Today’s Question: You made reference to setting a custom white balance in the camera based on a gray card. How can this be done?
Tim’s Quick Answer: The specific process will vary from one camera to the next, but in general that process is the same. You simply capture a photo of a gray card (or similar neutral object) and then use that photo as the basis of a custom white balance setting in the camera.
More Detail: The concept here is that if you capture a photo of a neutral object (such as a gray card) under the same lighting conditions as the subject you will be photographing, the color of that object as it is captured can be used as the basis of an automatic white balance adjustment for subsequent photos captured under the same conditions.
While a gray card is certainly a great tool to use in this process, it is also possible to employ any other neutral (non-colored) object, such as a bright white sheet of paper. Perhaps the most important part of this process is to be sure you are photographing the gray card (or alternative) under the same lighting conditions that will illuminate your subject.
In other words, this process works best when the lighting on your subject is relatively consistent and uniform. You can then place the gray card in that light, and fill the camera’s frame with the gray card. Once you have captured a photo of the gray card under the lighting conditions for your subject, you can set that photo as the basis of a custom white balance adjustment.
Again, the specific process will vary by camera model, but in general you can simply choose the custom white balance option within your camera’s menu system and then select the appropriate photo as the basis of that custom white balance.
I should hasten to add that this custom white balance option is different from the similarly named option that enables you to dial in a specific Kelvin value for the white balance compensation. The process described above offers a relatively automated approach to compensating for the color of light on your subject through the use of a “sample” photograph captured under the same conditions.