Digital Graphics Technology

The field of digital graphics has undergone rapid advances in recent years. Indeed the technological advances are such that the terminology used to describe the constantly changing formats and specifications could fill a small dictionary. It is helpful in marketing digital products to have a resource which simplifies this terminology and makes file extensions and abbreviations comprehensible. This paper is intended to provide that resource.

The smallest picture element of digital graphics is called a pixel. A pixel is a light source which can be charged electronically to output a colour of various intensity and saturation,(intensity refers to the strength of the light output or brightness) the combination of numerous pixels can create an image. The greater the density of the pixels the higher the resolution of the image. High resolution images can contain millions of pixels and superb clarity of detail.

Raster images are formed using a group of pixels. Raster images can easily be identified because of their inability to maintain defined curves and straight lines when an image is enlarged (or scaled up).In diagram one it is possible to see the individual blocks that make up a raster image when it is enlarged . Raster images are used in pictures or photographic files where each individual element (pixel) can be manipulated or altered. Because millions of pixels are required to form a photographic quality picture, the resultant files are large. In order to allow more images to be stored (particularly on removable media such as SD cards) the photo files are often compressed (made smaller). Various means are used to compress these files some of which result in a loss of detail (e.g. jpg. files referred to as lossy) while others retain the full detail (e.g. Bitmap files which are lossless). The file extensions indicate the way the files have been formatted or stored by a program and the colour depth is dictated by the number of bits or bytes (8 bits equals 1 byte) of information used to represent each pixel. A pixel using 8 bits of information (an 8-bit or1byte pixel) can produce an image with 256 colours whereas an image defined as true colour will require 24 bits (producing over 16 million colour combinations) or 32 bits per pixel. All image files use algorithms (mathematical formulae) to store the information required to reproduce an image either accurately (lossless) or recognisably (lossy). Raster images generally use the following file extensions –

• Bmp. – Bitmap an uncompressed format that is large in size but popular thanks to its adoption by Microsoft.
• Gif- Graphics interchange format is a lossless format but is limited to 256 colours making it suitable for cartoon and logo images.
• Png- Portable network graphics is an open source lossless format suited to images with large colour blocks and web usage. It superseded the gif format.
• Tiff- Tagged image file format that suffers due to its flexibility (tiff formats are well supported but not comprehensively supported by individual programs) They can be lossy or lossless and support 24 and 48 bit colour.