Tag Archives: Measuring Dynamic Range

Measuring & Exposing for Dynamic Range

Dec
12
2012
by Peter | 11 Comments

Reader, friend and fellow photographer Todd B asked me to go into more detail on how I measure the dynamic range of a scene and then decide how I will shoot the exposures for that scene. 

What I do is quite simple. I set my camera to Aperture Priority mode and the aperture and ISO I will be shooting with. I then set my metering mode to spot. I use aperture priority for this instead of Manual because I am just looking for numbers (shutter speeds) right now. I may, and probably will, end up shooting in a different mode, most likely manual. 

I then seek out the brightest and darkest areas of my scene. If the sun is in the shot, don’t measure it for many reasons. First off it’s not good for your eyes or your camera and secondly because of its brightness you will end up with exposures that in reality have very little use. If the sun is just at the horizon line you may be OK, but anything above that you are asking for trouble. But in most circumstances if the sun is in my image I will meter slightly to the side or above it. 

Also make note of one phenomenon, just as the sun hit the horizon it is not always the brightest region of the image and the clear sky above or a reflection off a cloud may actually register higher  Continue reading »

So how much dynamic range did I actually capture? Photomatix Pro HDR Histogram

Jan
23
2012
by Peter | 1 Comment

So how much dynamic range did I actually capture? Photomatix Pro 32 Bit HDR Histogram

Note! For this example, you must have the latest update to Photomatix HDR Pro V 4.1.3 or later. Please go to HDRsoft’s website and update or click check for updates  from your program’s help menu. 

How much range?

So you shot 88 frames 1 stop apart and for sure you must have captured all the dynamic range in the universe…or did you? Well how would we really know what the captured dynamic range was of all our exposures.
We really can’t count on our finished product, after all it’s really not a high dynamic range image, it’s just a tone-mapped one that simulates to our eye the range that was in our scene. And if we are heavy handed in our Tone-mapping we may even have a lower dynamic range than our single image is capable of.
So how can we tell what range we actually captured? Via a little known and little talked about feature that was added to Photomatix 4.1 (Fixed in V 4.1.3) – The HDR 32 Bit Histogram.
The what? The HDR 32 Bit Histogram. This histogram only works with the 32bit Intermediary HDR image that is generated before you go to tone-mapping. If you don’t allow the software to stop at this point before it continues on to the tone-mapping screen, perhaps you should. It may tell you some fun things.
Now unfortunately, I cannot vouch for the accuracy of this histogram. the truth is I really couldn’t find much about it anywhere. But I did find it.
To activate it when your 32 bit file is open, click ctrl/cmd H or go to view>HDR Histogram. At the bottom of that screen you will see “Estimated Dynamic Range” and it  is expressed as Contrast Ratio X:1. There is also a Log Scale from -6 to +6 and the resulting histogram for the file.
In the test I did with different files, it seems to be accurate. Is it exact? I have no way of knowing, but scene I knew to be low in dynamic range and those high in dynamic range seemed to fall in place exactly as I would have expected.
Here are a few examples of  32 Bit Images and their HDR Histogram.
In this one I knew it was low dynamic range and the resulting image was poor
 This was a very high dynamic scene and the contrast ratio proves that
Even though you would think this was high dynamic range because the sun was in it, it actually was typical for a mid day shot
This one was a 9 Exposure 1 Stop image. I actually thought it may have been a higher dynamic range. But it was very overcast that day or maybe I didn’t shoot it as well as I thought
Here is a chart so you can get an idea of what those contrast ratio mean in a practical sense
If you would like to know more specifics about Dynamic Range, checkout my buddy Sean’s website Cambridge in Colour
I thought this was interesting and fun to look at, it may actually be helpful down the road to look at what works and what doesn’t work and really what we are shooting. For me it fills ina few more parts of the puzzle and makes me more confident in what I do.
Anyway, Hope that helps,
PT