National Instruments IMAQTM - Manual (Page 92)

Chapter 6 Calibrating Images
© National Instruments Corporation 6-7 IMAQ Vision for Visual Basic User Manual
Choose the perspective projection algorithm when the system exhibits
perspective errors only. A perspective projection calibration has an
accurate transformation even in areas not covered by the calibration
grid, as shown in Figure 6-6. Set
CWIMAQLearnCalibrationOptions.CalibrationMethod to
cwimaqPerspectiveCalibration to choose the perspective calibration
algorithm. Learning and applying perspective projection is less
computationally intensive than the nonlinear method. However, perspective
projection cannot handle nonlinear distortions.
If the imaging setup exhibits nonlinear distortion, use the nonlinear
method. The nonlinear method guarantees accurate results only in the
area that the calibration grid covers, as shown in Figure 6-6. If the
system exhibits both perspective and nonlinear distortion, use the
nonlinear method to correct for both. Set
CWIMAQLearnCalibrationOptions.CalibrationMethod to
cwimaqNonLinearCalibration to chose the nonlinear calibration
algorithm.
Figure 6-6. Calibration ROIs
Using the Learning Score
The learning process returns a score that reflects how well the software
learned the input image. A high learning score indicates that you chose the
the appropriate learning algorithm, that the grid image complies with the
guideline, and that the vision system setup is adequate.
1 Calibration ROI Using the
Perspective Algorithm 2 Calibration ROI Using the
Nonlinear Algorithm
1
2