Is X Stops of Dynamic Range Misleading?

[Peter Moretti]

Cameras' dynamic ranges are usually characterized by number of stops. As we know a stop is doubling (or halving) of light.

So for a camera with 13 stops of dynamic range:

Stop 1 = Light1
Stop 2 = Light1 * 2
Stop 3 = Light1 * 2 * 2
Stop 4 = Light1 * 2 * 2 * 2
...
Stop 13 = Light1 * 2^12

What this doesn't tell me about is the *quantity* of the light for Light1 (or any other stop).

So I could have two cameras both with 13 stops of DR. But one could see deep into the shadows. While the other could handle bright light better, but be noisy in the shadows.

So both cameras could have 13 stops of DR, but handle light significantly differently.

Now I realize that there is the "native" ISO rating for cameras, but these seem to be rather inaccurate.

I feel that a helpful measure for DR would be to use Illuminance:

https://en.wikipedia.org/wiki/Illuminance

Minimum and maximum illuminance values would be very helpful for comparing how cameras handle light.

 

[C. Burkhart]

The biggest problem is around the issue of noise.
What is subjective is what one feels to be "usuable".
Some people feel that by doing some noise reduction in post it actually extends DR.
Some manufacturer's do the noise reduction in camera.
Other manufacturer's believe it is better to allow the enduser to do this.
Some noise feels like film to some enduser's. Others disagree.
Personally, I think that Helium is the first sensor that handles noise in a really strong way.
Previous to it, I never felt convinced and found RED's to be awful in low light.
So illuminance is only part of the equation.

The other factors involved also involve the light source of a shot.
Some cameras have greater DR in Tungsten by comparison to another camera, though they may be equal in daylight.
I have also never felt that RED cameras performed very well in Tungsten light either for instance. The nuance's just aren't there for me.
Though in daylight they do a great job.
But that is just my subjective opinion.

Further, does HDR qualify as DR ? The Alexa in fact uses a form of HDR which just happens to be very convincing. Especially for highlight roll-off.

There are so many variables involved it is really an endless debate.

 

[Marc Wielage]

This has been discussed quite a bit by Geoff Boyle over on the Cinematographers Mailing List:

http://cinematography.net/

I would also read what they have to say about dynamic range in the ASC Handbook and David Stump's Digital Cinematography: Fundamentals, Tools, Techniques, and Workflows:

https://www.amazon.com/Digital-Cine...=sr_1_1?s=books&ie=UTF8&qid=1500003281&sr=1-1

One thing that does help is to have a very well-designed and calibrated dynamic range chart like the Xyla from DSC:

Be warned that a precision chart like this is not cheap -- I think they start at about $3000.

 

[Phil Holland]

I own a Xyla that Marc has posted. It's one of three ways I measure and test Total Captured Dynamic Range. And I've mentioned it in the past, but I test it three ways to confirm the results.

The wiggle is indeed noise and the rather often subjective concept of "what is a usable stop" which refers to the noisier shadow tones.

That for me is a separate question than how my Dynamic Range a system can see.

Noise down there is a tricky issue, but if it's resolving detail and the measurement can be made at a full stop, it's a captured stop of dynamic range. If there's nothing there, it's just not there.

RED's spec is indeed dead on accurate in the sense of having the + in there as you can see and measure beyond 16 stops with Dragon and Helium, thought beyond 16 you really get into the "usable" conversation. Interestingly Panavision has "tuned" Dragon in the DXL to a pure 15-ish stops. Either way, we are dealing with more DR than film. But, I'll add, the reason in many ways having more DR is important with digital is how tones and colors are rendered and "where". This often is what leads to a pleasing highlight roll-off and rich tonality across the image.