A lot is being said about (and done with) raw capture files from digital cameras. I want to give a brief introduction, then launch into details about the one particular raw file I work with, the canon CR2 file that comes from my Canon 20D camera.

A raw file contains unprocessed information, as direct as you can get it (in digital form anyway) from the camera sensor. This has many advantages, if you have tools to work with it, such as the following:

• Raw data has not been processed by a lossy compression algorithm such as JPEG. JPEG does a great job, but in the form it is used by digital cameras, there is some data loss.
• Raw data is stored in greater resolution, providing more dynamic range. My camera has a 12 bit analog to digital converter, so the raw file holds 12 bit data. A JPEG file can hold only 8 bits per color channel, so there is inevitable data loss converting to JPEG.
• Raw data has not been adjusted for white balance or color space. The raw file may have a tag indicating the white balance or color space setting in the camera, but this is only a hint which may be ignored when you do raw processing.
• Raw data has not been sharpened or color adjusted in any way.

Does this mean that JPEG is bad, and should never be used? Not at all, it often does a fine job, and the DIGIC chips used in Canon cameras do a superb job in generating it. Above all, a JPEG file excells in convenience, they come out of the camera ready to use on the web, send to friends, to print at the local Walgreen kiosk.

Note also that the color space, white balance, sharpening, and saturation settings in the camera menu affect only the generation of the JPEG files by the camera.

If you are interested in a lot of technical details about the inner workings of the canon CR2 raw format, see the following links:

• Canon raw files: introduction
• The Canon CR2 format
• Raw links and resources