Seeing the Invisible

November 18, 2020  |  Driftless Area

Most digital cameras are designed with filters that allow the sensor to record visible wavelengths of light - but excludes infrared (IR) light. The reason for this: allowing the sensor to receive IR light typically results in unwanted color casts or blurry edges in an image - not so wonderful.

Something wonderful does happen though when that IR blocking filter is removed, and another filter is added to block visible light. The camera sensor registers the infrared light, and the camera imaging logic interprets that as "more infrared = lighter areas in the image". In my workflow, the resultant image initially has red/orange/purple hues, and mapping that to a black and white or sepia tonal scale can yield pleasing results. Here are some examples.

The image below shows an old railroad track bed that has been repurposed and resurfaced to create a recreational path. The plants register in lighter shades (reflecting a lot of IR light) while the rock walls register in darker shades.

This old railroad track bed that has been repurposed and resurfaced to create a recreational path. The infrared capture used...

This old railroad track bed that has been repurposed and resurfaced to create a recreational path. The infrared capture used to create this image registered plants in lighter shades while the rock walls register in darker shades.

In the next image, the opportunistic wall-hugging plant is green and the rock wall is a mix of dark shades. Not very remarkable to the naked eye. The infrared shot however records a remarkable degree of contrast. Slender lines which draw the eye to the center of interest are clearly visible.

The infrared capture used to create this image recorded a high degree of contrast between the naturally green foliage and the...

The infrared capture used to create this image recorded a high degree of contrast between the naturally green foliage and the earth-toned rock wall.

A short distance down the trail, these trees, which no longer need to be trimmed back for train traffic, have grown into a tunnel of sorts, providing cool shade on a warm day. In this image the grass and leaves register as brighter tones while trunks and blacktop register in darker tones.

Tree tunnel on the Root River State Trail

Tree tunnel on the Root River State Trail