Processing Infrared Photographs15th September 2013
I recently acquired a Canon EOS 5D that had been converted for infrared photography. In most DSLRs, there is a filter which prevents infrared light from hitting the sensor. This had been removed, and had been replaced with one that filters out light shorter than 590 nm in wavelength.
This particular conversion is particularly good for false colour infrared photography, however the images that come straight out of the camera need some post processing. I’ve been asked by a number of people on how to do this. Here is a short guide.
Taking the Picture
Firstly, make sure you are shooting RAW. This is important because we will have to significantly change the white balance. The white balance range provided by the camera is usually insufficient.
Secondly, check the RGB histograms. The red channel is the most important. DSLR light metering is tuned for visible light, and as a result the red channel often gets over exposed.
Try to get an even distribution on the red channel, without bunching at either end.
Adjusting White Balance
Straight out of the camera, images are very warm.
Very few image processing applications are able to set a white balance to an appropriate value, i.e. less than 2000K. The only two that I had any success with were Canon Digital Photo Professional and Capture One Pro 7.
In either application, find the neutral colour picker tool. Then select a part of the image that should appear white.
This should produce an image that appears much cooler.
Now that we have a balanced image, we need to swap the red and blue channels. Adobe Photoshop provides functionality to do this. Adobe Photoshop Elements can also be used, if combined with the Elements+ plugin.
Using the channel mixer tool, output all red information using the blue channel and output all blue information using the red channel.
This should produce an image with blue skies and golden foliage. It is for this reason that the 590 nm filter is referred to as the “goldie” filter.
Longer wavelength filters are also popular. Given similar processing, these filters produce whiter foliage and deeper blue skies. They are also often popular for black and white photography.
Many of the tools discussed here are proprietary and may not be financially viable for many photographers. I would be very happy to update this post with links to open source and free tools that can be used to achieve the same results.
For those looking for an infrared camera, I highly recommend Digital Landscapes, the stockist from which I purchased mine.