Removing Moiré Effectively
June 12, 2005
The original tutorial on removing moiré has been mentioned in a number of places on the web and I'm glad it has been of help to so many people. If you are looking for the full story on how this technique came about, the main "techniques" page still has that version of the tutorial.
With the appearance of Photoshop CS, there was a new blurring filter that was of particular use for this technique. You can find it under Filter>Blur>Average. If you are using Photoshop CS2, it is located in the same group of filters. It has helped simplify the technique and since so many non-MegaVision users have found the tutorial helpful, I have revised it to work with a standard copy of Photoshop - no plug-ins required!
There are a number of great sources on the web that discuss the effect of moiré. I will not delve into it further. I happen to use a medium format digital back so I encounter moiré on a regular basis. One of the attractive features of nearly all DSLR's is that they have an integral low pass or anti-aliasing filter. While it helps minimize the occurrence of moiré, it also means a sacrifice in sharpness that can never be fully compensated for. As with anything, you pick the best tool for the job.
By converting your image to Lab color (Image>Mode>Lab), you can inspect the three channels for moiré. If there is moiré in the Lightness channel, then you need the following technique. If there is only moiré in the "a" and "b" channels, then the first step is all that is required.