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National Instruments IMAQ Vision for Measurement Studio Filters, Convolution Filter

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Chapter2 GettingMeasurement-Ready Images

IMAQVision for LabWindows/CVI User Manual 2-10 ni.com

transformations. Formore information about these lookup tables, see

Chapter5, ImageProcessing,intheIMAQ Vision Concepts Manual.

•imaqLookup()—Convertsthe pixel values of an image by replacing

them with valuesfrom a user-defined lookup table.

•imaqEqualize()—Distributesthe grayscale values evenly within a

givengrayscale range. Use IMAQ Equalize to increase the contrast in

imagescontaining fewgrayscale values.

•imaqInverse()—Invertsthe pixel intensities of an image to

computethe negative of the image. For example, use imaqInverse()

before applying an automatic threshold to your image if the

background pixels are brighter than the object pixels.

Filters

Filteryour image when you need to im prove the sharpness of transitions in

theimage or increase the overall signal-to-noise ratio of t he image. You can

choose either a lowpass or highpass filter depending on your needs.

Lowpassfilters remove insignificant details by smoothing the image,

removingsharp details, and smoothing the edges between the objects

and the background. Youcan use imaqLowpass() or define your own

lowpassfilter with imaqConvolve() or imaqNthOrderFilter().

Highpass filtersemphasize details, such as edges,ob ject boundaries, or

cracks.These details represent sharp transitions in intensity value. You can

defineyour own highpass filter with imaqConvolve() or

imaqNthOrderFilter(),or you can use a predefined highpass filter with

imaqEdgeFilter()or imaqCannyEdgeFilter().The

imaqEdgeFilter()function allows yo u to find edges in an image using

predefinededge detection kernels, such as the Sobel, Prewitt, and Roberts

kernels.

Convolution Filter

The imaqConvolve()function allows you to use a predefined set of

lowpass and highpass filters. Each filter is defined by a kernel of

coefficients.Use imaqGetKernel() to retrieve predefined kernels. If the

predefined kernels do not meet your needs, define your own custom filter

using a 2D array of floating point numbers.

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