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The pluses and minuses of the iPhone Camera
Submitted by blackbear
Posted Nov 17 2009 08:17 PM
In a recent interview with Jeffrey Powers regarding the iPhone sensor suite, he talked a bit about the iPhone camera and the difficulties that it can create for real time vision applications.
In terms of science, it's definitely a really bad sensor, especially if you look at the older iPhone sensor, because it has what's called a rolling shutter. And a rolling shutter means that as you press capture or rather as the camera is capturing video frames or as you capture a frame, the camera then begins to take an image. And it takes a finite number of milliseconds, maybe 50 or so, before it is actually exposed to the entire frame and stored that off into a sensor. Because it's doing something that's more like a serial data transfer, instead of this all at once parallel capture of the entire frame. What that causes is weird tearing and odd effects like that. Which for photography, as long as it's not too dramatic, it's not a huge deal. For vision processing, it's a huge deal because it breaks a lot of assumptions that we typically make about the camera. That has gotten better in the 3GS camera, but it's still not perfect. It is getting better, especially when the camera's turned on the video mode.
The optics -- most people know that the 3G and the first gen phone don't have autofocus at all. So their optics is just a fixed-focus simple plastic lens that doesn't allow you to focus up close. So anybody trying to do macro imagery, something up close, you're just not going to be able to do it on the 3G or the first gen phone. And actually, when we set out to build our application, we specifically had to work around that problem, which is a lot of why our application was successful was because we did focus on that problem. Then in the 3GS, the autofocus mode was enabled which is actually a motor-based autofocus system that can autofocus not only on the center of the image, but also somewhere that you pick specifically. And one more thing is that the autofocus system, which again, this isn't directly tied to optics, but the 3GS autofocus system doesn't just change the focus, it also changes the exposure. Which is something a lot of people don't notice.