hdr; what is it and why?

HDR is an acronym for High Dynamic Range, a post-production process (a computer thing) that is gaining popularity rapidly the past few years.  I’ll try to explain some of the concept.

What happens is…  many of the sights we observe and want to capture with the camera have both “relatively speaking” bright highlights and dark shadows.  With our eyes and brain we can discern details within both those extremes (to a limit) which I understand is somewhere in the range of 7 to 8 “spectrums” (I don’t know what that means but I think of it like “octaves” in music).  Our camera film or digital sensor can discern only 2 to 3 of those “octaves”.

By using specialized software (I use Photomatrix Pro ver. 4) we can now blend a series of images (the very same object) that are captured with varying amounts of light such as 2 f-stops “under”, 1 stop “under”, correct to meter, 1 stop “over”, and 2 stops “over”.  We call this process “bracketing”.  It’s critical for the camera to not move between takes.  A tripod is very helpful.  You could blend 3, 5, 7, or even 9 images however many photographers feel that you don’t gain measurable definition by going with more than 3 “input” images.

Here’s my example of using 3 bracketed images.


The first image is exposed properly (by the averaging meter).  Note that this leaves the shadow areas (lawn and all the lower 1/3rd of the image) unpleasantly dark.







The next image is 2 f-stops darker.  It shows a vivid and realistic blue sky and clouds but leaves all the shadow detail in near-total darkness.






and… the 3rd shot is 2 f-stops lighter than the proper meter calls for.  Notice how this now shows the lawn details clearly but “blows out” the lighter tones of the puffy white clouds and light blue sky.





I’ve taken these 3 shots and blended them with the #4 image being the result.  Isn’t it marvelous that now we can see both the dark shadows and the vivid blue sky and puffy clouds.  It’s an amazing concept that now lets us enjoy photos true to what our eye and brain have seen from day one.   Please click on any of the images to enlarge…  You’ve likely seen some of these and said “Wow!” but were not aware of how it’s done.   HDR photos usually portray an extra feeling of depth and a sense of more realism.   The process is not automatic — there is a certain amount of art in making it look realistic.

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One Response to hdr; what is it and why?

  1. John Wisecaver says:

    Very , very interesting –I loved you octave analogy — it really worked for me.

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