High Dynamic Range – Into Visual Fantasy

I like to say that what we see depends on how we look. No matter how much we may think that a photograph is a “real image” and what you see is “just they way it looked,” photographs are always interpretations, full of assumptions, conventions, and the ever-present interplay among art, technique, and technology. This is particularly true in astrophotography.

Even the stunning images taken by telescopes such as the Hubble Space Telescope are actually highly artificial. Not only do they represent magnifications far beyond what our own eyes can achieve, they also are made possible by gathering light from fantastically feint objects. Furthermore, they usually represent an artificial spectrum, a selection of colours represented on the image that are not the “natural” appearance of an object at all. Astrophotographers, artists, and anyone else working with these images can select various wavelengths of light that were captured by the original camera and transpose them into what we see in the final image.

That’s all by way of introduction to the following image, which I made on the evening of 14 June 2013. It’s a High Dynamic Range rendering of the moon, generated from three different photos taken in succession but at very different exposures. One exposure was short enough to capture details in the sunlit areas to the right; one was long enough to capture “earthshine” on the left. Merged together in the computer, they make a stunning image – not what you see of the moon at night with your eyes, but the moon none the less. In this rendering, I have exaggerated colours for effect:

Moon in HDR

Two faces of the moon. A High Dynamic Range image made by combining three photos taken on 14 June 2014 at different exposures. The sunlit side, on the right, is many times brighter than the earth-lit side on the left. Photographed with a Nikon D800 body on a Meade 125TB Maksutov Cassegrain telescope, on an EQ4 motorized mount. The earthlit side was exposed at ISO 800 for 10 seconds. The sunlit side consisted of two shots at 1/3 and 1/30 second. The three images were combined with Dynamic-Photo HDR.

High dynamic range imaging does not have to result in “garish” images, however. The original intent of the method was to make more detail in shadow and in highlight visible. Here’s another rendering from the same evening that is a little more “realistic” but was prepared, essentially, the same way:

HDR2

The moon on the evening of 14 June 2013 – with both bright side and earthlit side represented in an HDR image.

Copyright © 2013 David Allan Galbraith
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