Use RAW Processing, Photoshop to remove those pesky chromatic aberrations
You've tried soaking them out and scrubbing them out. But you still get color fringing on the collar...and on other high-contrast transition areas of your digital photos. Here's how to whisk them away!
Here's a recipe for great images...but a color fringing disaster: I enjoy shooting wildlife, but it can be hard to find subjects that don’t need a long focal length. My “long glass” is limited to the Canon 70-200mm f/2.8 IL USM and the Canon 300mm f/4L. That means I often use a 1.4x or 2x tele-extender or (often called a teleconverter). But that still doesn’t give me a lot of magnification for the full-fame Canon 5D series I have used for several years (currently the Canon EOS-5D Mark III) so I often need to crop images significantly. That means I want to maximize image quality in every way possible. And that's where the trouble starts.
When using zoom lenses, even without a tele-extender, I can get an image that shows chromatic aberration, which is a color fringing at the transition from bright to dark areas. Color fringing tends to be worse when using less expensive lenses. This is also a common problem with wide-angle lenses, and with less-expensive lenses. It is less of a problem with Canon’s pro lenses, and it is further minimized by the newest II series lenses matched with the new III series tele-extenders. But it can show up in many images.
The fringe will be red-cyan, blue-yellow, or green-magenta, with the opposite colors on opposite sides of the bright object. Sometimes only one color of the pair will be noticeable and sometimes you will even see a mixture of two pairs.
Below is an example of the edge of a dogwood blossom taken with my Canon 24-70mm f/2.8L lens. This is one of Canon’s two mainstay pro lenses (along with the Canon 70-200mm f/2.8L) and it’s optical quality is excellent, but the artifact in this case is definitely noticeable. I have cropped the image considerably so it is easily seen here. Some people would feel it isn’t an important problem on the full image, but it is so easily corrected in recent versions of Lightroom and Adobe Camera Raw that doing so is, for me, a no-brainer. Edge effects such as this degrade the appearance of sharpness. It can also be corrected in Adobe Photoshop, but I prefer to deal with it and other lens corrections as early in processing as possible.
In this example there is a blue fringe along the left edge of the petal, shown in the left panel.
The correction is easy in Lightroom and Adobe Camera Raw. I’m using the newest versions, Lightroom 4 and Adobe Camera Raw 7, the version that accompanies Photoshop CS6. But similar corrections are available in Lightroom 3 and in the previous version of Adobe Camera Raw that accompanies Photoshop CS5.
In Lightroom 4, go to the Develop module and then the Lens Corrections panel. Click the Color tab and check the box for Remove Chromatic Aberration. In the earlier Photoshop CS5 and Lightroom 3, this correction appeared on the same dialog page as the other lens correction options, but the other options may be something you don’t need to do on many images. They are of most importance on architectural or structural images where perspective may need correcting and where pincushion or barrel distortion may be an issue. Those latter problems are characteristic of zoom lenses and cause horizontal and vertical lines to pinch in or bulge out near the edges of the frame. Generally, a zoom lens will manifest both distortions at different ends of the zoom range.
Here is the Lens Corrections panel in Lightroom 4. Click the Color tab for the Chromatic Aberration correction:
Or in Adobe Camera Raw 7 the Lens Correction tab is found here:
Sometimes the correction isn’t perfect. In some cases you may wish to make a further correction with a masked Hue and Saturation layer. Go to Layer > New Adjustment Layer > Hue and Saturation, and desaturate the appropriate colors in the dropdown list at the top to hide the color fringe. Never mind that this will make the rest of the image look awful.
Then hold the Alt key and click the mask icon at the bottom of the Layers panel; the one that shows a rectangle with a circle inside it. This will put an all black mask on the layer, blocking its effect everywhere. Hit the D key to set the default foreground color and then hit the X key to switch it to white. Choose a small brush and paint over the edges that show the problem color, to reveal the saturation adjustment in only those areas.
Alternatively, you can paint a quick mask over the problem areas and use it to create a masked Hue and Saturation adjustment layer. See my quick mask tutorial. Or there is always the option of some careful cloning.
A similar problem occurred for me recently when I photographed the annular solar eclipse (using a special solar filter designed for that purpose). The shots showed some chromatic aberration at a 100 percent view. Here’s a before and after with the before shown on the left. The aberration is seen on the left edge of the sun. The amount of cleanup is slight but it’s so easy, why not do it.
I shot images every 5 minutes as the moon moved across the sun and it was easy to batch this correction for all the images in Lightroom.
I’m glad it was easy because for the nine minutes it took the sun to move across my frame surrounding “totality”, I shot 1600 frames, in burst mode at 3 frames per second, to compile into a time lapse video. In Lightroom’s Develop module I selected the first image in the filmstrip, did the correction, then selected all the rest of the images (Edit > Select All) and clicked the Sync button.
I shoot RAW images 99.9 percent of the time, but in this case I had to shoot JPEGs in order to be able to write the files to the card at my Canon 5D Mark III’s “slow” burst rate of 3 frames/sec without filling the buffer. But the correction worked well for the JPEGs.
This might be a slightly unusual case, but the technique is something I often find useful.
And speaking of shooting the sun, mark your calendars: on August 21, 2017, a total solar eclipse will be visible across the country on a line from South Carolina to Oregon, with a partial eclipse visible in a much wider swath. An Internet search will turn up details.
You don’t need a filter to photograph (or look at) the fully eclipsed sun, but to shoot the partial phases check out the solar filters at www.thousandoaksoptical.com. I used a simple and relatively inexpensive sheet of Mylar solar filter material, stretched over the front of my lens and taped in place.