Camera intrinsic matrix

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There's no a simple single function that will give you camera intrinsic parameters. Calibration process requires a few steps:

1. Acquisition of calibration images (with chessboard pattern or with circle pattern)
2. Detecting chessboard corners(or blobs in case of circle pattern) with subpixel accuracy
3. Finding camera calibration paramters: intrinsic matrix and distortion coefficients with

The easiest approach is to use an example provided with OpenCV - calibration.exe. You can use it with your own images, so it'll do a calibration for you and give you camera intrinsic matrix and distortions coefficients.

Read below tutorial, it explains how OpenCV calibration example works and how to use it with your own calibration images: http://docs.opencv.org/doc/tutorials/calib3d/camera_calibration/camera_calibration.html#cameracalibrationopencv