RadImageEditor can open BMP images from its first release. The difference comes from the filter that the OpenFileDialog of OpenImageCommand uses in the different version.
In the official Q2 release (2011.2.712), which is the version that the CustomFormatProvider demo uses, the filter the BMP extension has been accidentally omitted, but BMP images could still be opened if you type their name in the File name text box. In addition, there was a typo in the way the "All images" part of the filter was set
In Q2 SP1 (2011.2.920) - the version used in this online demo - the BMP filter was still missing, but the typo in the All images filter was fixed and therefore, you are able to select images in this format.
In the internal builds after 2011.2.920 and the Q3 Beta, we have changed the logic in order to include all registered format providers (including BMP and custom ones that may be defined). You can see how it works in the Q3 Beta demo.
With all versions, you can implement your version of the command (using the correct filter). The custom command approach has been described here. The solution there is for the SaveCommand, but the walk through is the same for the OpenImageCommand.
All the best,
the Telerik team
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