How to use RenderScript with multiple input allocations?

Recently, I found render script is a better choice for image processing on Android. The performance is wonderful. But there are not many documents on it. I am wondering if I can merge multiple photos into a result photo by render script.

http://developer.android.com/guide/topics/renderscript/compute.html says:

A kernel may have an input Allocation, an output Allocation, or both. A kernel may not have more than one input or one output Allocation. If more than one input or output is required, those objects should be bound to rs_allocation script globals and accessed from a kernel or invokable function via rsGetElementAt_type() or rsSetElementAt_type().

Is there any code example for this issue?