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Raster Formats vs. Vector Formats
People always ask, “Which is better: Raster or Vector?” Actually, what they really ask is “What do you mean?” and ”What is Raster?” or “What is Vector?”'
Raster and Vector are types of graphic formats which are two different ways of describing a picture. Raster format describes an image, kind of like a photograph or a painting.
Vector format describes a graphic, like a logo or typeface. But even that is too simplistic of a description, because raster images can be used for logos and typefaces, and vector graphics can appear photo-realistic.
How each type of format describes the picture is where the difference lies.
Raster Images
Raster formats describe an image by using a set grid of PICture ELements (or pixels (yes, we know there's no "x" in "picture".)) Each pixel on this grid is assigned a value. Those pixels, when viewed, form your image.
The type of value that is assigned to the pixels determines the color space. In the simplest form each pixel is either "on" or "off", or "black" or "white".
This color space is commonly referred to as "bitmap"* because each pixel on the grid (or map) takes up one "bit" of data. The next form, greyscale expands on that and allows black, white and 254 steps of grey between them. Color is added into the next iteration by assigning values of Red, Green, and Blue (RGB) for additive primary colors or Cyan, Yellow, Magenta, and blacK (CMYK) for subtractive primaries. (For more information about additive and subtractive primaries check out Wikipedia's Entry on the subject of Primary Colors.)
There are other color spaces available, but we'll leave those for you to investigate on your own.
How clean a raster image can look depends on how many pixels they squeeze into a given area. This is called the resolution. The higher the number or pixels per inch, the sharper the image may appear. One of the drawbacks of raster images is that the higher the resolution, the lager the final file's size will be.
Looks like this file had a previous life as a low resolution / low quality JPG... (The boxes you see around the image is JPeg "Artifacting" it's one of the ways the JPeg format decreases file size, by destroying perceptually insignificant data (the quality level determines how insignificant the data is.))
The benefit of raster images is that it can be extremely good at reproduction of "natural" images such as photographs or paintings.
* The term "bitmap" is also used by many to describe all raster formats. There is also an old Windows format called bitmap that uses the extension ".bmp"
Vector Images
Vector formats describe an image using a description of how the image is made up instead of building it piece by piece. By graphing objects on a two dimensional plane using mathematical formulas it is able to describe lines, curves, circles, polygons and more complex shapes such as characters from a typeface. These objects can be filled and stroked with color.
The benefit of vector graphics is that they can be scaled and will print to the highest allowable resolution of your output device.
