Jpeg (or .jpg as you'll often see it on a picture file name) is the name for a type of image data compression. This means that although a photo might open on your screen at, for example 11MB, the file you open from might only take up 2MB of hard drive space.
So the obvious advantage of jpeg is its compactness for the purposes of emailing and storing image files.
But when a photographer captures an image in jpeg format on the camera, a number of “quality decisions” are made within the camera as it takes the data which the imaging chip captures, and it processes that data down onto the memory card. It will have taken certain choices regarding the colour, contrast and density of the image, and in doing so will have discarded some digital information which may have been useful, but cannot be regained later. A classic example of this is light skin tones in bright sunlight, where a jpeg image will be prone to blown highlights, where all detail is lost and the skin turns unnaturally white.
Also remember that jpeg is a compressed version of the original. A bit like taking a large photo print and folding it into half, quarter or whatever you need to make it fit a small space. When you unfold the photo later, it has creases in it, and high jpeg compression has the same effect.
Essentially jpeg is a great format for press work, where speed is of the essence, and amatuer photos where the pictures are for web use or inkjet printing. But photos destined for high quality applications, such as four-colour printing in brochures, need to be better than that.
This is where RAW comes in. Professional digital cameras can capture pictures in RAW mode, which is where all the data which the imaging chip captures is preserved and written down to the memory card. The big disadvantage of this is that if your camera is capable of capturing files which open at 24MB, the file stored on the card also takes up 24MB. So it's not so handy for email and storage. Also each camera model will have a different RAW format, so it's not a universal format which anyone can open.
So what's the big advantage of RAW then? Well, with a RAW file you lose none of the quality and data which a jpeg image loses, and the photographer keeps more image data, especially in difficult lighting situations. The colour, contrast and density can be decided once the image is on the computer, giving much more creative scope and greater quality.
The post-produced RAW file can then be converted to jpeg for delivery to the client, but leaving this as the last operation on the file ensures best quality is retained. So instead of compressing a file which has already been compressed once (in the camera when the photo was taken), the file is only compressed once at the time of saving to CD or for email.
Digital has come a long way in a very short time, and will continue to make leaps for some years yet. It has revolutionised the speed of delivery and the way photographers work (well, the ones who care for quality anyway). But it is generally at least expensive as film, and needs more understanding from photographers and clients alike in order to maintian high standards in publishing and PR imagery.
The advent of digital has placed an onus on photographers to learn to capture the best quality image with the technology they have, and for the client to understand the pitfalls and costs of getting it wrong, as well as the costs and benefits of getting it right.
Thanks to Tim Gander for producing this guide. © Tim Gander 2005. All rights reserved. This guide may be reproduced for personal and educational purposes only.