Stereo Camera Calibration Tool

Calibrates two Camera based on two checkerboard frame sequences and entered settings, exports them to disk or to a Node-Graph Editor

Quick Start

To open a tool go to 4D Tools >> Stereo Camera Calibration Tool.

Calibration has the next steps:

Note

To quickly move between tabs, you can use the Mode menu.

Stereo Camera Calibration: Input Data Tab

Frames for calibration are selected on this tab.

../_images/InputDataTabEmpty.png

The interface is divided into 3 parts:

Two Viewports:

Display frames of loaded sequences or video files

Frameline:

Allows you to move between frames

Buttons:

To interact with frame sequences

Edit Menu

Select Left Image Folder

.

Select folder to load images on the left viewport

Select Left Video File

.

Select video to load on the left viewport

Select Right Image Folder

.

Select folder to load images on the right viewport

Select Right Video File

.

Select video to load on the right viewport
../_images/PrevFrameWrapButton.png

Prev Frame

Left

Displays the previous image
../_images/NextFrameWrapButton.png

Next Frame

Right

Displays the next image
../_images/PrevSelectedFrameWrapButton.png

Prev Selected Frame

CTRL + Left

Displays the previous selected image
../_images/NextSelectedFrameWrapButton.png

Next Selected Frame

CTRL + Right

Displays the next selected image

Add Frame

Space

Adds the current frame to calibration

Remove Frame

Del

Removes the current frame from calibration

Clear All

.

Removes all frames from the calibration

Edit Left Source

.

Left viewport frame rotation and offset settings

Edit Right Source

.

Right viewport frame rotation and offset settings

How To Use

First of all load checkerboard image sequence or video file on each viewport. Use Select Left Image Folder or Select Right Image Folder buttons to load image sequence, Select Left Video File or Select Right Video File buttons to load video files, or Drag and drop folders or video files to the viewport. After that, use Frameline and Buttons to navigate and select images in frame sequences.

To set the frame rotation and offset of the whole sequence (when the video is out of sync), use the Edit Left Source or Edit Right Source.

Note

  • Supported video formats: .mov, .mp4, .avi, .mkv.

  • Supported image extensions: .jpg, .jpeg, .png, .exr, .tif, .tiff.

  • All images in a sequence must be the same size.

After choosing frames click on Next: Checker Board

../_images/InputDataTabLoaded.png

If the frame sequence does not meet the conditions, the button for moving to the next tab will be inactive, and the error message will be displayed next to it.

Tip

A few tips for getting a good camera calibration:

  • Try to capture the most diverse positions of the checkerboard, this will greatly increase the accuracy of the camera output parameters.

  • Try to choose as many different positions of the checkerboard as possible, this increases the accuracy of the calibration.

  • Do not select frames where the checkerboard is not fully displayed or has highlights, it can’t be detected.

  • Calibration requires at least 1 frame, but for a good result, it is recommended to add 20-30 frames.

Stereo Camera Calibration: Cheсker Board Tab

On this tab, you need to set the checkerboard parameters.

../_images/CheckerboardTab.png

Parameters

Num Columns:

number of columns of checkerboard cells

Num Rows:

number of rows of checkerboard cells

Cell Size (cm):

checkerboard square size in centimeters

First Square Color:

the color of the first square of the checkerboard

Edit Menu

Import From JSON

Import parameters from JSON file

Export to JSON

Import parameters to JSON file

Next: Calibrate

Calibrates cameras using input data

Next: To Results

If calibrated, moves to the Calibration Results tab

How To Use

In the parameters, specify the number of cells in the columns and rows, and the size of the cell in centimeters. You can also Import and Export parameters to json file. The viewport displays a preview of the checkerboard.

Attention

Make sure that you correctly specify the Num Columns, the Num Rows and the Cell Size (cm) of the checkerboard pattern.

After setting the parameters, click Next: Calibrate to start the calibration.

Calibration

During the calibration process, a window appears which displays the current state of the calibration. You can interrupt the process by pressing the Terminate button or the Esc key.

../_images/CalibrationProcess.png

When the calibration is completed, the next tab will automatically appear.

Stereo Camera Calibration: Calibration Results Tab

This tab displays the calibration results. Also on this tab, you can remove frames that spoil the calibration.

