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Correcting Color Fringes (Lateral Chromatic Aberration)
2005 KenRockwell.com

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INTRODUCTION

This is trivial with Photoshop CS2 because Adobe includes a filter for this. It's tougher in earlier versions of Photoshop since you have to go buy a filter or do some clever gyrations.

It works with any image, digital or scanned film.

Photoshop CS2

In Photoshop CS2 use the Lens Distortion Correction filter.

Choose: FILTER > DISTORT > LENS CORRECTION which gives you a new window with a preview and control sliders.

In the Chromatic Aberration box (towards the top) just move the two sliders until your image looks great.

Unfortunately Adobe got it wrong because these sliders correct the wrong colors. The correct sliders would be green/magenta and blue/red, since these are the colors one gets in photography due to secondary and primary lateral chromatic aberration. Adobe instead gives red/cyan and blue/yellow sliders.

Trick: These filters move pixels around in subpixel increments for exact results. You sometimes can lose a little resolution in the process of these mathematical gyrations. If you worry about this you can prevent mathematical losses by upsampling the image by a factor of two or some other integer, apply the filter and then downsample it to the same size. You change the image size under IMAGE > IMAGE SIZE. Double the DPI before the filter and then return it afterwards. This will slow down the process and can give slightly better results.

Versions before Photoshop CS2:

You'll have to try a third-party plug-in, or the RAW import converter if you have RAW images.

Good luck, this aberration doesn't bother me. I'd probably just paint over the aberration with the history brush to desaturate them if I needed to correct this!

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