Calibrations and templates
What’s a calibration ?
A calibration is a set of parameters that define how the input videos relates with each others, the input camera parameters, …
VideoStitch Studio provides you with an automatic calibration tool, that will optimize both your lenses’ settings (vignetting, …) and the camera rig setup.
VideoStitch Studio comes with calibration algorithms, to help you create a panoramic video. There are two kinds of calibration:
- Geometric calibration: computes the geometric parameters to stitch and merge the videos together in one single output panorama (yaw, pitch, roll, …)
- Photometric calibration: optimizes your lens settings (among others vignetting) so that your exposure looks even in the whole panorama
Our geometric calibration algorithm will try to find control points in your input videos and to match them. Once this step is done, we can merge your images together.
You can find a step-by step tutorial on how to use that feature on our Youtube channel:
To get an accurate panorama result, all your cameras need to have the same settings:
- Please do not use the camera zoom feature, or the GoPro4 Superview mode
- Choose the correct lens parameters when calibrating (for Gopros, the FOV is usually 120)
- If you have circular fish-eye lenses, do not forget to crop the input images
Applying the calibration
Our algorithm processes a couple of still images from your inputs in order to find the geometry parameters to match and merge them. It then uses these results to merge the whole input videos.
The algorithm is optimized on scenes in your video sequences that satisfy the following conditions:
- The camera rig and the scene it is recording are static, to solve synchronization issues and avoid motion blur and rolling shutter (those introduce image distortion).
- There are enough details in all the images: if in the overlap zone between two cameras there is only a piece of sky, ocean, … then the algorithm will not be able to find control points
- There are no (or really few, and not in the overlap zones) close objects. Objects closer than two meters away (approximately, depends of your rig) will introduce errors in the calibration
To specify which scenes the algorithm should use you can:
- Use the fully automatic mode, clicking on the “Add” button so that scenes are picked automatically from you input videos
- Manually add some frames (add the current frame in the timeline) if you think the scene satisfies the above conditions
Then, click on “1 – Calibrate Geometry” to launch the calibration.
Since VideoStitch Studio v2.1, you can also apply a “photometric” calibration. It will computes cameras’ response curve and vignetting, to improve your output quality.
Vignetting is a lens distortion effect that affects all the optical lenses. This effect is more visible close to the images’ edges, that tends to be darker than the center:
Using the input cameras’ response curve and vignetting, VideoStitch Studio is able to blend more smoothly the images. When applying exposure compensation, it will also improve the color correction by minimizing color and exposure differences between the inputs.
In VideoStitch Studio interface, check the box “photometric calibration parameters”, and then click on “2 – Calibrate photometry”. You will see the camera response curve and vignette coefficients appear.
You may sometimes want to improve the automatic calibration (when your scene doesn’t have enough details, or has close objects for instance). VideoStitch Studio is compatible with PTGui and Hugin software solutions, that can stitch together still images.
Using an external calibration
In “Edit > Preferences” (keyboard shortcut: Ctrl + ,), enter your calibration tool path: for instance “C:/Program Files/PTGui/PTGui.exe”.
Then, go to “Window > Calibration” and click on “Calibration from a file”.
You can find a tutorial on how to use VideoStitch with PTGui here (process with Hugin would be similar):
If you already have a calibration template created by PTGui or Hugin
Drag & drop a PTGui or Hugin file on VideoStitch Studio, or from the “Calibration from a file” tab click on “Browse calibration“.
Editing a calibration
Editing a calibration is done directly in PTGui / Hugin. You can also update your previous calibration in PTGui or Hugin (more accurate calibration, frames with a better calibration scene) directly from VideoStitch Studio. To extract the current frames, just click on “Edit > Extract stills to” (keyboard shortcut: Ctrl + Shift + E). Pick the same directory you were using before so that PTGui / Hugin can detect the inputs images have changed.
If you want to create a new calibration from scratch
Click on “New calibration” and select where you want to save your calibration template. You will then be prompted to enter your camera settings, and you are ready to start your calibration. If you are already a PTGui or Hugin user, this step should be straightforward. If not, we recommend you to check the tutorials available on our website for PTGui, or directly on PTGui or Hugin websites. There are plenty of tutorials that will get you started quickly.
Creating re-usable calibrations
You can create some good quality templates that can be used to instantly bootstrap new projects. These templates can be used to preview synchronization errors (you will not get any good calibration if your videos are not correctly synchronized).
These few guidelines should help you ensure quality calibration files :
- A single calibration file can not fit all the situations. It works best when it has been created for a specific ‘distance from the camera’. create calibrations for indoor, outdoor, or even finer intervals.
- Add control points to objects that are roughly at the same distance from the camera.
- Use videos shot with static cameras, in a bright and static environment.
- Add control points to all overlapping images