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.

So what if you come back from your shoot, and find that:

* there is too much camera movement to get a clean auto alignment (and you’re too lazy to manually align them)
* there is undesired movement in the frames – such as a moving person or cars
* you thought your camera was in auto-exposure bracketing mode, but instead you only got a series of shots with the same exact exposures
* you deleted one of your exposures in your set accidentally
* the shot is an action shot (eg. a bird, plane, or car racing) that makes it impossible to do a bracketed set

Can you still do HDR if any of these conditions apply? YES! That is possible with just one RAW. We shall call it the HDR1 process, which is short for HDR processing using one (single) exposure. In this article we will be discussing how to achieve HDR results using the HDR1 process and compare it to another image of the same scene with the same exact output settings in post processing so you can easily see the results between the two processes.

HDR1

With the HDR1 process – it is entirely possible to do an HDR out of any single RAW shot you want. Before we are able to merge the images, we have to create the bracketed set first. This is done by exporting the normal exposure (metered) exposure as a 16-bit TIF file. Yes, TIF files are huge, a 12 megapixel image is 71mb in size – but well worth it. Then you need to adjust the exposure to +2 and -2 and export those as TIF as well, so now you have your set as well. You could try going with a broader range ( such as +3, -3 or +4,-4 ) but the results typically won’t be quite natural.

Once you have your digitally-produced bracketed set of 2 or more “exposures”, then we take it into a HDR merging software such as Photomatix. Photomatix will have a different setting and you will sometimes have to manually assign the exposure value (EV) for each of the frame. This is different when you are dragging in a set of RAW files from a folder. Now you have your set of TIF files – you do not have to check the “align images” option, which speeds up the merging time considerably.

Here is a comparison of a shot taken with 3 bracketed shots and a HDR1 image. Can you spot the differences? Click on them both and they will open up in the same window, then you can click back/forward to compare the images.

HDR1 (single exposure)

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3-exposure HDR

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Results:
* The darks are darker ( more contrast ) in the 3-exposure HDR image
* More dynamic range (not much, though) in the 3-exposure HDR image
* Colors seem to be more vibrant in the 3-exposure HDR image
* More detail in the clouds in the 3-exposure HDR image

Other Examples

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