I remember seeing the photo above on Flickr once, and having my brain melt slightly from trying to figure out what went wrong.
The issue was the propeller was rotating as the camera detector ‘read out’, i.e. there was some motion during the exposure of the camera. This is an interesting thing to think about, lets have a look.
Many modern digital cameras use as their ‘sensing’ device a CMOS detector, also known as an active-pixel sensor, which works by accumulating electronic charge as light falls upon it. After a given amount of time, the exposure time, the charge is shifted row-by-row back to the camera for further processing. There is then a finite time where the camera scans down the image, saving rows of pixels at a time. If there is any motion over this timescale the image will be distorted.
To illustrate, consider photographing a spinning propeller. In the animations below the red line corresponds to the current readout position, and the propeller continues to spin as the readout proceeds. The portion below the red line is saved as the captured image.
First, a propeller which completes 1/10th of a rotation during the exposure:
Some distortion, but nothing crazy. Now a propeller moving 10 times quicker, which completes a full rotation during the exposure:
This is starting to look like the Flickr image at the beginning. 5 times per exposure:
This is a little too far, things have clearly gone mental. Just for fun, let’s see what some different objects look like at different rotation speeds, from 0 to 1 rotation per exposure.
The same propeller as above:
A fatter propeller:
A car tire:
We can think of the rolling shutter effect being some coordinate transformation from the ‘object space’ of the real-world object, to the ‘image space’ of the warped image. The animation below shows what happens to the Cartesian coordinate grid as the number of rotations is increased. For small rotations the deformation is slight, as the number increases to 1 each side of the grid is moved successively towards the right-hand side of the image. This is a fairly complicated transformation to look at, but simple to understand.
Let the image be denoted by , and the real object (which is rotating) be denoted by where are 2D polar coordinates. Polar coordinates are a natural choice for this problem due to the rotational motion of the objects.
The object is rotating at angular frequency , and the shutter progresses across the image at speed in the vertical direction. At position in the image, the distance the shutter has moved since the start of exposure is , and so the time elapsed is . In this time the object has rotated a number of radians . Putting this together,
which is the required transformation. The factor is proportional to the number of rotations during the exposure, and parameterises the transformation.
To get some insight into the apparent shapes of the propellers, we can consider an object consisting of propellers where is non-zero only for for . The image is then non-zero for
In Cartesian coordinates this becomes
which helps to explain why the propellers get that S-shaped look – it’s just an inverse tangent function in the image space. Cool. I’ve plotted this function below for a set of 5 propeller blades at slightly different initial offsets, as might be observed during a video recording. They look pretty much like the shapes in the animations above.
Now we understand a little more about the process, can we do anything about these ruined photos? Taking one of the warped images above, I can take a line through it, rotate backwards the appropriate amount, then stick those pixels onto a new image. In the animation below I scan through the image on the left, marked by the red line, then rotate the pixels along that line onto a new image. This way we can build a picture of what the real object looks like even if a pesky rolling shutter ruined our original image.
Now if only my photoshop skills were better I could extract the propellers from the original Flickr image, un-warp them, and slap them back on the photo. Sounds like a plan for the future.
To figure out the real number of blades in the photo at the top of the post and the rotation velocity we can look to this excellent post at Daniel Walsh’s Tumblr blog, where he definitely has the edge on mathematical explanation.
He works out that we can calculate the number of blades by subtracting the ‘lower’ blades from the ‘upper’ blades, so in this picture we know there should be 3. We also know the propeller is rotating approximately 2 times during the exposure, so if we try ‘undoing’ the rotation with a few different speeds around that we get something like this:
I’ve had to guess where the centre of the propeller is, and I’ve drawn a circle to guide the eye. Looking at that, the centre shouldn’t be too far off. There is unfortunately a missing blade, but there’s still enough information to make an image.
There is a sweet spot where everything overlaps the most, so picking this rotation speed (2.39 rotations per exposure), the original image and blades look like this:
It’s still a bit of a mess unfortunately, but at least looks something like the real object.
Earlier this year, researchers who used a telescope based at the South Pole called BICEP announced that they obtained evidence for gravity waves caused by the Big Bang itself. The results would provide direct evidence that a model of the Universe's origin called inflation had left its mark on the present-day Universe.
