Help with "purple fringing?"

Ricesim · Feb 6, 2012

Hello,

I'll start by saying I am super new to photography =P. I was wandering if I could get some advice on what I think is called "purple fringing" or maybe "chromatic abbrasion"? I'm am still learning terms ect. so bare with me =). So basically I picked up the Canon EF 50mm f/1.4 USM lens a few days ago and decided to do some shooting with it one day during training. After importing the photos to Light room I knowticed this purple like glowing edges on a few of the shots. My question is what kind of techniques can I use to minimalize this effect, and are the terms I used in the beginning the proper name for it?

Just to clarify I shoot with a Canon 60D, and this shot was taken with the Canon EF 50mm f/1.4 USM lens (ZEIKOS 58mm UV filter installed) in Raw with AWB and Auto ISO on, and in Adobe RGB.

This is one of the shots I first noticed it in.

Shot stats: f/1.4 1/60sec ISO 250 -1 step exposure RAW

This is the blow up portion where I am noticing the discoloration

Thanks guys =) I look forward to your advice.

Ysarex · Feb 6, 2012

The correct term is chromatic aberration -- CA.

The "dreaded purple fringe" is also an acceptable name for it.

It's a function of the lens or rather a dysfunction of the lens. It's exacerbated in many cameras by a poor match between lens resolution and sensor resolution. It's hard to design a perfect lens but it's even harder to design a perfect lens any of us can afford. So every camera lens combination I've ever seen will exhibit CA to some degree under stressful circumstances. You want to hope that you're not plagued by it as severly as the typical consumer with a $289.00 16 megapixel compact fitted with an 18X super zoom.

You'll see it at frame edges and along bright/dark edges.

If you shoot RAW files it can be easy to remove CA almost if not entirely. CA correction is a core function of a RAW file converter.

If you have noticeable CA in a processed camera JPEG you can try Photoshop's Lens Correction dialog -- there's a removal option there but it doesn't function as well as the CA removal in a RAW converter.

Last option is to try manual removal. Again in Photoshop you can target the problem color -- magenta blue or cyan green or both in sequence as needed and then decrease saturation and brightness using the Hue/Saturation dialog. This may require doing a rough area selection first or a History brush recovery afterward to avoid changing similar colors that are affected.

Joe

Edit: I'm not a Lightroom user, but Adobe ACR in Photoshop should be the same and ACR has a Lens Correction function that works pretty well. You have a Canon Camera which means you got DPP with the camera. DPP does really well removing CA -- you'll find it under Lens aberration correction on the tool palette.

Robin Usagani · Feb 6, 2012

almost all lenses have that problem. Even if you buy the 50mm 1.2L! That is what happen when you shoot it with wide aperture and has significant contrast. I wouldnt worry too much about it. Easy to fix and you cant really see it unless you really zoom in/crop it.

tirediron · Feb 6, 2012

I would consider that pretty minor CA.

mjhoward · Feb 6, 2012

The first thing I would do is try shooting it without that UV filter. CA is something that can usually be fixed in post, but if you don't like to do that, then you can try stopping down or just try not to shoot very light objects against very dark backgrounds (or vice versa).

Joey_Ricard · Feb 6, 2012

With the example you've show us this is minor.
Although it bothers you, as it would me (just because it is there), my action towards it would be based on what the intention of the image is.
Display on the web, small print, large print etc.

In my landscapes, you see this on tree branches contrasting with the sky occasionally and because I think it is noticable, I correct it the best I can right away.

If you have a version of photoshop CS there should be a filter called "lens correction", I think it is in same folder as the blur filters. Here you can zoom in and change the hue of the CA to an extent. I usually do this on a separate layer and then mask it and only apply opacity to the affected area.

Ricesim · Feb 6, 2012

Thanks a bunch for all the advice guys. I'll load them up in Photoshop and see what I can do. I am horrible a PS but I'm trying to learn it. Unfortunately I can't take any classes for it in Korea, seeing as how I don't speak Korean lol. ::cheers::

DiskoJoe · Feb 6, 2012

If you have to zoom in that far before you can see anything you really dont have a problem. This is not even noticable in the original size.

Dao · Feb 6, 2012

The EOS Digital Photo Professional software that shipped with your camera can correct the CA issue for you automatically especially you are using the Canon EF lens.

480sparky · Feb 6, 2012

GIMP has a plug-in called Darla's Purple Fringe Fix.

analog.universe · Feb 6, 2012

The software CA correction in RAW converters is optimal for fixing lateral CA, which occurs side to side, and reasonably uniformly. It's predictable enough that an algorithmic removal works nearly perfectly. Purple fringing is usually a result of longitudinal CA, meaning stuff in front the focal plane gets purple and stuff behind gets green. (usually green fringing just blends in, so it's not a problem, but if you're getting purple, you're likely getting green somewhere too). Since the image software has no way of knowing what's in front of and behind the focal plane, a blanket whole image filter doesn't usually get it done. Usually what I do is select the offensive area and then pull the saturation way down on the magenta channel. This works pretty reliably, unless you've got other magenta in that area that you actually want to keep.

KmH · Feb 6, 2012

Ricesim said:
Thanks a bunch for all the advice guys. I'll load them up in Photoshop and see what I can do. I am horrible a PS but I'm trying to learn it. Unfortunately I can't take any classes for it in Korea, seeing as how I don't speak Korean lol. ::cheers::

Your Photoshop came with educational materials. To access those materials, open Photoshop. and in the Applications bar click on Help > Photoshop help. Or, with Photoshop open just press the keyboard's F1 key.

You don't say which version of Photoshop you have.