Now I have the image, what else do I need to think about?
The first of these is white balance – how to set it and why. The others are artefacts of the image capture process – hot spots and lens flare. These usually need to be tackled before any post-processing. If they aren’t present, then you won’t have to worry about them.
White Balance (WB):
Good white balance is necessary to ensure that you get the colours you want, even in IR photography. Setting automatic white balance for infrared imagery is a little different than setting it for conventional digital imagery. While there is considerable discussion on the web about setting AWB for IR images, the use of green grass, or a similar bright green subject, seems to be an accepted approach. I use green grass, but you may have to experiment for yourself to determine what works for you. One of the many discussions on AWB in IR photography can be found in the first part of this article.
WB and Camera Profile:
Another aspect of post processing and WB considerations is to develop a custom camera profile. Lightroom and Adobe Camera Raw do not handle WB well in converted cameras, so a custom camera profile may be required. The details of how this is done are covered in a number of websites such as Luminescent Photo.
Hot Spots and Lens Flare
A ”hot spot” is defined as an area in an image (usually the centre) that is lighter or brighter than its surroundings. You can see this in the first image of this post. Details of dealing with these can be found here. For those interested, Kolari Vision has published a database of lenses susceptible to hot spots.
Lens flare, as seen in the second image here, tends to be more prevalent with IR light as the coatings on the optics, intended for visible light, do not work as well with IR light. Shooting away from sources of bright light, such as the sun, or using a lens hood, can reduce or eliminate flare. It can also be eliminated in software using a cloning process.
The best way for “processing” these that I have found is to try and avoid them all together.
Assuming that you have resolved any situations with WB, hot spots, or lens flare, then the next choice is whether you want to develop your image in false colour, or render it as a black and white one. I will deal with black and white conversions in the next article, but, for now, give an over view of one approach to false colour imagery.
The post processing of an image into false colour is best done with those from 590nm (used in this example) and 635nm filters, although it can be done with 720nm, but not to the same extent. The image, as seen below on the far left, is taken into Photoshop and then processed – Image>Adjustments>Channel Mixer. The Red and Blue channels are exchanged giving a false colour rendering of the image (the centre picture). Because the sky was a little green in the Channel Swapped image, further adjustments can be done with Levels and Hue/Saturation/Lightness and any other adjustments that you feel can enhance the image (final image, on the right).
Details of one particular workflow can be found in Chris Swarbrick’s article here.