Class CannyEdgeDetector

Canny edge detector.

Inheritance
Object
BaseUsingCopyPartialFilter
CannyEdgeDetector
Inherited Members
Namespace: AForge.Imaging.Filters
Assembly: TowseyLibrary.dll
Syntax
public class CannyEdgeDetector : BaseUsingCopyPartialFilter
Remarks

The filter searches for objects' edges by applying Canny edge detector. The implementation follows Bill Green's Canny edge detection tutorial.

note

The implemented canny edge detector has one difference with the above linked algorithm. The difference is in hysteresis step, which is a bit simplified (getting faster as a result). On the hysteresis step each pixel is compared with two threshold values: HighThreshold and LowThreshold. If pixel's value is greater or equal to HighThreshold, then it is kept as edge pixel. If pixel's value is greater or equal to LowThreshold, then it is kept as edge pixel only if there is at least one neighbouring pixel (8 neighbours are checked) which has value greater or equal to HighThreshold; otherwise it is none edge pixel. In the case if pixel's value is less than LowThreshold, then it is marked as none edge immediately.

The filter accepts 8 bpp grayscale images for processing.

Sample usage:

// create filter
CannyEdgeDetector filter = new CannyEdgeDetector( );
// apply the filter
filter.ApplyInPlace( image );

See the original AForge code for example images.

Constructors

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CannyEdgeDetector(Byte, Byte)

Initializes a new instance of the CannyEdgeDetector class.

Declaration
public CannyEdgeDetector(byte lowThreshold, byte highThreshold)
Parameters
Type Name Description
Byte lowThreshold

Low threshold.
Byte highThreshold

High threshold.
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CannyEdgeDetector(Byte, Byte, Single, Int32)

Initializes a new instance of the CannyEdgeDetector class.

Declaration
public CannyEdgeDetector(byte lowThreshold, byte highThreshold, float sigma, int radius)
Parameters
Type Name Description
Byte lowThreshold

Low threshold.
Byte highThreshold

High threshold.
Single sigma

Gaussian sigma.
Int32 radius
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CannyEdgeDetector(Single, Nullable<Int32>)

Initializes a new instance of the CannyEdgeDetector class.

Declaration
public CannyEdgeDetector(float gaussianSigma = 3F, int? gaussianRadius = default(int? ))
Parameters
Type Name Description
Single gaussianSigma
Nullable<Int32> gaussianRadius

Properties

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GaussianSigma

Gets gaussian sigma.

Declaration
public float GaussianSigma { get; }
Property Value
Type Description
Single
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GaussianSize

Gets gaussian size.

Declaration
public int GaussianSize { get; }
Property Value
Type Description
Int32
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HighThreshold

Gets or sets high threshold.

Declaration
public byte HighThreshold { get; set; }
Property Value
Type Description
Byte
Remarks

High threshold value used for hysteresis (see tutorial for more information).

Default value is set to 100.

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LowThreshold

Gets or sets low threshold.

Declaration
public byte LowThreshold { get; set; }
Property Value
Type Description
Byte
Remarks

Low threshold value used for hysteresis (see tutorial for more information).

Default value is set to 20.

Methods

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ProcessFilter(Image<Rgb24>, Image<L8>, Rectangle)

Process the filter on the specified image.

Declaration
protected override void ProcessFilter(Image<Rgb24> source, Image<L8> destination, Rectangle rect)
Parameters
Type Name Description
SixLabors.ImageSharp.Image<SixLabors.ImageSharp.PixelFormats.Rgb24> source

Source image data.
SixLabors.ImageSharp.Image<SixLabors.ImageSharp.PixelFormats.L8> destination

Destination image data.
SixLabors.ImageSharp.Rectangle rect

Image rectangle for processing by the filter.
Overrides

Extension Methods