[Rob Barron]

Mouldy, let me give you a brief explanation of different file types as that might help you:

Raw files:

(.crw or cr2 on Canon, .nef on Nikon etc) are files which are untouched by processing. They are big file sizes as no compression at all is applied to them (for all practical purposes anyway!)

.jpg files:

(usually refereed to as jpegs) are compressed files. The computer looks at areas of colour that are the same and uses algorithms to store the colour once and applies it to all locations where that colour exists rather than storing the location of every pixel in every colour. This means it can be stored in a much smaller memory space but fine detail is often lost. Also, every time you save a .jpg it is compressed again so if you keep opening and saving before closing, the quality will deteriorate each time until it becomes so awful it is no use anymore. So if you have not worked on a jog, you have only viewed it, choose NOT to save when closing as that will avoid compressing again.

jpegs are the ones to always use for websites as you show them at low resolution without them looking terrible and without them taking forever to download/open on screen.

.tif files:

Tiff files do use a type of compression but this is known as 'lossless' because it stores much more information and does not take out the minute detail. That means these pictures make superb prints but are much bigger than jpegs so are no good for showing on web sites.

Top quality jpgs usually start out almost as good as tiff files but because of the recompression problem, they will not look good after many saves whereas tiffs will. So, when working on a photo, keep it as a .tif file until you are certain you have done all the post processing you want to. Then save a copy as a jpeg and use that for web or lower quality printing purposes. I stick my tiffs over onto my external hard drive where they are backed up to avoid wasting space on my main computer hard drives.

Hope that gives you a bit of help.

Cheers,
Rob