What is RAW format in digital photography?

There seems to be a lot of confusion among digital camera neophytes about the differences between RAW, JPEG, and TIFF files.

This article is intended to be a very basic guide to these file types and how they are related in a typical digital camera.

Because of the digital camera industry’s relative youth, each camera maker has developed its own RAW formats. And as camera sensors improve, manufacturers change their formats accordingly, usually creating a new format for each new camera model, with the result that, as of mid-2005, there are more than 100 different RAW formats in existence

RAW data
When a digital camera makes an exposure, the imaging chip (whether it’s CCD or CMOS) records the amount of light that has hit each pixel, or photo site, which is recorded as a voltage level. The camera’s analog-to-digital circuitry then changes this analog voltage signal into a digital representation. Depending on the camera’s circuitry, either 12 or 14 bits of data are recorded.

Incidentally, if the camera records 12 bits of data then each pixel can handle 4 096 brightness levels (2^12), and if 14 bits, then each pixel can it can record 16,384 different brightness levels (2^14). (To my knowledge no current imaging chip records a true 16 bits worth of data).
What happens after you’ve taken the photograph now depends on whether you have the camera set to save images to the memory card as

RAW files or JPEGs.
If you’ve saved the file in RAW mode, when it is subsequently converted and saved to a TIFF or PSD format file, it can be exported in 16-bit mode, which means the 12 or 14 bits recorded by the camera are then spread over the full 16-bit workspace. If you’ve saved the file in-camera as a JPEG than it is converted by the camera’s software to 8-bit mode and you will only ever have 256 brightness levels to work with.

A second advantage of shooting a RAW file is that you can also perform the conversion to an 8-bit or 16-bit TIFF file. TIFF files are larger than JPEG files, but they retain the full quality of the image. They can be compressed or uncompressed, but the compression scheme is lossless, meaning that although the file gets smaller, no information is lost.

Lossless compression is a tricky concept, but an example should make it clear. Take this string of digits:
14745296533333659762888888356789

Now let’s see a way to store this string that doesn’t lose any digits, but still takes up less space:
1474529653[5]6597628[6]356789

Here the string “33333” has been replaced by “3[5]”— meaning a string of 5 3s, and the string “888888” has been replaced by “8[6]”—meaning a string of 6 8s. You’ve stored the same data, but the compressed version takes up less space. This is similar (but not identical) to the way lossless TIFF compression is done.

Professional photographers and other creative professionals are moving to RAW camera workflows because of the outstanding creative control they get over digital images However, clients and publishers have difficulty working with disparate RAW file formats and nobody can be sure that today’s RAW formats will be supported ten years from now.

Final thoughts
There are professionals who shoot in RAW and there are professionals who shoot in JPEG, and both do wonderful work. The decision to shoot in one or the other is a matter of preference, time, space, and desire or need to have the extra flexibility of RAW format. I personally take the extra time to work with RAW, as I think the extra image quality is worth it as you can see from the images accompanying this article.
The two images accompanying this article were taken with a Nikon D2Xs, moments apart, without any adjustments made to exposure settings (shutter speed, aperture, etc).  The photo on the left (1) was taken with the camera set on RAW format.  The photo on the right (2) was taken with the camera set on JPEG format.  As you can see, (1)  is much more eye pleasing and is a more accurate representation of the object.