Pixel resolution refers to the number of pixels in an image's columns and rows. There are two main types of computer graphics: raster images which use a grid of pixels and vector images which use mathematical relationships between points and paths. Common file formats include JPG, which is best for websites and emails due to its ability to be highly compressed into small file sizes at the cost of lower quality. There are two types of image compression - lossless, which compresses to an exact duplicate but not greatly, and lossy, which strips redundant data to allow for higher compression ratios but results in some quality loss.