Let me explain the difference:
- When light enters a camera which will form your photograph it is picked up by a load of sensors on your camera. The human eye is more sensitive to green than red or blue and as a result for each four pixels you usually have 2 green pixels, 1 red and 1 blue. The CCD (camera sensor) picks up a voltage across each of these pixels and that is recorded internally as a RAW file (it's the raw data and each camera manufacturer has their own file format although there are standards for it now)
- Unless you know how to interpret that image, it's not much use so the camera can automatically convert it to JPEG. In order to do that, it makes some assumptions which can be configured by the photographer such as white balance (colour is very different under different light - more of that another time), exposure, contrast and sharpness. You then get an image which is useful (for one thing it's what appears on the viewfinder/playback of the camera) and can be viewed immediately on your computer and stored/printed/emailed etc.
In theory the JPEG is ideal as it gives you what you want in a format you can use. There's two huge catches though:
- It assumes you've got those settings right - as soon as you edit the contrast, brightness, white balance, colour tone (eg. make the image a little less red) you are losing quality as you are modifying an already modified image
- JPEG is a "lossy" file format. What this means is that to create a JPEG image some of the information is compressed and therefore lossed a bit (ie. lossy). TIFF files are not lossy and recommended for editing - more for another day
I nearly always shoot in RAW and then use the RAW editor to make any minor tweaks (white balance, exposure and contrast are the main ones I look at). It's also particularly useful for under-exposed photos. I took a photo a while ago of a snow leopard and one image turned out to be badly under-exposed [see left]. Luckily I shot it as RAW because I was able to increase the exposure and ended up with what's on the right.... much better!!! As comparison I tried editing the file as if it was a JPEG (ie. taking the RAW file and converting to JPEG using the camera settings) and was able to improve on the image on the left somewhat. However, all the background leaves were unrecoverable and the eyes lost a load of detail. Although perhaps not the best example, I feel this does illustrate the benefit of RAW.
I do often find myself doing commissions where clients take the photos "unedited". Even then, I generally shoot RAW and run all the photos through a customised tool which converts them to JPEG and tweaks based on what I normally find works best (bit more contrast, and a slight reduction in red levels). It does mean it takes a bit longer, but it means if I want to go back and edit a photo a bit more I can do it without losing the quality. More importantly if for some reason there's a photo that would have been great had it not been underexposed I've got a better chance of recovering it (as my snow leopard friend would agree).