Take a close look at the following image. You will notice a straight line that was drawn by the pen tool just above the eagle’s beak.

In Photoshop, the pen tool is used to draw paths, which are a kind of vector graphic.

You have already seen what happens when a bitmap image is zoomed in to a high level. The image pixels are much more obvious, and the colour and edges of the image appear jagged and block like.

The following image shows the eagle image with the pen stroke zoomed in by a factor of 10.

You will notice that the general image has had a severe reduction in quality. The beak looks jagged and you can see blocks of colour throughout the image. The line drawn with the pen tool, however, is still crisp and sharp.

This is because the pen tool draws vector graphics. Unlike bitmaps, the shape of vector graphics is controlled by mathematical formulae and geometric algorithms (such as Bezier curves). When you scale a vector graphic, the formulae that describe it simply adjust the geometry of the graphic to the new size requirements without severe loss of quality or the presence of jagged colour blocks.

On the other hand, a bitmap image is based on a fixed array of pixels. If it is scaled up, more colour information has to be added so the size can increase. Where does the colour information come from for the larger bitmap? Basically, the program that is scaling the image has to guess in some way to arrive at the new colour values and at the best location in the bitmap for the colours. This resizing/guessing process can cause a reduction in picture quality.

Vector graphics can be scaled without the same kind of loss in quality because they are the result of formulae, not a fixed pattern of pixels. When they are scaled, they are still drawn to the exact specifications of the formula, but at a different size.

Vector graphics do not represent images with photographic realism. By their nature, vector graphics are limited in their use of colour and normally have an animated or artificial look. Vector graphics are great for geometric shapes, diagrams, and other instances where photorealism is not required, but they are not as easily shared across platforms as bitmap graphics. If you save a vector graphic as a bitmap image, it must be rasterized; that is, translated into a pixel array. Once this is done, the vector graphic will be a bitmap and will be subject to the same scaling problems.

The pen tools, the path selection tools, and the shape tools are all examples of vector graphics tools in Photoshop CS