How do I prepare images for all the Android resolutions?

Question

In iOS preparing graphics is simple. There are either a normal image (height x width) or a retina image which is @2x (2 times height x 2 times width).

However, since I'm new to Android, I see a ton of drawable-* folders in Eclipse where the * can be "hdpi" or "ldpi" or "mdpi" or "xhdpi" or "xxhdpi". Can someone very clearly and simply list for me what I must do to satisfy each of the display possibilities so my images will look right in each instance? I'm envisioning an answer will be a bullet list with each "*" listed and a sub-bullet list including the things that must be done.

I'd also really enjoy an answer that would start with the highest density and greatest dimension image and working down since I'll be creating in Photoshop and will be reducing quality from a master image.

Answer 1

i got this off of this site a while back, it still comes in handy

xlarge screens are at least 960dp x 720dp large screens are at least 640dp x 480dp normal screens are at least 470dp x 320dp small screens are at least 426dp x 320dp Generalised Dpi values for screens:  ldpi Resources for low-density (ldpi) screens (~120dpi) mdpi Resources for medium-density (mdpi) screens (~160dpi). (This is the baseline density.) hdpi Resources for high-density (hdpi) screens (~240dpi). xhdpi Resources for extra high-density (xhdpi) screens (~320dpi). Therefore generalised size of your resources (assuming they are full screen):  ldpi Vertical = 426 * 120 / 160 = 319.5px Horizontal = 320 * 120 / 160 = 240px mdpi Vertical = 470 * 160 / 160 = 470px Horizontal = 320 * 160 / 160 = 320px hdpi Vertical = 640 * 240 / 160 = 960px Horizontal = 480 * 240 / 160 = 720px xhdpi Vertical = 960 * 320 / 160 = 1920px Horizontal = 720 * 320 / 160 = 1440px  px = dp*dpi/160