Despite their futuristic appearance—for our money, they’re still the most sci-fi looking things to ever make their way into homes—LaserDiscs are in many ways an analog format. Notably, they stored video as analog data—and it turns out that you can actually see that data under a microscope.
We know this thanks to YouTuber Shelby Jueden, aka Tech Tangents, and it’s because in his most recent video, he decided to review a microscope he’s just purchased. The review is fine if you happen to be in the market for a microscope, but it’s when Jueden uses his new purchase to look at a copy of The Mind’s Eye (“A Computer Animation Odyssey”!) from his LaserDisc collection that things get really interesting.
The analog video data on LaserDiscs was stored in one of two ways. The chosen method determined the disc’s format: either constant angular velocity (CAV) or constant linear velocity (CLV). (A third format, constant angular acceleration (CAA), was introduced in the early 1980s.) CAV discs spin at a constant rotational speed—like a record player, albeit a lot faster (either 1500rpm or 1800rpm, depending on the video format). CLV discs, by contrast, are more like CDs; their rotational speed varies to allow the head to read data at the same speed throughout.
Each format had its pros and cons. On CAV discs, each revolution of the disc contained precisely one frame. This allowed for features like precise frame-skipping and perfect frame-freezing, which could be achieved by just playing the same track over and over, but it also meant that less data was stored on the disc: the outer tracks contained the same amount of information as the innermost, but “packed” more loosely. CLV discs, by contrast, could store more data because information was packed at a consistent density throughout, but lost some of the features that CAV allowed.
Why does any of this matter? It means that on a CAV disc, one can theoretically actually see the stored image data by looking at the disc itself. About 18 minutes into the video, just as Jueden’s about to slide The Mind’s Eye back into its sleeve and move on to looking at something else, someone in his chat wonders if he might be able to find a visible image on the disc. Jueden scoffs. “It’s not going to happen. We’re not going to find an image. We’re— I found an image!”
How is this possible? Well, each frame is stored as a series of horizontal scanlines, which are written to the screen from top to bottom. Because each track on a CAV disc is one frame, the same scanline will appear in the same place on each track—or, in other words, the video visible on each horizontal slice of the screen will stack up in a line along the radial axis of the disc.
Most of the time, this will just result in a garbled array of image data, but if something happens to be scrolling vertically on the screen—something like, say, the credits for a movie—at just the right speed, then suddenly, this happens:
The credits are clearly visible on the surface of the disc—and as the second shot shows, they correspond nicely to what’s on screen. The same turns out to be true of a capacitance electronic disc (CED), the RCA analog video disc format that served as Betamax to LaserDisc’s VHS. In fact, the results for CED are even more striking:
In today’s all-digital era, this seems like some weird sorcery. But really, all the video data that we stream from YouTube or store on our fancy SSDs is ultimately just … this. It’s just that somewhere along the line—in the original camera sensor, or via some sort of upstream digital conversion—it’s been rendered in 1s and 0s, and then compressed, optimised, and god knows what else. Looking at an actual image on a disc is weirdly nostalgic, and it’s also a fascinating insight into the way that data is stored—and, ultimately, what data is.
Source: Gizmodo