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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.
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