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AVL.ImageLocalMinima

Finds image locations characterized by locally minimal pixel values.

Namespace:AvlNet
Assembly:AVL.NET.dll

Syntax

C++
C#
 
public static void ImageLocalMinima
(
	AvlNet.Image inImage,
	bool inConsiderLowlands,
	float? inMinValue,
	float? inMaxValue,
	float inMinDistance,
	NullableRef<List<AvlNet.Extremum2D>> outLocalMinima,
	NullableRef<SafeList<AvlNet.Region>> outMinimaRegions
)

Parameters

Name Type Range Default Description
inImageAvlNet.ImageInput image.
inConsiderLowlandsboolConsider multi-pixel minima (lowlands) or not.
inMinValuefloat?Minimal value of minimum to be considered. Default value: atl::NIL.
inMaxValuefloat?Maximal value of minimum to be considered. Default value: atl::NIL.
inMinDistancefloat<0.0f, INF>Minimal distance between two found minima.
outLocalMinimaAvlNet.NullableRef<System.Collections.Generic.List<AvlNet.Extremum2D>>Found local minima. Can be null to skip this parameter calculation.
outMinimaRegionsAvlNet.NullableRef<AvlNet.SafeList<AvlNet.Region>>Regions of local minima (plateaus and singletons). Can be null to skip this parameter calculation.

Description

The operation finds local minima on the image inImage within specific region inRoi.

It returns three arrays of the same length:

  • Subpixel precise positions of the minima
  • Values of the minima
  • Regions of equally bright pixels around the minima

If the given image consists of more than one channel, they are averaged to obtain monochromatic image, so that the values of the extrema are of type float.

There are two types of local extrema:

  • Peak/hole: single pixel (strictly) brighter/darker than its neighbourhood (eight pixels). The extremum's position is determined with subpixel precision using gradient method with Sobel gradient. Returned region contains only one pixel.
  • Plateau/lowland: a connected set of equally bright pixels (strictly) brighter/darker from their neighbourhood. Returned position for this extremum is the center of mass of the plateau.

If parameter inConsiderLowlands is set to true, the filter finds both types. Otherwise, it finds only strict minima.

Parameter inMaxValue determines the maximal value of the minimum to be considered.

Examples

Example image

Output for example image

Remarks

If a plateau/lowland is concave, it's center of mass may lie outside it. In such case, the value of the extremum (which is equal to the common value of its pixels) may be different from the value of pixel indicated by position of the extremum.

Errors

List of possible exceptions:

Error type Description
DomainError Region exceeds an input image in ImageLocalMinima.

Function Overrides

See also