So what is this RAW format I speak about?
First lets see what happens when you take a photo as a JPEG. You have lined up your shot and press the shutter button, the light passes through the lens and onto the image sensor from here the data is passed onto a processing chip in the camera which takes this data and performs various “enhancements”, it will sharpen (non selectively), increase contrast, saturation, brightness and will perform noise removal. It will then compress the file as a JPEG by removing data which it thinks is not required, and there you have it, your JPEG image.
The information that was removed when the data was compressed into the JPEG format is gone and cannot be retrieved, this missing data could have held useful details in blown out highlights or in the under exposed areas of your photos that had you known it was there may have been able to rescue in post processing. This is where the RAW format sometimes known as digital negatives come into play. The RAW format offers a deeper and richer tone to colours and offers more control over the exposure levels during editing. Editing of a RAW file in post processing software will not degrade over multiple edits like a JPEG can.
Obviously there are uses for JPEG images, if your camera has a small buffer then shooting in RAW is going to affect the burst rate and will mean you won’t be able to take as many images in quick succession. The file sizes when using RAW are what put most people off, for a 10megapixel camera a single JPEG image can be around 3-5meg in size whereas the same image in RAW will be around 40-60meg and so if you're not careful you will quickly fill your memory cards.
I will try if I get time to follow up this article with some examples of using RAW images to rescue blown out highlights or underexposed regions in photos.