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Introduction
This document discusses the camera motions and lens adjustments used for testing the precision of the camera calibration.
Do the following camera movements/lens adjustments to test your camera calibration. The physical reference points and the virtual reference points (markers) relative position should not change from each other. In other words, they should move together.
IMPORTANT: If your camera is not genlocked, check the tracking and zoom (when applicable) delay values before you start testing.
Lens Calibration
This part of the test requires only camera lens adjustments.
IMPORTANT: The camera has to be completely still during the lens calibration testing.
Before you begin testing, select the SCENE control panel on the INPUTS control board and make sure that the Lens Distortion is turned on:
NOTE: The default value for Lens Distortion is On.
NOTE: Edge Expand increases the resolution of the render engine to compensate for the smaller image size the Lens Distortion may cause. It can be set to 0 or higher during testing. Higher values will increase pressure on the CPU and GPU as the render resolution increases.
Center Shift
First, test the Center Shift calibration.
Pay attention to the center of the image.
Point the camera to the bottom/contact point of the reference points, and then fix its position and rotation. Zoom in and out of the reference points. The contact point of the reference point should remain in the center of the image throughout the entire zoom range.
NOTE: You can turn on the Show Crosshair for this test (INPUTS control board \ MARKERS control panel \ Pin Values panel \ Show Crosshair).
NOTE: Aximmetry Camera Calibrator calibrates Center Shift even for Single Focal Length lenses.
NOTE: With a Single Focal Lenght lens, you cannot test the precision of the Center Shift calibration.
Field-of-View
Second, test the FOV (Field-of-View) calibration.
Use at least two markers for this test. Position at least one marker at around 1/3 or 2/3 of the image's width.
Pay attention to the wider center area of the image to include both markers (yellow highlight). Ignore the edges of the image (darkened area).
NOTE: To test the Field-of-View calibration of fixed focal length camera lenses (and for single-focal-length calibration of zoom lenses), use Panning and Tilting.
Zoom in and out freely on the reference points. Stop the zooming at arbitrary values to check the calibration. The reference points should move together all the time.
NOTE: Example of zooming showcasing a precise camera tracking calibration
NOTE: If you are testing a PTZ camera, you can stop the zooming at arbitrary values and pan and tilt the camera to test every main feature (PTZ: Pan-Tilt-Zoom).
Lens Distortion
Lastly, test the Lens Distortion calibration.
Position the reference points near the edge of the camera's FOV (Field-of-View). Alternatively, you can turn (pan) the camera left or right to achieve this.
Pay attention to the edges and corners of the image. The reference points should move in sync from edge to edge of the screen.
Set the camera at arbitrary zoom values and pan and tilt the camera. Keep the reference points in the frame all the time. The reference points should move together all the time.
For more precise testing, repeat these steps, focusing on every side and corner of the frames (left-right, top, bottom sides, and the four corners).
NOTE: Alternatively, to see the Lens Distortion calibration's effect, select the SCENE control panel on the INPUTS control board and turn on and off the Lens Distortion pin.
Tracking Calibration
Panning and Tilting
During pan and tilt motions, we turn the camera left-right (panning), and up and down (tilting).
These tests focus on:
- The Delta Head Transformation calibration of the tracking device.
- The Field-of-View calibration of fixed focal length lenses (or the single-focal-length calibration of zoom lenses)
But they are also affected by:
- The Field-of-View calibration of the camera lens,
- The Lens distortion correction of the camera lens (on the edges of the image),
- The measuring precision of the tracking system (since the camera does not rotate around its no-parallax point)
Pan and tilt the camera left-right, up-down.
The reference points (including the virtual grid and the studio floor) should move together all the time.
NOTE: Examples of left-right (panning, left side) and up-down (tilting, right side) movements showcasing a precise camera tracking calibration.
Dolly
Dolly movements are typically left-right, back-and-forth motions, where only the camera's position changes (but not its rotation).
These tests focus on:
- The measuring precision of the tracking system.
But they are also affected by:
- The Field-of-View calibration of the camera lens,
- The Lens distortion correction of the camera lens (on the edges of the image),
- The Delta Head Transformation calibration of the tracking device (the Delta Head Transformation's rotation values determine the tracking calibration's coordinate system's axes).
Move the camera left-right, back-n-forth, ideally at least a couple of meters in each direction.
The reference points (including the virtual grid and the studio floor) should move together all the time.
NOTE: Examples of left-right (left side) and back-and-forth (right side) dolly movements showcasing a precise camera tracking calibration.
