Well, first: my pet peeve – it’s “raw” not “RAW” since it merely means “unaltered.” (JPEG is an acronym for Joint Photographic Experts Group, which is why it’s capitalized. “raw” isn’t an acronym for anything, which is why it should not be, but lots of folks-who-should-know-better do it anyway. I have no idea why.)
That said… here’s a link to a short movie that goes over all this, and may be more clear than my ramblings below:
http://aperturef8.com/workshop/rawfiles.mov
Terms (definitions) “raw” and “jpg”:
A digital camera can put out basically two kinds of files: raw and jpg.
Raw files are simple: the numerical data from the A/D converter, right as it comes off the sensor, and saved directly to the memory card.
Jpg files take that raw data, and run it thru built-in software, which demosaics, sets color; exposure; white-balance; contrast; sharpness; gamma/color-space, etc, and level of compression. Once it’s done that, the raw data is discarded and the resulting jpg file is recorded to the memory card.
In most consumer cameras, jpg is the only option. Pro and advanced amateur cameras offer the photographer the option of just saving the raw file. (Some offer the option of saving both.) Better cameras will allow settings for the jpg parameters, such as “sunny/cloudy/interior” for white-balance; “sharpness level”; compression levels; contrast level and so on.
A raw (or RAW, if you prefer) digital file is the analog of an exposed piece of film. Neither the digital file nor the film have yet been developed.
You can take your film to the drugstore, or into your own darkroom.
You can let the camera develop the raw file to a jpg (ie have the “drugstore” do it) or you can take the raw (non-jpg) file and “develop” it yourself on your computer (ie, use your digital darkroom.)
It is at this point, for the very first time, with film or digital, that you have something you would consider an image: a “negative.”
With film, you can push process, or pull to alter the contrast; choose D76, X-tol, HC-110, T-Max, Microdol or Dektol for high grain or low or various effects; flash it before developing… there are a thousand and one ways in the darkroom to alter a negative… (not to mention all the tricks one can perform with the enlarger when making the final print, but we’re just talking ‘negatives’ now…)
You can do all these things to a raw file as well, either by setting your jpg options in the camera (which is a limited range of options, to be sure) or using your desktop computer, which gives you a limitless range of options (just as you’d have in the traditional darkroom, with an infinite number of chemicals and mixes.)
parallel steps:
digital
1) the light hits the sensor
2) transfer raw data file to computer (in-camera or on desktop)
3) use software to make image file(in-camera or on desktop)
analog/film
1) the light hits the film
2) remove film from camera
3) use chemicals to make negative (darkroom or drugstore)
at step 2) neither of these (digital file or film) are a viable “image”, and are exactly as recorded. These are the “originals.”
at step 3) the computer is either on your desktop(if you’re using raw files), or inside the camera (if you’re using JPG.) If it’s film, then either you develop it yourself in your own darkroom, or have someone else do it (ie drugstore.)
That is, if you leave the digital image in the camera, and have the camera’s built in software do the work for you, you get out a jpg file. That is the analog of taking your film to the drugstore for developing.
If instead, you take the raw file from the camera, and use your computer software to develop it under your own control, that is the equivalent of developing the film yourself.
Just as you can do a hundred different things in your own darkroom, when developing the film, you can do a hundred of the same things when “developing” the raw file using your computer.
In digital: the software is either in your camera or on your computer. It is not unexpected that you have more control over the process on your computer than in your camera, just as you have more control in your own darkroom than you have at the drugstore.
There is one big difference however: with film, once you’ve developed the negative, that’s it. You cannot start over if you don’t like the results. That is also true of digital jpgs.
However, with digital raw files , you -can- start over, and adjust your “negative” until it’s just as you like.
That is, jpg files have in fact had the actual numbers in the file altered during processing. The data in a raw file is -not- altered by the processing; the changes are made in a so-called “sidecar” file, so that the original raw data remains unchanged.
This probably the single most important distinction between having the camera do it, and doing it yourself. (Followed immediately by the fact that one has infinitely -more- control with the desktop software, of course.)
It is only upon opening that raw file in Photoshop (which also opens the sidecar file automatically) that the actual data is finally altered (the actual numbers are changed.)