What's the matter with the "mysterious patterns" on the back of the chair? Is there a bug in the world?

What's the matter with the "mysterious patterns" on the back of the chair? Is there a bug in the world?

After seeing off several seniors, the computer chair with patinaed armrests finally retired with honor. When the "current owner" of the chair, Wang, was preparing to take a photo to apply for scrapping, he accidentally saw "ripple"-like patterns on the back of the chair. The back of the chair is made of mesh, which is very organized vertically and horizontally, and it is impossible for it to mutate spontaneously. Not long ago, when Wang was chatting, he also talked to his classmates about the possibility of bugs in the world. Could it be that the world is running on a low-spec computer, so the computing power for rendering the fine mesh is insufficient?

Wang’s computer chair. Source: Photographed by Wang

This mysterious pattern with a peculiar style did not appear out of nowhere. In the scientific community, it is called moiré.

Magical ripples visible from both sides

Given two equally spaced vertical stripe patterns A and B, they look very similar, but the density of the stripes is different. When these two images are superimposed, the initial positions and densities of the stripes in the two images are different, so that the light and dark stripes block or enhance each other in space, forming light and dark stripes. Then a magical phenomenon occurs:

The stripes in the overlapping area did not become denser due to superposition, but instead gave rise to periodic "big black lines", which are much less dense than those in A and B and much thicker.

Moiré patterns formed by superposition of vertical stripes, source: google picture, Crective Commons License

The beat principle tells us that when two equal-amplitude sine waves with similar frequencies are superimposed, the amplitude of the synthesized signal will change according to the frequency difference between the two signals. The stripe pattern can be considered as a sine wave distributed in space, with bright stripes at the crest and dark stripes at the trough. The frequency is reflected in the density of the pattern in space. After the two high-frequency stripe patterns A and B are superimposed, the naked eye can no longer distinguish each other's stripes, and can only see the interference pattern. The frequency of the pattern is the frequency difference between the two signals A and B. This pattern is the moiré pattern.

Moiré is an interference image produced by overlapping stripes. It can be seen from any angle in real life. The "ripple-like pattern" that Wang found on the back of the chair is the moiré produced by the overlapping of the front and rear seat surfaces. If you observe carefully, you can even find it on the electric fan.

Moiré pattern on the fan, source: google picture, Crective Commons License

Moiré patterns formed by superposition of radial stripes, source: google picture, Crective Commons License

The moiré pattern on the fan is formed by the superposition of striped grids on the front and rear covers of the fan, and its shape is very similar to the magnetic flux lines of a bar magnet.

When we take photos wearing clothes with fine enough stripes, we can also find this wonderful pattern in the photos, but how can other stripes interfere with a single layer of striped clothes? Don't forget - the photosensitive elements of digital cameras, scanners and other equipment are regularly arranged with pixels, and their arrangement also has spatial frequency.

When we use our mobile phones to shoot the computer screen in front of us, at the right angle, frequency aliasing will occur between the camera's color filter array (CFA) and the sub-pixel layout of the screen, which also appears as a complex texture pattern.

Wang’s “eye protection” computer wallpaper, source: Photographed by Wang

There are also moiré patterns when you get close to the picture. Source: Photographed by Wang

Is the human eye better than a camera?

When you take a picture of the screen with a mobile phone, moiré patterns will appear. However, no matter which direction the human eye looks at the screen from, no patterns can be seen intuitively. Does this mean that the human eye is better than the camera in some aspects?

Don't doubt the beauty of your eyes! Before the theory of evolution explained the structure of the human eye, the Creator believed that the beauty of the eye's structure could fully prove the existence of God as the Creator. Even Darwin wrote in a letter to a friend at the time: Every time I think of the structure of the eye, I shudder.

In fact, the arrangement of visual cells in the human eye is not as regular as the arrangement of pixels in the photosensitive element. Without this periodic arrangement, no beats will be formed. Moreover, the pictures seen by the human eye are completely processed by the brain. The brain needs to synthesize the images seen by the left and right eyes at various angles. The synthesized image is no longer the original image, so the human eye cannot see moiré patterns on the screen.

The romantic and ethereal screen of the Winter Olympics

The "magical" moiré patterns when shooting the screen are indeed a nightmare for photography enthusiasts. These patterns appear on the photos like uninvited guests, reducing the image quality and visual experience.

