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National Instruments IMAQ Vision for Measurement Studio Calibrate Your Imaging System, Create an Image

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Chapter2 GettingMeasurement-Ready Images

IMAQVision for LabWindows/CVI User Manual 2-2 ni.com

3. Selectan imageacquisition device that meets your needs. National

Instruments offersseveral image acquisition (IMAQ) devices, such as

analog color and monochrome IMAQdevices as well as digital

devices.Visit ni.com/imaq for more information about IMAQ

devices.

4. Configurethe driver software for your image acquisition device. If

you havea National Instruments image acquisition device, configure

your NI-IMAQdriver software through Measurement & Automation

Explorer(MAX). Open MAX by double-clicking the Measurement &

Automation Explorer icon on your desktop. For more information,

seet he NI-IMAQ User Manual and the MAX online help.

Calibrate Your Imaging System

After you set up your imaging system, you may want to calibrate your

system.Calibrate your imag ingsystem to assi gn real-world coordinates to

pixelc oordinatesand compensate for p erspective and nonlinear errors

inherent in your imaging system.

Perspectiveerrors occur when your camera axis is not perpendicular to the

object under inspection. Nonlinear distortion may occur from aberrations

inthe camera lens. Perspective errors and lens aberrations cause images to

appeardistorted. This distortion misplaces information in an image, butit

does not necessarilydestroy the information in the image.

Usesimple calibration if you only want to assign real-world coo rdinates to

pixelcoordinates. Use persp ectiveand nonlinear distortion calibrati on if

youneed to compensate for perspective errors and nonlinear lens distortion.

Fordetailed information about calibration, see Chapter 6, Calibration.

Create an Image

To create an image in IMAQ Vision for LabWindows/CVI, call

imaqCreateImage().This function returns an image reference you can

usewhen callin go ther IMAQ Vision functions. The only limitation to the

size and number of images you can acquire and process is the amount of

memoryon your computer. When you creat ea n image, specify the type of

the image. Table 2-1 lists the valid image types.

Contents

Main IMAQ Page Important Information Warranty Copyright Trademarks WARNINGREGARDING USE OF NATIONAL INSTRUMENTS PRODUCTS Conventions Contents Chapter 1 Introduction to IMAQ Vision Chapter 2 Getting Measurement-Ready Images Chapter 3 Grayscale and Color Measurements Chapter 4 Blob Analysis Chapter 5 Machine Vision Page Introduction to IMAQ Vision About IMAQ Vision Documentation and Examples Application Development Environments IMAQ Vision Function Tree Page IMAQ Machine Vision Function Tree Creating IMAQ Vision Applications Chapter1 Introductionto IMAQ Vision Figure1-2. InspectionSteps for Building a Vision Application IMAQVision for LabWindows/CVI User Manual 1-6 ni.com Getting Measurement-Ready Images Set Up Your Imaging System Calibrate Your Imaging System Create an Image Page Source and Destination Images AcquireorReadanImage Acquiring an Image Reading a File Converting an Array to an Image Display an Image Attach Calibration Information Analyze an Image Improve an Image Lookup Tables Filters Convolution Filter Nth Order Filter Grayscale Morphology FFT Page Complex Image Operations Grayscale and Color Measurements Define Regions of Interest Interactively Defining Regions Page Page Page Page Programmatically Defining Regions Defining Regions with Masks Measure Grayscale Statistics Measure Color Statistics Figure3-4. Primary Components of a Color Image Comparing Colors Learning Color Information Choosing the Right Color Information Specifying the Color Information to Learn Using the Entire Image Using a Region in the Image Using Multiple Regions in the Image Choosing a Color Representation Sensitivity Ignoring Learned Colors Blob Analysis Correct Image Distortion Create a Binary Image Improve the Binary Image Removing Unwanted Blobs Separating TouchingBlobs Improving Blob Shapes Make Particle Measurements Page Page Convert Pixel Coordinates to Real-World Coordinates Machine Vision Locate Objects to Inspect UsingEdgeDetectiontoBuildaCoordinateTransform Page Using Pattern Matching to Build a Coordinate Transform Page Chapter5 MachineVision NationalInstruments Corporation 5-7 IMAQVision for LabWindows/CVI User Manual ChoosingaMethodtoBuildtheCoordinateTransform Figure5-4. Buildinga Coordinate Transform Set Search Areas Interactively Defining Regions Programmatically Defining Regions Find Measurement Points Finding Features Using Edge Detection Finding Lines or Circles Figure5-5. Findinga Straight Feature Finding Edge Points Along One Search Contour Finding Edge Points Along Multiple Search Contours Finding Points Using Pattern Matching Defining and Create Good TemplateImages Symmetry Feature detail Positional information Background information Trainingthe Pattern Matching Algorithm Defining a Search Area Setting Matching Parameters and Tolerances Match Mode Minimum Contrast Rotation Angle Ranges Testingthe Search Algorithm on Test Images Using a Ranking Method to Verify Results Finding Points Using Color Pattern Matching Defining and Creating Good Color TemplateImages Color Information Symmetry Feature Detail Positional Information Trainingthe Color Pattern Matching Algorithm Defining a Search Area Setting Matching Parameters and Tolerances Color Sensitivity Search Strategy Color Score Weight Minimum Contrast Rotation Angle Ranges Testingthe Search Algorithm on Test Images Finding Points Using Color Location Convert Pixel Coordinates to Real-World Coordinates Make Measurements Distance Measurements Analytic Geometry Measurements Instrument Reader Measurements Display Results Page Calibration Perspective and Nonlinear Distortion Calibration Defining a Calibration Template Defining a Reference Coordinate System Page Page Learning Calibration Information Specifying Scaling Factors Choosing a Region of Interest Choosing a Learning Algorithm Using the Learning Score Learning the Error Map Learning the Correction Table Setting the Scaling Method Calibration Invalidation Simple Calibration Save Calibration Information Attach Calibration Information A Technical Support Resources Web Support NI Developer Zone Customer Education System Integration Worldwide Support Glossary Numbers/Symbols A B C Page D E F G H I Page J K L M N O P Page Q R S T Page Index A B C D E F G H I Page Page L M N O P R S T V W Z