Digital images can usually be divided into two distinct categories. They are either bitmap files or vector graphics.

Bitmaps

A bitmap image is a computer file used to store a picture. It consists of tiny blocks called pixels. Each pixel a one solid colour that when it is arranged in a grid with millions of other pixels will make up the image – just like you would do with mosaic tiles. Here is a close of an eye. You can clearly see all the coloured pixels that make up the image.

You can usually tell if the file is a bitmap by the file extension. Among these are:

  • BMP: an outdated and limited file format.
  • EPS: a flexible file format that can contain both bitmap and vector data.
  • GIF: mainly used for internet graphics
  • JPEG: mainly used for internet graphics and a default file format for most point-and-shoot cameras
  • PICT: file format that can contain both bitmap and vector data but has now been superseded by other more common formats
  • PNG: mainly used for internet graphics
  • PSD: the native file format of Adobe Photoshop (which can also contain vector data such as clipping paths)
  • RAW: a default file format for most mid to high end cameras
  • TIFF: a popular and versatile bitmap file format

Vectors

Instead of using pixels, vector based images are images that are completely described using mathematical definitions. The image below shows the principle. To the left you see the image itself and to the right you see the actual lines that make up the drawing.

Those individual line is made up of either a vast collection of points with lines interconnecting all of them or just a few control points that are connected using so called Bézier curves. It is this latter method that generates the best results and that is used by most drawing programs.

File extensions:

  • AI: the native file format of Adobe Illustrator (which can also contain vector data such as clipping paths)
  • EPS: a flexible file format that can contain both bitmap and vector data.
  • SVG: a new standard for internet graphics

Advantages

of bitmaps

  • much easier to create the appearance of “natural” media, such as areas of watercolours bleeding into each other
  • more universally available interchange file formats; most bitmaps can be read by most bitmap-based software and certain file formats such as jpeg and png can be read and written by every paint program. This is not, unfortunately, the case with vector file formats where many programs can only deal with their own file formats and a very limited choice of others such as eps may be available.

of vectors

  • pretty much resolution-independent. It is possible to rescale up to what ever size you want to without the blockiness (pixelation) you would get from doing this with bitmaps
  • everything can be easily changed, just by moving the points.
  • as it’s just maths, the file sizes are a lot smaller than if they where bitmaps
  • mathematically precise

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