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Tuesday, November 14, 2017

The truth about red

Why does red pop out at you? The first question to answer is whether that’s actually true.

Tilt-a-Whirl, by Carol L. Douglas
“Your color temperature reference seems to be something other than degrees Kelvin of a black-body radiator. Can you explain?” an engineer wrote me yesterday. The simple answer is that, to the painter, color is not a property of electromagnetic radiation, but a sensory perception question.

During the past few weeks, I’ve told you that much of what we accept as truth about color perception is just social convention. Today I’d like to talk about what (we currently think) is true. Science is constantly discovering new things, and in a hundred years, this understanding might be as obsolete as phrenology.

There are two basic theories of how we perceive color. The Young-Helmholtz Theory tells us that the retina’s three types of cones are sensitive to either red, green or blue. Ewald Hering proposed that we interpret color antagonistically. In other words, it’s either red or green, blue or yellow, black or white. Both theories appear to be true.
Deflatable, by Carol L. Douglas. The orange life jackets stand out because they're the complement to the blue water.
The range of color (the “gamut”) that normal people can see is limited by this antagonism. We can see yellowish-green easily enough. We can’t see reddish-green because the cones in our eyes can’t perceive red and green simultaneously. Furthermore, we can’t see colors that are outside the limits of our receptors. Of course, the brain is always outsmarting us, so there are times the brain thinks it can see these so-called impossible colors.

Color perception doesn’t just happen on the retina; the visual cortex is involved, too. Some parts of the spectrum get a bigger response in the visual cortex than others, but that depends on what light conditions the visual system is adapting to.

Palm shadow, by Carol L. Douglas.
We’ve all noticed this in practice. On a clear day, a red dinghy bobbing on the turquoise waves stands out. In gloom it is hardly noticeable. Our perception of reds falls off fast in low light conditions. This is why one can’t fall back on truisms like “the retina perceives red first.” The human brain is far too wily for that.

Our mind practices something called color constancy. It’s how we understand that an apple is green whether we see it in the blue light of dawn, the true light of midday, or in the golden light of the setting sun. If we use a viewfinder to isolate the color of the apple, we often realize that what we’re seeing is anything but green. Still, our mind stubbornly processes the object as green.

This is an adaptive process that probably helps keep us alive, but it often mucks painters up. It’s hard to render unusual lighting effects when your brain is trying so hard to normalize them for you.

The same thing happens with lighting levels. That’s why it’s so important to check values against neighboring objects as we go. Our brain constantly adjusts our perception to normalize lights and darks.

Castine lunch break, by Carol L. Douglas
So why does red stand out? The answer is complex. In certain situations, such as a leafy green tunnel of a road, a red stop sign does, indeed, stand out. It’s the complementary color to its environment. But much of our reaction to color is a learned response. We notice red stop signs because we’ve trained ourselves to notice them. We believe red is an energetic color because society tells us so.

I use red to prime my canvases not because I believe it has special properties, but because it's the complement of the dominant color in my environment, which is green.

Tomorrow, I’m going to introduce you to the 19th century cult leader who, more than anyone else, gave us our modern ideas about color. 


Ron said...

Yes we can see reddish-green. We know it as yellow. When the red and green sensitive cones in our retinas are both stimulated at the same time to about the same extent, we perceive yellow.

Ron said...

Yes, we can see reddish-green. We know it as yellow. When the red and green sensitive cones in the retina are stimulated simultaneously to the same extent, we perceive yellow.

Carol Douglas said...

That is only true in additive color lighting, it is not true in retinal perception. I think. Wish a neuroscientist would weigh in here.