Vector & Raster Images

A digital image can either be a Raster or Vector image. There are many differences between these two types and each one has it's own purpose, advantages and disadvantages.

Raster Graphics

These types of graphics are made up of a grid of many pixels (A bitmap), and are the most common kind of graphics seen on a computer. For example, images imported from a camera or found the internet are raster images. Typically the larger and higher quality the image is, the more pixels it will contain and the larger the size of the file will be as information has to be stored for more pixels. For example a image of size 100x100 will contain significantly less pixels than an image of size 1800x2100, and the latter will take up a lot more disk space. To deal with the issue of larger file sizes, various raster file types with different compression algorithms were developed that compress the image and reduce the file size. Formats such as JPEG and GIF are good examples of this. The downside to raster graphics is that they cannot be resized or altered without losing quality, for example if a JPEG image is resized to be made larger, it will look 'blocky' or 'pixelated' and look very low quality. For this reason, raster graphics are not as useful for images such as logos which need to be resized often.
http://www.techterms.com/definition/rastergraphic

Below is in example that shows what happens when part of a raster image is enlarged;


http://vector-conversions.com/images/raster_vs_vector_1.jpg

Vector Graphics

Unlike Raster Graphics that are made up of thousands of pixels, vector images are composed of lines, curves and shapes defined by mathematical expressions. They are made up of Vectors or Paths, which are drawn through Control Points. These points have an absolute position on the x and y axis of the image and contain information on it's location and the direction the vector is meant to take. A colour, shape and fill can also be assigned to each vector. The main advantage of using a Vector file is that it can be resized to any size at all without loss of quality. This is because it is not made up of a set amount of pixels, instead a vector file describes how the image is to be drawn out by paths or vectors. This is useful for businesses who need to resize images such as logos. A vector image can be created and edited in programs such as Adobe Photoshop, Adobe Illustrator and Inkscape and file types associated with it include SVG (Scalable Vector Graphics), EPS (Encapsulated Post Script), and DRW (Drawing).
http://www.techterms.com/definition/vectorgraphic
http://en.wikipedia.org/wiki/Vector_image_format

Below shows what happens when a vector image is resized in comparison to a resized raster graphic. (Although the image itself is not a vector as they cannot be placed in this document)

http://en.wikipedia.org/wiki/File:VectorBitmapExample.svg