Understanding HDR part II – The Dynamic Range

Churches in Denmark are usually small white churches, but once in while you come by a red one. This one is in Gershoej on Zealand. Photo by: Jacob Surland, www.caughtinpixels.com

What does High Dynamic Range exactly mean? To understand High Dynamic Range, you need to understand Dynamic Range first. Now that we are clear on what EVS is, we can talk about the Dynamic Range in terms of Exposure Value Steps  (If you missed Part I of this series, you might want to read Understanding Exposure Value Steps first).

In photography the Dynamic Range is the difference between the darkest and brightest part of a scene. Some scenes have a bigger difference (brighter or darker areas) than others do, they have a higher dynamic range.

Imagine a scene with some really dark shadows, like under trees, and some really bright sunlit areas and the Sun itself included (like the photo above). If you take a photo of this scene, your camera will leave some areas either completely white or completely black. This is because the dynamic range is incredibly high. The difference in the intensity of the light is huge and a camera can not record it all in one photo. Infact, the human eye is much better at that.

How much light a camera can capture, from the darkest area to the brightest area is called the Dynamic Range of the camera and it is measured in Exposure Value Steps or EVS.

Not two brands or camera models has got the same dynamic range and the difference from camera to camera is quite big. In the end it comes down to, how sensible to light the sensor inside the camera is, but also how the camera uses the sensor. Two camera models using the same sensor, might not have the same performance.

If you have a scene and you can’t get a good shot of it, without blowing either the highlights or the shadows, you can extend the dynamic range, by shooting two additional photos, one darker and one brighter.

Now you have three photos, including one to cover the highlights better and one to cover the shadows better. These must be merged using a piece of software. And this new merged photo is the High Dynamic Range photo. A photo that has extended the native dynamic range of the camera.

Let’s say, that you shoot the dark one at exposure compensation -2 and the bright one at exposure compensation +2. This way you extend the cameras limited dynamic range by 4 EVS, (that is -2 in the dark end and +2 in the bright one).

Dynamic Range in three shots

Three exposure bracketed shots at -2, 0 and +2.

A camera has a native dynamic range. My Fuji Finepix x100 has got a dynamic range of 12.4 EVS, while my Nikon D800 has got a dynamic range of 14.4. The Canon 5D Mark III only has got 11.7 EVS in the dynamic range. All cameras are different.

But what does this mean? Let’s stick to the example of -2, 0 and +2.

Dynamic Range example

In case of the Canon 5D Mark III, then it has got a dynamic range of 11.7 EVS, the total dynamic range will then be 11.7 EVS +4 EVS  (2 EVS extra for dark and 2 EVS extra for the bright exposure) = 15.7 EVS. That’s an increase of the dynamic range covered of 34%!

The Nikon D800 will be 14.4 EVS + 4 EVS = 18.4 EVS. An increase of approx. 28%.

Sony A7R is 14.1 EVS + 4 EVS = 18.1 EVS. An increase of approx. 28%.

As you can see from these three high end cameras mentioned, even high end cameras from leading camera brands are very different. Canon in general has got less dynamic range, than Sony and Sony has less than Nikon. And this pattern goes all the way to entry level cameras.

How do you find out about such things? Well, I always find my information on specific cameras at www.dxomark.com. They have an extensive database of sensor tests and it is very likely that you will find exactly your camera there too.

And if you are in the market for a new camera, and haven’t chosen brand yet, this is something you seriously should take into consideration, before choosing your brand.

Auto Exposure Bracketing (AEB) options are important!

As an HDR photographer, you are very interested in what options you have for bracketing your shots. How many shots can you bracket? Can you do it on a timer or remote control? How many EVS can you have between your shots?

This is really important stuff for the HDR photographer!

While the Canon 5D Mark III, from the example above, is the camera with the lowest dynamic range, it does have the most flexible bracketing system of the three and it it can cover more dynamic range, than any of the others. It allows 7 shots of up to 3 EVS between each shot.

7 shots at 3 EVS between each shot will be: -9,-6-,-3, 0, +3, +6 +9. That is a HUGE dynamic range covered. However, having 3 EVS between each shot can give bad results in post processing, and I don’t recommend it, but even at 2 EVS you get a huge dynamic range coverage.

