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Conversion of camera intrinsic parameters (pixels to meter)

asked 2013-02-18 02:45:38 -0500

Bedivere gravatar image

I am currently developing a project involving a camera and a distance sensor, but I stumbled on a problem, I have obtained the camera's parameter through calibration step , however I discovered that the obtained parameters are measured in pixels (e.g. focal length [860, 899], etc).

Is there any formula to convert this to unit distance (meter) ? I tried a few calibration techniques but all returns the same measurement in pixel.

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answered 2013-02-18 03:46:51 -0500

The calibration obtains is related to the resolution used, ie: focal length will be different with another resolution. Do you really need metric values or normalized? In the second case, you can normalize focal by resolution( 860/640, 899/480 for example). Metric system can be obtain (in 3D coordinates, not in focal length) by specifying size of square in calibration process in meters (or centimeters, etc.).

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I need the camera parameters in metric value (meters or centimeters). Previously, i have obtained the parameters in pixel value and also in its normalized form, however from my understanding we need something called scale factor in order to convert this to metric. Is there any formula how to solve this?

I tried to specify the size of square when calibrating (i used 19mm) but i dont know how to get the metric parameters after this.

Bedivere gravatar imageBedivere ( 2013-02-18 17:53:40 -0500 )edit

If you specify the size of squares, you obtain extrinsic parameters in metric mode. For intrinsics, the value in millimeters don't change anything? If you want to calculate the size of object in image, you only know the apparent size in image, but the scale factor doesn't come from the focal, but from the distance of object to the camera plane. If you can access to the focal parameter, you can infer the distance (see information write on photographic camera lenses where focal parameter is also write in meter).

Mathieu Barnachon gravatar imageMathieu Barnachon ( 2013-02-19 03:32:34 -0500 )edit

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Asked: 2013-02-18 02:45:38 -0500

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Last updated: Feb 18 '13