Photoshop Processing Techniques for Improving Your Prints Part 1: Chromatic Aberration

4 Feb

Chromatic aberration is one of those naturally occurring, technical imperfections of your camera lens that can take your favorite photograph and moderately reduce its overall quality if not handled properly. What is chromatic aberration? Well, you may or may not be familiar with the term although if you’ve looked at enough photographs I guarantee that you’ve seen it before, even if you didn’t notice it. Wikipedia defines it this way…

“Chromatic aberration manifests itself as “fringes” of color along boundaries that separate dark and bright parts of the image, because each color in the optical spectrum cannot be focused at a single common point. Since the focal length f of a lens is dependent on the refractive index n, different wavelengths of light will be focused on different positions.” (http://en.wikipedia.org/wiki/Chromatic_aberration)

OK that’s pretty technical. Without getting too convoluted, I define chromatic aberration as color fringing that usually occurs around objects as magenta, blue, red or green outlines or highlights. Chromatic aberration basically occurs from a combination of light, subject matter, aperture selection, and lens quality. It is mostly noticeable in the background of images along horizons and is especially noticeable in mountain scenes captured during the daytime where minor patches of snow are evident.  In some photographs, a small amount of chromatic aberration is acceptable and is usually an easy fix in Adobe Camera Raw or in Photoshop with just the click of a button or the movement of a slider.

Where fixing this problem gets tricky is if there is quite a bit of chromatic aberration that appears in different colors or if you are a perfectionist like I am. Before we get ahead of ourselves let’s quickly discuss how Photoshop or ACR fixes this problem. From how I understand it, what the software actually does is it picks up your image and moves it slightly so that it covers the areas of fringing. However, this isn’t a local selection – it is actually a ubiquitously occurring process in that it moves the entire picture so all areas of your image are affected. The problem with this is that it affects the overall image quality because there is a minor loss of resolution every time this movement is performed. Secondly, the image shift depends on the color so fixing a magenta color fringe won’t necessarily rectify a red one and vice versa. In that particular case, using the software results in a compromise where the color fringing effects can be offset and reduced, but not completely fixed.

Let’s look at an example at how I circumvented both of these issues.  Do you notice the bluish-green fringing around the flowers in the before image below?

Before

Before

After

After

What you are looking at is a small portion of an image that was commissioned by a local bank in Colorado to use for the front of their 2013 calendar. Because the image was being used at approximately 8.5 x 11 for mass distribution I wanted to make it look as good as possible. This was a small fix and it can be a little time consuming. However, if delivering the highest quality product to your clients is must for you (like it is for me) then it is worth the time.  I find the easiest way to fix this problem is with the color replacement tool in Photoshop. In this case, I simply use the color of the flower petals or a neutral grey and trace away the noticeable effects of the chromatic aberration with the color replacement tool. The most important aspect of this method unlike other quick fixes is that it does not sacrifice image quality or resolution. Conversely, it actually makes your image higher quality! I hope you found this post helpful I’d love to read your comments or questions regarding it! My goal is to follow up this post with another blog about Photoshop techniques in the near future.

2 Responses to “Photoshop Processing Techniques for Improving Your Prints Part 1: Chromatic Aberration”

  1. John March 14, 2013 at 5:38 pm #

    This is nicely written and the last paragraph is good for those that have to put a very good picture in a limited space. Your Colorado calendar is superb. I never saw the flowers so close up but you capture this very nicely. Keep up the good work!

    • wildmoments March 16, 2013 at 11:10 pm #

      Thanks John – I am glad you enjoyed my article. I am also glad you saw my calendar. Do you live in Colorado? Thanks again!

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