A publicly known technology transforms an image captured by an onboard camera into a projective image (bird's-eye image) representing the vehicle periphery (a state of the vehicle periphery viewed from above the vehicle).
A recently disclosed technology calibrates (adjusts) a camera when the camera or an electronic controller to control the camera is replaced or when a camera position or posture is misaligned while in use.
In the disclosed technology, the camera uses a transformation rule (parameter) to transform an image captured by the camera into a projective image. The transformation rule may come incorrect due to replacement of the camera or misalignment of the camera position or posture. In such a case, the technology assumes the camera to be an adjustment-targeted camera and corrects the transformation rule.
The description below explains a method known as the technology to correct the transformation rule.
When adjusting the camera's transformation rule at a factory, a specially shaped and sized calibration pattern is painted at a predetermined location of the ground in the factory. A vehicle is moved to a predetermined place to adjust the camera's transformation rule. This determines a positional relationship between the calibration pattern and the vehicle and accordingly determines a positional relationship between the calibration pattern and the camera provided for the vehicle. An arithmetic operation is used to adjust the camera's transformation rule.
A car dealership may not be able to ensure a special place to adjust the camera's transformation rule when adjusting the camera's transformation rule. To address this, the technology disclosed in patent literature 1 places one calibration pattern in a partially overlapping range between a capture range of the adjustment-targeted camera and a capture range of an adjacent reference camera (no adjustment needed). The technology adjusts the transformation rule determined for the adjustment-targeted camera so that the calibration pattern matches coordinates of the calibration pattern in the video in an image space that is projection-transformed according to a transformation rule determined for the reference camera.
In adjusting the camera's transformation rule by placing the calibration pattern at arbitrary location in the car dealership, the capture range of the adjustment-targeted camera overlaps with the capture range of a camera serving as a candidate for the reference camera and the calibration pattern is placed in the overlapping range. Otherwise, adjusting the transformation rule determined for the adjustment-targeted camera is difficult.
Additionally, depending on positions to place the calibration pattern, accuracy of the captured image of the calibration pattern is low, disabling accurate adjustment.