But in reporting on the results, our own Matthew Francis suggested that the discovery was not as definitive as it might be, writing "the story of BICEP2, inflation, and primordial gravitational radiation is just beginning." And since then, it became clear that there was a complicating factor—dusty material in our own galaxy—and that the BICEP team's way of controlling for it left a little something to be desired (it involved using processed data obtained from a PDF used in a conference presentation).
Yesterday, the team that put the PDF together in the first place released its own analysis. And they've determined that BICEP was probably staring at dust, rather than the earliest moments of the Universe.
Over the past few years, studies of genomes have confused what we thought we knew about the origin of animal life. Instead of the simple sponges being the earliest branch off the animal tree, a group of relatively complex organisms, the ctenophores, seem to be the earliest branch. That finding has some serious implications, as it suggests that a nervous system evolved twice.
Now, some more traditional biology may upset the family tree even further. Old samples taken from the seabed near Tasmania contain examples of two different species that may belong to a phylum entirely unknown to us—one that split off near the base of the animal tree. The strange creatures also have features that suggest they may be related to remains from the Ediacaran, a period in which the first animal life appears in the fossil record.
The samples actually date from a research cruise taken nearly 30 years ago, where a "sled" was dragged along the ocean floor and samples returned to the surface. The new species weren't recognized as interesting when they were first found, so they were left mixed in with the rest of the collection, which was fixed with formaldehyde and then dumped in 80 percent ethanol. The samples suffered a bit of further abuse when one of the authors wanted to refresh the alcohol and was given 100 percent ethanol instead. (The paper actually notes, "Unfortunately absolute alcohol was provided without comment instead of the requested 80 percent ethanol.")
We now turn our attention to the audio signal chain as John P. Hess defines the different components needed when recording on set for digital video.
We are still working on the new iteration of FilmmakerIQ, but we wanted to get this third part of our Audio Series out to you. Great things are coming stay tuned.
This lesson is proudly sponsored by RØDE Microphones:
The other videos in this Series:
The History of Sound at the Movies
The Science and Engineering of Sound
If you like geology, you’re used to relying on an active imagination. Most geologic processes occur too slowly to see them play out for yourself. Many of the exceptions are dangerous enough that you might not want a front row seat or are rare enough that the odds of being there to witness them are disheartening. Sometimes, though, the Earth throws us a bone—or in this case, a gigantic slab of granite.
One interesting way that rocks weather and crumble apart is called “exfoliation.” Like the skin-scrubbing technique, this involves the outermost layers of exposed igneous or metamorphic bedrock sloughing off in a sheet. Over time, this tends to smooth and round the outcrop—Yosemite’s Half Dome providing a spectacular example.
We’re not entirely sure just what drives the peeling of an outcrop’s skin like this, but the classic explanation is that it’s the result of bringing rocks that formed at great pressure up to the surface. Once there, the outer layers can expand slightly, creating a physical mismatch with the layers below them.
Mario is just a video game, and rocks don’t have legs. Both of these things are true. Yet, like the Mario ghosts that advance only when your back is turned, there are rocks that we know have been moving—even though no one has ever seen them do it.
The rocks in question occupy a spot called Racetrack Playa in Death Valley. Playas are desert mudflats that sometimes host shallow lakes when enough water is around. Racetrack Playa gets its name from long furrows extending from large rocks sitting on the playa bed—tracks that make it look as if the rocks had been dragged through the mud. The tracks of the various rocks run parallel to each other, sometimes suggesting that the rocks had made sharp turns in unison, like dehydrated synchronize swimmers.
Many potential explanations have been offered up (some going back to the 1940s) for this bizarre situation, as the rocks seem to only move occasionally and had never been caught in the act. One thing everyone could agree on was that it must occur when the playa is wet and the muddy bottom is slick. At first, suggestions revolved around especially strong winds. One geologist went as far as to bring out a propeller airplane to see how much wind it would take.
One item on the long list of strange facts about quantum mechanics is that the mere possibility of something happening is often just as good as it actually happening. For example, the fact that a photon could potentially travel down a given path can be enough to create an interference pattern that requires the photon to take that path.
