Resizing images clearly

well i think you confusing ppi and dpi not the same thing, printing uses dpi usualy 300, but sometimes they will acceot 150, now if you have cammara you usually cant set the dpi you are actually setting the maximum size for that picture. Wich in return set the resolution on screen. Usually you go from LArge to small the outcome when you have low resolution and you "up" the resolution the results are preatty bad depending on how detail oriented you are.