Shooting in RAW format
imposes several inconveniences like:
-
large file sizes
-
long lag between shots
-
requirement for
post-processing
-
no support for RAW by photo
labs
that make this format
impractical in many situations, so why bother?
The full list of benefits
will vary from camera to camera, but what’s stated here should be true for most
Minolta DiMAGE cameras.
RAW is the only format in
which the photos are recorded with 12 bits per pixel of colour information, for
each of red, green and blue channels. JPEG and TIFF formats (as out of the
camera) give you only 8 bits of colour depth. This means that in RAW we have up
to 4096 distinct values of data in each channel, as compared to only 265 in the
other formats. While the immediate difference is quite hard to notice, the
post-processing can quickly lead to posterization, especially in very light
shades. Having this extra depth available makes photos more resilient to
post-processing.
For example if the original
photo is too dark, you can make it much lighter without noticeable degradation
of detail level. Making it 4 times brighter still gives you 1024 levels of
detail, while on a 8-bit photo it will reduce down to 64. It’s true that noise
is amplified together with the detail, but it looks much subtler when there’s
enough colour depth.
In a 5Mpixel camera it
doesn’t matter whether your image is JPEG or RAW if all you’re going to do with
it is display it on the web or print in small format – there’s more than enough
detail to handle these situations. But if you consider heavy cropping of your
images (for example to combat the zoom limitations) or large prints (bigger
than A4), then all the detail you can get becomes very precious.
All photos are originally
shot as RAW. If you select a different format, the RAW image is converted
in-camera to the desired format. The in-camera interpolation algorithm is a
compromise between reasonable quality of output and the time it takes to
convert the RAW image into the final RGB map. It has to work in a limited
amount of memory and has to be quick enough for the camera lag to be minimal,
and it has to be good for all the images.
When you shoot in RAW, the
camera stores the image as it was captured by the sensor, and all the conversion
takes place in your computer after the image has been downloaded. The difference is that at this stage you can
afford the time to run less efficient but more sophisticated algorithms, and
experiment to select one that gives you best results for a particular photo.
Typically the algorithms differ in their ability to produce clean edges and
handling of noise – depending what your photo contains, some will produce
better results than others.
The “viewing-ready” formats are
fully processed in-camera as soon as the photo is taken. If you shoot with a
wrong white balance setting, or the auto doesn’t guess the right settings for
you, your only recourse is post-processing with seldom a satisfying result, and
very quickly leading to posterization (you have only 8 bits of colour data to
play with).
RAW images are white-balance
independent. The camera’s WB setting is stored with the image, but it does not
affect its content. Consequently, you are able to play with the colour temperature
until you are completely satisfied with the result, and in the end still have
all 12 bits of colour data available to you.
What has been said about
white balance, applies to colour space as well. The sensor has its own
characteristic and it needs to be adjusted for proper display on other devices.
If you are really particular about colour space accuracy, you could create a
colour profile of your individual camera rather than relying on the series
average embedded in your camera by the manufacturer – there are tools that can
help you doing that. Such colour profile can be fed into a RAW converter, but
I’m not aware of any camera that can download a colour profile (although some
may be individually tuned in factory).
Similar kind of benefit is
related to the ability to select gamma profile and image contrast before the
interpolation is done. It has
significant impact on the noise level and uniformity of flat surfaces. Outside
of RAW the gamma curve is fixed, and you have only one shot at the contrast
setting, which is often too granular to be useful.