Multiple PS Eye Cameras Calibration
Calibration is a process of computing accurate camera positions and orientations from a video of user waving a small glowing object called marker (for color/color+depth cameras). This step is essential and required for multi-camera system setup.
- 1 Importance of high frame rate
- 2 Glowing Marker
- 3 Step 1: Running iPi Recorder in Calibration Mode
- 4 Step 2: Record Calibration Video
- 5 Step 3: Stop Recording and Check Recorded Video
- 6 Step 4: Take Note of Height of Your First Camera Over the Ground.
- 7 Step 5: Process Calibration Video in iPi Mocap Studio
- 8 Step 6: Check Calibration Quality
- 9 Step 7: Check Ground Plane
- 10 Step 8: Set Scene Scale Using Camera Height as Reference
Importance of high frame rate
You should record calibration video at the same resolution as your action video and at the same (or higher) frame rate.
Calibration at a different resolution may lead to reduced accuracy because cameras usually have different minor distortions at different resolutions (caused by internal scaling algorithm).
Calibration at low frame rate may lead to reduced accuracy because of increased synchronization errors.
Mini Maglite flashlight is recommended for calibration. This is a very common flashlight in US and many other countries. Removing flashlight reflector converts it into an ideal glowing marker easily detectable by motion capture software.
If you cannot get a Mini Maglite, you can use some other similar flashlight.
Alternatively, you can use Sony Move motion controller with white light turned on.
Step 1: Running iPi Recorder in Calibration Mode
Run iPi Recorder and choose one of the darkening modes in "darkening for calibration" list (for Sony PS Eye cameras)
or set Exposure to reasonably small value (for DirectShow-compatible web cameras)
This is important because it helps to reduce motion blur during calibration.
Video will look dim in calibration mode.
Step 2: Record Calibration Video
Start video recording.
Move the marker slowly through your entire capture volume (front-top-right-bottom-left-back-top-right-bottom-left). Start from top and move the marker in a descending spiral motion.
Put the marker to the ground at each corner and at the center of capture volume. At least 4-5 ground points are needed for the correct detection of the groundplane.
Step 3: Stop Recording and Check Recorded Video
Check the video and make sure that:
- There is no significant motion blur (image of marker looks like a round spot rather than an ellipse or a luminescent line)
- Most of the time (80%-90% of all recording time) marker is visible in all cameras
Step 4: Take Note of Height of Your First Camera Over the Ground.
Take note of height of your first camera over the ground. You will need this parameter later.
Step 5: Process Calibration Video in iPi Mocap Studio
To process calibration video please do the following:
- Create new calibration project in iPi Mocap Studio:
- Press New button or select File > New Project menu item or use Ctrl+N (2)
- Choose Calibration project type in New Project Wizard.
- Set the diagonal Field of View (FOV) for your cameras.
- Adjust the Region-of-Interest to cover the part of video that contains the glowing marker (3).
- Normally, you need to use default calibration settings
- Auto-detect initial camera positions turned on
- If calibration fails to detect initial camera positions correctly, you can turn this checkbox off and set camera positions manually. But in most cases it will be easier to re-record calibration sequence.
- Auto-adjust camera FOV turned off
- Use this mode only if you do not use Sony PS3 Eye camera and do not know camera field of view
- Regular calibration mode
- In rare cases when Regular mode fails to calibrate, you can use Extended and Extreme calibration modes. It will take much more time, but may help to calibrate correctly if you have high percent of marker misdetections. Usually this is caused by incorrect camera positioning or poor lighting conditions
- Auto-detect initial camera positions turned on
- Click Calibrate button and wait while the system finishes calibration (4).
Step 6: Check Calibration Quality
Resulting scene should look like this:
Make sure you have Good or Perfect calibration result.
Step 7: Check Ground Plane
Ground plane should be detected automatically. Ground points are marked by yellow color.
- Make sure that ground points are actually near the ground plane.
- If ground plane is detected incorrectly, select ground points manually.
- Expand Manual Calibration Adjustment expander.
- First, unmark all ground points by pressing Clear all points button.
- For each ground point, click on it in 3D view and press Mark as ground button.
- You can cancel marking point as ground point by pressing Unmark ground button.
Step 8: Set Scene Scale Using Camera Height as Reference
Now cameras in your scene are properly oriented relative to other cameras and relative to ground plane. But you still need to find one more parameter: scene scale.
Use Сamera #1 height over ground to set correct scene scale.
- Save results to calibration project file or using Save scene... button on Scene tab (6).