View Full Version : Correction of Lateral Chromatic Aberration
Brian C. Miller
This weekend I was scanning some E6. The scene is of a spring waterfall runoff, and it has a zillion droplets splashing through the air. Unfortunately, all of the small droplets are essentially shifted from white to blue due to lateral chromatic aberration. (It's that fringe that's cyan on one side and magenta on the other, from an Epson scanner lens.)
Besides having Lenny drum scan the film, what can be done to eliminate or at least reduce it?
Is there a GIMP plugin? Or a plugin for Photoshop Elements?
Long time member,but I have not posted in a year .
ACR in CS5 has a LCA correction too. You might see if the ACR version in Elements has it. Light room has it also.
ACR may have to configured to have JPEG and TIFF files open in it, a functionality in CS5, maybe 4. Elements again ?
You do get something for the $700 PS costs. You can download a free trial from Adobe good for 30 days. It is fully functional. CS6 Beta is also out.
In any case you just move some sliders to fix the issue. If the problem is confined only to the water you will need a mask to isolate.
The version of Photoshop that I use (CS4) has chromatic aberration correction in the camera RAW import dialogue.
You can scan to DNG format using ViewScan or other scanning software and import to Photoshop via RAW. Then, in the sixth tab from the left, move the "defringe" sliders to clear up the image.
If only part of the image shows fringing, hold down the SHIFT key while clicking the "Open Image" button in the RAW import dialogue. This will open the image as a Smart Object. This will allow you to alter the RAW import settings on the fly by double clicking the icon in the "Layers" panel.
What you need to do is Right-Click or Control-Click the line in the layers panel for your image (Not the icon. The text.) then select "New Smart Object via Copy" from the popup menu that appears. The RAW dialogue will reappear. This time change the settings so that optimize the areas of concern in your image. When you click the "OK" button, you will have two layers containing the same base image, each with different importation settings.
Make sure the bottom layer has the settings for the overall image and see to it that the top layer has settings for the "problem" areas for your image.
Rename each layer to something that you can remember: "Overall" and "Fix Fringe" or something similar.
Next, using your selection tools (Magic Wand, Quick Select, Selection Brush, Quick Mask or Color Range Select) to select only the parts of the top (Fix Fringe) layer that you want to keep. Finally, using the "Layers > Layer Mask > Reveal Selection" menu choice, mask out the parts of the image that you DON'T want to have the correction applied. This will allow the bottom layer which you DON'T want to make the changes to show through.
Tweak the layer mask using the "Feather" slider or the "Refine Mask" feature in your "Mask" panel.
You can also make a very precise and re-editable layer mask using a "Vector Mask" if you are so inclined.
This technique is also good for correcting backlit or crushed/blown-out areas of an image.
Learn more about Smart Objects and techniques for using them from the book, "Adobe Photoshop for Photographers" by Martin Evening.
The book is available on-line at: http://www.photoshopforphotographers.com/
It is a very worthwhile book to own if you are serious about Photoshop. I keep mine in the place of highest honor for my book collection: The bathroom! ;)
You can correct CA with PTLens: http://epaperpress.com/ptlens/index.html
You can run it as a stand alone and as a plug in with Photoshop, Elements and PhotoLine.
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