Can anyone give me a guide to making Startup Screens?

[magickero]

I made a startup screen in JPG format but I don't know how to make it into a .big file. I'd prefer a guide and not an "I'll do it for you" because of a bad experience recently. Thanks!

[ibelieve]

At first you make it into the right fsh file and than you use biggui to make it into the big file.