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DetectEdges_AsRegion_Mask

Header:	FIL.h
Namespace:	fil
Module:	FoundationBasic

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

Applications: Consistent detection of pixels that belong to contours of variable or unpredictable shape, e.g. screw thread outline or a custom piece of textile.

Syntax

void fil::DetectEdges_AsRegion_Mask
(
	const fil::Image& inImage,
	ftl::Optional<const fil::Region&> inRoi,
	fil::EdgeMaskFilter::Type inEdgeMaskFilter,
	float inEdgeThreshold,
	float inEdgeHysteresis,
	float inMaxJoiningDistance,
	const int inMinBlobArea,
	fil::Region& outEdgeRegion,
	fil::Image& diagGradientMagnitudeImage
)

Parameters

Name	Type	Range	Default	Description
inImage	const Image&			Image from which edges will be extracted
inRoi	Optional<const Region&>		NIL	Region of the image from which edges will be extracted
inEdgeMaskFilter	EdgeMaskFilter::Type			Type of edge filter used for computing gradients
inEdgeThreshold	float	0.0 -	35.0f	Sufficient edge strength; edges of that strength will always be detected
inEdgeHysteresis	float	0.0 -	15.0f	Value by which the edge threshold is decreased for edge points neighboring with sufficiently strong edges
inMaxJoiningDistance	float	0.0 -	0.0f	Maximal distance between edges that can be joined
inMinBlobArea	const int	0 -	1	Minimal area of an edge blob
outEdgeRegion	Region&			Region of the found edges
diagGradientMagnitudeImage	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.

Hardware Acceleration

This operation supports automatic parallelization for multicore and multiprocessor systems.

Errors

List of possible exceptions:

Error type	Description
DomainError	Unsupported edge mask filter in DetectEdges_AsRegion_Mask.