On the dynamic range of RAW...

Started Nov 30, 2004 | Discussions thread
Stan Powers
Stan Powers Veteran Member • Posts: 4,648
Thanks, Brian!

Always appreciate your cogent style. Excellent presentation!

Stan

Brian G. wrote:

Hi All,

I was fooling around with my new camera trying to see exactly where
the limits were regarding captured detail and dynamic range, and I
thought it might be useful to show some of this in the forum.

One of the strongest arguments for shooting RAW is that a 12-bit
RAW image file simply contains more image information/expanded
dynamic range, compared to an 8-bit jpg. You can process a RAW
image multiple times, (once for highlights and once for shadow, for
example) and blend the results to give a photo with more dynamic
range than would be possible shooting in jpeg. It is sometimes
argued that you can always bracket exposures with jpegs to do the
same thing, but the two methods are not equivalent. In fact, there
is at least one serious drawback to bracketing jpegs- your subject
must be static. The technique is useless if anything moves. With
RAW processing, you are manipulating a single image, so the
technique can be used for any subject at all, even if it's in
motion.

I thought I would show an example. This particular scene was not
selected because I thought it would make a good photograph, rather,
I picked it because I knew it would be tough on the camera. The
room was dimly lit except for some very bright sunlight coming in
through the window. I metered for the desk, and got this shot as a
baseline:

.
As you can see, there are areas that are completely blown out, and
areas that are completely black. But the camera captured much more
than this...
We can take the RAW file and push it up +4EV to bring out detail in
the shadows:

The candeholder on the desk and the chair at lower left are now
visible, for example. You can recover shadow detail on a jpeg also
(Shadows and Highlights slider, in Photoshop, for example) but
usually not to the same extent as you can manage in RAW.
What about all that lost highlight detail? Here, if you've shot
jpeg, you are out of luck. You cannot retreive detail that is
simply not present in the image. But because the shot was done in
RAW, we can process it again, this time at -4EV:

Notice how the camera did record detail that appeared blown in the
original exposure- the curtains and the background landscape are
good examples. These areas would have been completely and
irretrievably lost had this been shot in jpeg
.
The images with recovered highlight and shadow detail can then be
blended for a result with much more dynamic range. Now, this
particular final blended image is a very quick, and quite
frankly, very poor job. I just threw it together for illustrative
purposes. If I was serious, it could be made to look very nice,
blend-wise:

If you compare this shot to the first one (the one that the camera
actually gave me) you will see that, desipite the poor blending
job, this image contains much more detail in both the highlights
and the shadows. And again- although you can often recover some
shadow detail with jpegs, if your highlights go to white, they are
lost forever. Not so with RAW.

I just thought this might be useful for anyone wondering about the
benefits of RAW. Hope it was helpful for someone.

Kind Regards,
--
Brian (el picador, Sir Brian)

Digital Image Gallery:
http://mywebpages.comcast.net/spiritmist/Brian_G_Digital_Image_Gallery/index.htm

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