Automate merge files into stack

Hi all,

I need to find a way to do the following:

Merge 4 currently open images into a single stack into separate layers.

Screen all layers

Extract the top three layers into a new file

Flatten both images and save as .tif

Any ideas?

Even scripting the 1st two steps would be great.I've tried "Merge files into stack", but it won't let me automate the "add open files" part of that.

Thanks.