JPG vs RAW

A question I am asked frequently is "Do you shoot in JPG or RAW? "

The answer is actually, both.  As a former (and sometimes current film photographer, I need the latitude that RAW images provide.  However, when I do not intend to process the images, JPG is definitely a more efficient format.  If you have a few minutes, let me begin to explain....

Most beginning digital photographers use the JPG setting in their cameras.  This setting allows the software in the camera to "process" the data captured by the sensor into a viewable image.  The photographer has control over the white balance, exposure and ISO and when you preview the picture on your camera's rear screen, for the most part, what you see - is what you get.  If you don't like it, you just change the settings and shoot again.  The best parts of digital photography is that you get instant feedback, and retakes are free!.

So, what do I mean when I say that the camera "processes" an image to produce a JPG file?  Well, in simple terms - the camera's digital sensor captures image data from whatever you point it at.  The data comprises information about colour, light, white balance and focus.  In JPG mode, the camera analyses the data and discards a portion that the software "thinks" is unnecessary.  It does this by "compressing" the data.  The compression is referred to as "lossy" referring to the discarded or lost data.  

But what data is lost?  Well, let's say that an image contains 6 shades of blue.  That's pretty subtle and may not even be discerned by someone looking at a printed picture.  So the software smooths it out into 3 shades, by discarding (losing) some of the data and smoothing out the remaining information.  This same process is used for gradations in light intensity and other elements of the photo.  Very cool and efficient.  File sizes are manageable and the pictures usually look great!

Sounds like the camera takes a great picture so what the heck is RAW?  And why use the RAW mode?  Wait for part 2......