White Balance and Color Temperature – Part 2 of 4

White balance is entirely controlled by our camera. We can set our camera to a certain white balance (color temperature) and that causes our camera to “see” that color temperature as white. If we set our camera’s white balance to 2500K then a light source whose color temperature is 2500K will be seen by our camera as white. If on the other hand we set our camera’s white balance to 7000K, then any light source whose color temperature is 7000K will be seen by our camera as white. The placement of our camera on the color temperature chart is entirely determined by what we set the white balance to, and it’s completely under our control.

Certain light sources we can change their color temperature.  We do this by putting a gel filter over the light.  When we gel a light it causes the light’s color temperature position to “slide” on the chart.  Other light sources it’s just not practical for us to change them.  You really can’t put a gel filter over the sun. And trying to gel light bulbs in your house is a pain too. The easiest light source we have that can be gelled is our flash.

Knowing this about the camera and the light sources we can now see what control we have:

ItemAmount of Control
SunNone
Light BulbsNone
Camera FlashGel Filters
Camera White BalanceTotal Control

Visually this would look like this:

Now this figure probably looks overly complicated, but it’s not too bad!  Let’s walk through it and see what it’s telling us.

Top row, here we have the Red, White, and Blue chart showing the progressing from warm/low kelvin color temperatures on the left to cool/high kelvin color temperatures on the right. The 2nd row we have three light sources, a light bulb, daylight (clear day), and cloudy – notice all are locked in place.  This is because from the table above we don’t have any control over the light source, so we can’t slide its position on the chart. The 3rd row we have our flash. There are actually three flashes on this row.  There is a flash covered with a warming gel (orange colored shade), which slides the flash to the left on the chart. There is a flash with no gel, so it doesn’t slide left or right, it has a fixed position.  And then there is a flash with a cooling gel (blue colored shade), which slides the flash to the right on the chart. Finally at the bottom is our camera (white balance), which we can slide to the left or right without having to use filters.  We just set the white balance in the camera to what we want.

As long as we have the white balance of the camera set to the same color temperature of the light source, white will be white, the image won’t look warm or cool visually. So for example, say we are taking pictures indoors and set the camera white balance to tungsten:

Notice the bulb is locked in place and we adjust the camera white balance to match. The light bulb color temperature is then white.  What if it’s outside on a clear sunny day:

Again, the light source is locked in place and we adjust the camera white balance to match. So now the light from the sun is white.  Same if it was cloudy outside:

The cloudy light source is locked and we adjust the camera white balance to match. So for these three examples where we only have a single light source, our whites will be white, no color temperature shift in the images.

But what happens if we have multiple light sources in a scene? Let’s say we are indoors taking pictures with a flash:

Here we run into some problems. Let’s try setting the camera white balance to be between the two light sources.  The light bulb will appear warm to the camera because it’s to the left of the camera (on the Red side).  The flash will appear cool to the camera because it’s to the right of the camera (on the Blue side).

So where can we adjust the camera white balance to? What if we set it to tungsten:

If we set the camera white balance to tungsten, then anything illuminated by the light bulb will look normal but anything illuminated by the flash will appear cool. Remember, it’s all about the perspective from the camera’s position. Here the flash is to the right of the camera, so from the camera’s point of view the flash is a cool light source. This will cause problems with pictures, while anything in the image illuminated by the light bulb will appear normal, anything illuminated by the flash will have a blue cast to it.

Ok, how about we set the white balance of the camera to the flash:

Well now from the perspective of the camera the tungsten light bulb will appear warmer because it’s to the left of the camera on the chart. So we’ve got the opposite problem, anything illuminated by the flash will appear normal and anything illuminated by the light bulb will appear warm and have a red/orange cast.

What can we do to fix this?  In the next part we’ll discuss how this can be fixed.

Checkout the first post in this series, Gelling your flash, as easy as Red, White, and Blue.

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