lanky Girl

3.4 Images and Graphics

In DITA on October 25, 2009 at 11:52 pm

This week in DITA we have been looking at Graphical image formats.

Raster images

Raster images work well for complex graphic such as scenery as they record continuous information. Cells are usually arranged in a grid and each cell has a numeric value that represents its content. These cells are often referred to as picture element or pixels for short. (Butterworth,2009)


GIFs were developed by Compuserve in 1987.  GIF Files support 256 colours as they are in a 8-bit format meaning they record 8-bits of information for each of the pixels. Because of the limited nature of GIF files they are better to use for logos or line drawings. GIFs can also be animated unlike JPEGs which are static images. ((Butterworth,2009)

JPEG’s were developed by the by the Joint Photographic Experts Group. JPEGs are able to support 16 million colours because of iTs 14-bit format. Compression is more successful in JPEGs than in GIFs as JPEGs employ a technique called lossy where the colours are subtly modified by creating patterns. The loss in colour data is not normally detectable to the human eye which means that JPEGs are very good at storing photographic information.

PNGs like JPEGs are in 24-bit format but they compress images without the lossy technique. However the PNG files tend to be larger than JPEGs.

Image formats is important in web design because large files can affect the  time a page takes to render. Depending on the topic of your page you would have to decide whether to compromise on resolution or page rendering.

Vector images are different because they are made up geometric point, lines and curves which are based on mathematical equations.

Here is a link to an embedded formatted image that is blocky because of the pixels.


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