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National Instruments IMAQ Vision for Measurement Studio Acquiring an Image, Reading a File

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Chapter2 GettingMeasurement-Ready Images

IMAQVision for LabWindows/CVI User Manual 2-6 ni.com

Acquiring an Image

Use one of the following methods to acquire images with a National

Instruments image acquisition (IMAQ) device:

•Acquire a single image using imaqEasyAcquire(). When you call

this function, it initializes the IMAQdevice and acquires the next

incoming video frame. Use this function for low-speed single capture

applications where ease of programming is essential.

•Acquire a single image using imaqSnap(). When youcall this

function, it acquires the nexti ncoming video frame on an IMAQ

deviceyou have already initialized using imgInterfaceOpen() and

imgSessionOpen().Use this fun ction for high-speed single capture

applications.

•Acquireimages continually through a grab acquisit ion. Grab functions

perform high-speed acquisitions that loop continually on one buffer.

UseimaqSetupGrab() to start the acquisi tion. Use imaqGrab() to

returna copy of the current image. Use imaqStopAcquisition() to

stop the acquisition.

•Acquirea fixed number of images using a sequence acquisition. Set up

the acquisition using imaqSetupSequence().Use

imaqStartAcquisition()to acquire the number of images you

requested duringsetup. If you want to acquire only certain images,

supplyimaqSetupSequence() with a table describing the number of

frames to skip after each acquired frame.

•Acquireimages continually through a ringed buffer acquisition. Set up

the acquisition using imaqSetupRing().Use

imaqStartAcquisition()to start acquiring i mages into the

acquired ring buffer.To get an image from the ring, call

imaqExtractFromRing()or imaqCopyRing().Use

imaqStopAcquisition()to stop the acquisi tion.

Note Youmust use the imgClose() to release resources associated with the image

acquisitiondevice.

Reading a File

Use imaqReadFile()to open and read data from a file stored on your

computerinto the image reference. You can read from image files stored in

severalstandardformats:BMP,TIFF,JPEG,PNG,andAIPD.The

software automatically converts the pixels it reads into the type of image

you pass in.

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