Automatic White Balance

We all know the problem with the exposure metering. If the subject is predominantly bright, e.g. a white-painted house facade, then this leads to a wrong exposure. The facade is then not white, but gray in the picture. If, on the other hand, the subject is predominantly dark, e.g. a black dog in the full-frame shot, then the dog is not black either, but gray. That’s why we use exposure compensation in such situations. But what about automatic white balance?

How does automatic white balance work?

Unfortunately, manufacturers are a bit cagey about exactly which algorithms they use for white balance. However, there are two basic assumptions that can be used:

• Assumption 1: The brightest part of the image is white and is used for white balance
• Assumption 2: In the subject, all (basic) colors occur in approximately equal proportions

Here is an example for assumption 1:

Here, the automatic white balance worked without any problems. The image is completely without color cast (the bluish reflections on the front come from the blue sky and are therefore not a color cast).

And an example for assumption 2:

The automatic white balance also works as expected in this case. Since all colors occupy more or less the same areas, the result is without a noticeable color cast.

But even if not all colors are present in the subject, the automatic white balance usually works very well. Even if only two colors dominate the image, especially if they are complementary colors, the camera’s algorithm achieves good results:

However, it should be assumed that the automatic white balance will always fail if there is a strong color dominance in the image. In the case of a monochrome subject, the camera would have to “think” that the lighting has a distinct inherent color, i.e. that it is not color-neutral. The camera would then try to remove the supposed color cast by shifting the colors toward the complementary color. So, in the case of a solid yellow subject, it would compensate the colors toward blue. As a result, the image would be more or less gray.

The following photo was taken with automatic white balance:

I see no reason to correct the white balance.

Don’t ask me how this is possible. With such intense colors, the white balance should actually fail. And I can’t imagine that the small white reflections on the rhinestones are enough for the correct white balance.

In fact, I very rarely feel the need to correct the automatic white balance (since I shoot exclusively in RAW format, this happens in post-processing, of course). Only with incandescent light does the automatic white balance usually deliver a result that I personally find too yellowish:

A white balance on the gray book cover gives the following result:

However, white balance is always a matter of personal taste.

Conclusion

At least on our cameras, automatic white balance works perfectly fine in most situations. Therefore, AWB is also the default setting on our cameras.

What is your experience with automatic white balance? Please let us know in the comments.