Generally speaking, in order to display the same content on a large screen, the pixel density is relatively low, and the moiré phenomenon is more obvious, which becomes more and more difficult in situations where large-screen broadcasting is required. It is worth mentioning that at the opening ceremony of the Beijing Winter Olympics that stunned the world, the world's largest LED screen at the time was a floor screen made up of 42,208 50-centimeter-square LED modules. The LED light mask was atomized to reduce the granularity of the pixels and eliminate the periodic discontinuity of the image, achieving a nearly perfect anti-moiré effect and providing a pure, undisturbed video display at all focal lengths for camera broadcasting, which is truly unique.

The opening ceremony of the 2022 Beijing Winter Olympics, source: wiki

The light and shadow coat in the city sky

Just as moiré reduces the image quality of a photo, its appearance on a building often destroys the architect's ideal visual effect. The existence of moiré often reduces the beauty of a building. Some designers, considering safety factors or hoping to present a transparent effect, will design the facade into nested metal grids, which will produce disordered moiré patterns. This pattern will make office workers feel dizzy and unable to concentrate, and will cause visual interference to passers-by and vehicles. It can be regarded as another major light pollution besides the mirror reflection of the glass curtain wall.

Viewed this way, moiré appears to be nothing more than chaotic interference patterns that affect the visual experience.

Knowing yourself and your enemy can turn danger into advantage - Sun Wu

If we just stay at the unknown impression of the mystery of this visual phenomenon, then we may think that these patterns represent the will of gods, just like the people in the past who believed in tortoise shell divination. However, staying at the surface can never satisfy human beings. Curiosity is their innate background, which interferes with the world of exploration to produce unique patterns. When we discover and analyze the generation laws behind the phenomenon, we can make the presentation of moiré patterns controllable instead of accidental.

Dali Boutique in Taiwan, my country, source: google picture, Crective Commons License

The Dali Boutique Museum stands in Kaohsiung, Taiwan. The glass and metal grilles on the exterior walls are arranged in an alternating manner. By translating the pattern of the moiré effect, the protruding front of the building will show different smooth shapes when viewed at different distances, like a huge flowing cross (careful readers will find that this shape is quite similar to the moiré captured by Wang’s computer), as if covering the building with a layer of "light and shadow coat".

The development and application of the moiré phenomenon by those who seek the world's beauty and their technological peers are emerging in all aspects of life with each passing day. In the field of security, the moiré produced when scanning banknotes greatly improves the anti-counterfeiting performance; in clothing design, moiré enriches the expressiveness of clothing; in packaging design, designers intentionally combine the pull-out action of opening the package with the moiré effect. One of the most typical examples is the winning work of the 2018 Global Packaging Design Awards - the packaging design of NORD STREAM Seafood Food Company. The designer LOCO Studio uses a pull-out packaging box with the silhouette of seafood printed on the inner box. When the inner box is pulled out, the moiré animation of the seafood swaying can be seen from the fence of the outer box, which impressively conveys the message that the ingredients are "fresh".

From the world around us to our homes far away, the magical ripples of moiré, visible from all directions, are emerging from the hazy fog of the world and entering the human homeland with the help of science and technology. The moiré lattice formed by stacking graphene is affecting the forefront of science. The application of technology in architecture, packaging, and clothing highlights art and beauty. The world is ingeniously innovating in the integration of scientific exploration and technological practice. The ever-changing world flowing in human vision shows in progress:

Science is a kind of beauty.

The application of science creates a more beautiful world.

References:

[1]https://www.ceta.com.cn/210/202301/2497.html

[2]https://www.thepaper.cn/newsDetail_forward_16703944

[3] Yang Guang, E Yuping, Wang Jiajun. Research on packaging interaction design based on moiré generation rules[J]. Green Packaging, 2023, (06): 107-111. DOI: 10.19362/j.cnki.cn10-1400/tb.2023.06.022.

[4] https://www.unstudio.com

[5] Ma Yibo. A preliminary study on the application of architectural form based on moiré effect[J]. Architect, 2022, (05): 99-106.

[6] Dacen W ,Ellis T ,Esmeralda A , et al.Mixed-dimensional moiré systems of twisted graphitic thin films.[J].Nature,2023,620(7975):750-755.

Author: Li Wenjie Popular Science Author

Reviewer: Li Ming, Researcher, Institute of High Energy Physics, Chinese Academy of Sciences

The article is produced by Science Popularization China-Creation Cultivation Program. Please indicate the source when reprinting.