Loading in all the different kind of textures that FS supports in a tool can be a quite challenging task. Some scenery object use 8 bit textures, others 32 bit, or compressed DXT textures. Some objects even still use the old RAW textures with a palette. And in FsX the DDS format has been added to this long list.
For my MDL Tweaker tool I have used the graphical DLL files by Martin Wright to help me reading the different (compressed) textures that FS supports. But yesterday when working on ModelConverterX I can across another library that can also help me with this subject, GFL SDK. This is the library that is behind the XnView thumbnail viewer as well. Using this library made my job of loading textures a lot easier and the library also provides some functionality to edit the textures (in case I ever need that).
So if you are having trouble with loading all those different texture formats in your tool, you might want to check out this nice library as well.