Learning the error map, Learning the correction table, Setting the scaling mode – National Instruments IMAQTM User Manual

Page 93

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Chapter 6

Calibrating Images

IMAQ Vision for Visual Basic User Manual

6-8

ni.com

Note

A high score does not reflect the accuracy of the system.

If the learning process returns a learning score below 600, try the following:

1.

Make sure the grid complies with the guidelines listed in the

Defining a Calibration Template

section.

2.

Check the lighting conditions. If you have too much or too little
lighting, the software may estimate the center of the dots incorrectly.
Also, adjust the threshold range to distinguish the dots from the
background.

3.

Select another learning algorithm. When nonlinear lens distortion is
present, using perspective projection sometimes results in a low
learning score.

Learning the Error Map

An error map helps you gauge the quality of the complete system. The error
map returns an estimated error range to expect when a pixel coordinate
is transformed into a real-world coordinate. The transformation
accuracy may be higher than the value the error range indicates. Set

CWIMAQLearnCalibrationOptions.LearnErrorMap

to

True

to learn

the error map.

Learning the Correction Table

If the speed of image correction is a critical factor for the application, use
a correction table. The correction table is a lookup table that contains
the real-world location information of all the pixels in the image. The
correction table is stored in memory. The extra memory requirements for
this option are based on the size of the image. Use this option when you
want to simultaneously correct multiple images in the vision application.
Set

CWIMAQLearnCalibrationOptions.LearnCorrectionTable

to

True

to learn the correction table.

Setting the Scaling Mode

Use the scaling mode option to choose the appearance of the
corrected image. Set

CWIMAQLearnCalibrationOptions.CorrectionScalingMode

to

cwimaqScaleToFit

or

cwimaqScaleToPreserveArea

. For more

information about the scaling mode, refer to Chapter 3, System Setup and
Calibration
, in the IMAQ Vision Concepts Manual.

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