Saturday, September 12, 2009

Expose for the Red Channel

Originally uploaded by Dalantech.
Digital sensors seem to favor the color red over the other two primary colors (blue and green). Shooting digital is pretty much the electronic equivalent of shooting with Fujichrome Velvia slide film -saturated colors that saturate even more when you under expose the scene a little. Not a big problem as long as you know what to look for.

Just remember that the overall luminance histogram will lie to you...

When shooting against a yellow flower, a Violet Darter like the one I've included with this post, or anything that has a lot of red in it ignore the luminance histogram. Look only at the RGB histogram display and expose for the red channel. If the reds are all the way over to the right of the histogram then they are over exposed and you'll lose a lot of texture detail. I try to under expose the red channel by about a third of a stop (guessing at it by looking at the histogram on the camera) and in post I'll push the exposure until I'm just starting to over expose the reds. The goal is to get a well exposed image without completely blowing out the red data so that the texture in the scene is preserved.

How you light a scene will also make a big difference in how well you can expose the subject and not blow out the red channel...

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