Camera Calibration Wizard¶

Welcome to the Cylinder and Plate Camera Calibration Wizard¶

This mainly states the input and output of this wizard. Click “Next”.

Select Images¶

Click “Add Images...” and locate one or more images you want to use for this calibration.

Specify Output Folder¶

You are asked to define a folder where the output of this calibration will be written. Preferably make a new empty folder as output folder as multiple files will be written.

Specify Camera Info¶

The predefined cameras are defined in Predefined Cameras and Targets. Choose one of these or in case you are using another camera, choose “Custom” and specify the “Pixel Size” in millimeters. This is the physical size of each sensor corresponding to a single pixel in the camera. This can usually be found in the camera specification. Note that the sensor size does not directly affect the results in the 3D-DIC analysis. But in order to have physically correct camera calibration parameters (focal length,..., etc), the effective sensor size needs to be correct.

Specify Calibration Target Info¶

The predefined calibration targets are defined in Predefined Cameras and Targets. It is also possible to choose a “User defined” calibration target. If the calibration images contain different calibration targets, check the checkbox at the top with label: “Specify individual target for each image”. Otherwise keep it unchecked.

Specify Type of Mesh Extract¶

Just click next and thereby choose the (default) manual checkerboard extraction. The automatic checkerboard extraction is still experimental (May 2016).

Define Unit Cell for Image no. X¶

The first image in the list you specified will also be automatically loaded and shown in the PreProcessor view. Here you need to define a unit cell of the checkerboard pattern. The wizard window should be relatively self-explanatory and contains 5 steps to carry out before clicking the “Next” button.

When you have clicked the 4 points in the image to define the unit cell, click the “Next”-button.

Extend Mesh for Image no. X¶

Now, the 4 points defining the unit cell in the previous window should have been converted to a 2x2 mesh with four elements and two arrows (one green and one red) in the center. The blue ring defines the origin of the three-dimensional target coordinate system. What you want to do here is to extend the mesh to cover as much as possible of the calibration target. This is done by pressing the arrow keys on your keyboard. If you press the “Up” key, a single row is added at the top of the mesh. Corresponding mesh extensions are carried out by using the “Down”, “Right” and “Left” keys. If the mesh gets distorted during the extension of the mesh you can click the “Optimize DIC” button. The mesh will then be optimized according to the checkerboard pattern in the image, and you can continue the mesh extension. Before you click the “Next” button make sure you run a final optimization by clicking the “Optimize DIC” button. Before you continue, the image in the PreProcessor view should look something like the image above.

Specify Cylinder Curvature for Image no. X¶

Specify the curve direction of the target cylinder. It will either be the green or the red arrow shown in the image. In the example case it is the green arrow.

Calibrate Camera for Image no. X¶

You are now ready to calibrate the first camera model, i.e. the camera model for image no. 1. Click the “Calibrate” button.

The results from the camera calibration as well as the camera model parameters are printed in the text-view. The most important numbers here are the “Residuals” in the image (pixel) and the target (mm) domain. These should not be too high. As a rule of thumb, the residuals in the image domain should ideally be a value less than 1.0. The residuals in the target domain follow the residuals in the image domain. When you now click “Next” you start with the calibration of image number 2 in the list you defined.

The four last steps:

• Define Unit Cell for Image no. X
• Extend Mesh for Image no. X
• Specify Cylinder Curvature for Image no. X
• Calibrate Camera for Image no. X,

will be carried out for all images you specified in the start of this wizard.

Merge Camera Models for All Images¶

When you have gone through all the images in the list you specified, you will be able to merge all camera models into a single camera model. Click the “Merge” button as shown in the Figure below:

The results from the merging procedure will be shown in the text view. The prameters for the merged camera model will be shown, and it is important to check the residuals for this merged camera model. The residuals will usually be somewhat higher than for the individual camera models for each image.

Camera Calibration Wizard Finished¶

If you wold like to see the files generated by the wizard, click the “Open Output Folder” button. Normally it will be the file called “cmod_merged.ecc” that will be used when generating input for a 3D-DIC analysis.