Chapter 6
Calibrating Images
©
National Instruments Corporation
6-9
IMAQ Vision for LabWindows/CVI User Manual
Simple Calibration
When the axis of your camera is perpendicular to the image plane and lens
distortion is negligible, use simple calibration. In simple calibration, a pixel
coordinate is transformed to a real-world coordinate through scaling in the
horizontal and vertical directions.
Use simple calibration to map pixel coordinates to real-world coordinates
directly without a calibration grid. The software rotates and scales a pixel
coordinate according to predefined coordinate reference and scaling
factors. You can assign the calibration to an arbitrary image using
imaqSetSimpleCalibration()
.
To perform a simple calibration, set a coordinate reference (angle, center,
and axis direction) and scaling factors on the defined axis, as shown in
Figure 6-7. Express the angle between the x-axis and the horizontal axis
of the image in degrees. Express the center as the position, in pixels, where
you want the coordinate reference origin. Set the axis direction to direct or
indirect. Simple calibration also offers a correction table option and a
scaling mode option.
Use the
system
parameter to define the coordinate system. Use the
grid
parameter to specify the scaling factors. Use the
method
parameter to set
the scaling method. Set the
learnTable
parameter to
TRUE
to learn the
correction table.
Figure 6-7.
Defining a Simple Calibration
1
Origin
X
Y
dy
1
dx
