So, I’m in process of making a set of coasters as a gift.
I found an outrageously high resolution star chart from 1821, and cropped it down to isolate Canis Major (My sister loves her dogs), and wanted to get 6 coaster-ready squares from it.
Enter Pine Tools. Saved me a bunch of headache: http://pinetools.com/split-image
I cropped the image to be 2:3 aspect ratio first, then sent it to pine tools to be split up to tiles.
First, here’s a lower-res version of the main image:
Here are a couple of the resulting tiles…