Something similar is true regarding a phenomenon called quantum interference. A team of researchers from the University of Vienna has now taken advantage of this idea to create a bizarre imaging technique where the photons that actually strike the object being imaged are discarded. The image itself is then built other with photons that were entangled with the discarded ones.
Interference is the ability of two waves, such as photons, to interact either additively or destructively. In the quantum world, whether or not interference occurs depends on the ability to distinguish the two things that are interfering. If they are distinguishable, interference cannot occur. But you don't have to actually distinguish between them in order to block interference. As the authors of the new paper write, "The mere possibility of obtaining information that could distinguish between overlapping states inhibits quantum interference."
If there is such thing as a perfect motorcycle accident, this might be it: a motorcyclist crashes full speed into a car that's changing lanes. That's bad. The crash launches his body into a spinning mess in the air. That's definitely bad. But yet somehow he manages to flip and land standing up on the car's roof.
THIS IS A SNEAK PEAK AT A NEW AUDIO COURSE SERIES!!
FilmmakerIQ.com and RØDE Microphones are proud to give you a sneak peak at the first lesson in our six part course which will cover science/microphones, recording, editing, foley, and ADR. We are also hard at work behind the scenes updating the site to include even more interaction which should be live in the coming weeks. Until then - enjoy this lesson on the history of sound at the movies.
The inclusion of sound at the movies was one of the most dramatic changes in all of film history. Dive into the early experiments of Edison trying to incorporate sound from film's inception, through the experiments in the early 1920s, the Jazz Singer and the industry sound overhaul, and finally the multi-channel surround and modern movie sound technologies.
This video is proudly sponsors by RØDE Microphones.
Mankind’s greatest invention. [video]
Most people know that the Pacific Ring of Fire is related to boundaries between tectonic plates, but there’s a common misconception about where the magma comes from to fuel those volcanoes. At those boundaries, called subduction zones, a plate made of denser oceanic crust dives beneath a continent (or another oceanic plate). It’s not that the diving plate heats up and melts as it sinks downward, though.
Actually, the minerals in the diving plate contain lots of water, and that water migrates upward as the plate slowly warms up. The addition of water to hot mantle rocks lowers the melting point of the rock, and this effect is enough to convert some mantle rock into magma. Since magma is less dense than solid rock, it works its way upward toward the surface, resulting in the arcs of volcanoes we see along subduction zones.
Within this simplified picture, however, there are complexities and open questions. Does the water simply rise directly into the mantle rocks above, or does it take a more tortuous path? Is that water the cause of all the magma production in an area, or does some magma form because the flow of mantle rock brings some up to lower pressures where it can melt?
Okay I’m pretty sure McDonalds Coke is way different from normally bottled Coke. Next time you have it, close your eyes and think of apple pie, and taste the interesting resemblance. Or am I crazy. Comments here.
Times were tough before the GoPro. [x]
After a two year hiatus from creating their visually brilliant music videos, alternative rock band OK Go are finally back with their latest mind-blowing clip for ‘The Writing’s on the Wall,’ a single from their forthcoming album Hungry Ghosts. The video is 4-minute barrage of optical illusion techniques performed live in-camera (primarily anamorphic projection) that borrow ideas from artists like Bernard Pras, Felice Varini, Bela Borsodi and maybe even a nod to Jay-Z’s Blueprint 3 album cover. All of the scenes are performed one after another in a single take, but probably took untold months of preparation. Love the last shot that reveals the crew.
Update: A bit more about how they did it over on Rolling Stone.
As plastic is made from oil and oil is made from dead dinosaurs, how much actual real dinosaur is there in a plastic dinosaur?
I don't know.
Coal and oil are called "fossil fuels" because they formed over millions of years from the remains of dead organisms buried underground. The standard answer to "what kind of dead stuff does the oil in the ground come from?" is "marine plankton and algae." In other words, there are no dinosaur fossils in those fossil fuels.
Except that's not quite right.
Most of us only see oil in its refined forms—kerosene, plastics, and the stuff that comes out of gas pumps—so it's easy to imagine the source as some uniform black bubbly material.
