Removing color defects (chromatic aberration) I. in Photoshop

Color defects can often be very eye-catching on digital photos. They can be inadvertently caused by the optics (chromatic aberration) or electronically by the image sensor (purple fringing). Now we’ll explain the simplest method to decrease or remove this annoying phenomenon.

(photo detail)

No doubt, this annoying purplish phenomenon is a color defect.
The following procedure is effective when the picture only contains a small amount (or none) of purple-related hues.

If other areas of the image-e.g. a purple flower or someone dressed in purple-contain the same or a similar color, choose the Polygonal Lasso Tool (press L) for selection. The red arrow shows its icon on the left-side toolbar.

With the tool, simply select the area around the color defect. You needn’t be very accurate. Click a place where you want to start the selection. Click another place and the tool connects the two points. Click several more times to create a fence around the area you want to correct. Click the starting point again to finish the selection.
The marquee can extend over the edges of the photo, as you can only change the content within the image.

Photoshop will also leave unselected areas unchanged.

After selecting the area, zoom the image on the Navigator panel on the upper right to make your task easier. By using a 500% zoom, the purple stains will be easy to handle. Click Image/Adjustments/Replace Color in the menu to display the Replace Color dialog. Now you can select one or more colors and set their properties individually. By now you must have guessed that we’ll be using this dialog to reduce the purplish discoloration.

Let’s take a look at the settings this dialog offers.
Fuzziness can be set between 0 and 200 and controls the extent the changes will effect the selected color and the hues related to it. Values close to 0 mean only hues most closely related to the selected color are affected, while values around 200 make the changes include more distant relatives (e.g., blueish hues for purple). The extent of changes can be seen on the preview image, if you have chosen the Selection radio button.

You can make the actual changes under Transform. Hue lets you pick the color you want to use instead of the selected one. Saturation controls color saturation: -100 fades colors out, while +100 gives extra saturation. With Lightness, you can make the color lighter or darker.
You’ll find 3 eyedroppers on the right, the first one being active as a default. This icon is for picking the color you need. The eyedropper with a ‘+’ sign lets you specify additional colors, while the icon with the ‘-‘ is for removing one.

Take the first eyedropper above the previously zoomed photo and click an area where the color defect is strong. The color chosen for modifications (in this case, the color of the aberration) is now purple. We’ve used a medium value for Fuzziness, That is, about 100, which is usually appropriate. Most of the time, 200 leads to the application selecting too many colors. Set the value so that, on the preview picture, only the aberration’s colors shine white.

As in our picture the defect shows in the foliage of a tree, we want to see green leaves instead of purple. Set Hue to show a greenish color. Never mind if it is lighter or more saturated, just aim for a greenish one.

If Preview is selected, you can check the changes on the original photo. It is strongly recommended to select this check box!
Now set Lightness so that the changed color has an appropriate brightness. In our example we got a very bright green, so we have set Lightness to a value of -18.
Finally, set Saturation according to your liking. In the example, the green area to change is rather saturated, so we set it back strongly, to -73. If additional unwanted colors remain, choose the eyedropper with the ‘+’ sign to include them in the changes. In the sample picture, there were some blueish discolorations after removing the purple ones, so we made them vanish, too.

If you’re satisfied with the result, click OK. Finally, click somewhere outside the marquee to cancel the selection.

The result:

before / after