A comment on one of my shots (shown here on the left) made me look into a problem this picture shows. This picture is taken with the cheap kit lens on my DSLR. Not exactly the best lens in the world. Now take a look at the right side of the picture. I think you’ll notice the problem immediately. The effect you see here is called chromatic aberration.
You’ll see it better in the cutout here on the right. Chromatic aberration stems from the fact that light is composed of all the colors of the rainbow and everything in between. When the light passes through a lens not all colors are refracted the same, meaning not all colors will focus in the same spot. This leaves you with a blue fringe (in this case) right where there is a big difference in contrast, like in this window. In this HDR picture the effect is even worse than in a “normal” picture.
Now, how to solve this? Normally I use Photoshop Lightroom to directly export the RAW files to Photomatix to create the HDR. Nothing in that workflow would be able to reduce the effect. Then, as by accident, I came across the HDR Cookbook by another Flickr user called Farbspiel (he commented on the picture above too, so it was very accidental ;)!). One part of his cookbook talks about how to reduce chromatic aberration, so I decided to give it a try. Farbspiel recommends opening the RAW files first in Adobe Raw Converter, reducing the chromatic aberration there, and then save the files as TIFFs. After you’ve done that, startup Photomatix, open the TIFFs and do your HDR magic, and save the resulting file again as a TIFF. Now you can edit this tonemapped picture in Photoshop to your needs.
The result was stunning. You can see it here on the left. The chromatic aberration was not completely gone, but I blame the cheap lens. I did some more work in Photoshop to reduce the blue fringe and I also made some other decisions in the tonemapping, so the picture looks a bit different, but overall I’m quite pleased. What’s do you think?