But fossil fuels bear fingerprints of their creation. The various characteristics of these fuels—coal, oil, and natural gas—depend on the organisms that went into it and what happened to them. It depends on where they lived, how they died, where their bodies ended up, and what kinds of temperature and pressure they experienced.
The dead matter carries its story—altered and jumbled in various ways—for millions of years. After we dig it up, we spend a lot of effort stripping the evidence of this story away, refining the complex hydrocarbons into uniform fuels. When we burn the fuels, their story is finally erased, and the Jurassic sunlight that was bound up in them is released to power our cars.Through photosynthesis, organisms used sunlight to bind carbon dioxide and water into complex molecules. When we burn their oil, we finally return that CO2 and water to the atmosphere—liberating millions of years worth of stored carbon dioxide all at once. This has some consequences.
The story carried by rocks is a complicated one. Sometimes pieces are missing, discarded, or transformed in a way that misleads us. Geologists—both in academia and the oil industry—work patiently to reconstruct different aspects of these stories and understand what the evidence is telling us.My favorite book about Earth science, Walter Alvarez's T. rex and the Crater of Doom, is a firsthand account of the research that determined what killed the dinosaurs. The story is told not as a contest between rival academic theories, but as the unraveling of a mystery through detective work.
Most oil comes from ocean life buried on the seabed. But the poetic idea that our fuels contain dinosaur ghosts is in some ways true as well. There are a few things required for oil to form, including quick burial of large amounts of hydrogen-rich organic matter in a low-oxygen environment.Because, in a sense, oxygen will cause the fuel to burn.
These conditions are most often met in shallow seas near continental shelves, where periodic nutrient-rich upwellings from the deep sea cause blooms of plankton and algae. These temporary blooms soon burn themselves out, dying and falling to the oxygen-poor seabed as marine snow. If they're quickly buried, they may eventually form oil or gas. Land life, on the other hand, is more likely to form peat and eventually coal.
This paints a picture like this:
But hydrocarbon formation is a multi-step processYou can read more about it here. and lots of things can affect it. A huge amount of organic material washes into the ocean, and while most of it doesn't end up in oil-producing sediments, some of it does.If you want to spend a day reading a bunch of articles on hydrocarbons and ocean sedimentation, you can check out a few here, here, here (paywall), here, and here. If you get tired halfway through, like I did, and want a change of pace, you can instead read an insane conspiracy theory website claiming that oil is not dead organic matter and that there's actually an infinite supply of it. This fact is apparently concealed from us by the New World Order and/or the Illuminati. Some oil fields—like Australia's—seem to have a lot of terrestrial sources. Most of this is plants, but some is certainly animals.And it's worth noting that there were some aquatic dinosaurs—like Spinosaurus.
No matter where it came from, only a small fraction of the oil in your plastic dinosaur could be directly from real dinosaur corpses. If it came from a Mesozoic-era oil field fed heavily by land matter, it might contain a slightly larger share of dinosaurs; if it came from a pre-Mesozoic field sealed beneath caprock, it might contain no dinosaur at all. There's no way to know without painstakingly tracing every step of the manufacturing process of your particular toy.
In a broader sense, all water in the ocean has at some point been part of a dinosaur. When this water is used in photosynthesis, bits of it are used to build the fats and carbohydrates in the food chain—but a lot more of that water is in your body right now.
In other words, your plastic toys contain a lot less dinosaur than you do.
Yet most of our measurements of G come from an updated version of a device designed by Henry Cavendish back in the 1700s. And rather annoyingly, these measurements don't agree with each other—they're all close to a single value, but their error bars don't consistently overlap. Now, researchers have made a new measurement of G using a method that certainly wasn't available in the 1700s: interference between clouds of ultracold atoms. And the value that they have come up with doesn't agree with many of the other measurements, either.
The gravitational attraction being studied here is that between a cloud of cold rubidium atoms and a 500 kg tungsten weight. The tungsten was arranged in a cylinder that surrounded the device that contained the rubidium atoms. It could be shifted up to pull the atoms back against the downward force of the Earth's gravity or shifted down to accelerate the atoms further.