Using LEDs To Determine A Video Camera’s True Framerate

Interpolation and digital cropping are two techniques which are commonly used by marketing folk to embellish the true specifications of a device. Using digital cropping a fictitious zoom level can be listed among the bullet points, and with frame interpolation the number of frames per second (FPS) recorded by the sensor is artificially padded. This latter point is something which [Yuri D’Elia] came across with a recently purchased smartphone that lists a 960 FPS recording rate at 720p. A closer look reveals that this is not quite the case.

The smartphone in question is the Motorola Edge 30 Fusion, which is claimed to support 240 and 960 FPS framerates at 720p, yet the 50 MP OmniVision OV50A sensor in the rear camera is reported as only supporting up to 480 FPS at 720p. To conclusively prove that the Motorola phone wasn’t somehow unlocking an unreported feature in this sensor, [Yuri] set up an experiment using three LEDs, each of which was configured to blink at either 120, 240 or 480 Hz in a side-by-side configuration.

As [Yuri] explains in the blog post, each of these blinking frequencies would result in a specific pattern in the captured video, allowing one to determine whether the actual captured framerate was equal to, less than or higher than the LED’s frequency. Perhaps most disappointingly about the results is that this smartphone didn’t even manage to hit the 480 FPS supported by the OV50A sensor, and instead pegged out at a pedestrian 240 FPS. Chalk another one up for the marketing department.

Never Twice The Same Color: Why NTSC Is So Weird

Ever wonder why analog TV in North America is so weird from a technical standpoint? [standupmaths] did, so he did a little poking into the history of the universally hated NTSC standard for color television and the result is not only an explanation for how American TV standards came to be, but also a lesson in how engineers sometimes have to make inelegant design compromises.

Before we get into a huge NTSC versus PAL fracas in the comments, as a resident of the US we’ll stipulate that our analog color television standards were lousy. But as [standupmaths] explores in some depth, there’s a method to the madness. His chief gripe centers around the National Television System Committee’s decision to use a frame rate of 29.97 fps rather than the more sensible (for the 60 Hz AC power grid) 30 fps. We’ll leave the details to the video below, but suffice it to say that like many design decisions, this one had to do with keeping multiple constituencies happy. Or at least equally miserable. In the end [standupmaths] makes it easy to see why the least worst decision was to derate the refresh speed slightly from 30 fps.

Given the constraints they were working with, that fact that NTSC works as well as it does is pretty impressive, and quite an epic hack. And apparently inspiring, too; we’ve seen quite a few analog TV posts here lately, like using an SDR to transit PAL signals or NTSC from a microcontroller.

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Camera Trick Lets You See Sound Waves In Falling Water

From this still image you’d think the hose dispensing the water is being moved back and forth. But watch the video after the break and you’ll see the hose is quite steady, as is the standing wave of water. It’s bizarre to be sure. Knowing how it works makes cognitive sense, but doesn’t really diminish the novelty of the demonstration.

This is the second time [Brasspup] has posted a video of this phenomenon. The newest version does a great job of showing several different patterns. But even the first segment from a year ago, which has over 4 million hits, shows the water moving against gravity. We also saw a similar rig in a links post a year ago.

We’d call it an optical illusion but it’s really more of a technological illusion. The water is falling past a sub-woofer speaker which is tuned to 24 Hz. At the same time, the camera filming the demonstration is capturing 24 frames per second. As was mentioned then, it’s much like flashing a light to freeze the water in mid-air. But the flashing of the frames is what causes this effect.

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