Camera Calibration

Overview

ZED cameras undergo an extensive and rigorous multi-step factory calibration process to ensure accurate camera parameter estimation. This calibration defines key characteristics such as focal length, field of view, and stereo alignment, which are essential for various computer vision and imaging applications.

This applies to both stereo cameras (ZED, ZED Mini, ZED 2, ZED 2i, ZED X, ZED X Mini, ZED X Nano) and monocular cameras (ZED X One), which are factory-calibrated for their intrinsic parameters.

The following parameters can be retrieved for each eye and resolution:

• Focal length: fx, fy.
• Principal points: cx, cy.
• Lens distortion: k1, k2, k3, p1, p2.
• Horizontal, vertical and diagonal field of view.
• Stereo calibration: rotation and translation between left and right eye (stereo cameras only).

Stereo Cameras

Stereo cameras expose the intrinsic parameters of both the left and right eye, as well as the stereo transform (rotation and translation) between them, which is required for depth computation.

Using the API

Camera parameters are available in CalibrationParameters. They can be retrieved using getCameraInformation().

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CalibrationParameters calibration_params = zed.getCameraInformation().camera_configuration.calibration_parameters;
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// Focal length of the left eye in pixels
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float focal_left_x = calibration_params.left_cam.fx;
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// First radial distortion coefficient
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float k1 = calibration_params.left_cam.disto[0];
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// Translation between left and right eye on x-axis
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float tx = calibration_params.stereo_transform.getTranslation()[0];
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// Horizontal field of view of the left eye in degrees
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float h_fov = calibration_params.left_cam.h_fov;

Monocular Cameras

Monocular cameras, such as the ZED X One, have a single lens and are factory-calibrated for their intrinsic parameters only (focal length, principal point, lens distortion and field of view). As they have a single optical sensor, no stereo transform is provided.

When using a monocular camera through the sl::CameraOne class, calibration parameters are available in a single CameraParameters object (instead of the CalibrationParameters used for stereo cameras). They can be retrieved using getCameraInformation().

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CameraParameters calibration_params = zed_one.getCameraInformation().camera_configuration.calibration_parameters;
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// Focal length in pixels
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float focal_x = calibration_params.fx;
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// First radial distortion coefficient
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float k1 = calibration_params.disto[0];
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// Horizontal field of view in degrees
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float h_fov = calibration_params.h_fov;

Recalibrating your camera

While the factory calibration is typically more accurate than user calibrations, you may need to recalibrate your camera in specific situations, such as when placing glass in front of the lens, when operating underwater, or after a strong impact or exposure to extreme temperatures.

• ZED Calibration tool: a GUI tool shipped with the ZED SDK to fine-tune the intrinsic and extrinsic parameters of a stereo ZED camera. This tool only works with stereo cameras and cannot be used to calibrate a monocular ZED X One camera.
• ZED OpenCV Calibration tool: an open-source, OpenCV-based tool to perform a guided checkerboard calibration of ZED stereo cameras and custom stereo rigs (e.g. a dual ZED X One Virtual Stereo system), generating calibration files compatible with the ZED SDK.