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National Instruments IMAQ Vision for LabWindows TM /CVI Acquiring an Image, Reading a File

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Chapter 2 Getting Measurement-Ready Images

IMAQ Vision 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 IMAQ device.

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

this function, it initializes the IMAQ device 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 you call this

function, it acquires the next incoming video frame on an IMAQ

device you have already initialized using imgInterfaceOpen() and

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

applications.

• Acquire images continually through a grab acquisition. Grab functions

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

Use imaqSetupGrab() to start the acquisition. Use imaqGrab()

to return a copy of the current image. Use imaqStopAcquisition()

to stop the acquisition.

• Acquire a fixed number of images using a sequence acquisition.

Set up the acquisition using imaqSetupSequence(). Use

imaqStartAcquisition() to acquire the number of images you

requested during setup. If you want to acquire only certain images,

supply imaqSetupSequence() with a table describing the number

offrames to skip after each acquired frame.

• Acquire images continually through a ringed buffer acquisition.

Set up the acquisition using imaqSetupRing(). Use

imaqStartAcquisition() to start acquiring images into the

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

imaqExtractFromRing() or imaqCopyRing(). Use

imaqStopAcquisition() to stop the acquisition.

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

acquisition device.

Reading a File

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

computer into the image reference. You can read from image files stored

in several standard formats: BMP, TIFF, JPEG, PNG, and AIPD. 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 Patents Contents About This Manual Chapter 1 Introduction to IMAQ Vision Chapter 2 Getting Measurement-Ready Images Chapter 3 Making Grayscale and Color Measurements Chapter 4 Performing Particle Analysis Chapter 5 Performing Machine Vision Tasks Chapter 6 Calibrating Images Page About This Manual Conventions Related Documentation IMAQ Vision NI Vision Assistant NI Vision Builder for Automated Inspection Other Documentation Introduction to IMAQ Vision About IMAQ Vision Application Development Environments IMAQ Vision Function Tree IMAQ Machine Vision Function Tree Creating IMAQ Vision Applications Chapter 1 Introduction to IMAQ Vision National Instruments Corporation 1-5 IMAQ Vision for LabWindows/CVI User Manual Chapter 1 Introduction to IMAQ Vision IMAQ Vision 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 Acquire or Read an Image 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 Complex Image Operations Making Grayscale and Color Measurements Define Regions of Interest Defining Regions Interactively Page Page Page Tools Palette Transformation Defining Regions Programmatically Defining Regions with Masks Measure Grayscale Statistics Measure Color Statistics Figure 3-4. Primary Components of a 32-Bit Color Image Figure 3-5. Primary Components of a 64-Bit Color Image Note You can also use imaqExtractColorPlanes() to process the red, green, and blue components of a 64-bit image. Comparing Colors Learning 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 Performing Particle Analysis Create a Binary Image Improve the Binary Image Removing Unwanted Particles Separating Touching Particles Improving Particle Shapes Make Particle Measurements Page Page Page Page Page Page Performing Machine Vision Tas ks Locate Objects to Inspect Page Using Edge Detection to Build a Coordinate Transform Page Using Pattern Matching to Build a Coordinate Transform Chapter 5 Performing Machine Vision Tasks National Instruments Corporation 5-7 IMAQ Vision for LabWindows/CVI User Manual Choosing a Method to Build the Coordinate Transform Figure 5-4. Building a Coordinate Transform Set Search Areas Defining Regions Interactively Defining Regions Programmatically Find Measurement Points Finding Features Using Edge Detection Finding Lines or Circles Finding Edge Points Along One Search Contour Finding Edge Points Along Multiple Search Contours Finding Points Using Pattern Matching Defining and Creating Good Template Images Symmetry Feature Detail Positional Information Background Information Training the Pattern Matching Algorithm Defining a Search Area Setting Matching Parameters and Tolerances Match Mode Minimum Contrast Rotation Angle Ranges Testing the Search Algorithm on Test Images Using a Ranking Method to Verify Results Finding Points Using Color Pattern Matching Defining and Creating Good Color Template Images Color Information Symmetry Feature Detail Positional Information Training the 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 Testing the 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 Identify Parts Under Inspection Classifying Samples Reading Characters Reading Barcodes Reading 1D Barcodes Reading Data Matrix Barcodes Reading PDF417 Barcodes Display Results Page Page Calibrating Images Perspective and Nonlinear Distortion Calibration Defining a Calibration Template Defining a Reference Coordinate System 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 and Professional Services Glossary Numbers A B Page C D E F G H I Page J K L Page M N O P Q R S T V Index Numerics A B C D E F G H I K L M N O P R S T U V W