Tip: Driving Through Aerial Perspective

I had a very interesting experience over the Christmas break. I found myself in a land of big skies and long roads with very little to do for two days. We were driving from Salt Lake to Denver through Wyoming's high lands.

To keep myself entertained I brought the art book I have been reading for the last two months. No, it is not that big a book but I am finding that it is not a book that you can read quickly, especially if you hope to learn what the author it trying to share.

The book is titled "Carlson's Guide to Landscape Painting". The book was originally recommended to me by John Hughes, but after a quick look I was not impressed. It is entirely black and white and was published more than 80 years ago. Nevertheless, I decided to buy a copy after it was again recommended by Stapleton Kearns. I was very happy to find that it was the least expensive book I have purchased (it cost me less than $10 with shipping!).

So, back to my story. I was reading Carlson's chapter on aerial perspective. Aerial perspective is the term he uses to describe the effect of atmosphere on color. This is important because it is "our primary means of creating a sense of space and air in an otherwise two-dimensional canvas." In other words, Carlson believed that the color shifts caused by the distance between the viewer and an object are the best way to give depth to a painting.

I had heard of Carlson's rules governing color gradations, perhaps you have too. As he states them, "all colors become cooler as they receded from the eye" (the only exception being white) and "all things become lighter in value as they recede from the eye", or "all things become cooler in color and lighter in value as they recede into the distance." The photograph included here illustrates this principle.

Carlson goes on to explain why this occurs. Basically it has to do with certain light waves being dispersed by elements in the air. Air contains moisture, tiny particles of dust, and other similar material that causes a scattering of light as it passes through them. The degree of scattering depends on the wavelength of the light, which corresponds to the color of the light. Because light with the shortest wavelength (blue) is scattered most, the colors of all distant objects tend toward blue. Light of longer wavelengths (such as red) is scattered less. Here is an example of one of the book's lackluster diagrams. It illustrates that light must travel through more atmosphere nearest the horizon. Therefore, more of the warm colors are lost as objects recede into the distance.

Are you wondering what this has to do with my drive through Wyoming? Well, as I read from Carlson's book that "it is the yellow that fades out of the landscape as it recedes from the foreground", I looked down the long straight road and saw that he was right. The intensity of the yellow lines on the road did decrease until all I could see was a light value where the yellow lines had been. Take a good look at this picture to see if you can see the same effect.

The loss of warm colors can also be seen where warm hues are mixed with other hues, such as brown, warm red, and orange. Greens, for example, turn a cool blue the further we are away from them. This occurs because the yellow is lost from the color as the distance increases. According to Carlson, even the reds will "eventually give way to the blue."

This leads me to the other "aha" moment that I was able to experience during my drive. It has to do with how a blue sky varies in color and value as it approaches the horizon. Prior to this I had missed the fact that the hue of the sky changes even without a fading sun.

Here is what Carlson says, "The arch of the sky...seems to assume a lighter and slightly warmer, perhaps greener, cast in its descent toward the horizon. This gradation of color and value may be said to roughly resemble a large but attenuated rainbow." In other words, the highest point in the sky will be violet-blue. As you move toward the horizon the color changes to a true blue. Further down the blue takes on a greenish tint. Eventually, a yellowish green shade approaches a rose hue nearest the horizon.

I almost didn't believe this as I red it but then I put it to the test and scanned the sky in front of me. Sure enough, there it was! The color shift was subtle but it was there.

Here is a picture that shows a large portion of the sky, similar to what I was seeing in Wyoming. You can actually see the shift Carlson describes.

The color change is even easier to see in the snippets of sky color that I have included below. You can also begin to see the transition to rose in the last image.

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The darkening of the sky nearest the horizon really surprised me. Carlson explains this phenomenon as follows, "This darkening, mentioned above, is more readily understood when we appreciate that the densest atmosphere is at the earth's surface, and that any color or light seen through it (along the ground as it were) has to penetrate a denser veil before reaching the eye of the observer, so dense a veil that it almost casts a shadow."

That's it! I can only learn so much in two days. I hope this was as insightful to you as it was to me. Maybe "Carlson's Guide to Landscape Painting" is a book you will want for your own library.