What is white balance shift?
White balance shift is a setting on the EOS cameras that allows a photographer to bias the colours in images in either blue, amber, magenta or green directions. This colour shift can be used to add or remove colour shifts that may occur when shooting in mixed lighting conditions. Typically think flash and daylight, flash and indoor lights, street lights and daylight and so on. White balance can be shifted from -9 to +9 in both blue / amber and green / magenta directions, or combinations of blue/amber and green/magenta shifts. The blue/amber shift is equal to five mired for each step.
Camera instruction manuals say that one step of shift in the blue/amber direction is equivalent to five mired shift. The mired (micro reciprocal degree) is a measurement used to express colour temperature.
So with some maths; if the camera is set with a Kelvin white balance of 5200K, then full shift of 9 units to the blue direction is a 45 mired shift, making the temperature actually 4214K. A full shift in the amber direction would give a colour temperature equivalent to 6789K.
As a test I shot a scene with a 7-stop bracket in the B/A direction to give me the original image, plus six others from B9 through to A9. Here’s the camera’s mid-point and the extremes to show the effect.
Mired shift only applies to the blue/amber direction as this is colour temperature shift, however in many software applications working with RAW images, a tint control is available that offers green/magenta shift and so it is also provided in camera.
Extended range of Kelvin temperature
By calculation if you use the full blue/amber shift while using the camera set to it’s lowest 2,500K temperature the result is 2,247K and with the camera set to 10,000K it is 18,182K.
What is white balance bracketing?Your camera can be set to bracket with white balance, for each picture taken the camera will create three files on the card, one at the set white balance and two with the shifted amount. Bracketing can only be in either the blue/amber or magenta/green directions. The maximum amount of bracket is 3-steps.
If the camera can be set to different amounts of bracketed pictures – like the EOS 5D Mark III, and EOS-1D series – cameras then it will create more files for each shot, for me that’s up to 7 shots on the EOS 5D Mark III.
When would I want to use white balance bracketing?
Most of the time the camera’s white balance gets a great result for JPEG shots, but sometimes in strange combinations of lighting the automatic system can be thrown off. The use of the bracketing function will ensure that the camera can produce a usable file with no post production. If you shoot mostly JPEG images then white balance bracketing can help you out by providing multiple versions of a picture straight from the camera – just choose the one that looks best.
In some cases you might want to, and can, combine white balance shift and white balance bracketing.
However, for many photographers the solution is not white balance bracketing but RAW shooting…
RAW shooters – do it later
If you shoot exclusively RAW images then white balance is something that invariably happens as part of your RAW image post production workflow. If you shoot JPEG then white balance shift and white balance bracketing may be useful for critical applications where JPEG images straight from the camera are required to be supplied. However any shift applied in the camera will still affect how the image is displayed on the camera LCD.