Practical Guide to Machine Vision Software: An Introduction with LabVIEW

14Image Calibration and Correction

If the camera axis is not perpendicular to the object, perspective errors will occur. Due to perspective errors, the acquired image might be distorted and the distortion will vary according to the distance and angle between the objects and camera lens. To reduce perspective errors, the alignment of the camera's axis with respect to objects is important. In addition, you may observe nonlinear distortions caused by optical errors (lens distortion) in camera lens. These distortions can be corrected by using NI Vision calibration tools. During the correction process, you can also acquire conversion information for converting from pixels to the real-world dimensions. This will allow you to measure the size and location of objects in physical measurement units using vision analysis.

In this chapter, image calibration and correction methods using NI Vision Calibration tools are discussed to increase the accuracy of image processing results. By using the calibration tools, an image is calibrated to obtain conversion information in real-world units as well as corrections for image distortion. Then, the image along with the calibration information is saved to a file. The file with the imbedded calibration information is used to correct newly acquired images. This results in a distortion corrected image and measurements are made in physical measurement units.

14.1 Method for Creating an Image Correction File

To generate an image calibration file, a grid ...