The Moiré Effect

You might have noticed this while cleaning or replacing window screens: hold two mesh screens together and twist one slightly, and suddenly, large curving waves and ripples appear before your eyes.

This happens because the openings in the two grids line up in some spots—letting light through and creating bright areas—while in other spots, the mesh lines crisscross to block the light, creating dark areas. Although neither screen has any curved lines on its own, overlapping two regular grids produces an entirely new visual interference pattern.

The effect takes its name from *moiré*, a French word for watered silk with a wavy, rippled finish. You can easily spot it in everyday life, such as looking through striped window blinds at a fence behind them or folding a mesh laundry bag over itself.

Snap a photo of your computer monitor or TV screen with your smartphone, and you will often see colorful, shimmering rainbow waves across the display. Many people assume their camera lens or display panel is broken, but this is actually a textbook moiré effect.

Your monitor is built from millions of tiny pixels arranged in a tight grid. Inside your smartphone, the image sensor that captures light is also laid out in a fine grid of light-sensitive points. On top of that, monitor pixels consist of tiny red, green, and blue subpixels, and camera sensors also use alternating color filters. Because these tiny color grids misalign slightly differently for each hue, the resulting interference shimmers with rainbow bands.

As the monitor's pixel grid clashes with the camera sensor's grid, the camera samples light only at fixed intervals. When the detail on the screen is finer than the sensor can properly resolve, it registers as large, artificial ripple patterns that never existed on the actual screen. This is why tilting your phone slightly or stepping back a few inches makes the waves dance and shift instantly.

Technically speaking, moiré in digital photography is a type of signal distortion known as aliasing. It occurs when a repetitive pattern is finer than what the camera sensor can resolve. Unable to capture the pattern's true frequency, the sensor misinterprets it as a false, lower-frequency wave.

To solve this, traditional digital cameras placed a special optical low-pass filter (OLPF), also called an anti-aliasing filter, directly in front of the sensor. By slightly blurring incoming light, it softens repeating details that are too fine for the sensor to handle. While this eliminates moiré ripples, it comes at the cost of razor-sharp image detail.

Today, modern camera sensors pack far more megapixels, raising their resolution limit well beyond most everyday textures. Because subtle optical softness in lenses also acts as a natural blur filter, many cameras now omit the low-pass filter entirely to prioritize maximum sharpness. Remaining moiré and false colors are cleaned up through on-camera image processing or editing software. However, once an interference pattern is baked into raw pixel data, it is notoriously hard to separate from genuine detail—which is why shooting finely woven fabrics with an ultra-sharp lens can still trigger moiré today.