Fighting "Purple mould"
Some of the best lenses I own, though being fast and having other good specs, produce terrible purple fringing on my DSLR. Because of that reason some shots were rejected by photostocks. Available tools like AdobeCameraRaw didn't help either. I think some photographers may also suffer from this problem, so I decided to publish this tutorial.
First, let's make two layer duplicates:
Apply Find Edges to the topmost layer, then duplicate it and change the overlay mode of the duplicate (fourth layer) to 'screen', so that we can select only contrasty edges:
Now we can merge two upper layers. After that choose 'Select > Color Range'. In the opened window choose «Highlights» in the list and tick the «Invert» option
Now we need to feather the selection a little bit, it depends on image resolution and the degree of purple fringing. In this case I chose 'Select > Feather > 2 pixels'. By the way, now we can delete the upper layer, which was only needed to make temporary mask. Now go to 'Image > Adjustments > Hue/Saturation', move the 'Saturation' to 0 and select 'Magentas' in the pull-down list. It may be necessary to zoom in the area containing chromatic aberrations and to correct the unwanted colors with the levers over the color strips. You can also use the eyedropper tool to select color range. After that, if needed, desaturate other unwanted colors. In my case I chose 'Yellows' and pushed the saturation down for about 70 percent.
You can completely desaturate the selection, but in that case there's a possibility of getting unwanted artifacts. If You successfully removed the color fringe, You can remove the selection (Select>Deselect) and change the upper layer mode to 'Saturation'.
If You're satisfied with the result, the layers can be merged.
In my opinion, the described method is more effective than removing the purple fringe by just using 'Sponge Tool' in Desaturate-mode, although this tool also can be used. It's also possible to use the described process in batch mode if You create a corresponding action. It's only necessary to pick up the needed parameters, especially when using 'Hue/Saturation', because the used lens/camera plays a big role here.
Finally, photos that were changed with the help of described technique were accepted by photostocks. I hope that this tutorial might be helpful to You, because it can be sad, if the photographic masterpiece is impaired by "purple mould".
