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I created some QR code just for fun, then tried to read them with my phone. When I display them on laptops, my phone read them just fine. But when I tried to read the exact same codes displayed on CRT screen.. none of them succeeded, from the mini one with very short text (10 characters) to the large one with very long link, displayed as full screen image. Later I read here that reading on CRT is not supported anyway. So, I'm curious, why QR code can't (or maybe hard) to read on CRT screen? Is it refresh rate, the color, the brightness, or anything else?

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up vote 5 down vote accepted

Watch a CRT and then an LCD through a phone camera.

That flickering you can see on the CRT but not the LCD is due to the refresh rate and how CRT's work (the wikipedia article briefly talks about it). It makes it much harder for the camera sensor to cleanly pick up what's on screen, since a big dark bar will run through it every few milliseconds.

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Thank you, so it's that runaway bar then – Martheen Cahya Paulo Mar 16 '11 at 9:23
@martheen It's not the dark bar but that the image on a CRT is 'painted' a very small piece at a time, your eyes just can't see this, but the camera can. The camera can't get a good image because it only sees the painted part, which is a small part of the whole image. – Rich Homolka Mar 16 '11 at 16:23

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