How to scale down image for multiple screens?

Question

If I have an image 240 by 240 pixels designed in Adobe Illustrator (for example) at 240 dots per inch for high density screens, what would be the best way to save a version of this image for medium density screens? Should I keep the image at 240 by 240 pixels and reduce the dots per inch to 160? Or keep the image at 240 dots per inch and shrink it to 160 by 160 pixels? Or some other variation?!

Answer 1

AFAIK DPI is ignored, it's only relevant for printing where it tells the printer how many pixels to print per inch, there is always exactly one screen pixel per bitmap pixel*, so as the other comment suggests, you just need to scale the image using the ratios 3:4:6:8.

*Essentially, anyway.