So this layer mask thing turns out to be really simple. Here's what about an hour's work this morning has achieved with one out of seven large images (which had already been overlapped yesterday) and one small area at the middle left. In other words I have taken the images I had yesterday and just added masks to the background layer (the Linz aerial photography) so as to make the foreground layers (the historic aerial imagery) show through the lake bed.
So I have decided to use regular boundaries on the mask because this is just a representation, however I am considering all the angles. You can see bits of lake poking through here and there, that is because I actually don't have a historic image to cover that bit, because I didn't get the entire range of them scanned originally. I will just wait until Retrolens scans that series and then fill them in later.
There are a couple of other things to work on:
- finding a way to lighten up the darker images to make them look similar to the lighter ones so we don't have that banding with different coloured images. They obviously scanned differently when they put them through the scanner.
- Using the cage deform tool in Gimp to deform some of the aerials to make them line up better. This will make them blend better at the edges because that is an ongoing issue.