camera intrinsic parameters

Camera intrinsic parameters are the handful of numbers that describe a camera's own internal optics — the fixed traits baked into that particular lens and sensor, no matter where you point it. They answer the question: once a ray of light enters this camera, exactly which pixel does it light up? Two cameras sitting in the same spot, looking the same way, can still produce different images because one has a wide lens and a big sensor and the other a long lens and a tiny one. The intrinsics capture precisely that difference.

There are usually four to five of them. The focal length (often two numbers, for the horizontal and vertical directions) sets how zoomed-in the view is — a long focal length magnifies a narrow slice of the world, a short one drinks in a wide scene. The principal point is the pixel where the optical center lands, usually near the middle of the image but rarely dead-on because sensors are never mounted perfectly. Skew, a fifth number that is almost always zero in modern cameras, accounts for pixel rows and columns that are not perfectly perpendicular. Bundled together these form the intrinsic matrix, the recipe that converts a direction in front of the camera into a precise pixel coordinate.

Intrinsics belong to the camera, not the scene, so they stay the same as the robot drives around — that is what makes them so valuable. Once measured, a robot can interpret every image from that camera consistently. They are distinct from extrinsic parameters, which describe where the camera is and which way it faces in the world.