National Instruments IMAQTM Benutzerhandbuch

Highpass filters emphasize details, such as edges, object boundaries, 
or cracks. These details represent sharp transitions in intensity value. 
You can define your own highpass filter with 

CWIMAQVision.Convolute

 

or 

CWIMAQVision.NthOrder

, or you can use a predefined highpass 

filter with 

CWIMAQVision.EdgeFilter

 or 

CWIMAQVision.CannyEdgeFilter

. 

CWIMAQVision.EdgeFilter

 

allows you to find edges in an image using predefined edge detection 
kernels, such as the Sobel, Prewitt, and Roberts kernels.

CWIMAQVision.Convolute

 allows you to use a predefined set of 

lowpass and highpass filters. Each filter is defined by a kernel of 
coefficients. Use the CWIMAQKernel object to define the filter. Use 

CWIMAQKernel.LoadKernel

 to load a predefined kernel into the 

object. If the predefined kernels do not meet your needs, use the 

CWIMAQKernel.SetSize

 method to set the size of the kernel and the 

CWIMAQKernel.Element

 property to set the data in the kernel.

CWIMAQVision.NthOrder

 allows you to define a lowpass or highpass 

filter depending on the value of N that you choose. One specific Nth order 
filter, the median filter, removes speckle noise, which appears as small 
black and white dots. For more information about Nth order filters, refer to 
Chapter 5, Image Processing, of the IMAQ Vision Concepts Manual.

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 particle analysis.

Grayscale morphological transformations, which include erosions and 
dilations, compare a pixel to those pixels that surround it. An erosion keeps 
the smallest pixel values. A dilation keeps the largest pixel values.

For more information about grayscale morphology transformations, refer 
to Chapter 5, Image Processing, of the IMAQ Vision Concepts Manual.