Occasionally I run across photoshop tips that are extremely useful, and for which I have an immediate need. Since Photoshop has about 1 million tips out there, it is hard to keep track of the particular ones you have used. I have decided I will be storing them in my blog for future reference. Perhaps someone reading this will also find this helpful. This particular problem I encounter occasionally when scanning slides, which could be the sign of my aging Poloarid SS4000 film-scanner. Particularly in scanning my recent underwater slides, a couple of images had bad cases of chromatic aberrations (color fringing, typically in high contrast area where colors are focused differently). The tip below was particularly effective in eliminating this optical defect. As with all things Photoshop, there are many ways to get at the same result, I just found this one worked well for this case.

1. Convert to 16-bit mode if you aren’t already.
2. Convert the image to LAB mode.
3. Select the A and B channels, by clicking on A in the Channels palette, then shift-clicking B. You should see a rather weird rendering of your image with everything at 50% luminance, but the color fringes should be clearly visible.
4. Run the Dust & Scratches filter at whatever settings are necessary to get rid of the color fringes.
5. Go back to the Channels palette and select LAB channel.
6. Go to the History palette and select the bottom (last) history state as the source for the History Brush. (Look for the little box on the left of the history state, and click it to make a little brush icon appear.)
7. Select the next-to-last history state, which will undo the effect of the Dust & Scratches filter.
8. Using the History brush, paint out all of the objectionable color fringes in the image.

Sample image correction: