Measurement tool, calibration method, calibration apparatus, and computer-readable recording medium

A calibration method of calibrating a stereo camera by a measurement tool that includes a first member having a surface including a chart to be used for calibration of a stereo camera, and a measurement member arranged on the surface of the first member, the measurement member including a light source configured to emit light with a uniform intensity regardless of a position on the surface, and a second member configured to cover the light source and radiate the light from a plurality of first holes and a plurality of second holes having a size larger than the first hole, the calibration method comprising the steps of:

• obtaining a captured image that includes, as a subject, the measurement tool captured by the stereo camera;
• specifying a position of a maximum brightness in figures of the plurality of first holes included in the captured image based on a position of a maximum brightness in figures of the plurality of second holes included in the captured image, and measuring a displacement in an orientation of the measurement tool from a directly facing position with the stereo camera based on the specified position of the maximum brightness in the figures of the plurality of first holes;
• and
• determining a calibration parameter for calibrating the stereo camera based on the displacement in the orientation of the measurement tool and the captured image.

A calibration apparatus comprising:

• a receiver configured to receive a captured image that is captured by a stereo camera, the captured image including, as a subject, a measurement tool that includes a first member having a surface including a chart to be used for calibration of the stereo camera, and a measurement member arranged on the surface of the first member, the measurement member including a light source configured to emit light with a uniform intensity regardless of a position on the surface, and a second member configured to cover the light source and radiate the light from a plurality of first holes and a plurality of second holes having a size larger than the first hole;
• a measurer configured to specify a position of a maximum brightness in figures of the plurality of first holes included in the captured image based on a position of a maximum brightness in figures of the plurality of second holes included in the captured image and to measure a displacement in an orientation of the measurement tool from a directly facing position with the stereo camera based on the specified position of the maximum brightness in the figures of the plurality of first holes;
• and
• a determiner configured to determine a calibration parameter for calibrating the stereo camera based on the displacement in the orientation of the measurement tool and the captured image.