How to eliminate purple fringing?

[john_wolf3]

Hi all. Is anyone aware of any program or plug-in that removes purple

fringing effectively and with reasonable efficiency (like not

spending hours on each image)?

Thanks

[nom]

Well, it's not so difficult to remove it with Photoshop anyway... The areas near the purple fringing are usually almost black and white, so most of the times I just select the area and just desaturate as much as needed. If there is more color information nearby then I desaturate only for the red.

 

But if someone has a better/easier way to do it I would also like to know of course.

[john_demott]

If your purple fringing is in fact caused by chromatic aberration in the lens (such as a wide angle lens), then one of the best solutions is the Debarrelizer plug-in available from the Imaging Factory. It is a shareware program with a 30 day trial.

 

In a lens that exhibits CA, the red, green and blue channels are displaced differently and the amount and direction of displacement depends on the distance and direction from the center of the image. The debarrelizer plug-in allows you to correct for this type of displacement (as well as correcting barrel or pincushion distortion if your lens suffers from either of those problems). It is fairly easy to use. Once you have determined appropriate correction factors for a particular lens, you can simply apply those factors to all images taken with the same lens.

 

By bringing the color channels back into registration, the colored fringes largely disappear and the sharpness of the image is also improved. If you simply select the purple fringe areas in Photoshop and then desaturate them you will eliminate the purple but you will still have fuzzy transitions in areas that should have sharp, high contrast edges. If you apply an unsharp mask filter to those fuzzy transitions, you can get some unattractive artifacts because the channel displacement still exists-it is just concealed by the desaturation. Debarrelizer greatly reduces those problems.

 

Panorama Tools has a freeware tool to do the same thing but it is difficult to use and only works on 8 bit files. Picture Window Pro also can correct CA, I think, but it is not a plug in; it is a complete editing program.

[gary_a._hill]

"Purple fringing" is not chromatic aberration, it is "blooming", a phenomenon of CCDs when they are over exposed.

[emre]

Maybe it is both?

<p>

<a href="http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=000ckk">How to remove chromatic aberration halos digitally ?</a><br>

<a href="http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=005nvy">Canon G5 purple �fringing�</a><br>

<a href="http://www.dpreview.com/learn/Glossary/Optical/Chromatic_Aberrations_01.htm">Chromatic Aberration</a> article on dpreview

[william_bloodworth]

If the image is from a camera using a standard bayer pattern color filter array, and the "fringing" is mostly diagonal, it is most likely color artifacts caused by the interpolation of the color data - insufficient color resolution. Typical digital cameras using bayer pattern color filter arrays have color resolutions disproportionate to the overall resolution - each photosite on the sensor senses only one color (red, green or blue). The color then has to be reconstructed via algorithm to produce RGB values for each site (pixel). The particular pattern of the bayer CFA makes purple artifacting most common, and mostly in rendering diagonal edges.

[neil_gundel1]

Here is a method that is new as far as I know - I just discovered it this evening. It is useful for removing the highly saturated purple glow that often occurs at the boundaries between very bright and very dark areas on a digital camera, and which does not respond to chromatic aberration correction.

 

The cure is based on the highly saturated purple color, which almost never occurs in nature. To isolate these areas, convert the image to LAB mode in Photoshop, where the saturated purple corresponds to bright areas in the A channel and dark areas in the B channel.

 

By doing a Image/Calculations and taking the difference between the A and B channels, loading that difference as a selection, you almost have the perfect selection to isolate the purple areas. Once the selection has been converted to a mask for a new hue/saturation adjustment layer, you need to do a curves adjustment to steepen the contrast in the layer mask so that only the very deeply saturated purple is removed. The effect is further limited by choosing only the purple colors in the hue/saturation layer.

 

This might sound complicated, but it's really very easy to do.

Even better, this recipe can be recorded in an action that seems to work nearly perfectly on every image I have tried it on.

 

If you want to try it, I copied my action into a set you can download.

 

This was recorded in Photoshop CS3 - I don't know which other versions it might work in, but here it is:

 

http://naturalportraits.com/purple_fringe.atn

 

Once you have downloaded this,(just paste the url into your browser)

just go to the actions pallete, and choose "Load Actions"

 

Thereafter, you can run this action on any single-layered image, or even as a batch on a whole folder of images.

 

If this does not pretty much completely eliminate the purple, you might need to play with the color range in the Hue/Saturation layer that I created. I created this to work with my Canon DSLR's & it's anyone's guess if it works as well for other brands/models. The easiest way to play with this, is to uncheck the last step in the action before running it. Then the Hue/Saturation layer and the mask will be intact, and you can play around with the slider on the "Magentas" adjustment until the fringe is gone.

 

Also, the final step converts back from LAB to the ProPhoto color space, which is my normal working colorspace. You might want to delete this step and record a new step that converts to your own normal color space instead (and choose "flatten" as the option).

 

Good luck!