Chapter 6
Calibrating Images
©
National Instruments Corporation
6-7
IMAQ Vision for LabWindows/CVI User Manual
Choose the perspective projection algorithm when your 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 the
mode
element of the
options
parameter to
IMAQ_PERSPECTIVE
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 your 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 your system
exhibits both perspective and nonlinear distortion, use the nonlinear
method to correct for both. Set the
mode
element of the
options
parameter
to
IMAQ_NONLINEAR
to choose 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 learning score above 800 indicates that you
chose the appropriate learning algorithm, that the grid image complies with
the guideline, and that your vision system setup is adequate.
Note
A high score does not reflect the accuracy of your system.
1
Calibration ROI Using the Perspective Algorithm
2
Calibration ROI Using the Nonlinear Algorithm
1
2