../_images/ResultTabCorrect.png

The interface is divided into 3 parts:

Two Viewports with camera data:

Display frames of calibrated sequences and calibrated camera data

Frameline:

Allows you to move between calibrated frames

Buttons:

To interact with image sequences or export data

Edit Menu

../_images/PrevFrameWrapButton.png

Prev Frame

Left

Displays the previous image in the sequence
../_images/NextFrameWrapButton.png

Next Frame

Right

Displays the next image in the sequence

Remove Frame

Del

Removes the current frame from calibration sequence

Return Frame

.

Return the current frame to calibration sequence

Return All Frames

.

Returns all frames to the calibration sequence

Recalibrate

.

Starts a calibration without removing frames

Export Cameras to Files

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Exports cameras to JSON files

Export Cameras to Wrap4D

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Exports cameras to node-graph

Export All to Wrap4D

.

Exports all calibrated data to node-graph

How To Use

After calibration, the frames where the checkerboard was found will be shown with the grid of the detected checkerboard. Frames where a checkerboard was found on two frames in sequences are displayed in green on the frameline. If the checkerboard was not found on at least one of the frames, it will be marked in red.

../_images/ResultTabNotCorrect.png

Note

The displayed board is two columns and two rows smaller than the specified board.

Due to various factors, the checkerboard can be detected incorrectly, сheck the entire calibrated sequence at how the checkerboard was detected on each of the frames. Frames where the checkerboard was detected incorrectly can be removed from the sequence, and the entire sequence recalibrated.

Note

The camera with index 0 (which is calibrated from the images on the left viewport) will always be positioned at the world origin and look straight ahead.

After that, you can Export the results either to disk or to Wrap4D graph.

Export Results

Calibrated cameras can be exported in three ways: Export Cameras to Files, Export Cameras To Wrap4D Graph and Export All to Wrap4D

Export Cameras to Files

Exports cameras to disk for the specified paths.

../_images/ExportToDisk.png

Export Cameras To Wrap4D Graph

Exports cameras to the Node-Graph Editor along with the UndistortImage and UndistortCamera nodes.

Use this option if you need to use calibrated cameras in a Wrap or Wrap4D. To export, you need to specify the following parameters in the pop-up window.

Enable Undistortion:

If set, then undistort nodes will be created along with the cameras.

Boundary Type:

The Boundary Type parameter that will be set in the undistort nodes

Undistortion Type:

The Undistortion Type parameter that will be set in the undistort nodes

Reset Optical Center:

The Reset Optical Center parameter that will be set in the undistort nodes

../_images/ExportWrap4DOptions.png

After accepting the parameters, nodes appear in the Node-Graph Editor immediately.

../_images/GraphAfterCalibration3.png

Export All to Wrap4D

Exports to Node-Graph Editor, cameras, checkerboard geometry with texture and checkerboard transforms. Matches the rendered checkerboard geometry with an undistorted checkerboard images.

Use this option if you want to check the calibration accuracy.

To export you need to select the export folder and specify the paths to: cameras, checkerboard geometry, texture, checkerboard transforms folder, and specify the parameters for undistort nodes.

../_images/exportAllPathDialog.png
Create Intermediate Directories:

if set, nonexistent directories in the file path will be created

Boundary Type:

The Boundary Type parameter that will be set in the undistort nodes

Undistortion Type:

The Undistortion Type parameter that will be set in the undistort nodes

Reset Optical Center:

The Reset Optical Center parameter that will be set in the undistort nodes

After accepting the parameters, nodes appear in the Node-Graph Editor immediately.

../_images/exportAllGraph.png

Using MergeImage, you can see how the rendered checkerboard matches the checkerboard on the undistorted image.

Render

UndistortImage

MergeImage
../_images/ExportAllRender.png ../_images/ExportAllUndistortImage.png ../_images/ExportAllMergeImage.png

Setup Saving and Loading

You can save the calibration setup and open it at any time.

New Setup

CTRL + N

Clears all data from the current setup

Load Setup

CTRL + O

Loading a setup from a file

Save Setup

CTRL + S

Saving the setup to the previously specified path

Save Setup As

CTRL + Shift + S

Saving the setup to the specified path

Note

If the sequence folder paths don’t exist, you can re-import them. In the pop-up window with the question “Clear input and calibrated data?”, you must click “No”. In this case, the sequence will be loaded and the calibration data will not be lost.