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Three Ways to Fight Moiré

Three Ways to Fight Moiré
Have you ever encountered a strange pattern that seemingly appears out of nowhere and ruins your digital pictures? This is called moiré. It’s the kind of thing that sometimes shows up in intricately woven fabrics or other fine patterns. It appears when two patterns—such as the weaving in a suit jacket and the pixels on a digital SLR’s sensor—don’t quite line up. When they’re close but not exact, they overlap in a strange way that creates the appearance of a third pattern, as evidenced in the illustration shown here. The two sets of thin lines are exactly the same, but rotated slightly they create a third set of wide, dark lines where the patterns intersect. This is moiré.

Now that you know what moiré looks like, how do you fix it? Here are three simple approaches to prevent this distracting pattern from ruining your pictures.

1. Stop it before it starts. If you’re photographing someone in a business suit, for instance, or any clothing with a finely woven pattern, pay extra special attention. You’re not likely to see moiré through the viewfinder, but you can often spot it upon LCD review. Zoom in on the image on the rear of the camera to check for moiré. If you find it, you’ll want to move closer or farther from the subject in order to change the ratio between the two interfering patterns. If you’re 5 feet from a subject and you spot moiré, move up to4 feet or back to 6 feet and that interference is likely to disappear. Like so many things, an ounce of prevention is worth a pound of cure. If you can stop it before it starts, you’ll save yourself a tricky post-production repair.

Three Ways to Fight Moiré

2. Speaking of repairing moiré in post, there are multiple approaches to accomplish this in Photoshop. For starters, I always try the simplest. Select the area where the issue exists.

 If it’s on a lapel, for instance, or the side of a jacket, simply use the lasso tool to manually draw a selection around the affected area. I typically feather that selection to ensure no hard edges are created and then move on to step two.

Switching to a paintbrush with a fairly large brush size (the kind of thing that can fill up the selected area with just a few passes) and a soft edge, dial in a relatively low 50 percent opacity, or even lower if you’d like to build up a more subtle change with several clicks. Next, hold the option key to turn the brush tool temporarily into an eyedropper and then sample the correct color you’d like to use to paint over the damaged area. This loads the correct color from the jacket, for instance, and enables you to paint away the rainbow effects of moiré with just a few clicks of the mouse. Half the time, the moiré is only color-based and this simple technique eliminates it completely. The rest of the time, you’ll need to go a step farther, working to repair luminosity changes brought about by the interference.

Three Ways to Fight Moiré

3. When the color repair doesn’t solve the problem, the moiré is likely impacting the luminosity of the image as well. To address this, again start by making a selection of the area in need of repair. (This time you could instead make a color-based selection of the affected spot by using Select>Color Range, for instance. Or you can stay with the physical selection drawn by hand with a lasso of choice. Do take care, however, to camouflage the edges of the selection by feathering them and hiding them in shadows and along natural edges in the scene. In any case, the next step is to make a new blank layer and using the selection, fill that portion of the layer with the ideal color to replace it. This could be the same color that was selected in the previous repair. If it’s a navy blue blazer, choose an ideal navy blue tone from an adjacent pixel. Then click the Eye icon next to this layer to temporarily hide it from view.

With the area to be repaired selected and filled with color on a new layer, return to the background image and duplicate it from the background onto a new layer by clicking the background layer in the Layers palette and then typing Command+J on Mac or CTRL+J on Windows. Then, click the eye icon next to the background layer to temporarily hide it from view.

Three Ways to Fight Moiré

Next, return to the new layer with the image information—this should be the background copy—and create a plain white layer on top of it. Then, change that layer’s Mode to Color. This will turn the image black and white but only by appearance, not by actually throwing out the color information. This step allows you to see only the brightness of the tones in the image, letting you focus on any pattern that appears based on luminosity changes rather than from funky colors.

Three Ways to Fight Moiré

Next, click on the image layer below the white layer to make it active and use the Hue/Saturation control (Command+U on Mac or CTRL+U on Windows) to drag the hue and saturation until the moiré pattern is minimized or, ideally, until it disappears completely. You may have better luck applying this adjustment to specific color channels, such as red or blue, which may contain the majority of the pattern interference. 

Three Ways to Fight Moiré

Once the moiré pattern has largely disappeared, click OK to render the correction. Now you’ve still got an image that looks to be black and white, so you’ll need to reactivate the color-only layer atop the stack to render the repaired area in its correct color. Then, just command-click the color-only layer to reselect the repaired area, then return to the white-only layer and click the Add Layer Mask icon in the Layers palette. This will mask away all but the repaired area. Repeating this process on the background copy layer will restore the original color to the untouched portions of the image, leaving just the repaired pattern influenced by the color fill layer. The area that was suffering from a distracting moiré pattern will now look just fine.

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