This is a file type plugin that allows reading and writing of JPEG XR (aka HD Photo) image files. There has been an HD Photo plugin before, developed by Rick Brewster, that is no longer being maintained, however. That's why I decided to rewrite it and add some minor improvements (jxr file extension support, option to save as 8bpp grayscale, fixed and much improved metadata support).
Almost all pixel formats supported by JPEG XR can be loaded. However, Paint.NET requires the image to be stored as 32bpp RGBA in memory, so other source image formats will be converted first if required (this means you'll loose HDR data for example).
You can save images in the following pixel formats:
32bpp RGBA (alpha channel)
Optionally, you can retain the Exif metadata from your source image (if present) and apply it to your JPEG XR image. To do that, check the appropriate setting in the save file dialog. This could be handy if you edit JPEG images from your camera and want to resave them as JPEG XR. NOTE: This should work with most metadata tags, but hasn't been tested thoroughly.
Installing the plugin is easy. Follow the steps described in the official documentation.
Source code and binary files are hosted on Codeplex.