I'm trying to figure out whether it's possible to use the fill tool to remove a solid colour (e.g white) background from an image file, so that the background is transparent for PNG layer export. Not knowing how to do this, I have to sit and manually erase the whole background of some fairly large image files which isn't a good long term solution for me. All I want to be able to do is click once and clear all the colour data.

Any thoughts?