Is Camera Calibration needed to get measurements from an image?

Question

I am working on an android application that measures distances (euclidean distances) from a digital image. I know that in order to get real world measures like cm or meters I have to use an object with a known dimensions. Is Camera Calibration needed to get measurements from an image if I am using an object as a reference?

Thanks.

Answer 1

Short: No

Long: Camera Calibration (parameters) are in terms of optimization an additional term (sometimes a polynom) which can improve the resulting accuracy.

Think about it as an regression: If you have enough data to fit an higher order polynomial with a better insample/outsample error then you should should use the additional parameter(s). If you don't have enough data then you overfit and the insample/outsample error will be worse.

Especially in photogrammetry camera calibration parameters need to have a certain angle and camera position or combinations of them (relative to the object which you measure). Otherwise you wont be able to calculate the parameter with an significant value.

Answer 2

Antonio Criminisi's PhD thesis contains all the basics on this issue. See this answer to a related question.