The moiré effect in photography and videography
Moiré is one of the most common flaws in videography and photography. Wavy lines appear in the image. Moiré is caused e.g. by the interaction of regular patterns or structures in the subject with other regular structures of the camera sensors.
The camera sensors (CCD chips) are designed such that the light- and color-sensitive pixels are arranged in a regular pattern above and below one another. Most sensors have square pixels, but there are also other pixel shapes, such as hexagons, triangles or rhombuses.
If the subject then has a regular structure, e.g. a brick wall, wire mesh or woven clothing, moiré can occur, appearing as wavy lines and color changes. The effect is most pronounced when the overlapping patterns, e.g. honeycomb, are very similar or even identical.
But moiré can also arise outside of a camera when net-like fabrics such as fine grids or fly screens are placed one over the other. Overlapping the different patterns creates new patterns that were not previously contained in the net structure.
These fine nets are used in film and photo studios as well as in theaters, e.g. to reduce contrast and/or create depth or other visual effects in illumination. Two or three layers of netting can also be used to achieve the desired effects, e.g. to dim the background. The moiré effects described above can occur in precisely these situations.
Cotton tulle, a knit fabric with exact, uniform, honeycomb, hexagonal mesh grids, is often used in videography and photography (Figure 2).