Currently, there are quite a number of different graphics file formats. Nevertheless, all of them can be divided into two groups. These are files that store vector graphics and bitmap graphics files stored. Raster graphics – is when the image is stored in the form of small dots – pixels. Accordingly, the quality of such images is limited by two factors: it is actually the size of the image in pixels and a resolution image – that is, the number of pixels per unit length (the most common pixels per inch). Files stored in raster graphics are jpg, gif, bmp, tiff, png, psd and others.
Vector Graphics – is when the image is stored in an array numbers describing the construction of images in the form of curves and key points – tops. Formats of vector graphics – swf, cdr, max, ai, partly pdf. In practice, web graphics are mainly used in two formats, raster graphics – jpeg and gif, and one format vector graphics – swf. Much less frequently used format png. Jpeg and gif formats differ in different image compression algorithm. Since the web file size still plays a very significant value for several reasons, therefore lightweight image file significantly increases the speed of loading images.
For different "types" of pictures fits a particular format graphics. Determining the required format – the basic ability to web – designer. For photos, portraits, pictures, large, rich intricate details – best format jpeg. Compression algorithm of this format works so that, when the "weight" of a picture, and therefore quality image as it "blurs" are poorly distinguishable sharp transitions between colors, and there are stray colored pixels as a side effect of the algorithm.