Rebel Fish sees people asking questions like, “what resolution should I save my file at? 72 or 300?” It doesn’t matter at all. Resolution just determines the number of inches the file will be set to, but the number of pixels (the true measure of an image’s resolution) won’t change (unless you’re manually changing an image’s size as WELL as its resolution).
You can see this for yourself (and if you don’t quite understand resolution/dpi/etc., you should try this!):
Open Photoshop
Create a new document: width 10 inches, height 10 inches, resolution 72 pixels/inch
Pull up the image size dialogue (image/image size)
Turn OFF the resample image check box.
You’ll see you have an image that is 720 pixels by 720 pixels (which makes sens: 10 inches x 10 inches at 72pixels/inch)
Change your resolution to 300 ppi
You will see the width and height change to 2.4 inches, but the number of pixels hasn’t changed.
IT IS STILL THE EXACT SAME FILE. The same resolution, the same amount of data. You’re just representing it with different math.
Some publications may require a certain resolution, e.g., you may be required to export a file at 4×4 inches at 300 dpi. That’s a 1200×1200 pixel image. You could export it at 12×12 inches at 100 pixels/inch and you’d have the exact same file, but the magazine may whine at you.
Whining isn’t sexy.
RF
Here’s another post with much more detail.