In preparation for this article I spent some time on Google, which usually is counter-productive. But it brought to light the lack of thought given to today’s topic, which is color theory. More specifically, color theory as it pertains to color temperature and white balance.
As I said in our last discussion of white balance, we think of the color of light as a continuum from cyan to yellow. We think this so ardently, that we even decided to use a temperature measuring scale to analyze it. This is the Kelvin temperature scale and cool light measures in the higher numbers, warm light registers in the lower numbers, with our pure white light in the middle (usually around 5500 degrees.)
And this, of course, is a simplification. Light does not just shift along a single line graph from blue to yellow. More accurately, we should think of it shifting along a four quadrant graph, with yellow and blue making up one line and green and magenta making up the other. So I went in search for an image of this graph. It’s not out there. Nowhere. I searched for kelvin chart, kelvin graph, four section kelvin, manually selecting kelvin, manual white balance, and several other Hail Mary’s. But I always got either a kelvin chart, or a two dimensional representation of color space (which is not our topic today.) I searched for “manually selecting kelvin on sony A7” and before finding what I wanted, I found Nikon D7100s for sale. That’s how little people think about the true nature of color shift.
So I shot my own.
This is a far more accurate way of thinking about the way that color can shift. Only a few cameras even give you this option when selecting kelvin. There aren't even images of it to search for. So most people are taking most of their pictures with inaccurate color. And of course, this chart is a simpler way of presenting the color wheel itself. However, it does should the green and magenta color shift, as indicated by G and M. It also shows the cyan and yellow shift and indicates them with, of all letters, A and B.
When you do a custom white balance, what you are creating is a series of corrections to the way the camera sees light. If you make a custom white balance it might say B2 M1, which would mean correct with two points of cyan and one of magenta. If you only saw or corrected for the cyan - yellow shift, your image would still be too green.
This, in a nutshell is the reason for manual white balance. The auto functions revolving around white balance only correct for the yellow - cyan shift - not the magenta - green. So you are not correcting for literally HALF of all the ways your camera can incorrectly record light. When you use some form of white balance correction tool (color checker, grey card, etc.) you can correct for all four quadrants.
I’m sure I’ll do a video revolving around custom white balance technique in the future. Keep a look out.