Removing Moiré Effectively
December 10, 2002
Recently I took the Advanced Color Correction course from Dan Margulis. If you haven’t seen his “Professional Photoshop” book before, check it out. Rather than relying on the “technology of the day”, Dan approaches color correction and image enhancement with time-tested, production oriented techniques. You can get a synopsis of his first course at www.ledet.com/margulis
I took along an image that I was having particular difficulty with. It was shot with a MegaVision S3Pro digital back mounted on a Horseman Digiflex with a Nikkor 105mm Micro. This is a very sharp lens, however with that sharpness comes the increased likelihood of moiré. I had a Powerbook that I was shooting to (with the Hotlink box - FireWire conversion for the S3Pro back), so I spotted the moiré and used a Caprock Re-Screener filter and adjusted my camera to subject distance. Although this approach worked and the moiré disappeared, my preferred shot was one of the earlier images with the moiré visible.
On the MegaVision users group (e-mug) we have discussed various techniques to reduce moiré in post capture. Color moiré is easy to deal with. Blur the color information and the problem goes away. This can be done either by blurring the “a” and “b” channels in Lab color, using “RGB Fixer” in MegaVision's PhotoShoot software, or using a plug-in such as “Moire Eraser” from Camera Bits. What do we do when there is luminance moiré? If you change your RGB image to Lab Color in Photoshop and view the “L” channel, you will see swirling patterns (as visible on page 8) that are seemingly impossible to fix. Full credit for the follow technique belongs to Dan. He still finds it difficult to believe this is a problem we see with any kind of regularity. I think he should come assist us for a day of photography. ;-)