Bye Bye Green Screen, Hello Monochromatic Screen

April 9, 2024 by 60 Comments

It’s not uncommon in 2024 to have some form of green background cloth for easy background effects when in a Zoom call or similar. This is a technology TV and film studios have used for decades, and it’s responsible for many of the visual effects we see every day on our screens. But it’s not perfect — its use precludes wearing anything green, and it’s very bad at anything transparent.

The 1960s Disney film makers seemingly had no problem with this as anyone who has seen Mary Poppins will tell you, so how did they manage to overlay actors with diaphanous accessories over animation? The answer lies in an innovative process which has largely faded from view, and [Corridor Crew] have rebuilt it.

Green screens, or chroma key, to give the effect its real name, relies on the background using a colour not present in the main subject of the shot. This can then be detected electronically or in software, and a switch made between shot and inserted background. It’s good at picking out clean edges between green background and subject, but poor at transparency such as a veil or a bottle of water. The Disney effect instead used a background illuminated with monochromatic sodium light behind the subject illuminated with white light, allowing both a background and foreground image to be filmed using two cameras and a dichroic beam splitter. The background image with its black silhouette of the subject could then be used as a photographic stencil when overlaying a background image.

Sadly even Disney found it very difficult to make more than a few of the dichroic prisms, so the much cheaper green screen won the day. But in the video below the break they manage to replicate it with a standard beam splitter and a pair of filters, successfully filming a colourful clown wearing a veil, and one of them waving their hair around while drinking a bottle of water. It may not find its way back into blockbuster films just yet, but it’s definitely impressive to see in action.

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Hackaday Links: April 7, 2024

April 7, 2024 by 12 Comments

Folks with a bit of knowledge about network security commonly use virtual private networks (VPNs) when out and about. Whether you’re connecting to public WiFi or somebody passes you a questionable Ethernet cable at a hacker con, it’s nice to have a secure endpoint to tunnel all of your traffic. As a secondary bonus, connecting through a VPN can obscure your physical location. It’s that second feature that has a bunch of people jumping on the VPN bandwagon as they try to dodge the recent porn age checks that have gone into effect in a number of states. According to a recent article in PopSci, one particular VPN provider saw a 275% jump in demand on the same day that PornHub cut off access to users in Texas. While the debate over underage users accessing adult content is far outside of our wheelhouse, anything that gets more users connecting to the Internet via encrypted means is arguably a net positive.

If you wanted somebody from the Geek Squad to set up that VPN so you can get back on PornHub to work securely from the local coffee shop, you might be out of luck. Reports have been coming in that Best Buy’s mobile nerd division is seeing sweeping layoffs. Geeks were told to stay home on Tuesday and await a call from corporate, at which point many got the surprising news that they no longer had a job. The /r/GeekSquad subreddit has been a rallying point for staff who got the axe, with the user [jaym026] posting what we assume is an AI-generated inspirational speech from Optimus Prime. Of course, it sucks for anyone to lose their job, especially with the way things are these days. Still, we’re willing to bet almost none of those affected will look back on the day they were let go from an increasingly irrelevant brick-and-mortar electronics store as a low point in their professional careers.

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Fictional Computers: The Three Body Problem

April 5, 2024 by 54 Comments

If you intend to see the Netflix series “The Three Body Problem” or you want to read the Hugo-winning story from Chinese author [Cixin Liu], then you should probably bookmark this post and stop reading immediately. There will be some mild spoilers. You have been warned.

While the show does have some moments that will make your science brain cringe, there is one scene that shows a computer that could actually be built. Would it be practical? Probably not in real life, but in the context provided by the show, it was perfectly feasible. It could have, however, been done a little better, but the idea was — like many great ideas — both deceptively simple and amazingly profound. The computer was made of human beings. I’m not talking like Dune’s mentats — humans with super brains augmented by drugs or technology. This is something very different.

Background

This is your last chance. There are spoilers ahead, although I’ll try to leave out as much as I can. In the story, top scientists receive a mysterious headset that allows them to experience totally immersive holodeck-style virtual reality. When they put the headset on, they are in what appears to be a game. The game puts you in a historical location — the court of Henry VIII or Ghengis Kahn. However, this Earth has three suns. The planet is sometimes in a nicely habitable zone and sometimes is not. The periods when the planet is uninhabitable might have everything bursting into flames or freezing, or there might not be sufficient gravity to hold them on the planet’s surface. (Although I’ll admit, I found that one hard to grasp.)

Apparently, the inhabitants of this quasi-Earth can hibernate through the “chaotic eras” and wait for the next “stable era” that lasts a long time. The problem, as you probably know, is that there is no general closed-form solution for the three-body problem. Of course, there are approximations and special cases, but it isn’t easy to make long-term predictions about the state of three bodies, even with modern computers.

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On the left, the main board of the dual board computer, with the CPU and a bunch of connectors visible. On the right, the addon board is shown, with all the extra connectors as described in the article

A Nifty F1C100S Dual-Board Computer

April 2, 2024 by 15 Comments

The F1C100S (and the F1C200S) is a super simple CPU to use – it’s QFN, it has RAM built-in, and it can run Linux. It just makes sense that we bring it up to you once again, this time, on this dual-board computer by [minilogic]. The boards look super accessible to build for a Linux computer, and it’s alright if you assemble only one of them, too – the second board just makes this computer all that much nicer to use!

