Friday, 13 July 2018

Does white balance totally correct color shift due to lens glass or coating?


I'm about to create custom profiles for my camera and in order to do so I need to shoot pictures of color reference card.


I don't really understand the impact of the lens I choose to create the reference pictures. I can imagine that if my lenses are from the same brand and generation I should have accurate results. But what if I take some reference pictures using, say, old lenses with yellow radioactive coatings and other ones with modern coatings?


Will a rigorous white balance adjustment (using a neutral grey reference card for instance) be enough to get perfectly accurate results, or should I create custom profiles for each lens + sensor combination because white balance adjustment won't be able to correct color transmission variations?



Answer



Short answer: Yes, you need to create separate profiles for each camera/lens combination. Unless the light in your test passes through the same lens, the system has no way of knowing what characteristics for which to correct. Applying a profile created using one lens and then expecting it to properly correct a significantly different lens would be like putting a colored gel in the optical path and expecting the color profile you created without the gel to to somehow magically remove the changes the gel creates!


Long answer: There's no such thing as "perfect" white balance. Color management can only go so far in reproducing on a display medium what exists in the real world. Different materials that look the same color under one type of light will appear to be slightly different colors under different lighting conditions. And even if there were such a thing as perfect color correction, where are the perfect eyes that could see it? Everyone perceives color in their own unique way!


For all practical purposes if your lenses are very similar in terms of color transmission you won't notice a difference when changing lenses. Other factors will likely introduce more variation than that between two of your lenses. But if you wish to get as close to "perfect" as possible, then you need to go a step further.


And, having said that, the best way to create custom profiles is to use the same lens with the camera that you intend to use when that profile is applied. It is also important to shoot under the same light (or as close as is practical) when you create your reference files as what you plan to shoot under when you shoot the photos to which your profiles will be applied. The more different the light is between your profile shots and the shots to which you will apply those profiles, the less accurate your results will be.


And if you are truly interested in color management to the degree your question indicates, shoot more than just a grey card. Use a colorchecker chart such as the Xrite ColorChecker Passport



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