Today’s Question: In Adobe Camera Raw under Lens Corrections and Remove Chromatic Aberration it’s limited to only 2 colors, purple and green. Nothing seems to work at all, no matter how I adjust the dials! What is going on here?!
Tim’s Quick Answer: If you’re not seeing an effect with the controls for removing chromatic aberrations, it is most likely an indication that you’re not using settings appropriate to the image you’re working on. I recommend increasing the Amount value for both purple and green to the maximum, and spreading the Hue control handles to the extreme ends of the scale. You should then see a rather significant loss of color along contrast edges in the photo, and you can then fine-tune the controls as needed for the photo.
More Detail: The controls you’re referring to are the Defringe controls, and they operate independently from the “Remove Chromatic Aberration” checkbox. In other words, you don’t need to turn on the “Remove Chromatic Aberration” checkbox in order to employ the Defringe controls.
In general I find that turning on the “Remove Chromatic Aberration” checkbox adequately resolves color fringing in about half of the photos that exhibit such fringing. For the other half of images that require this adjustment, the Amount and Hue sliders for purple and/or green must be used to produce a good result in the photo.
The Amount sliders (for purple and green) determine the degree to which the colors present in chromatic aberrations will be reduced in saturation. The two slider handles for the Hue sliders (for purple and green) determine the specific color range to be affected.
By maximizing the hue spread and the Amount setting for purple, you’ll be reducing saturation for colors ranging from cyan to red, including purple and magenta in between. In other words, colors within that range will turn gray.
Similarly, maximizing the hue range and the strength of the adjustment for the green sliders will cause colors ranging from orange through cyan (including green) to be reduced in saturation.
With this approach, you should see a relatively large gray area along contrast edges within the photo. Obviously you don’t want to actually remove so much color that you end up with a gray band along contrast edges in the photo. So you can then refine the settings as needed.
My general approach when it comes to using the sliders is to start with a high value for Amount, and then expand the Hue range until I can see gray fringing along contrast edges in the photo. I’ll then reduce the Hue range until only the problematic colors are being affected. I then reduce the value for Amount to establish a value that is just enough to remove the chromatic aberrations without causing new problems for the photo.