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An extensive look at moir patterns, Part 2: Reduce moir patterns in digital photographs

Added on Thursday 22nd of May 2008 07:24 am EST
 
Application:
Adobe Photoshop CS/CS2/CS3
Operating Systems:
Microsoft Windows, Macintosh


While moiré patterns often appear after scanning, they can sneak into your digital photos as well. Arm yourself with these defense mechanisms to improve your digital image quality and reduce digital interference.

To help you eliminate moiré-pattern mishaps in digital photos, we’ll:
 

  • Explain what causes a moiré pattern to appear in a digital photo.
  • Provide you with some photography tips to reduce the possibility of moiré patterns appearing in your digital photos.
  • Show you a few different Photoshop techniques that will help you eliminate—or at least reduce—moiré patterns from digital photos.

In the previous issue of Inside Photoshop, we began an extensive look at moiré patterns. We discussed what moiré patterns are, what causes them, and how you get rid of them. We focused primarily on moiré patterns in scanned images. However, you’ll likely notice an occasional moiré pattern, like the one shown in Figure A, creep into your digital photos as well. So what causes this phenomenon in your digital photos and how can you get rid of it? Let’s take a closer look and find out.


A
Can you magnify a section of the guys suit where moiré is strong?

Why moiré patterns appear in digital photographs
When dealing with digital photos, moiré patterns appear primarily because of line interference between the photo subject and the grid pattern on the digital camera’s sensor. Also, digital cameras that shoot lower-resolution images without anti-aliasing filters are more prone to capturing pictures with moiré patterns than cameras with built-in anti-aliasing filters that can shoot at higher resolutions.

Avoid moiré patterns when shooting digital photos
When taking digital photos, there are certain techniques you can apply to reduce or prevent these annoying moiré patterns from appearing. If you see a moiré pattern when you’re previewing your photo, these techniques may help:
  • Move the camera back or forward a couple of inches. Occasionally, this will fix the problem or at least lessen it.
  • Decrease the depth of field. The less you have in focus, the less apt it is for a moiré pattern to appear.
  • Hold your camera at a slight angle.
  • Take multiple shots of the same subject from slightly differing angles. You may notice the moiré pattern doesn’t appear in the same place in each image, allowing you to piece the good portions of the various images together in Photoshop.

Remove moiré patterns from digital photos
One of the best ways to eliminate moiré patterns from digital photos is to switch to Lab color mode and make a few image adjustments. To show you how it’s done, download the image moire.zip from the URL given at the beginning of this article, and extract the file moire.jpeg. Then, launch Photoshop and open the file. As shown in Figure A, there is a very intense moiré pattern in the man’s suit, which we’ll show you how to fix.

To remove moiré patterns in Lab color mode:
  1. Choose Image > Mode > Lab Color to convert the image to Lab color mode.
  2. Select channel a in the Channels palette (Window > Channels), as shown in Figure B.
  3. ...