The Blog of Patrick C. Cook

The photography blog of Patrick C. Cook.

Winter Wonderland

This scene looks like a winter wonderland, doesn't it?


Actually, it's a hot summer day in Massachusetts with lush trees and grasses all exploding with green colors of various shades and intensities. The primary reason why this image shows so much white color is because plants reflect near infrared, which a digital camera that has been converted for infrared is able to record. But there's a bit more to the story.

Plants reflect the green portion of the humanly visible spectrum of light, which is why the human eye perceives many plants as green. However, the plants are not actually green, rather they are reflecting green. Digital cameras converted for near-infrared have a filter placed in front of the camera's sensor that blocks the majority of the visible spectrum and allows only a portion of the near-infrared spectrum through the filter. In some conversions, the chosen filter allows some of the visible spectrum to also pass through the filter, as is the case of the camera I used to capture the above image.

In this case, because I used a converted camera with a 665nm (nano meter) near-infrared filter, I was able to process the image to bring out the blue in the sky because a 665nm filter allows a portion of the red visible spectrum to pass as shown to the left. (Note: The 850nm filter blocks all of the visible spectrum.) The image processing trick to obtain a blue sky from red is to use Photoshop's channel swap tool which allows you to swap red colors with blue colors, effectively changing the red in the image to blue. The end result is a blue sky in the image (which is much more appealing than a red sky).

I enjoy infrared photography because the final image is not only a product of field work, but also processing. In the field you mine for images in the near infrared spectrum, not quite knowing what you have in the field - you just never know what gems-in-the-rough you'll return from the field with, to be polished with amazing software tools available to us.