Have you ever wondered how much that extra exposure value (EV) range would help improve your next HDR image? Would, an image taken at 3 exposures at -2,0,and+2 EV be better than an image taken at -4,0 and +4 EV? This article will help you determine this issue. Does using more exposures really improve image quality?

Depending on the camera you use, you might run into some technical limitations. Some cameras (such as the Canon EOS 5D) is only able to take an auto-exposure bracketing (AEB) set of 3 exposures with the maximum range of 4 EV. If you want to do 5 or 7 exposures you need a tripod and have to do some creative exposure adjustments to get the extended range. Nikon’s D200 and above offers up to 7 auto-bracketed exposures going up to +4 and -4 EV I believe, totaling a range of 8 EV in total! I know someone on flickr who does a whopping 17 exposure HDR!

Well, when we get down to it, it’s really the image quality result is what we aim for. I have an auto bracketed set of a scene here in Las Vegas of the west valley wall. I believe I captured 5 auto bracketed exposures, at -4, -2, 0, +2 and +4 EV. We will try to mix the exposures up so you can see what works well and what does not. Note that these are images exported as tiff via Photomatix using the same exact Details Enhancer settings, and has not been further processed in another software.

A) EV -4,-2,0,+2,+4 (all 5 exposures merged)

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B) EV -2,0,+2 (3 exposures)

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C) EV -4,0,+4 (3 exposures)

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D) EV -4 +4 (2 exposures)

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So you can see very little difference between A and B. C seems to be a little faded and washed out due to the higher range differential than A and B. D is obviously very noisy and not a satisfactory result. If you compare B and C,I think the smaller EV range results in a better image quality. The local contrast using 5 exposures seem to be higher (A), but otherwise the tones and color definitions are extremely similar. After further edits in Lightroom I figure you could not tell the difference between the A and B.

So, in conclusion, I would say that it is not worth the extra effort if you did a 5-exposure HDR versus a 3-exposure HDR – where you save time is in the HDR merging and also file storage savings. I am now happy with the -2, 0, +2 EV maximum range on my Canon EOS 5D.

If anyone has any input about 7 or 9 exposures and higher, please let me know.

HDR stands for High Dynamic Range, or some people call it HDRi with the “i” being imagery. Either way it is the same thing. It is really a technical process in which a series of two or more exposures of the same scene are shot with varying exposures are combined — or merged — into one image that has a substantially higher dynamic range than any one of those shots in the bracketed set.

“Dynamic range” as defined by dcview.com is “the amount of detail your camera can record between highlights and shadows in an image.” Another way to put it is the ability to capture more details both in the highlights and lowlights in an image, especially if there is more than 2-stop difference between parts in the image — for example, a bright sky and a cave, or an interior view of a window looking out during the day.

The bracketed sets are usually all at the same settings except for the shutter speed. It really helps to have a camera with an actual AEB feature (I know the Nikon D40 and D40x does not have this feature) and a continuous high drive mode, especially if you are not using a tripod. The auto bracketed images can vary in EV (exposure value) depending on how much dynamic range you want. I like to push it to -2, 0, and +2 EV for any given shot because it will give me the most dynamic range — as opposed to -1/3, 0, +1/3 EV — which won’t yield any noticable difference.

Another way to vary the exposures on the images is to vary the ISO — but that can only be found on high end models such as the Canon EOS 1D series. For all intents and purposes, our auto-bracketed shots will be done with varying shutter speeds.

The Process
In this example we have three exposures of the same scene, taken at -2, 0, and +2 EV. You can see after it has been merged in an HDR program like Photomatix Pro 3, that the result has a unique look of its own. You can see that the shiny surface of the car is much more glossy and reflective, and the headlights seem to have much more detail in them. What you end up with a 12.8 megapixel 16-bit tiff file that is roughly 71mb in size. You can take the .tiff and head over to your favorite image editing software.

Comparing JPG vs HDR
So you might think, “well, I don’t want to spend the extra 10 minutes editing this pic in HDR” or “I don’t want to sift through 3 images of the same thing after I download it” — well I hope these two images will prove to you that it is in fact, well worth the effort.

Comparing edited RAW vs HDR
Ok, so that last example isn’t exactly fair, an unedited JPG straight from the camera surely won’t stand up to a processed HDR image. Well here we have the same metered exposure (EV 0) RAW file that I edited in Lightroom. As you can see the left image is much nicer and more balanced than the JPG above, but it still pales in range and detail compared to the tone mapped HDR image on the right.