# Image processing and Camera Calibration

I have several related questions about camera resolutions.

1. If I calibrate my camera to a particular resolution say 640x360, can I use it for another resolution like 1024x768?

2. Also, I want to know as to how many centimeters does 1 pixel contain in my image. It varies from system to system. How do I find that?. Also, it is not compulsorily square in shape? So I have to find the length and width of it. How do I do that?

3. I am using a logitech c170 which is a low speed cam. Is it okay to get an error around 8mm when I am trying to measure the distances in the image and compare them with real-time distances?

$$\frac{distance \times 2 \times tan(\frac{\theta}{2}) } {horizontal resolution} = \frac{1m\times 2\times tan(\frac{57.5}{2}) } {640px} = 0.0016m/px = 1.6mm/px$$