In Photoshop file size matters.

It matters to the outcome of your picture. When you use Photoshop the file size can make or break the picture you are turning into a work of art. This page is not applicable to the "Quick Fixes" or certain other effects. It is mostly needed for effects having some kind of texture.

When you go to the store with your pictures on a disk or thumb drive, that electronic medium contains what is known as digital information. The information is on the disk in a form known as a file. A file is merely your picture in digital format.

The file is made up of something known as pixels. A pixel is an electronic dot. Pixels are measured in P.P.I. That is Pixels Per Inch. If you enlarge a picture as far as you can in Photoshop you will see individual squares. Each square is a pixel.

Pixels as seen in Photoshop.

You will not be able to clearly see the pixels unless you are using a program like Photoshop. It is designed that way. Here is the same sample as it is seen in Windows Picture and Fax Viewer.

Many people get confused when they speak of P.P.I. and D.P.I. D.P.I. is how many dots per inch a printer offers. It is mechanical. P.P.I. on the other hand is an electronic quantity of how many little lights (pixels) per inch you see on a computer screen or a television screen.

Just remember (D.P.I.) dots are mechanical and (P.P.I.) pixels are electronic.

A file size is the number of pixels in the whole file, or in one picture. The dimensions are how many pixels wide and high the file is. File size and file dimensions are not directly related. I won’t go into that here because for our purposes the only important thing is the dimensions.

"File Size" is 4 pages.

Continue here.