A moire pattern is a visual artifact that appears in digital photographs as wavy, rainbow-colored lines or rippling distortion over fine, repetitive details. It occurs when the regular pattern of the subject (fabric weave, window screens, roof tiles, brick patterns) interacts with the regular grid of pixels on the camera’s sensor. The two patterns interfere with each other, creating a false pattern that does not exist in the real scene.
What Causes Moire
Digital sensors capture images using a grid of individual photosites (pixels) arranged in rows and columns. When you photograph a subject that also has a regular, repeating pattern at a frequency close to the sensor’s pixel pitch, the two grids create an interference pattern. This is the same principle that makes overlapping chain-link fences or window screens produce shimmering visual effects when viewed from certain angles.
Moire is especially common with cameras that lack an optical low-pass filter (OLPF or anti-aliasing filter). Some manufacturers remove this filter to maximize sensor sharpness, since the OLPF works by slightly blurring the image to prevent pattern interference. Without it, the sensor captures finer detail but becomes more susceptible to moire on patterned subjects.
Common Moire Triggers
Fabric and clothing. Tightly woven suits, herringbone patterns, fine pinstripes, and silk ties are the most frequent culprits in portrait and fashion photography. The weave pattern aligns with the sensor grid at certain distances and focal lengths, producing color fringing and wavy distortion.
Architecture. Repetitive building elements like brick walls, roof shingles, louvered vents, and window grilles can trigger moire, especially in real estate and architectural photography where these patterns fill large portions of the frame.
Screens and displays. Photographing computer monitors, televisions, or LED panels often produces moire because the pixel grid of the display interacts with the pixel grid of the sensor.
Prevention and Removal
The most effective prevention is to change your distance or angle relative to the patterned subject. Moving closer, stepping back, or tilting the camera slightly changes the spatial frequency relationship between the pattern and the sensor, often eliminating the moire entirely. Changing to a longer or shorter focal length has a similar effect. Slightly defocusing the patterned area (if it is in the background) also prevents interference.
In post-processing, most photo editing software includes a moire reduction tool or adjustment that desaturates and blurs the false color in affected areas. Shooting in RAW gives you more data to work with when correcting moire compared to JPEG. For persistent moire on critical subjects, consider cameras with an anti-aliasing filter or use an external AA filter that attaches to the front of the lens.