Android app

Hi,

Im developping an android app.

when i create an android project, in android folder, i see all folders which will contains my images, in portrait mode for example, we have these folders with an image of the size below :

res-long-port-hdpi : 480 x 800
res-long-port-ldpi : 240 x 400
res-notlong-port-hdpi : 480 x 800
res-notlong-port-ldpi : 240 x 320
res-notlong-port-mdpi : 320 x 480

So does it mean that i should have only this sizes of images for my app ? what is the difference between res-long-port-hdpi and res-notlong-port-hdpi. i have exactly the same image in these folders ?

thanks for help.