Hi.. as SR points out in the article - the camera dpi is not relevant.. the only thing that is important is the resolution of the camera in megapixels (up to a point of course)..

Also, if you uncheck the "Resample Image" checkbox in the Resize Image dialog, you can tell PS to treat the image as a different size. Anytime you resample an image you are either throwing away image information (if making it smaller) or interpolating new information (if making it larger). Either way, the image quality degrades. Keep in mind that this will scale the image proportionally. If you need to change the aspect ratio, you should do that with the crop tool first.

Good Luck..