Today’s Question: How do you determine a color cast visually on prints? In one application for membership I was told 4 of my images had color cast in the prints.
Tim’s Quick Answer: It can be surprisingly difficulty to accurately evaluate whether there is a color cast in a print. Your best bet is to use a light source with a 5000 Kelvin rating to illuminate the print, and to surround the print by a pure white background.
More Detail: The human visual system includes a feature referred to as “white point adaptation”. What this basically means is that our visual system attempts to eliminate the effect of a color cast caused by the light illuminating a scene. So, for example, if you see a white object illuminated by a yellow light source, you “know” the object is white even though it actually appears with shades of yellow.
This white point adaptation can effectively cancel out the color of the light source, but it can also cause you to automatically correct for other color problems in a scene, such as when viewing a printed image.
To help compensate, you want to ensure that the print is viewed with a clear reference for what actual white looks like. A 5000 Kelvin light source is the basis of print evaluation with most color management standards, and therefore is the illumination source that should generally be used to evaluate prints.
In addition to a bright and neutral light source to illuminate the print, a pure white background surrounding the print will provide your visual system with a clue as to what white looks like, and thus you’ll be better able to detect a color imbalance in the print.
Of course, even at this point it is not always easy to see the actual color cast in a print. We all have different color vision abilities, both in terms of the accuracy of our vision as well as our ability to differentiate small differences in color. I have found that with practice it becomes easier to detect a color cast in the prints, but it can still be a bit of a challenge to be able to see such a color cast clearly.
I recommend practicing the process of critically evaluating prints under the viewing conditions described above, and you’ll likely find that it becomes easier to detect a problematic color cast in a print.