The way jit.alphablend seems to work is that any cells that were fully transparent on input are converted to fully opaque black on output, i.e 255 0 0 0.
I would prefer if the full transparency of the cell was preserved, e.g. 0 0 0 0.
This would mean I could take the output and use it again for alphablending further down the line.
I'm having a go at writing my own abstraction to do this, but any advice, or links to an object that may do this already, would be appreciated.