One of the most confusing, and most asked about, elements of producing an image from a near-IR capture (meaning getting a nice looking image) is setting the white-balance. The why and how is not well understood and documentation is often misleading, with most people leaving their cameras in auto mode, which in near-IR photography is the worse thing to do.
One of the better articles to start with is Cambridge Color’s article on understanding white-balance: http://www.cambridgeincolour.com/tutorials/white-balance.htm
This article, good as it is, is however written for normal visible light photography and focused (excuse the pun) on getting the ‘right’ coloured image for the temperature of the light source at the time. In near-IR photography we are already outside the norm and use the white-balance point solely as a processing control, a dial or lever, to set the colours we want in our final image.
A lot of people will say “for this frequency, set the custom WB from the foliage, the sky or some white card… etc. etc.“; however, the really important point, that a lot of people miss, is that there is no ‘correct’ white-balance for a near-IR image, it is just a creative control option – it is a dial, a lever, to use to get the effect you want.
What does it do ?
Probably the best way to show what the control does is this graph from the Cambridge Color article:
The “white-balance point” is actually a profile, used in processing the image, to interpretate the captured light range (near-IR etc.) into more of the visible range. Remember a bayer sensor is capturing the blue, green and reds of a scene (not the frequencies). A camera’s white-balance function is normally to adjust (compensate) the intensity of the blue, greens and reds for the temperature of different light sources.
Referring to the diagram above, the higher the light source temperature (K), the more it will compensate the intensity of the blues and greens, over the extreme reds we capture in near-IR, and visa-versa for lower temperatures. Unlike in normal photography, where you would want to select the temperature as close as to the real light source at the time, we are just selecting the temperature we want based on artistic choice (impact to the image). It is why I prefer the term “colour-profile” rather than “white-balance”, as we are not trying to match the light source to what was there when the image was captured, just use the function to choose the colours we want more of in our image.
Setting in-camera vs in-processing
Personally, I set colour-profiles (the WB) in both the camera and the import software making my final image from the RAW file. In the camera so that I get a good approximation of what the (pre channel-swapped) image will look like and in the computer software (Capture 1, Lightroom etc.) for the final processed from RAW image. As the example below shows, a few nudges of the slider can often make a significant difference.
Setting the colour-profile in the camera (if the camera has a custom WB option) is very rudimentary and often limited, which is why I view it really as just a visual approximation tool. With some previous cameras, which had poor custom WB capability, but still captured RAW, I set the display to mono (B&W), which is better than trying to view an all red image on a small screen. Cameras that can’t do custom white-balance, nor RAW, make for poor cameras for this type of photography and are better avoided.
I usually have my cameras, as a viewable starting point, set at around:
- 2200K to 2700K for single-band near-IR capture (590nm, 720nm etc.)
- 5000K for dual-band, mixed near UV and IR (not far off normal visible light settings)
When the raw files are imported by the computer software (Capture 1 being my current personal preference), I then fine tune the processed image to the colour-profile I want (remember there is no absolute here, it is just an artistic choice) using the software slider or colour-dropper.
As this collection of 720nm processed images shows, the colour-profile used can make a significant difference to the final image – it shows six different set points, showing the subtle differences that come from varying the colour-profile (white-balance). The bottom six images, for reference, are the channel-swapped versions of the top six.
720nm image with different WB colour-profiles
In near IR and UV photography, setting the colour-profile (WB) is as important as the exposure, focus and ISO. Most people are not aware of its importance as most modern cameras are good at ‘auto WB’ for visible light photography.
- In near IR and UV photography, setting the colour-profile (WB) is as important as the exposure, focus and ISO.
- There is no such thing as the ‘correct’ white-balance for a near-IR image – it is just a creative control.
- Don’t leave your camera in AUTO WB mode – if you can, set a custom WB in the camera, even if just for the preview before resetting the colour-profile in post-capture processing.
- If using RAW capture, always fine tune the WB in the import software – it is an important creative control and can make all the difference to an outcome of the final image.