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ThresholdImage_Dynamic


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

Syntax

C++
C#
 
void avl::ThresholdImage_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 inFuzziness,
	avl::Image& outMonoImage,
	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 - 65536 5 Horizontal radius of internal mean blur
inRadiusY Optional<int> 0 - 65536 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)
inFuzziness float 0.0 - 0.0f A tolerance for inMin/MaxRelativeValue that results in intermediate output values
outMonoImage Image&
diagBaseImage Image& Diagnostic blurred image.

Description

The operation transforms each pixel value to the maximum or minimum level thus creating binary image. The result of the transformation depends on the relative pixel intensity:

  • Pixel values that are brighter than local average of the pixel neighbourhood by at least inMinRelativeValue and at most inMaxRelativeValue are transformed to the maximum level.
  • Other pixel values are transformed to the minimum level.

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.

Parameter inFuzziness (set to 0 by default) allows to perform fuzzy thresholding which linearly interpolates those pixel values that differ by at most inFuzziness from the border intensities; thus creating smooth transition between minimum and maximum values in the resulting image.

In the multichannel images the operation uses an average of channel values in each pixel, thus the resulting image is always monochromatic.

Hints

  • Define inMinRelativeValue to obtain white pixels for objects which are brighter than the neighborhood.
  • Define inMaxRelativeValue to obtain white pixels for objects which are darker than the neighborhood.
  • Increase inRadiusX (and optionally inRadiusY) to define a bigger neighborhood.
  • Use inFuzziness to add some smooth transitions between black and white pixels in the result.

Examples

ThresholdImage_Dynamic performed on the sample image with inMinRelativeValue = 5.0, inMaxRelativeValue = auto, inFuzziness = 0.0.

ThresholdImage_Dynamic performed on the sample image with inMinRelativeValue = 5.0, inMaxRelativeValue = auto, inFuzziness = 10.0.

See Also