Visual Adaptation… our friend… and our enemy.

Visual adaptation… it just amazes me how the brain adjusts to contrast, brightness, color and even shape, and how quickly it does so.  If we see magenta, our brain adds green to try to make it neutral. If we’re looking at a flat (in contrast) image, our brain adds contrast until it looks normal to us. And believe it or not, I’ve seen through simple observation that our brain even compensates for shape, and very quickly! I created visual examples of these happenings, and the one for shape is just a grid of lines which I skewed. In the example below, I show the skewed version of the grid next to the perfectly square version. In my workshops, we are able to overlay them, so the effect is more apparent. After looking at the skewed version for 20 or 30 seconds, and then looking at the square version, the square version actually appears to be skewed in the opposite direction. You can even sense it as the brain tries to correct the skewed version. Try it with the the following images, and try to stare at the center of the skewed image for about 30 seconds. Don’t move your eyes, but stare directly at the center. Really concentrate on that center. Then, after 30 seconds, shift your vision to the square version looking at its very center. If it works properly, you should be able to see the effect. I would suggest you click on the image to enlarge it to get the full effect.

Try the same thing now with the image of the magenta dots on gray. Stare at the center for about 30 seconds, concentrating on keeping your vision focused at the cross in the middle of the screen. Try to not let your eyes move around. After 30 seconds or so, the pink dots should almost completely disappear. Then, shift your vision over to the plain gray square with the cross in the center, and you should see green dots for a short time, until your brain once again compensates. Again, click on the image for a larger view.

So what does this mean for photographers?

Visual adaptation is our friend in everyday life, but our enemy when trying to balance color, adjust contrast, and determine proper brightness in an image. The most common problem we run into is, when looking at our camera screen or monitor in a very dark room, or at night outside, we tend to underexpose because the image looks much brighter to use than it really is.

How do we deal with it? Use the histogram! Also, it’s very important that we have a neutral setting of the right brightness in which to do our computer work. If we are in a greenish room, our brain pumps in magenta, throwing off our perception. The thing is, though, in any type of room environment, if we stare at a monitor that has an image that is off color, it will begin to look normal to us almost immediately. Having an off color room environment simply adds to the brain’s confusion.

I like to keep a “perfect” image open on my desktop, or even prints of “perfect” images hanging on the wall. That way, I have kind of a visual touchstone to bring me back to neutral. These images can even be generated using a perfectly gray ramp or step wedge, or if you do a lot of portraiture, incorporate that with an image with “perfect” skin tones as reference.

The phenomenon of visual adaptation is a thing to keep in mind and to be aware of, and remember… our brain is constantly and very quickly adjusting to whatever we throw at it! Amazing…

~ by Harold Ross on June 24, 2011.

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