Square Pixels

http://en.wikipedia.org/wiki/Pixel

you must remember to distinguish physical pixels (as they exist within the display device itself, which varies depending on the type of display. they might be round, rectangular or square depending on the device.) and the electronic representation of the pixels in memory. since electronic images are built up of rows and columns of pixels, the pixels are by necessity rectilinear, otherwise you'd have space between them. Half-tone images however are made up of round pixels (or hexagonal ones.) with a fixed pitch but with varying diameters. They are used on the printed page however.

Bite size info for me, thanx!

When you talk about electronic images, nearly all images are pixel mapped. They are square. Most images are made of pixels that relate to discrete memory locations. A pixel is the smallest piece of any image. When you blow them up to a high enough scale, they will always be square unless they are averaged to keep you from seeing the block edges. If you started out with 64 by 64 pixel image and enlarged it, you would be looking at maybe 16 by 16 as your full image and the edges are much more defined so it shows the blocks much more clearly. The only reason you don't see them all the time is most images exceed the ability of the display to show them. The hard part is to keep the image sharp enough and filter out the edging on the blocks so you don't normally see them. Most images start out as 800 X 600 or greater.

The exception is vector graphics which are actually drawn in lines and nothing above applies.