I was recently exploring the many frozen waterfalls and ice caves near Munising, Michigan and the Pictured Rocks National Lakeshore. I was particularly amazed when I came across this blue green curtain of ice across the mouth of a deep cave. I had been to this location this past fall, and there wasn’t even a waterfall. The stream that flows here must be seasonal–probably flowing primarily in the spring. The deep caves in the cliffs in this area were probably scoured out when torrents of water rushed over the cliffs from the melting glaciers at the end of the last ice age.
This image faithfully represents my experience of this place. But since the human eye can experience a much greater range of brightness than can be captured with a camera, viewed on a screen, or printed on paper, I had to use a special technique called High Dynamic Range (HDR) photography to create it. There are basically three steps to HDR photography. First, I had to take three different exposures of the scene: a dark one exposed for the snow so that the highlights would not be overexposed; a medium one exposed for the waterfall; and a light one exposed for the cave so that there would be detail in the shadows.
The second step in HDR photography is to use software to combine these three images into a single image that encompasses the full range of all three exposures. You can do this in Photoshop, but most people use a programs specifically designed for this. I used Nik HDR Efex Pro since it integrates nicely into my Photoshop workflow.
This combined, or High Dynamic Range photograph, captures the complete range of tones from bright highlights to dark shadows in the original scene. But there is no computer screen or paper that is able to display this vast range of tones. So the third step in HDR photography is to use software to translate the HDR photograph into an image that can be viewed on a screen or printed.
There are many different strategies for this tone mapping or compression step and HDR software often has a bewildering array of controls to generate images that range from the very natural looking to the bizarre. Early in its evolution HDR photographers seemed most enamored with the strange effects that could be generated with this technique–but I prefer a more natural look. I think of HDR photography as one more tool to help me capture the amazing beauty of the natural world.