While writing my article on Custom Effect optimizations (http://developer.nokia.com/Community...ia_Imaging_SDK) I encountered two points that I believe might be improved in future versions of the SDK (it's possible though that I'm overlooking issues at least the second change would create).
1.) Helper methods: Many things of what you have to do when implementing Nokia::Graphics::Imaging::ICustomEffect have to be done for each filter in pretty much the same way. It would be great to add helper functions to the SDK that already implement getting access to the data inside an IBuffer object or creating buffers in a suitable way for the SDK. Also helpers like the ForEachRow and SourcePixelRegion provided in the Managed Base class would be nice. (I guess those would have to be implemented as a Windows Phone DLL rather than a WinPRT component like the SDK itself.
2.) Ability to share buffers with the rest of the imaging pipeline. Currently when using a custom effect to render from a 1024x768 BGRA8888 Bitmap to another 1024x768 BGRA Bitmap the SDK code has to copy the data from the original Bitmap into the Buffer provided by the custom effect and after the effect has finished processing the SDK has to copy the data from the target buffer to the target image. Meanwhile the custom effect could be provided with the external Buffer, read directly from there and write directly to the target image. In case resizing or ColorMode conversions have to be done by the SDK it could still create it's own buffers for the conversion (which it is likely to do already) and provide those to the custom effect.