Shulou(Shulou.com)11/24 Report--

Picture taken from Shanghai Metro Line 1 tunnel advertisement [1] When you walk through the subway every day, I don't know if you have noticed such a phenomenon. As the train gradually accelerated, a constantly changing picture appeared outside the window. I don't know what kind of mood everyone had when they first met each other. Did they see through the secret at a glance? Anyway, when Xiaobian first saw it, he felt that this was a black technology. His short knowledge made everyone laugh...

However, in fact, physicists had already made prototypes 200 years ago.

Phenakiscope

In the winter of 1832, Belgian physicist Joseph Plateau and Austrian mathematician Simon Stampfer invented the Phenakiscope almost simultaneously.[2] In the beginning, Fenach mirrors often draw patterns on disks and then rotate them. Through the slit device with uniform stripes, we can observe the effect of animation, which is also the effect of animation originally proposed, and now looks similar to a GIF animation of a few seconds.

The schematic diagram drawn by Yusuf Prato in his paper does not move, and the editor adds some special effects to it to make it move.[3] The principle behind this is also very simple. If the slits match the rotation frequency of the pattern, people can see the animation pattern of each subsequent frame in turn when they look through one slit position. Using persistence of vision, the originally short frame-to-frame changes are compensated for by "brain compensation."

Animation seen through slits--actually, it wasn't long before people realized there was a persistence effect. In 1824, Peter Mark Roget, a professor at the University of London in England, first proposed the role of human observation in his research report Explanation of an optical illusion in the appearance of the spokes of a wheel when seen through vertical apertures. Although the discussion of hallucination formation in this article seems obviously out of date at present, it does not detract from its importance in the history of film and animation.

Prato Portrait [6] It is now generally believed that persistence of vision is due to the fact that the optic nerve impression of the object does not disappear immediately after the object is removed, but lasts for a short time. Prato was a student at the time, and the invention of the Fenach mirror was probably influenced by this study. But Prato later paid a painful price for his obsession with persistence of vision, focusing sunlight into his eyes for 25 seconds and losing his sight altogether. When you do experiments, you must standardize the operation

Next, I will show you some beautiful patterns of Fenach mirrors ~

The images above are excerpted from collossal [7] and from a video production course at Okayama Prefectural University, Japan.[8] Going back to the original Fenach mirror, when the slits and patterns don't match, the image people see will drift. Of course, in the actual observation process, the flicker and deformation of the picture caused by the rotating slit will affect the observation result. Most of what we see now, including the ones shown above, are made with computer software.

3D Animation 3D Phenakiscope

Today, Fenach mirrors are much more than flat surfaces. They allow animation in three dimensions. The principle is still very similar, but instead of using slits, we use strobe lights instead. In fact, we have seen this principle as early as in life or in movies. For example, the rain control skill in "The Amazing Thief Group"

When the first light comes on, you see a raindrop, and when the light turns off and turns on a second time, another raindrop happens to be near the rain you saw earlier, and your brain mistakenly thinks it's the same raindrop, and incorrectly concludes that the rain is still. [9]

Another example is the inverted fan that is usually seen

The fan that looks like it's spinning backwards, image from Giphy, and we're going to look at some near-real 3D animation.

People Wave- Lego Figures Doing the Wave [10]

Christmas Day-

Fish Eating Fish [12]

Jumping Frogs [13] In fact, there are many companies that use this form of animation for advertising.

Airbnb "Paris" video shooting scene [14] Video From Where Video On The Subway

A new way to play subway advertisements derived from the 1980s [15] After reading so many animations above, I don't know if you have come up with the principle of video on the subway?

The lamppost in the subway now uses projection and continuous long screen to carry out video delivery in a rare way, mainly because of the cost. In fact, hundreds of lampposts can be installed continuously on hundreds of meters of tunnel walls to achieve the same effect. All we had to do was set the order of the pictures on each lamppost, and we could make the picture move continuously, just like the kinescope in an old TV set, scanning row by row or column to form the dynamic picture that the human eye would eventually see.

The images recorded at 960 fps during subway operation. Photo excerpt from the question "How is the advertisement outside the window of Shanghai subway realized?" It's Not Enough

All of the above is how to present a dynamic picture. Then, how do you record a moving picture? The two are actually similar, and that's how movies are made. Now if we challenge ourselves to something even more interesting, like recording the propagation of light.

Ramesh Raskar from MIT finally achieved this task, recording the entire process of light traveling through a Coke bottle. [17]Coca-Cola doesn't give sponsorship money--in fact, light travels really, really fast. A beam of light travels from the head of a Coke bottle to the end of a Coke bottle in fractions of a nanosecond. And only a handful of photons can be observed externally in this process. If you can't see it clearly once, repeat it millions of times. Eventually, we'll see an image like this.

Have Fun

Those advertisements in the subway were actually not run by staff holding up billboards! Image from Giphy Reference Link

[1]Tudou-Shanghai Metro Line 1 Advertising

[2]Fenach mirror- wikipedia

[3] Correspondance mathématique et physique (in French). 7. Brussels: Garnier and Quetelet. 1832. p. 365.

[4] Peter Mark Roget - wikipedia

[5]PDF version of the original paper

[6] Joseph Plateau - wikipedia

[7] First Animated Gif

[8]Okayama Prefectural University Video Production Course Portfolio

[9]CAS Institute of Physics Q & A Column No.128

[10] Simon de Groot - Lego Figures Doing the Wave

[11] PANTOGRAPH07 - クリスマスゾートロープ

[12] Kevin Holmes - Fish Eating Fish

[13] Kevin Holmes - Jumping Frogs

[14]Airbnb "Paris" Advertising Video

[15]Liu Shuliang-Dynamic advertisement outside subway window, here is its past life and present life

[16]Know the question "How is the advertisement outside the window of Shanghai subway realized?" Next Kon Tiki's answer

[17] Ramesh Raskar - TED Talk

This article comes from Weixin Official Accounts: Institute of Physics, Chinese Academy of Sciences (ID: cas-iop), author: Cloudiiink

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