One the main board, you get the CPU itself, a couple USB ports, headphone and mic jacks, a microphone, a microSD socket, power management, SPI flash chip, plus some buttons, headers and USB-UART for debug. Add the second board, however, and you get a HDMI video output socket, a RGBTTL LCD header, LiIon battery support, RTC, and even FM radio with TV input.

One problem with this computer – it’s not open-source in the way that we expect and respect, as there’s no board files to be seen. However, at least the schematics are public, so it shouldn’t be hard, and the author provides quite a bit of example code for the F1C100S, which softens the blow. Until the design files are properly published, we can at least learn from the idea and the schematics. If you like what the F1C100S CPU offers, there are other projects you can take things from too, like this low-cost handheld we’re patiently waiting for, or this Linux-powered business card.

How Star Trek Breached The Defences Of A Major Broadcaster

April 1, 2024 by 40 Comments

Back in 2020 in the brief lull between COVID lockdowns in the UK, I found myself abruptly on the move, with a very short time indeed to move my possessions into storage. As I was going through the accumulated electronic detritus of over four decades, I happened upon a grey box with some wires hanging out of it, and more than a few memories. This was a Sky VideoCrypt decoder, and the wires were part of the so-called “Season” interface to attach it to the serial port of a PC. It had this modification in the hope of catching some unauthorised free satellite TV, and in its day this particular hack caused some headaches for the broadcaster.

When More Than 4 Channels Was A Novelty

Patrick Stewart, as Captain Jean-Luc Picard. Composite image, via Wikimedia commons.
Break encryption? This man can make it so. Stefan Kühn, CC BY-SA 3.0.

In the 1980s and early 1990s, there was very little in the way of digital broadcasting on either satellites or terrestrial networks, almost everything on TV was sent out as standard definition analogue video. The four terrestrial channels where I grew up were all free-to-air, and if you had a satellite dish you could point it at any one of a variety of satellites and receive more free-to-air channels if you didn’t mind most of them being in German. Premium satellite programming was encrypted though, either through a range of proprietary analogue schemes, or for the British broadcaster Sky’s offering, through their VideoCrypt system. This used a 64 kB buffer to store each line of video, and rotate it round any one of 256 points along its length, resulting in an unintelligible picture.

Sky was the UK’s big gorilla of premium broadcasters, a role they kept for many years, and which was only eroded by the advent of streaming services. As such they snapped up exclusive first access to much of the most desirable content of the day, restricting it to only their British pay-to-subscribe customers. A viewer in the UK who grumbled about Star Trek Next Generation not being on the BBC could at least cough up for Sky, but if they didn’t have a British address they were out of luck. It was in this commercial decision, whether it was based upon business or on licensing, that Sky unwittingly sowed the seeds of Videocrypt’s demise.

 

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A Threat Level Monitor For Everyone

March 31, 2024 by 25 Comments

A TV news pundit might on any given evening in 2024 look at the viewers and gravely announce that we are living in uncertain times. Those of us who’ve been around for a bit longer than we’d like to admit would see that, scratch our heads, and ask “Have we ever not lived in uncertain times?” If all this uncertainty is getting to you though, you can now reassure yourself as [Ian Williams] has, with a threat level monitor which displays the UK’s current level of projected fear threat level.

The build is fairly straightforward in hardware terms, with a Raspberry Pi Zero and a Pimoroni e-paper display pHAT. The software grabs the current level of doom from in this case the UK government’s website with a nifty bit of Python code, and turns it into an easy to read alert level bar.

So if you’re genuinely worried that the sky might fall upon your head you can now gain reassurance from a small piece of electronic hardware. If you feel things are really going south though, how about converting your basement into a fallout shelter?

A Practical Guide To Understanding How Radios Work

March 30, 2024 by 8 Comments

How may radios do you own? Forget the AM/FM, GMRS/FRS radios you listen to or communicate with. We’re talking about the multiple radios and antennas in your phone, your TV, your car, your garage door opener, every computing device you own- you get the idea. It’s doubtful that you can accurately count them even in your own home. But what principles of the electromagnetic spectrum allow radio to work, and how do antenna design, modulation, and mixing affect it? [Michał Zalewski] aka [lcamtuf] aims to inform you with his excellent article Radios, how do they work?

A simple illustration compares a capacitor to a dipole antenna.
A simple illustration compares a capacitor to a dipole antenna.

For those of you with a penchant for difficult maths, there’s some good old formulae published in the article that’ll help you understand the physics of radio. For the rest of us, there are a plethora of fantastic illustrations showing some of the less obvious principals, such as why a longer diploe is more directional than a shorter dipole.

The article opens with a thought experiment, explaining how two dipole antennas are like capacitors, but then also explains how they are different, and why a 1/4 wave dipole saves the day. Of course it doesn’t stop there. [lcamtuf]’s animations show the action of a sine wave on a 1/4 wave dipole, bringing a nearly imaginary concept right into the real world, helping us visualize one of the most basic concepts of radio.

Now that you’re got a basic understanding of how radios work, why not Listen to Jupiter with your own homebrew receiver?