How to fix Purple Fringing

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When capturing objects with a very high local contrast, you often get a halo of purple/reddish colors along the contrast edges. See how the Professor removes this optical artifact known as purple fringing.

 

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.

Tip728-img1                       Purple fringing                                 Purple fringing fixed in Capture One Pro 7

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 ‚ÄúPurple fringing‚ÄĚ 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 ‚ÄúPurple fringing‚ÄĚ.

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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:

Tip728 img4V2                Original                                Simple desaturation                  Capture One Lens Tool

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.

Tip728 img5              Original showing purple fringing                     Fringing removed in Capture One Pro 7

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.

Another example:

Tip728-img4            Original with strong purple fringing                  Fringing removed in Capture One Pro 7

The ‚ÄúPurple Fringing‚ÄĚ 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,

Niels

The Image Quality Professor

Niels V. Knudsen

Niels V. Knudsen is Phase One’s Image Quality Professor. He is responsible for breakthrough advancements in image quality both in Phase One’s medium format camera systems and in its digital imaging software.

7 thoughts on “How to fix Purple Fringing

  1. Theo

    Hello Niels,
    This is fantastic! Thanks a lot for posting this solution. The combination of the purple fringing correction and the desaturation in the advanced color editor has removed all undesired fringing wthout losing any sharpness. Thanks a lot!

    Reply
    1. The Image Quality Professor Post author

      Hi Theo,

      Thanks for your comment. Glad that it was helpful.

      All the best,
      Niels

      Reply
      1. The Image Quality Professor Post author

        Hi all,

        We’ve been experiencing some issues with the blog in the last couple of days. Unfortunatly it has not been possible to leave any comments. But the issue has been resolved now, so if you haven’t seen your comment/question posted, please repost it and I’ll reply as quickly as I can.

        Have a nice Sunday everyone.

        All the best,
        Niels

        Reply
  2. Reto Hadorn

    Hello Niels,

    I am one of those who did write their comment too early…

    I would appreciate if you could explain why we get purple and turkis fringing with CA and only purple fringing with… purple fringing. For now, I was only aware of CA and appreciate the efficiency of C1′s removal tool.

    Why is purple fringing not covered by CA removal?

    Thanks in advance

    Reto

    Reply
    1. The Image Quality Professor Post author

      Hi Reto,

      The Chromatic Aberration, that automatically gets removed when using a Lens profile in Capture One, deals with the type of Chromatic Aberration originating from the problem that the focal length of a lens is depending on the wavelength of the light.
      When this is the case the magnification of the R, G and B plane in the image are not the same, resulting in slightly misalignments of the color planes. The different magnifications can be measured and to fix the problem you basically apply individual magnification corrections to each color plane.

      Even though that Purple Fringing is related, the problem of the lens acting a little different depending on the wavelength of light is something you cannot correct by simple means. Our advanced Purple Fringing algorithm needs to analyze the image for the fringing color and verify that it actually is caused by fringing and not just a color that naturally exist in the image. When working with such algorithms there will always be a tiny risk that the algorithm tries to remove colors, it shouldn’t have removed.

      All the best,
      Niels

      Reply
    1. The Image Quality Professor Post author

      Hi Tom,

      I’m glad that it was helpful.

      All the best,
      Niels

      Reply

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