The graphic shown above is the Eagle image from the Photoshop samples folder at 1200% zoom. You can see at this finely grained view that the image is really composed of many individual blocks of colour. At a normal zoom level (such as 100%) the blocks would be very tiny and your eye would perceive this information as a smoothly continuous image.

At a basic level, elements of digital images (like the small blocks of colour just mentioned) can be represented as individual numbers (digits) in a range of possible values. When you edit a digital photo in Photoshop, you are actually using your computer to perform operations on these numbers. Computers deal with numerical information with amazing speed and efficiency, and this is what makes image processing software like Photoshop CS so powerful and flexible.

A little bit of understanding about digital images can help you when you work with Photoshop. If you know something about pixels, bitmaps, and vector graphics, you will have some insight into what the Photoshop CS program is actually doing when you edit an image. You will understand why there are some tools for vector graphics, and why some tools are for bitmap images. Perhaps more importantly, you will have an idea of what a pixel, bitmap, or colour value is when they are mentioned in the context of a Photoshop tool, function, procedure, or image file format.

In the following lesson, you will explore the concepts of pixels and bitmap images. You will learn about vector graphics and how they differ from bitmaps, and you will also learn a little about image re-sampling and its implications in regard to image editing.