Sometimes you find it by accident when placing one object on top of another, when performing a specific zoom on a high-definition image, or when using a scanner. Lines that are not there, squares that appear from nowhere, strange effects that are also very familiar. The official name is moiré pattern, and it is linked to an old type of French silk, but we also discover it in nature, and it has very interesting applications.
Visual tricks, optical illusions, things that are not there and that our eyes-brain system insists on interpreting. From color in black-and-white images to uniform balls passing through photographs that disappear and strawberries that are not red these illusions surprise and frustrate us, but we keep coming back for more. Some of them are very frequent, almost everyday.
Explaining the moiré pattern
Want an example? Then we must talk about the moiré pattern or simply moiré following its French connection, although that is not its real origin.
The word comes from the English mohair which in turn comes from the Arabic expression mukhayyar something like chosen perhaps referring to a good-quality fabric.
But back to the pattern itself; there isn't just one. Among the most common, the line moiré stands out:
In relaxed terms, the moiré pattern is an interference derived from the superposition of two hatched patterns or grids of lines placed at a certain angle, or when those grids have slightly different sizes.
The result of the interference is a new pattern with a visual effect called “wave-like or fluctuating”. The animation shown above reveals that a non-linear interaction of the optical patterns of the lines creates a new visible pattern of overlapping parallel bands (light and dark).
The interference has a greater impact when we use transparencies, and the pattern becomes more complex if the lines are not exactly parallel.
However, that is just the tip of the iceberg. Moiré patterns also work with dots (whether random or uniform), triangles, and many other things.
Moiré in manga and beyond
Moiré patterns appear quite frequently in manga volumes, essentially a printing error when two halftones of different size or thickness end up superimposed. But on more than one occasion, the moiré pattern is something desired.
For example, in shape moiré, the pattern creates a kind of amplification on a piece of text or a figure that was “stretched” and repeated on each horizontal line.
Practical applications
Finally, the moiré pattern is used to measure material fatigue. In general, you just have to introduce a pattern on the object to be studied, take it as a reference, and then make a superposition with the same pattern, this time deformed by stress.
Make your own moiré patterns
Want to make moiré patterns at home? Start by searching for PNG patterns with transparent background, use your favorite editor to superimpose two copies of the same pattern, and play with the zoom.
More details: Wikipedia
