What does moire mean?

Moire fringe is a kind of high-frequency interference fringe of photosensitive element on digital camera or scanner, and it is a kind of color high-frequency irregular fringe that will appear in pictures.

When the spatial frequency of the pixels of the photosensitive element is close to the spatial frequency of the stripes in the image, a new wavy interference pattern, the so-called moire pattern, may be generated. The grid texture of the sensor constitutes such a pattern, and when the thin strip structure in the pattern crosses the sensor structure at a small angle, this effect will also cause obvious interference to the image.

This phenomenon is very common in some fine-grained situations, such as fabrics in fashion photography. This moire fringe can be displayed by brightness or color. The measure to eliminate this interference is to use anti-aliasing filter (also called low-pass filter) in front of the sensor, but this filter will reduce the resolution of the lens. So on this issue, we must make a trade-off and compromise between moire and resolution. Different models of cameras have different problems and different choices.

Moire patterns in life

For photographers, moire is very troublesome, and some unintentional moire often makes the work less perfect. In addition to the screen, as long as there is a periodic structure, it is possible to shoot moire patterns, such as striped shirts, screen grids, exterior wall decoration of high-rise buildings and so on.

So is the publishing industry. Due to the limited resolution of the printer or scanner, moire fringes may also appear if the fine structure of the picture to be processed is equivalent to the resolution. In our daily life, most moire fringes represent the distortion of images, and people need to find ways to avoid moire fringes.

However, moire fringes are not useless. You can see that there are rich stripe patterns on banknotes all over the world, which is actually an anti-counterfeiting measure. These miniature printed patterns are easy to form moire fringes in the process of scanning and copying, which increases the difficulty of making counterfeit banknotes.