Canon EOS 1D Mark IV - digital camera

The main purpose of RAW image format is to capture a photo with as little processing as possible. In a JPEG file, several parameters are applied to the image, such as white balance, saturation and contrast, among other things; then the file is compressed using a lossy scheme. With RAW format you are generally getting as much information as your digital camera can record with, so in essence, RAW acts very much like a digital negative. The advantage of having a large amount of data in each image is that the photographer has more to work with in post-processing, and can cull out any unwanted data manually. The disadvantage is that the files are very large, causing more room to be taken up on the camera's memory card, and also slowing down the camera's ability to capture shots because of recording time.

Another thing to be aware of with RAW format is that each digital camera manufacturer creates their own proprietary type of RAW, so not all photo processing software will work with all RAW photos.