Most cameras only allow to bracket 3 shots at maximum 2 EVS, as shown in the figure above (giving -2, 0 and +2 exposures). This extends the cameras native dynamic range with 4 EVS. And for many situations this is just fine.

If you are in the market for a camera, investigate the options! I was surprised to find out, that Nikon D3100 didn’t have any bracketing options. But there might be others, that don’t have it, and some models have more flexible bracketing options.

Personally I find it very important, that the native dynamic range of the camera is high. Using my D800 or D600, I capture almost the same in one shot, as the Canon 5D Mark III does in a -2, 0, +2 series. And this I personally find a huge advantage.

How to compensate for lacking bracketing options

I also have cameras that only do 3 exposures in bracketing, and they also support 3 EVS between each shot, but I really avoid doing this, unless I am caught in a difficult situation.

The reason why I avoid 3 Exposure Value Steps in my bracketing, is that I end up with nasty artifacts, in the post processing, because the HDR software can not put it together properly. What I do instead of increasing it them to 3 EVS in bracketing steps, is to shoot two series.

If you shoot a scene at -2, 0 and +2, then you can adjust the exposure compensation on your camera (the +/- button – look for it, and you will find it). If you adjust it to -1, and then shoot your series again, you will then get: -3, -1, +1. And if you kept your camera on a tripod and was careful, when you adjusted the camera, you know have 6 shots:

-3, -2, -1, 0, +1 and +2

And if your scene was too dark, you just adjust +1 instead of -1, and get 6 shots of:

-2, -1, 0, +1, +2 and +3

This you can do on almost any camera, and this is what I do, if caught between a rock and a hard place. And in really extreme situations you can shoot 3 series or adjust the compensation different. The camera is flexible enough, if you accept a little manual work.

If you are considering to buy a new camera and intend to shoot a lot of HDR, this is important stuff, that needs to be investigated before buying a new camera. I was misguided when I bought my Fujifilm X100 Finepix camera. It does have AEB, but not at 2 EVS, only at 1 EVS. I can take -1, 0, +1 and because it has a native dynamic range of 12.4 EVS, that sums up to 14.4 EVS in the high dynamic range photo, which is exactly what my D800 delivers in one photo. This is clearly not very optimal for me, and I end up using the X100 far too little.

And a funny thought – does that make the Nikon D800 photo a less High Dynamic Range photo, just because it can cover the same dynamic range in one photo, while the X100 needs 3 shots? What is High Dynamic Range? It is not clearly enough defined.

How to trigger the bracketed series is important too

When you start shooting HDR photos, you pretty quickly learn that, using a tripod is worth the effort. Even slightly moving cameras, can make a post-processing difficult. The most optimal thing, is not to touch the camera at all, while the camera shoots the bracketed shots.

Canon and Nikon offers the option of a timer 2 seconds, before the camera starts shooting the bracketed series. Usually two seconds is enough for the tripod stop stirring after you touched it.

Sony A7/A7R allows the use of a remote control. It would have been nicer to be able to use the timer (one device less to keep track of). The Sony NEX-7 does not allow any kind of remote triggering.

But as mentioned several times in this article, investigate the specific camera model, before buying it. Otherwise you might end up being disappointed. And it is expensive to be disappointed with a camera.

CONTINUE TO PART III about Histograms here.

Further readings

2 thoughts on “Understanding HDR part II – The Dynamic Range

  1. Thank you for really informative and clearly explained article!
    It is worth to mention for anyone using Canon DSRL for HDR photographing (or basically anything for that matter), you should introduce yourself with the Magic Lantern (http://www.magiclantern.fm/), which is a free stack of additional features that may be added in addition to stock firmware.
    It notably extends the HDR features so that you may take up to nine (9) photos with 0-5 EV increment. In addition this all can be made automatic so that camera analyzes the histogram and takes as many frames as is needed to cover the full range.
    Here’s a short article about usage: http://hdrphotographer.blogspot.com/2012/11/tutorial-how-to-use-magic-lantern-for.html
    I highly recommend!

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