Walking In An I/R Wonderland

Springtime quickens the hearts of infra red enthusiasts everywhere, although the diehards will tell you that every season is an infra red season. 

Digital photography has sparked a spectacular revival in infra red photography, the eighties and nineties having been something of a heyday for film infra red.  Now we have the option of creating faux I/R in Photoshop, using a filter on a camera or perhaps having a camera permanently converted.  For some years I had been quite happy just to use an SRB screw-in opaque I/R filter on my Nikon D70 for taking infra red pictures.  Subsequent models had a stronger anti-alias filter that made this impossible but there is now a whole new generation of cameras, particularly CSC ones, that don't use an anti-alias filter and so can be used for infra red photography. The add on opaque red external filter does require that auto focus be turned off, but with a wide angle lens pre-focusing just below infinity seems to work fine.  However, the acquisition of a D90 made the D70 available for conversion.  This was done by Advanced Camera Services of Watton near Thetford. Although not cheap they do a fine job.  You get a full camera service as well as the conversion to I/R, so you do get value for money; my six year old D70 came back looking like new.  You need to set a custom white point on the camera and make a DNG profile and camera profile for the raw file converter.  Khromagery.com provides guidance for this.  I am finding that clicking on Auto white point in the raw file converter is working slightly better than as shot.

The ability to introduce colour into a digital infra red image must be one of digital I/R greatest advantages over film. It is of course, not true colour but beguiling effects can be achieved.  I had already experimented with painting colour onto an I/R image and also using curves in Photoshop to produce the colour, the layers being masked out and painted back in where required, but it was Neal Malton of Peterborough who introduced me to the seductive, indeed addictive technique of "channel swapping".  

With the Nikon D70 I found that over-exposure by about 1.3 stops helps to avoid colour blotching in the sky if using the external filter, a problem that sometimes only becomes apparent when the colour is introduced.  My Nikon also exhibited a hot-spot with I/R with a particular lens that is also only a problem when channel swapping but is easily resolved by selecting a centre circle with a well feathered round marquee tool and using auto levels. This hot spot no longer occurs post-conversion. The removal of the anti-alias filter has also resulted in improved sharpness. The colours resulting cannot always be predicted; you be may pleasantly surprised or you may decide it would be better left in mono, in which case a quick click on the mono box in channels mixer or in gradient map will bring up an already well adjusted monochrome version.  Indeed, although channel swapping was a priority for the infrared converted camera, it has been a pleasant surprise to see how well it works for straight mono.

The procedure for channel swapping is to select a custom white point with the eyedropper tool in the raw file converter.  This removes the red (where the external filter has been used) and creates a sepia sky and bluish foreground.  At this stage saturation may also be increased.  In Photoshop first adjust levels by clicking on auto (yes I did say auto, it works).  Now go into channel mixer and open the red channel, taking the red slider down to 0 and the blue slider up to 100.  In the blue channel take the blue slider down to 0 and the red slider up to 100. You should now have a blue sky and sepia foreground with the customary light I/R foliage.  For users of Elements the hue and saturation adjustment layer will do much the same thing by taking the hue slider almost all the way over to the left.  Some tweaking of the colour balance may be necessary to get the desired tone in grass and foliage.

Finally, and after having vigorously argued the case for channel swapping, I should add that the converted camera may also produce lovely effects without any channel swapping at all!

For an in-depth guide to these techniques I have provided links to Clive Haynes, ACS and Khromagery websites