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What is Infrared photography?

I just want to explain what I mean when I say "Infrared photography" to those who might be curious. My Infrared gallery shows the results, which is what really matters, but for those of you who want to know a little more, read on. Samples of my own infrared photography can be seen in the album "Near infrared" so let me start by explaining what it's all about.

Near infrared is the spectrum of light which falls between visible light and true infrared. The spectrum is described in wavelengths and the part of the spectrum called near infrared (used for these photos) is 650 to 1000 nm (nano meters). Beyond 1000 nm is where true infrared starts and this is the stuff of navy seals and James Bond. The spectrum of light I use for these images behaves just like visible light and as luck would have it digital sensors can detect it and we can modify it with lenses and apertures just like visible light.

Because we can't see it and because it effects sensors, camera manufacturers put filters in front of the sensor in a digital camera to block it. The camera I use for infrared photography has been modified professionally (that means not by me) to replace the infrared filter with a visible light flter. It only lets in the near infrared wavelengths that I want to use. This makes the camera unusable for anything else but it is now a true near infrared camera.

Post processing.

It is entirely possible that the appeal of infrared photography is the fact that you have to do post processing to get anything at all pleasing. Because of the filter's efficiency in blocking the whole visible spectrum of light from the sensor, the remaining light doesn't pass into the 3 color channels of the camera system (Red, Green and Blue) evenly or predictably.

Addition: I now use a custom camera callibration template that I created using the Adobe Labs DNG profile editor. It allows me to move the color balance back to the center before I convert the raw imaged for further processing. A full explanation is available here.

The followinw 4 images illustrate what post processing does. From left to right is the flow of processing.
Original
Channel swapped
Balanced
Final
Original image from the camera. Heavily biased towards the red channel. Swapping color channel RED and BLUE gives a somewhat more realistic color palette. Correcting the levels of each color channel helps, but sometimes the effects are subtle. Finally using a mid tone sampler in the "Curves" adjustment layerrenders a final color palette to taste. The result for this image is almost sepia.

The ways to achieve this and when you stop is all up to the individual.

Colorization (or hand painting)

One other technique used often with infrared photography is to hand paint an item to make it stand out or to give an arty, painterly effect. This again is a matter of taste.

The simple example below is a black smith's workshop which could not be rendered in the "right" color using infrared but by adding a color layer and painting the workshop the effect is interesting. Below, before and after I painted the workshop. (The nice thing about painting like this is that you don't need a ladder)

Original
Painted workshop
Fully processed infrared image with a poor color palette
Giving the barn a new coat of paint (in the actual color selected from a full spectrum photograph) makes all the difference.

References that will make me look like the beginner I am.