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National Instruments IMAQ Vision for Measurement Studio Nth Order Filter, Grayscale Morphology, FFT

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Chapter2 GettingMeasurement-Ready Images

©NationalInstruments Corporation 2-11 IMAQVision for LabWindows/CVI User Manual

Nth Order Filter

TheimaqNthOrderFilter() function allows you to define a lowpass or

highpass filter depending on the value of Nthat you choose. One specific

Nthorder filter, the median filter, removes speckle noise, which appears as

smallblack and whitedots. Use imaqMedianFilter() to apply a median

filter. For more information about Nth order filters, see Chapter 5, Image

Processing,oftheIMAQVision Concepts Manual.

Grayscale Morphology

Perform grayscale morphology when you want to filter grayscale

features of an image. Grayscale morphology helps you remove or

enhance isolated features, such as bright pixels on a dark background.

Use these transformations on a grayscale image to enhance non-distinct

features before thresholding the image in preparation for blob analysis.

Use imaqGrayMorphology()to perform one of the fo llowingseven

transformations:

•Erosion—Reduces the brightness of pixels that are surrounded by

neighbors with a lower intensity.

•Dilation—Increases the brightness of pixels surrounded by neighbors

witha higher intensity. A dilation has the opposite effectas an erosion.

•Opening—Removesbright pixels isolated in dark reg ions and smooths

boundaries.

•Closing—Removesdark pixels isolated in bright regions and smooths

boundaries.

•Proper-opening—Removesbright pixel sisol ated in dark regions and

smooths the inner contours of particles.

•Proper-closing—Removesd ark pixels isolated in bright regions and

smooths the inner contours of particles.

•Auto-median—Generatessimpler particles that have fewer details.

Formore information ab out grayscale morphology transformations, see

Chapter5, Image Processing,oftheIMAQVision Concepts Manual.

FFT

Use the Fast Fourier Transform (FFT) to convert an image into its

frequencydomain. In an image, details and sharp edges are associated

with mid tohigh spatial frequencies because they introduce significant

gray-levelvariations over short distances. Gradually varying patterns are

associated with low spatialfrequencies.

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