Here we are again face to face with the exacerbating chromatic aberration. It is a color noise in fact – so let’s get rid of it.
Load the photo in Paint Shop Pro
If possible choose one with an annoying color noise. How to detect color noise? It is very simple: most often it is present in the form of purple-cyanide color borders at the edges and corners of a photo. In case of digital photos the defect can be just a purplish discoloration around objects with high contrast difference. This can be observed mainly at the meeting of the sky and another item on the photo, such as the edge of a building or the foliage of trees.
In the sample photo we have cut out a part where the purplish discoloration can be clearly seen around the edges of the foliage (cyanide on the other side).
When time is short
If time’s pressing and you have this kind of color noise (that is the problem arises from the discoloration along borders with high contrast difference, then you can apply the one-step elimination. Choose Adjust/One Step Purple Fringe Fix menu. Fixing takes a pretty long time if the picture is bigger.
Of course, this method is not perfect, just like any autocorrection. It tries to spot the unfitting parts and colors automatically, which is not always successful. The left picture above shows the original state while the right one is the result of the one-step fixing. It can be seen that most of the purplish discoloration is gone, however, not all of it. At the same time some breaks and fading arose too. For example, you can detect a white patch on the right side at the bottom, which is because the software washed out not just the purples here but the blue of the sky as well.
Down with aberration!
The more apparent, optical chromatic aberration (a color noise) should be removed with another method instead. Its menu can be found under the previous menu, under Adjust/Chromatic Aberration Removal.
It opens the window shown above. At the top of the window you can se the usual original state (Before) and the result (After). Their size can be adjusted with Zoom value at the bottom and the two icons on its right. Before/After windows have another role apart from providing preview. After clicking on Pan under Before/After, drag the selection marquee in the appearing window to select which parts of the photo should be shown in the preview. Here it is only useful to select the parts with color noise. Once you have set these, click with the left mouse button in the Before window and drag it over the problematic area and draw a square. This will serve as the sample area, whose average color will appear as Sample 1 in the middle section of the window. Several samples can be selected and they all will each appear under Sample (with a growing number). Rangewindow shows the average color range of the color noise samples. The first thing to do is to find the color noises in the picture and select the typical areas. 2-3 sample areas will be sufficient. With each area the software re-calculates the color range. If you wish to delete a sample just click on its name and then click on Remove in the bottom-right corner of the window.
The width of the fringe with color noise can be set on the bottom of the window at Radius. This defines the size to be fixed. This is rarely more than 5-10 pixels. Under this check Show Differencesmarker and the Before window will show the mask of the faulty area only. If you check Result on new layer option, the modified picture appears on a new layer. This comes really handy when filtering was too much and you would like to take back a little from the effect. In such a case the modified new layer can be mixed with the original one under it by decreasing opacity of the upper layer (Layers palette, Opacity slider).
Finally, there’s a Color Range adjustment option on the bottom right side of the window. This influences the sample color range, which means that it affects the scope of removal too. When set low, the purple-greenish discolorations will be faded only mildly, while when set high they will be more powerfully removed.
Selecting the scope
We took a sample of the problematic foliage, set Radius to 5 and Color Range to 40. The purplish discoloration of the edges is almost completely gone in the end-result. However, the edges of the foliage are a bit greenish now. Luckily this is not really annoying, and so we can say that our activity was successful. If you are more meticulous and apply the above-mentioned double-layer method, you can achieve even more satisfactory results. You might as well say goodbye to color noise completely without any drawbacks.