David Pogue's Digital Photography: The Missing Manual

RAW or JPEG?

If you have a typical pocket camera, skip this section. It's reserved for the owners of SLRs and a very few advanced, more expensive smaller cameras.

It's about the RAW file format. Understanding it requires some background.

See, most cameras work like this: When you squeeze the shutter button, the camera studies the data picked up by its sensors. Based on this analysis, the software makes decisions about how much to sharpen the photo, which white balance setting to use, how to set the exposure levels, how saturated the colors should be, how high the contrast ought to be, and so on. The camera crunches the raw data from the sensor, locks in all of these settings, and spits out, onto your memory card, a processed, finished JPEG graphics file.

For millions of people—including plenty of professionals—the resulting picture quality is just fine, even terrific.

But there's another crowd, consisting of professionals and advanced amateurs, who can't stand the thought of all that in-camera processing. They'd much rather make all of those creative decisions themselves. They'd prefer that the camera not process the original image data at all, and instead deliver every iota of original picture information onto the memory card. That way, later, these pros can process the file by hand once it's been safely transferred to the computer, using a program like Photoshop, Photoshop Elements, Picasa, iPhoto, Lightroom, or Aperture.

That's the idea behind the RAW file format, an option in every ...