False colour digital infrared photography

raw IR thumbnailYou now have a filtered colour IR image, like the one at the right, and a normal full colour image, like the one that appears below it. How do you get to a false-colour IR image like the third image on the page, where most objects appear normal, but things with high infrared reflectances are various shades of red?

It's relatively simple--you do the same thing in your image editor that film manufacturers do in their factories--you create an image in which IR is rendered as red, red as green, and green as blue. Effectively, the light to which each layer of the film is sensitive is displaced by one section of the color spectrum from the light that it will pass when the film is developed. If this sounds complex; it isn't. All you need to do is substitute an IR channel layer for the red layer in the standard colour image, the red channel from the standard image for the green channel, and the green channel for the blue channel.

standard colour thumbnail1. Load both images into your editing program.

2. Use whatever command is needed (in Photoshop it is the split command in the menu attached to the channels palette; similar commands seem to be available in most image editors) to split both images into greyscale versions of the red, green, and blue image channels.

false colour IR 3. Merge the red channel from the IR image, which is really mostly an infrared channel, with the red channel from the standard image and the green channel from the standard image. Assign the IR channel image to red, the standard red image to green, and the standard green image to blue in the merged image. This will create a new RGB false-colour IR image, usnign the same conventions as "normal" false-colour infrared film. The exact details of how to accomplish this will vary, but most image editors can probably do it.

You now have a standard false-colour infrared image. If either the camera or the subject moved at all between exposures, there may be some artifacts caused by mismatches between the images--note the advancing clouds and some palm fronds in the third image.

next--very false colours

back--basic techniques

Photographic homepage

Online gallery

All images and text on this site are copyrighted by Ross A. Alford and may not be reproduced without permission