Soukie's Place

keeping track of random thoughts

The Eye and HDR Photography

Photo of hills at a lake

Gallery of images with high dynamic range

Sight is easily the most important sense we have, and not quite easily fooled with imitations. Although ‘3D’ seems to be all the rage nowadaysWas this article first published when intended I could not have this reference. But I am going to leave James Cameron’s new landmark film alone, and get a closer look at HDR photography with examples taken by Steven Richards — happy birthday, man!, even if we turn a blind eye to the stereoscopic nature of vision, the other eye still packs enough powers to put TVs and pictures to shame.

Eye in Numbers

  • A glossy photograph has a contrast ratio of 100:1
  • Contrast ratio reproduced in a movie theater is around 500:1
  • Cameras give useful results with contrasts going up from 200:1 to 1,000:1.
  • Human eye has an immediate or static range of 100:1 up to 1,000:1 (depending on definition and source)
  • A daylight scene might have a contrast ratio of 5,000:1
  • An indoor scene with daylight visible through a window is over 100,000:1
  • Given time to adjust, human eye adapts across dynamic range of more than 1,000,000:1
  • There are some 5 million cone cells (color sensitive) and 90 million rod cells (black and white) in the retina.

Nature is presenting us with differences between bright light and deep darkness which have contrast that dwarfs the reproductions we can make on canvas, paper, screen or television. The human eye is well equipped to handle these huge differences (at least given a few moments). The camera is not capable of this (and even if it was, the paper or screen are even more limiting factors) and that is why people came up with techniques for capturing and representing more than can be ordinarily possible.

The eye is often compared to a camera but this comparison is misleading. Our sight is based on biochemical and neurological processing that makes it difficult to quantify. A good example of this is how the rod cells in the retina of the eye require less light than the cone cells that differentiate between colors. This is, of course, why we cannot tell colors easily in low-light conditions. But the rod cells do not react to all light frequencies so an interior of a submarine lit only by red lights allowed the captain to look through the periscope into the night without waiting for his eyes to adjust to the darkness outside.

To present images with high dynamic range (hdr), the problem is essentially how to reduce the real scale of contrast using a much smaller range while keeping all the details. In practical terms, this means that the sky and clouds are not quite so bright on hdr pictures as they are in reality, and the areas hidden in shadows are rendered in lighter tones. On a regular picture, the details of the sky might be completely washed out into white, and the dark shadows lost in black.

Some examples of the hdr technology are shown in the galleryActivate galleries by clicking on the picture (a magnifying glass appears), or click this link. Navigate between pictures by clicking the right or left half of the image., together with a chart and an example illustrating how it is done. Today, the process is much simpler than it used to be, especially when you have a camera that enables bracketing and some photo editing software that contains hdr features but the art of creating compelling images is not any easier.

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Steven Richards, January 16, 2010:

Love the article, very interesting, Thanks :)

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