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Making Things See by Greg Borenstein

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Converting to Real-World Distances

But what about these pixels’ actual depth? We know that the color of each pixel in the depth image is supposed to relate to the distance of that part of the scene, but how far away is 96 or 115 or 224? How do we translate from these brightness values to a distance measurement in some kind of useful units like inches or centimeters?

Well, let’s start with some basic proportions. We know from our experiments earlier in this chapter that the Kinect can detect objects within a range of about 20 inches to 25 feet. And we know that the pixels in our depth image have brightness values that range between 255 and 0. So, logically, it must be the case that pixels in the depth image that have a brightness of 255 must correspond ...

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