You are here: Start » Function Reference » Image » Image Thresholding » ThresholdToRegion_Dynamic

ThresholdToRegion_Dynamic

Header:	AVL.h
Namespace:	avl
Module:	FoundationBasic

Thresholds an image relatively to the average pixel value in a local rectangular neighborhood.

Applications: Useful in case of uneven illumination.

Syntax

void avl::ThresholdToRegion_Dynamic
(
	const avl::Image& inImage,
	atl::Optional<const avl::Region&> inRoi,
	atl::Optional<const avl::Region&> inSourceRoi,
	int inRadiusX,
	atl::Optional<int> inRadiusY,
	atl::Optional<float> inMinRelativeValue,
	atl::Optional<float> inMaxRelativeValue,
	float inHysteresis,
	avl::Region& outRegion,
	avl::Image& diagBaseImage
)

Parameters

Name	Type	Range	Default	Description
inImage	const Image&			Input image
inRoi	Optional<const Region&>		NIL	Region in which pixels are written
inSourceRoi	Optional<const Region&>		NIL	Region from which pixels are read
inRadiusX	int	0 - 65535	5	Horizontal radius of internal mean blur
inRadiusY	Optional<int>	0 - 65535	NIL	Vertical radius of internal mean blur (Auto = inRadiusX)
inMinRelativeValue	Optional<float>		5.0f	Minimum relative value of a pixel that is considered foreground (Auto = -INF)
inMaxRelativeValue	Optional<float>		NIL	Maximum relative value of a pixel that is considered foreground (Auto = +INF)
inHysteresis	float	0.0 -	0.0f	Defines how much the threshold criteria are lowered for pixels neighboring with other foreground pixels
outRegion	Region&			Output region
diagBaseImage	Image&			Diagnostic blurred image.

Description

The operation is a cousin of ThresholdImage_Dynamic yet computes a region instead of an image. The resulting region contains only those pixels of the input image, which are brighter at least by inMinRelativeValue and at most by inMaxRelativeValue than the local average. If any of the parameters inMinRelativeValue, inMaxRelativeValue is not set, it is assumed to be, accordingly, -infinity or infinity.

Pixel neighbourhood used to compute the local average is a rectangle of dimensions $(2 \cdot \text{\textbf{inRadiusX} }+1) \times (2 \cdot \text{\textbf{inRadiusY} }+1)$ centered at the pixel being processed.

In the multichannel images the operation uses an average of channel values in each pixel.

Hints

Define inMinRelativeValue to extract objects which are brighter than the neighborhood.
Define inMaxRelativeValue to extract objects which are darker than the neighborhood.
Increase inRadiusX (and optionally inRadiusY) to define a bigger neighborhood.

Examples

ThresholdToRegion_Dynamic performed on the sample image with inMinRelativeValue = 5.0, inMaxRelativeValue = auto.

Errors

List of possible exceptions:

Error type	Description
DomainError	Region exceeds an input image in ThresholdToRegion_Dynamic.
DomainError	Roi exceeds image dimensions in ThresholdToRegion_Dynamic.
DomainError	Source roi exceeds image dimensions in ThresholdToRegion_Dynamic.