National Instruments IMAQTM - Manual (Page 86)

© National Instruments Corporation 6-1 IMAQ Vision for Visual Basic User Manual
6
Calibrating Images
This chapter describes how to calibrate the imaging system, save
calibration information, and attach calibration information to an image.
After you set up the imaging system, you may want to calibrate the system.
If the imaging setup is such that the camera axis is perpendicular or nearly
perpendicular to the object under inspection and the lens has no distortion,
use simple calibration. With simple calibration, you do not need to learn a
template. Instead, you define the distance between pixels in the horizontal
and vertical directions using real-world units.
If the camera axis is not perpendicular to the object under inspection or the
lens is distorted, use perspective and nonlinear distortion calibration to
calibrate the system.
Perspective and Nonlinear Distortion Calibration
Perspective errors and lens aberrations cause images to appear distorted.
This distortion misplaces information in an image, but it does not
necessarily destroy the information in the image. Calibrate the imaging
system if you need to compensate for perspective errors or nonlinear lens
distortion.
Follow these general steps to calibrate the imaging system:
1. Define a calibration template.
2. Define a reference coordinate system.
3. Learn the calibration information.
After you calibrate the imaging setup, you can attach the calibration
information to an image. Refer to the
Attach Calibration Information
section of this chapter for more information. Depending on your needs, you
can either apply calibration information in one of the following ways:
• Convert pixel coordinates to real-world coordinates without correcting
the image
• Create a distortion-free image by correcting the image for perspective
errors and lens aberrations