This app was designed solely as an example of using Renderscript to create high performance image processing algorithms on mobile devices. It contains nothing else other than an implementation of Canny edge detection showing on a camera feed. Settings and thresholds can be edited in a settings file in the device. Using a Samsung Galaxy S5 it achieves near 30fps at 720p, which is much faster than a non-parallel implementation using existing libraries such as OpenCV.
It has been poorly tested on a range of devices so it may not function correctly on many devices. This is mainly due to hardware drivers' differences in building and executing renderscript.
The source code is available on github at: https://github.com/kerrj/RenderscriptCanny
Note: On some devices the app may output "Sorry, something went wrong when initializing renderscript" and display a black screen. This is a bug specific to renderscript drivers on your phone which I have not found a solution for. Should I find one, it will appear in a later patch.