Getting Rid of Magenta Fringe in Fine Detail

Discussion in 'Digital Darkroom' started by neil_poulsen|8, Dec 24, 2008.

  1. I have a problem with the edge effect that shows a magenta fringe on the edges or dark against white areas. This is really a problem when taking photos of trees against a light color sky. The tree's branches will have a magenta cast. Looks terrible.
    I don't think that this is a chromatic aberration problem. That has more to do with off axis locations when using wide-angle lenses. From what I've heard, it's a problem when a dark area is juxtapositioned directly next to a light area. e.g. trees against an overcast sky. It can occur with any lens, not just wide-angles.
    What's the best way of getting rid of this? Is there software designed to attack this problem? I know that this is a common problem.
  2. I'm sure there are better ways, but what sometimes works for me is to select magenta in "color, hue & saturation" in Photoshop and desaturate it. It turns it black which is less noticeable.
  3. This is called chromatic aberration and it effects different cameras, and different camera and lens combinations to different degrees from really pesky to not at all. For me it is the worst with a Canon EOS-1Ds Mark II and hasn't been a problem with the D3 /D3x /D700 except with a 28mm f/2.8 AI-S lens that I rarely use.

    What software are you using to process with? Are you shooting raws? Both Adobe Camera Raw for Photoshop CS4 (and probably CS3) and as used in Lightroom have controls to deal with it. In Lightroom I would first try going to the Detail pane in the Develop Module and try attacking it by using Defringe: Highlight Edges.
  4. As Ellis said, + you can use the chromatic aberation tool that will work perfectly im sure.
  5. It could be either chromatic abberration or "blooming." The former is a lens issue and the latter is a sensor issue that is visible when blown out areas are adjacent to darker areas - as with your branches against the sky. This is a very common issue.
    The first step to dealing with it is to try, to the extent possible, to avoid overexposing the sky or other bright area behind/next to the dark subjects. This is not always possible, but worth paying attention to. (With landscapes that include this you can try a graduated neutral density filter or combine multiple exposures.)
    The second step is to use the controls in your RAW conversion program or in Photoshop or equivalent that can adjust the offset between different color channels. In PS CS3 you can find this under Filter -> Distort -> Lens Correction. Use the abberration controls on this page while zoomed in to see if you can eliminate or minimize it.
    A third step if this doesn't either eliminate the problem or reduce it to the point where it is not noticeable is to do some further post-processing. (It is important to decide whether or not the artifacts will actually be visible in your final photograph. If not, spending a lot of time that is only visible at 100% magnification on the screen is not worthwhile.) There are several things you can try in post. You can try to use the magic wand to select the color areas and then desaturate them or alter their color. In some cases you can even desaturate the entire area enough to make the problem invisible. Sometimes you can use the clone stamp tool to replace the bad areas with similar material from elsewhere in your photography, etc.
  6. It does sound like chromatic aberration, but if you're using Adobe Camera Raw, try turning off noise reduction entirely.
  7. Post the a sample so we can see exactly what you're talking about. Since you already know what chromatic aberration looks like and you're sure this is not the issue, you need to post the image in question.
  8. Definately it could be CA, but check the depth of field also. I get it sometimes when the edges are getting just a bit soft and the "bokeh" becomes a fuz, somtimes purple tinged. Edge of the frame could be getting into the OOF area.
  9. As mentioned a post of an affected image would help to identify the problem. Another question: is this a digital camera image or a scanned film image?

    It might be blooming if it's a digicam image. Blooming in CCD sensors (camera, scanner or otherwise) is an inherent characteristic of this type of device and occurs when charge from intensely illuminated pixels spills over into adjacent pixels. So you will get bleeding from light areas into adjacent dark areas. Blooming can also occur in CCD scanner images but it will manifest itself in a different way and in my experience is never seen in a normally exposed scan.

    From your description it doesn't sound like CA. I think CA will generally be most visible at light/dark transitions and usually only at the edges of the image, but it sounds like you're getting this magenta cast right through the tree's branches and not just at the edge transitions. Another possibility might be diffraction if you're stopped right down, but without seeing the image it's hard to say.

    If it's blooming I think it would be tough to fix without a lot of hand retouching. The only thing I can add to what has already been suggested is to try either the burn tool or the desaturate tool in PS to manually attack the problem branches. It will be time-consuming but at least it won't affect the rest of the image.

    Of course there's always film, film doesn't bloom ;-)
  10. I sure appreciate everyone's responses.
    I'm pretty sure that it's a blooming issue. I've attached an example, which is pretty close to the center of the image. Actually, it's a crop area from a panarama that was made by combining three images side-by-side using Photo Merge. But, the fringing is the same in each of the original images.
    I'm really interested in the Defringe option in Lightroom that Ellis speaks about. I don't have Lightroom. But, if it can help this problem, it would be a good purchase for that reason alone.
    Note, I have a Kodak SLR/c which has no anti-aliasing screen. I really like this camera for many reasons, for it's excellent color and the resolution that I obtain. But, I suspect the lack of an anti-aliasing screen may increase the fringing that I speak about.

Share This Page