05
Dec
09

Compressing dynamic range..

These days dynamic range is all the rage. A quick trip to any of DPReview’s discussion groups will find many heated threads over which camera can capture more dynamic range than the other. Certain camera models like the Pentax K-7 has in-built HDR modes to achieve the HDR look. Camera’s don’t have the same type of range our eyes do. There is only so much the sensor can capture between the brightest highlights and darkest shadows without clipping. Film proponents always favor the look of film with its graduated roll-off when overextending the highlight range. This is very similar to our eyes. Digital simply clips the channel. Once the brightness exceeds 255 for that pixel, everything over 255 simply becomes white. Similarly, If you compensate by decreasing the exposure to keep the highlights in check, the shadows might become blocked since the limit is 0 and everything under becomes black. HDR achieves its effect by multiple captures and combining them so that the shot will effectively have much greater dynamic range. Tone mapping then compresses the HDR source back into standard dynamic range, compressing the range. Compressors are used quite frequently in the audio industry. When you compress an audio signal, the loudest and quietest portions are confined to a smaller space and equalizes the character of the sound. Vocal tracks are compressed to align itself in terms of sound and characters from the rest of the instruments.

For a few months, there was a flood of photographs circulating on the web that was quite evident that it had gone through some serious Photomatix tone mapping. Nothing was spared, including portraits of children, cars, buildings and landscapes. I liked the style, but decided that stepping it down a few notches by popping a few lithium pills would let me play around with the technique without looking like “yet another” traditional HDR effect.

I shot this with Mandy under a bridge in the summer. True to my strobist roots, I perched a 580exII in a Q39 on top of an avenger boom arm, and added a bit of coarse gridded light to her arm and cement support column to add a bit of separation. I struggled a bit getting my Pocketwizard Flex’s to sync because of interference, but I’ll be talking about that one in a upcoming blog post.

The shot looked edgy, but I turning up the shadows a bit by effectively compressing the dynamic range (tone mapping).

You will need to mask out the areas that you are adjusting in Photoshop, so a good tablet really pays off here!

The end result after color toning and a few other tweaks was this shot. The conservative tone mapping allows a unique surrealistic end-product that has quite a bit more character than the out-of-camera raw. The 1ds3 that I was using at the time had great shadow recovery, so I was able to achieve this with 1 exposure. Depending on your equipment and your exposure, you will have to decide your starting point. With off-camera lighting, I can decide where I want my mid points and high lights, so I started with a -2 exposure to give myself extra breathing space when dialing back up the shadows in Photoshop.

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