In computer vision a camera matrix or (camera) projection matrix is a matrix which describes the mapping of a pinhole camera from 3D points in the world to 2D points in an image.
Let be a representation of a 3D point in homogeneous coordinates (a 4-dimensional vector), and let be a representation of the image of this point in the pinhole camera (a 3-dimensional vector). Then the following relation holds
where is the camera matrix and the sign implies that the left and right hand sides are equal up to a non-zero scalar multiplication.
Since the camera matrix is involved in the mapping between elements of two projective spaces, it too can be regarded as a projective element. This means that it has only 11 degrees of freedom since any multiplication by a non-zero scalar results in an equivalent camera matrix.
Read more about Camera Matrix: Derivation, Normalized Camera Matrix and Normalized Image Coordinates, General Camera Matrix
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