File formats

GIF - graphic interchange format

Gif creates a table of up to 256 colours from a pool of 16 million. If the image has fewer than 256 colours, Gif can render the image exactly. Gif achieves compression in 2 ways. 1st it reduces the number of colours of colour- rich images, there by reducing the number of bits needed per pixel. 2nd it replaces commonly occurring patterns with a short abbreviation: Instead of storing white,white,white,white,white it stores 5 white.

RAW - raw data

Raw is an image output option available on some digital cameras. Though lossless, it is a factor of 3 of 4 smaller than TIFF files of the same image. The disadvantage is that there is a different RAW format for each manufacturer, and so you have to use the manufacturers software to view the image.

TIFF - tagged image file format

TIFF is a very flexible format that can be lossless or lossy. TIFF is used almost exclusively as a lossless image storage format that uses no compression at all.

PSD - Photoshop document

PSD is a layered image file used in Adobe photoshop - is the default format that photoshop uses for saving data - is a proprietary file that allows the user to work with images individual layers even after the file has been saved.

PNG - portable network graphic

PNG is also a lossless storage format. However in contrast with common TIFF usage, it looks for patterns in the image that it can use to compress file size. The compression is exactly reversible so the image is recovered exactly.

JPEG - joint photographic expert group

JPEG is a commonly used method of lossy compression for digital photography. The degree of compression can be adjusted, allowing a selectable trade off between storage size and image quality.