Infrared and “false color” processing   Leave a comment

My photographer friend Esther Duffy asked how it is possible that I am able to come up with versions of the same infrared photo in different colors. So I’m going to do my best to explain “false color” and what it means in infrared photography. Infrared light has no color, because it exists outside the range of visible light, which contains the colors we see. Depending on the IR filter you choose when you convert your camera, you can allow some of the color red, which exists at the end of the visible spectrum before we head into IR, to reach your sensor. Mixing this red light with the IR light allows us to place color in our IR photos. But the color will not match “true color,” which we get when we shoot regular photos because all the colors of the visible spectrum are not available. Other than red, none of the other visible colors are recorded in an IR photo. “False color” is generally color that differs from “true color.” False color has many scientific and tactical uses. An example: in military applications, sophisticated infrared cameras can photograph foliage and based on the amount of light it reflects, render colors that can show the difference between live foliage and dead foliage that is being used for camouflage. To the human eye, it all looks green. But in IR, colors can be rendered based on reflectiveness, and dead foliage will not reflect light the same as live foliage. In more traditional IR photography, “false color” is the result of how we process the image using software like Photoshop. What’s fascinating, and unknown until we get to work, is how the colors will render based on the reflectiveness or absorption of the light.

Above is a digital infrared image as it comes out of the camera. You can see the overall red cast. This is an image shot with a 665nm enhanced color converted Canon EOS 20D and a custom white balance. ( I’ll cover white balance in a future post. As you might imagine, it is quite different than in traditional, visible light photography.)

With my tonal range looking quite healthy, I now move the image from Camera Raw and into Photoshop (above.) I apply a classical adjustment in levels by using the eyedropper to click on a white point and a black point. This is no different than what I do with my traditional, visible light images. This is the result. It is a “false color” image because these are not the colors we would see with our eyes or a regular camera. But I have done no trick photography here. All I’ve done is set the white and black point and the colors were rendered based on the absorption and reflectiveness of the infrared light and the small amount of visible red light.

Now, I move into Photoshop’s channel mixer, which is probably the most popular tool for processing IR images. It is here that we apply the classic infrared “Wood effect,” which I have discusses in prior posts. The first step of a common “channel swap” involves removing all the color from the red channel and replacing it with blue. I select the red channel and set the red slider’s value from 100 to 0. I then change the blue slider’s value from 0 to 100. The result is this very cool pink color added to the highly reflective foliage. Sometimes this step adds a green cast to the darker parts of the image, but it did not here. I call this a “half swap” because it’s just half of the full channel swap process. But many times I will choose to stop here if I really like what I have. If I do stop here, and the image has a green cast, it can easily be removed with the Hue/Saturation control or in curves.

In the image above, I complete the “channel swap” process. I move to the blue channel and reverse the red and blue sliders as I did in the red channel, applying 0 to the blue channel and 100 to the red channel. And there you have it, a typically processed “false color” infrared photograph!

Of course, nothing says you have to process your IR image to a certain protocol. Experimenting is a lot of the fun with digital IR. For the above image, after setting the white and black point in levels, I bypassed the channel mixer and went right to the “Hue/Saturation” control. As I played around with the various combinations by adjusting the sliders, I noticed that only the reflective foliage, and not the rest of the image, was changing colors. I settled for this interesting green.

And if wild and crazy is your style, feel free to, as the legendary baseball announcer Jack Buck once said, “Go crazy, folks. Go crazy.” It’s not my thing, but it just might be yours! Experiment, play, explore, take chances. Have fun!

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