Add zoom factor to interactive calibration tool

[rogday]

Can be useful when the screen is smaller than the image from camera.

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[asmorkalov]

👍

[alalek]

It makes sense to call putText() after the frame's resize.
Or resize input frames after its capture as the first step.

[rogday]

It makes sense to call putText() after the frame's resize. Or resize input frames after its capture as the first step.

I don't think putText() is the offender here - board detection is much more computationally expensive. The purpose of this PR is for the camera output to fit onto the screen. If we resize the frames first, I believe the results of the calibration will differ, and small boards (or boards that are too far) won't be detected anymore.

[alalek]

I agreed, that resizing of input frames is a bad idea (just because we don't get intrinsics for original resolution).

But I still believe that putText() should be done after the resize operation (to keep UI messages clear).