage License.

This plugin (FreeImage Plugins) is part of the Creative Edition

The Creative edition costs $499 per domain.

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?