densities ratio for android

Hi,

i have a question about densities ratio.

we have differents ratios on android : ldpi, mdpi, hdpi, xhdpi. i read that ratios between them is : ldpi : 0.75 mdpi : 1 hpdi : 1.5 xhdpi : 2

but when i see default image in that folders in my titanium project in android/images folder. i see that the default image in mdpi folder is : 320x480 px and the default image in hpdi folder is : 480x800 so it doesn't respect the ratio 1.5 the same thing for ldpi..

can anyone explain me that ?

thank you