Chromatic Errors, and how to get rid of them

The other day a friend dropped by and showed me the latest photos of her trip to Dublin. It was a nice trip with some sunshine, the perfect starting point for good photos. She handed over her point-and-shoot camera, a tiny 3 Megapixel Fuji camera, and I flipped through the images, stopping here and there for a closer look, and admiring some of the places I had been to before (it’s funny how some areas do not change in years). Her images were certainly of a high quality, many of them nicely composed and well exposed.

Then she asked what I would think about Canon’s 40D? I replied that this would definitely help her to create technically better photos, and that it should be a big leap towards better photography for her. I was trying to be polite and said that her pictures already look good given the limitations of her current camera. She looked at me, puzzled, and said: “What do you mean – ‘limitations’? Everyone loves my shots, even when they come from that tiny P&S camera”. I replied that this may be so, but the technical quality of her shots is just, well, pixel crap. Beautiful shots, that can not be enlarged to anything beyond 6″x8″, at least not when expecting high quality prints.

Ah. I shouldn’t have said that. She demanded proof. She did not believe that her photos were really that bad. And I presented her proof by zooming into the photos she had already uploaded to her PC. I told her what to look for (strange color seams, usually in high contrast areas of the picture) and where (usually close to the image borders). When going through image after image on her hard disk, she could not believe what she saw.

Here’s one example from my tiny Sony Cybershot DSC P-72 (which I have trashed recently as I did not use it any longer):

Copenhagen/Denmark, by Mark Zanzig
Mark Zanzig/zettpress

Chromatic Errors Example

When looking for those color seams you need to really go close, i.e. at least 100% view in Photoshop (or your image editing software). In this example, you clearly see the yellow border on the left side of the tower, and a purple border on its right side. Also note the dark blue border in the lower left corner of the cutout. Believe me, these borders were not there. Not in Copenhagen, Denmark. Not when I did this shot back in February 2005. And I guess you won’t find these borders today. :-) But you see them in the image, because the lens was really bad, and the software of the camera could not correct the problem (at least not good enough).

But wait – isn’t this just a problem of cheap point-and-shoot cameras? No. The problem appears also with professional equipment. Take a look at another example, a RAW photo file from my Canon 1ds mark II and the beautiful EF 16-35/2.8L wide angle lens:

Munich Nymphenburg Castle
Mark Zanzig/zettpress

Example for Chromatic Error
Close up, showing chromatic errors in the left area of the image

Uh. Can this be true? You spend $$$$ on a professional camera and lens and get such pixel garbage in return? Actually, yes. The physical problems of a 35mm wide angle lens are still visible, even when it is a very good lens, and a very good camera. Also, please remember that the cutout represents just about 0.8% of the total image (133,952 of 16,613,376 pixels), so the problem might only become visible when doing large high-end prints. But anyway, it makes the photo look bad.

But fortunately, Adobe Photoshop Lightroom comes for rescue!

Here’s what to do: import the RAW file to Lightroom, then switch to “Develop” mode. Scroll down for the lens corrections section (on the right hand side), and there you will find the tool that deals with this problem. Quickly, and effortlessly:

Adobe Photoshop Lightroom Lens Correction

Just toy around with the controls for Red/Cyan and Blue/Yellow to see the effect. I find that it works best to use the control that matches the color seams in the image, i.e. when you see a red and/or cyan seam, use the Red/Cyan control; when you see a blue and/or yellow seam, you use the Blue/Yellow control.

The result is pretty impressing:

Chromatic Errors corrected by Lightroom

The visible chromatic errors have now been corrected; there are no seams to be seen anywhere in this section. The walls now look as they are in reality: a light grey, with bright white borders and all shades of grey within the windows.

Neat.

3 Responses to “Chromatic Errors, and how to get rid of them”

  1. Richard Wong says:

    Great article Mark. Chromatic aberation is one of my top pet peeves because I see so many images published with it in there. Many people either don’t notice it, or don’t know what to do about it. Some lenses are easier to correct than others. I can eliminate it almost 100% of the time w/ my Tamron 17-35, but some other lenses is so severe that its impossible to get rid of it all.

  2. Peer says:

    This also seems to go in the same direction: http://www.digikam.org/drupal/node/319

  3. Martina says:

    These are all nice pictures. I like this place.