The digital calibration is used to create a reference dataset. It needs to be performed only once, as long as nothing moves. If one camera gets displaced, you’ll to start over.
TL;DR: blue boxes are for the yellow markers, purple boxes are the detection zones (the zone where we’re going to try to detect your markers)
1- Calibration panel/bar
1.1- Calibration panel:
- best option when shooting against a window or a busy background
- best for small setups (18 cameras or less in a tight configuration)
- DIY instructions: https://xanglecs.com/blog/diy-bullet-time-calibration-panel-close-up
1.2- Back-lit calibration bar:
A calibration bar or panel is essential in order to have a reference on which you’re going to aim all of your cameras at (pre-calibration). It is also going to be used to apply digital calibration to smooth out all imperfections. The back-lit calibration bar is great for a full-360 setup or a large setup where you need all cameras to see the exact same markers. For 18 cameras or less, you can get away with a calibration panel which is way easier to use. It is recommended to have your markers as close as possible to the top and bottom edges of the frame (but keep them in the frame). Buy on xangle.store
* The two items above are optimal, but you can always make this work with very minimal equipment. A simple light-stand with two yellow tape is going to work properly in most cases.
2- Pre-calibration
Place all of your cameras on your structure and aim at your calibration bar. Try to be as precise as possible to avoid too much cropping after the digital calibration is applied. Use either the live view at the back of the camera or the live-view in Xangle to perform the pre-calibration. In both cases, use the grid to line-up with with the markers
3- Digital calibration module
From Xangle, navigate to the Calibration module and take a reference shot (trigger). The purple box is the common detection zone for all cameras. Make sure the markers are always inside these boxes on all frames. The blue box is for the markers, thus, this one is different from one camera to another. In ideal situations, you’ll never have to fine-tune the blue boxes. In cases where you have a bright window behind your calibration bar, it can help to manually place the blue boxes. To apply the manual calibration (blue box adjustments), click on “regenerate”.
Make sure the purple boxes cover markers for all frames. You can fine-tune the blue box to surround the markers.
3..2 Buttons & functions
- Recalibrate: recalculate values after you change any settings (using the same image set)
- Regenerate: apply the manual calibration and generate a new mp4 preview
3.3- Calibration module
- Click on the camera number to enter a full-screen view. Use the left/right keys to navigate from one frame to another
- Use the mouse wheel to zoom inside the image (to fine tune the blue boxes)
- The central marker is not detected by Xangle. That is used only for you to properly aim at the center (make sure it is at the actual center on all cameras). The exact center between the two yellow markers is used as the final center point for the crop
- How to find the center spot? The distance from the center is up to you. Use two ropes with the same length, attach each of them to the the first and last ball heads, then tighten up to the center point. Put a marker on the floor as a reference. On a full 360 setup, cut 3 ropes at a length of your radius, attach to 3 ballheads, and tighten to your center point.
3.4 - Tips & tricks
- Make sure that ALL markers are INSIDE the purple boxes. These are the detection zones. Leave enough space around but make sure you’re not picking up similar colors in the background.
- If you make your own calibration panel, make sure you leave enough black padding around your two markers. Try also to avoid using reflective material (panel and markers) as this might induce variation in the colors depending on the angle
- The default color for the markers is yellow. If your markers are not yellow, you simply need to do a "pick color" (detection panel)
- The cameras don’t need to all be at the same distance from the calibration bar. We correct the distance variations digitally. This means you can use straight bars with angles instead of a circular truss.
- Prior to doing the digital calibration, make sure that all of your lenses are properly focused. A larger (blurry) marker is going to give you incorrect values