Purple fringing occurs because the lens doesn’t behave the same way on all the different wavelengths of the incoming light. This is of course something that the lens designer tries to compensate for, but lenses are almost never perfect.
Purple fringing is often related to how much the lens shows chromatic aberration and it is more likely to see purple fringing when using a lens wide open compared to using it stopped down.
The Lens Tool in Capture One Pro 7 offers a method to remove purple fringing from your images.
The image to the left shows purple fringing along the spoke that reflects the sun. To the right you see the image after having applied “Purple fringing” correction in the Lens Tool in Capture One Pro 7.
Purple fringing correction is an optional correction feature in the Lens Tool. To enable purple fringing correction you simply set the checkmark for “Purple fringing”.
When using the purple fringing correction, Capture One Pro 7 uses an intelligent algorithm that takes the behavior of light in a lens into account. The algorithm can estimate the original color underneath the fringing and it is not just a simple desaturation of the purple color.
In the image below you can see how the purple fringing correction algorithm in Capture One Pro 7 can bring back the blue of the sea along the spoke. I have also made a simple correction by doing a simple desaturation of the color of the fringing to show you the difference:
In the image in the middle the purple fringing is removed, but an unnatural gray edge occurs instead. In the image to the right you can see that the fringing has been removed and replaced with the color of the blue sea.
Wide-angle zooms are often prone to fringing. In the examples below I have a strong contrast against the bright sky.
This is a zoom into the top left corner of the image. The purple fringing is seen on the dark side of the edge between the bright sky and the shadow side of the wooden construction.
The “Purple Fringing” algorithm in the Lens Tool does a very good job of removing the purple fringing in most images. But as the algorithm has to deal with colors and contrast in an image, it may not always remove all the fringing as it can be very difficult to distinguish between fringing colors and real colors in the scene.
In such cases you will have to desaturate the purple fringing color using the Advanced Color Editor in a local adjustment layer.
All the best,
The Image Quality Professor
The digital pioneer, Niels V. Knudsen, is Phase One’s Image Quality Professor and founder of the IQP blog. Moreover, he is responsible for breakthrough advancements in image quality both in Phase One’s medium format camera systems and in Capture One Pro.