OpenCV Android is preferred due to the ease of use on an Android platform, although there maybe limitations. Here are some references that might help:
1.The best way to learn Image Processing on an Android platform is via implementation. Try running and understanding the existing OpenCV4Android Samples on Android Studio/Eclipse. They are available on https://github.com/joaopedronardari/OpenCV-AndroidSamples .
The description of each sample is available on the OpenCVAndroid Samples page. Mixed Processing, Camera Control, Image Manipulations and color-blob-detection deal with pre-processing and image manipulations. They comprise:
RGBA and GRAY preview
Canny (Edge Detection)
Finding Features
Colour Effects
Histograms
Sepia
Sobel Filter
Zoom
Pixelize
Posterize
Watershed transformation
Markers (blob detection)
Since you will be working on a Java platform ,the OpenCV Java tutorials will be of use.
http://web.stanford.edu/class/ee368/Android/ has sample projects.
4.Check out The Android Arsenal, for Image Processing libraries.
Note:A Mat object has to be converted to a Bitmap object, in order to display it on the device screen (ImageView).
