How-To: Modded camera looks at Kinect infrared output

Craft & Design Technology
How-To: Modded camera looks at Kinect infrared output



Scanner of books, winner of laser contests, and North Dakota maker Daniel Reetz has plans to turn his Microsoft Kinect into a scanner. His first step? Hack a Canon Powershot A540 to capture light in the infrared spectrum. Of course you can use an IR camera for lots of other fun things, but Dan’s focusing on reverse-engineering the way Kinect uses a IR. The matrix of IR speckles above, captured close-up, is of particular interest.

Microsoft’s new Kinect sensor is garnering a lot of attention from the hacking community, but the technical specifics of how it works still aren’t clear. I am working to understand the technology at a fundamental level – my interest is in the optical side of Kinect. My ultimate goal is to make the sensor nearsighted, so that the depth resolution can be used to scan small objects. The first step in understanding a technology is to look at it — that’s why teardowns like this one at iFixit are so important.

Unfortunately for us humans the Kinect projector is infrared (or near-infrared) — probably somewhere between 900 and 1020nm. My guess is that it’s around 904nm, because it’s cheap to produce those lasers, but that’s just a guess; I haven’t measured anything yet. That means that by design, we can’t see the projection directly with our eyes. But we can see it with a camera. Almost all CMOS sensors in digital cameras ARE sensitive to infrared. In fact, they are so sensitive that there is a filter placed between the lens and the sensor to prevent IR from messing up your pictures. It’s called the IR cutoff filter.

[The image above is] interesting in a few different ways. One can easily see that the Kinect IR speckle-field is a 3×3 matrix of random dots. One can also see that they are differentiated by intensity and have a centered registration dot. So it is not purely random speckle.

Kinect Hacking 101: Hack a Powershot A540 for Infrared Sensitivity


4 thoughts on “How-To: Modded camera looks at Kinect infrared output

  1. Scott says:

    Those centered dots are almost certainly the zero diffraction orders from the diffractive optical elements that are used to produce the speckle pattern.

    You see the same phenomenon with laser pointers and those toy pattern generating holograms.

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Becky Stern is a Content Creator at Autodesk/Instructables, and part time faculty at New York’s School of Visual Arts Products of Design grad program. Making and sharing are her two biggest passions, and she's created hundreds of free online DIY tutorials and videos, mostly about technology and its intersection with crafts. Find her @bekathwia on YouTube/Twitter/Instagram.

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