Set up a guide layer in Photoshop for cropping
I am looking to set up a single .psd file I can use for my iPhone splash screens, the main document at 640x1136 and a "guide layer" at 640x960 that I can use to generate the slightly smaller splash screen from the same image file.
What's the best way to create this "guide" layer? It obviously needs to persist across crops so I can use it again and again.
You can create slices from guides in Photoshop which would make this process easy. This allows you to create a template file saved with predefined guide lines for your 640 x 960 area. When you are ready to save you can access the slice tool with the C key and use the option Slices From Guides
This allows you to output the smaller splash screen image file when you Save for Web. It's similar to resizing the canvas, but could allow a slightly quicker workflow. To hide the guides you can uncheck View → Show → Guides
You have two options:
1) You may want to crop by canvas resize: Image â†’ Canvas Size...
And resize height to 960 using the upper end as your anchor
2) You can draw a square shaped object setting its size to 640x960 and hide it. When you need to crop something with it, just click it while holding Ctrl to create a selection.