You may be aware that light (whether ambient, flash, or a continuous light source) reflecting off a colored ceiling or wall will reflect that color into your photograph. Likewise, color reflections from a background will adversely cause your subject to take on a tint that isn’t actually present.
In the best case scenario, you may only have to explain why your photos of a subject have erroneous colors. In the worst cases, those erroneous color tints can lead to erroneous conclusions. For example, a tire photographed on a blue background will likely take on a blue color cast. This could be mistakenly interpreted as evidence that the tire or tire piece exhibited signs of high heat, which includes the “bluing” of certain surfaces in the tire.
Setting a custom white balance (WB) with a calibrated white or gray target won’t remove the unwanted background color casts because the target is usually placed between the light source(s) and the subject. In that position, it would yield a proper WB for the light falling on the target, but it wouldn’t receive the tinted reflections of light from the background. As custom WB is designed to do, it would properly render the actual reflected color cast on the subject—even if is unwanted.
But if the WB target was in position to receive background reflected light, the custom WB function would try to neutralize that color cast, which would adversely affect every other color. That would be the worst of both worlds.
Let’s see how different color backgrounds work in practice.
For these examples, I photographed a manual tire spreader on different solid color backgrounds in my Studio Lab. [Click on photo below to enlarge, then click on back arrow to return to this post.]
The tire spreader was made from uniformly-colored cast metal. It had no paint or other color applied to it. Before making any of the photographs below, I set a custom WB using a Calibrite gray WB target.
Here is the resulting photograph with the blue background paper. It’s easy to see the blue cast in the vertical surfaces, but even the horizontal surfaces have picked up an unwanted and incorrect blue tint. [Click on photo above to enlarge, then click on back arrow to return to this post.]
Replacing the blue background paper with red changed the improper color cast from blue to red. Again, the tint was most evident in the vertical surfaces, but was also noticeably visible on the more textured horizontal surfaces—especially when compared with those same surfaces in the blue background photo. [Click on photo above to enlarge, then click on back arrow to return to this post.]
Replacing the red background paper with white removed the color cast, but now the vertical surfaces were significantly brighter than the horizontal surfaces. This was not what the spreader looked like if you held it in your hands. [Click on photo above to enlarge, then click on back arrow to return to this post.]
Changing to a black background paper retained the neutrality of the white paper, but now the shadows were darker than they appear to the naked eye. In fact, black cards or black reflectors are often specifically used to absorb light and create deeper shadows. [Click on photo above to enlarge, then click on back arrow to return to this post.]
A neutral gray background paper added no color cast, nor did it overemphasize highlights or shadows. In conjunction with a custom white balance, a neutral gray background provides the most natural and true colors, textures, and shapes of your subject. [Click on photo above to enlarge, then click on back arrow to return to this post.]
After testing and measuring numerous gray background papers, I found Superior Seamless #4 Neutral Gray Seamless Paper to be the most neutral gray background paper available. I’ve been using it ever since. Here’s a link to that paper: https://superspec.com/product/neutral-gray-seamless-paper/
Takeaways:
-1- Non-neutral background colors negatively affect the accurate rendition of your subject in a photograph.
-2- Colored backgrounds impart their colors onto your subject.
-3- Setting a custom white balance (WB) with a calibrated white or gray target won’t remove the color cast, but will accurately capture the actual reflected color. This is as it should be since capturing accurate actual color is the purpose of setting a custom WB.
-4- Although black and white are neutral tones, black overemphasizes shadows while white overemphasizes highlights.
-5- A neutral gray background gives the most natural and true colors, textures, and shapes of your subject. It’s all I ever use for any forensic photography.
