On the dynamic range of RAW...

Started Nov 30, 2004 | Discussions thread
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Brian G. Veteran Member • Posts: 6,531
On the dynamic range of RAW...

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)

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