问题
Can you derive the size of a physical object image displayed on a phone's screen from its size on the CCD sensor? When you know the dimensions of a physical object, its distance from the camera and the camera's focal lenght, you can determine the size of the image produced on the camera's CCD sensor.
As I described here, I calculate how much larger the phone's screen is in pixels than the CCD sensor in millimeters. So if an object's dimension on the CCD is x, the screen is n-times larger than the sensor, then the object's dimension on the screen is x * n pixels.
Is my assumption right? I measured the value of n for the iPhone 4 but based on the size of the screen in mm (50x70). And the screen is ca. 15 times larger than the sensor (according to my calculations). I took several pictures of a known object from a known distance and the dimensions I got from my calculations were more or less equal to the dimensions of the object's image displayed on the screen.
Still, however, I'm not sure about the correctness of this approach. I will be grateful if you say a few words about it. Thank you.
回答1:
I'm not sure all this math is going to get you much of anywhere. In the real world (unless you're mounting the camera on a tripod and putting your subject a fixed distance), objects could be any distance from the phone.
If you have a target of known composition (say, a AR target or QR Code) printed at a known size (1 inch square), you can definitely compute the size of another object in the same focal plane based on counting pixels.
Or maybe in pictures (CC licensed photo from psd):
来源：https://stackoverflow.com/questions/11920285/how-to-determine-the-size-of-a-physical-object-image-on-a-phones-screen