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AVL.DetectEdges_AsRegion_Mask(AvlNet.Image, AvlNet.Region, AvlNet.EdgeMaskFilter, float, float, float, int, AvlNet.Region, AvlNet.Image)

Extracts a pixel-precise region of continuous edges. Faster, yet less accurate version.

Namespace:AvlNet
Assembly:AVL.NET.dll

Syntax


public static void DetectEdges_AsRegion_Mask(
	AvlNet.Image inImage,
	AvlNet.Region inRoi,
	AvlNet.EdgeMaskFilter inEdgeMaskFilter,
	float inEdgeThreshold,
	float inEdgeHysteresis,
	float inMaxJoiningDistance,
	int inMinBlobArea,
	out AvlNet.Region outEdgeRegion,
	out AvlNet.Image diagGradientMagnitudeImage
)

Parameters

inImage
Type: AvlNet.Image
Image from which edges will be extracted
inRoi
Type: AvlNet.Region
Region of the image from which edges will be extracted, or null.
inEdgeMaskFilter
Type: AvlNet.EdgeMaskFilter
Type of edge filter used for computing gradients
inEdgeThreshold
Type: System.Single
Sufficient edge strength; edges of that strength will always be detected
inEdgeHysteresis
Type: System.Single
Value by which the edge threshold is decreased for edge points neighboring with sufficiently strong edges
inMaxJoiningDistance
Type: System.Single
Maximal distance between edges that can be joined
inMinBlobArea
Type: System.Int32
Minimal area of an edge blob
outEdgeRegion
Type: AvlNet.Region
Region of the found edges
diagGradientMagnitudeImage
Type: AvlNet.Image
Visualization of the gradient magnitude

Description

The operation extracts edges from the inRoi region in the inImage image and stores the result in the outEdgeRegion region. The extraction process is the same as in DetectEdges_AsPaths_Mask, the only difference being the data type of the result. This filter returns a region rather than array of subpixel-precise paths computed by DetectEdges_AsPaths_Mask.

The extraction process starts from gradient computing, what is done using chosen non-recursive filter with fixed size mask.

On the so computed gradient image threshold with hysteresis (as in ThresholdImage_Hysteresis) is performed with inEdgeThreshold and inEdgeHysteresis parameters. After this step only gradients which are strong enough are present. The resulting edge region can be much too thick, thus it has to be thinned. To achieve this, the non-maximum suppression is used. Every pixel with at least one of its neighbors having larger gradient is no longer considered to be an edge pixel (only neighbors in the direction of pixel's gradient matter).

Examples

DetectEdges_AsRegion_Mask performed on the sample image with inEdgeMaskFilter = Sobel, inEdgeThreshold = 20, inEdgeHysteresis = 5.

Remarks

For more information about local coordinate systems please refer to the following article.

Hardware Acceleration

This operation supports automatic parallelization for multicore and multiprocessor systems.

Hardware acceleration settings may be manipulated with Settings class.

See also