a27 July 2012

Tutorial: Does number of exposures really matter?

Most tutorials about HDR photography recommend taking 3 photos with 1.5 or 2 EV spacing in most situations. Although it is true in the majority of cases, there are scenes when 3 photos with even 2 EV spacing won't cover whole dynamic range of the scene.

In this short post I will try to show differences in the final image look based on the number of exposures taken: 3, 5 and 7. All photos were tone-mapped in Photomatix Pro 4.2.3 using the same settings. No further editing was done on any of them.

Also move your mouse pointer over any of the images to see previous one in the sequence. This will make it easier to compare images.

Here is a photo tone-mapped from only 3 exposures at 1.5 EV spacing:
Note how much detail is lost in this shot both in shadows and highlights. The sky is faded out (and the sun is almost completely blown out) and the forest lacks contrast. It is a sign that whole dynamic range of the scene wasn't covered.

So now let's try with 3 photos taken at 3 EV spacing (there are some cameras, not many, which allow to do this):
Move your mouse over to compare with previous photo
Much better (there is some blue in the sky, the sun doesn't seem to be completely blown out and we have some contrast in the forest too). However, the tonal gradations aren't smooth really. Look at the clouds in the left for instance - they are pretty much one colour making the clouds look rather flat and boring.

So to fix this we instead take 5 exposures at 1.5 EV spacing, this would ensure smoother tonal gradations:
Move your mouse over to compare with previous photo
Now it starts to look good :) Note how clouds look more 3-dimensional now due to some extra tonal gradations.

Finally let's try with 7 exposures at 1.5 EV spacing:
Move your mouse over to compare with previous photo
In this case the difference is rather subtle. There is a bit more detail in the clouds and also some of the highlights around the sun were restored. Although the difference seems to be insignificant it really matters when this image is viewed in large size.

So answering the question in the subject of this post: yes, it matters. Sometimes 3 exposures is enough but there are cases when 5 or 7 (or even more) are required to get good results.

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