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False Colour Mapping

It is quite easy with packages like Photoshop to take the infrared, red, green and blue channels and combine them to produce various effects.

Infrared channel Red and infrared channels
Infrared Infrared + Red

The first thing I want to show is the difference between the 'pure' infrared photograph and the one that combines the near infrared light with red. This is the image that might be taken through a red number 25 filter. The pure image is also shown here for comparison. If you want to take a pure infrared photo with an SLR you will have to use a tripod because you will not be able to see through the filter. In any case the effective speed of the film is reduced by one or two stops. Which you use for your infrared photography depends on your taste and, possibly, how lazy you are since using a red filter is much easier. [I have to admit that, as the response of the digital camera does not exactly match the infrared film, this is not an exact demonstration.]

Colour (RGB) For colour infrared film the colour channels are remapped and infrared is added in. The Ektachrome film we use maps infrared to red, red to green and green to blue and produces a result like that on the left. The distinctive magenta foliage is a result of the combination of the green of the plants, now mapped to blue, and the red from the infrared light.
An alternative mapping, which is quite interesting to look at, comes if you just replace the green channel with the infrared one so that infrared 'becomes' green. I did this using Photoshop and produced the result on the right here. I doubt if this has any scientific purpose but I like it. It is not possible to produce this mapping using the Ektachrome film and would be very difficult without a camera able to record all four channels. Colour (RGB)
Colour (RGB) Finally, if you bleed some (in this case about 50%) of the monochrome infrared channel into the real colour scene you produce a result that starts to take on the appearance of a hand-tinted photograph.

All the images on these two pages were manipulated using Photoshop and sourced from the infrared, red, green and blue channels taken using a Sony PC-7 digital camcorder working in PAL. A Hoya R72 visually opaque filter was used to enable the camera to record the near infrared light content of the scene.

More background on infrared photography
Technical background Thermal Imaging NASA IR Video Camera
IR 'Colour' Mapping Imaging Abstracts Noctovision
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