CameraCalibration
Description
Note
At the moment this node can not directly be connected to the SfM pipeline in the UI. That would be obviously a nice feature to have. The camera models and parameters can be manually copied to the CameraInit settings. This node just needs a bit more work before using it directly into the Meshroom graph. If someone is interested to contribute to this feature, we would be glad to provide assistance.
The internal camera parameters can be calibrated from multiple views of a checkerboard. This allows to retrieve focal length, principal point and distortion parameters.
Name |
Description |
|---|---|
Input |
Input images in one of the following form: - folder containing images - image sequence like “/path/to/seq.@.jpg” - video file |
Pattern |
Type of pattern (camera calibration patterns) - CHESSBOARD - CIRCLES - ASYMMETRIC CIRCLES - ASYMMETRIC CCTAG |
Size |
(Size of the Pattern) - Number of inner corners per one of board dimension like Width (7) Height (5) (0-10000) |
Square Size |
Size of the grid’s square cells (0-100mm) (1) |
Nb Distortion Coef |
Number of distortion coefficient (0-5) (3) |
Max Frames |
Maximal number of frames to extract from the video file (0-5) (0) |
Max Calib Frames |
Maximal number of frames to use to calibrate from the selected frames (0-1000) |
Calib Grid Size |
Define the number of cells per edge (0-50) |
Min Input Frames |
Minimal number of frames to limit the refinement loop (0-100) |
Max Total Average Error |
Max Total Average Error (0-1) |
Debug Rejected Img Folder |
Folder to export delete images during the refinement loop |
Debug Selected Img Folder |
Folder to export debug images |
Output |
Output filename for intrinsic [and extrinsic] parameters (default filename cameraCalibration.cal) |
Details
Sensor Calibration
To calibrate a sensor a multistep process is required but can be completed from within Meshroom. Ensure that the camera settings, lens, and zoom settings remain consistent or the calibration will be different as these parameters chance. You may want to calibrate your camera setup if your sensor is not in the predefined database. To calibrate we will need a well lit flat surface or display and some somewhat accurate measuring tool or printer.
Generate a checkerboard calibration grid or use the grid from art toolkit github here: https://github.com/artoolkit/artoolkit5/blob/master/doc/patterns/Calibration%20chessboard%20%28A4%29.pdf
If using a display and measuring tool simply display the grid pattern full screen on your display. Measure the width of one of the grids in millimeters and keep this value handy.
If printing and using a flat surface ensure the page is not curling or distorted in any way as this will adversely affect calibration.
Record a video, or a set of still pictures with the checkerboard in many different angles and locations within the sensor. To get an idea of what this looks like there is an example video: https://vimeo.com/141414129.
Create a new node by right clicking within the empty space in the Graph Editor. Utils > CameraCalibration. Verify the following attributes:
Size of the pattern: This is the number of corners, in other words it is one less than the total number of squares counting both colors.
Size of the square in millimeters: If using the printed version 20mm squares is the default, verify size or measure directly.
Note the output folder or set your desired output path
Open cameraCalibration.cal.txt from the output folder. The format of the file is:
// int #image width
// int #image height
// double #focal length
// double #ppx principal point x-coord
// double #ppy principal point y-coord
//DistortionParams:
// double #k0
// double #k1
// double #k2
Remove the CameraCalibration node as its outputs cannot be used in the Graph Editor at this time (v.2021.1).
Verify Advanced Attributes are checked. By clicking the 3 dots in the top right of the attributes panel.
Set CameraInit > Attributes > Intrinsics > InitalizationMode to Calibrated
Set CameraInit > Attributes > Intrinsics > Distortion Params to the K0,K1,K2 values.
Validate CameraInit > Attributes > Initial Focal Length
Validate CameraInit > Attributes > Focal Length
Validate CameraInit > Attributes > Sensor Width
Validate CameraInit > Attributes > Sensor Height
Validate CameraInit > Attributes > Principal Point
Patterns
CHESSBOARD https://github.com/artoolkit/artoolkit5/blob/master/doc/patterns/Calibration%20chessboard%20(A4).pdf
Chessboard calibration video sample https://vimeo.com/141414129
CIRCLES
ASYMMETRIC_CIRCLES https://nerian.com/support/resources/patterns/
ASYMMETRIC_CCTAG https://github.com/alicevision/CCTag
A list with other camera calibration tools and patterns can be found here https://github.com/natowi/CameraCalibTools
Here you can read some more on the theory on camera calibration in general: http://docs.opencv.org/3.0-beta/doc/tutorials/calib3d/camera_calibration/camera_calibration.html