RAW Files: Who Needs Them?

by Patty Hankins & Bill Lawrence


Maybe you've noticed that your digital camera has a setting for shooting files called RAW - or you heard that Photoshop CS can read RAW files - and you're wondering do you need to use RAW files? The answer is - it depends!

On our three Canon digital cameras - we shoot everything in RAW mode. And when we use our Nikon 775 - one of the frustrations is that it doesn't have a RAW mode setting. But not everyone needs to use RAW mode if their camera has it, or to go out and get a camera just because it has RAW mode.

What is RAW mode?

Raw files essentially represent the raw or unprocessed (though it may have some lossless file compression) output of the digital sensors used to take the images. If your camera is set to record a JPEG or TIFF file, then when the image is taken, a processor in the camera will convert the raw sensor data to the appropriate format after image processing (e.g. sharpening, applying color correction for white balance, changing contrast, potentially changing the bit depth in the color channels). If you shoot in raw mode, your camera doesn't do any of this processing, it simply stores the sensor data. These files tend to be larger than fine mode jpeg files (e.g. on our Canon D30, a jpeg file is roughly 1.3MB, and a raw file is roughly 2.8MB), though not as large as uncompressed TIFF files (About 18 MB for a 16-bit file).

Why shoot RAW mode?

There are a number of reasons to use RAW mode. First, as we've noted in previous columns, jpeg files have a quality loss due to compression. Usually, this is undetectable if saved once with only mild jpeg compression. But, if you've got a great shot and want to really enlarge it, why put up with needless loss of quality in the image?

Second, for those cameras that support greater than 8-bit per channel color bit-depth, the raw mode files retain the full color bit depth. (Warning: TECHNICAL EXPLATION AHEAD - the non-technical explanation is in the next paragraph) Most digital cameras record sensor information in three colors (red, green, blue). For each of these three color channels, they can have some number of discrete levels they can record. An 8-bit per channel bit depth for a file means that the file can have 256 levels (28), 0-255. These files are sometimes also called 24-bit files, for 8 bits in each of 3 channels. Black would be 0 in all 3 channels, white would be 255 in all 3 channels. This combination produces almost 17 million possible colors; why would anyone want any more? The human eye (at least ours.) would not be able to tell an 8-bit per channel file from a 16- bit per channel file (another common format) if the starting point was a well-exposed photo without any editing.

The advantage of the higher bit-depth is that exposure isn't always perfect all across an image. A big group photo taken outside on a sunny day, for example, will tend to produce dark shadows if you avoid blowing out the highlights. But what if you want to bring out important detail in the shadows (say, Aunt Millie's face)? Sometimes the color balance is off (you'll know it when you see it - things that are supposed to be white have an orange or blue cast that affects the entire image). In both of these cases, having the extra information will let you expand specific parts of the color spectrum to fix an undesirable aspect in an exposure. You can do this to some extent with an 8-bit per channel file, but do it too much and you get posterization effects. Our Canon D60 and D30 can record 12-bits per channel of information, but it gets clipped to 8-bits if we use jpeg files. We don't want to throw away that extra information if we can avoid it.

The final reason that we use raw mode is that we have control over how the image is processed though editing it on our computer - rather than having the camera process it. This way, we can decide about the level of sharpening, and make any necessary adjustments to the white balance. We'll have an article on white balance in a future issue that will explain how and why you might want to adjust it manually. For now, just trust us that the ability to adjust the white balance is a lifesaver. At one event Patty photographed last year, the flash misfired on the most important shot and everything in the photo was blue (think award winner, dignitaries, award, literally everything was a shade of blue). Since we could set the white balance manually - it only took a couple of seconds to get the colors looking much better. If she hadn't shot in RAW mode, we might still be trying to adjust them.

Who should use RAW mode?

If you edit your images on your computer, then RAW files give you much more control over the base image to edit, since you get to make decisions about image processing, rather than the camera. If your camera has a RAW mode - give it a try and see the difference it makes in what you can do with the files your camera produces.

If you print your photos straight from your camera, either on your own printer or by taking them to someplace like Ritz Camera or Wal- Mart for printing, then RAW files are most likely more trouble than they are worth. We're not sure if one-hour printers can handle RAW files, and the files are most likely larger than the JPEGs you're currently creating. But keep them in mind for the times that you do plan on doing (or having someone else do) some editing of your images.


"Reprinted from Zongoo.com Daily Press & Consumer Information"