If you've noticed, in my post about Image/Photo Resizer, I have mentioned about resolutions and megapixels. Then the previous post on Resolutions, I've touched on display resolutions. Are they different? No, they are the same. In fact, if you ever tried taking a 1.3MP picture and display it on a 17" (1280x1024) monitor, it will fit just about snugly on the screen at 100%. That is because 1280x1024=1,310,720 which is about 1.3 million pixels or megapixels (MP).
MP also determines the file size of your image, as it specifies how much details of a picture will be stored in the file. Therefore in Image/Photo Resizer, I have mentioned that lowering the resolutions will result in smaller files and in turn allows you to upload pictures faster. Of course, the side effect of lowering resolutions is that your image will lose some details and thus won't be as sharp as the original.
So yeah, it's all about the megapixels.
I've found a nifty little website called Megapixel Overview Chart that helps you to quickly calculate the megapixels and translate them to estimated file sizes. The site also have other handy tools like Bandwidth Calculator, Color Converter etc.
