ClassesClasses | | Operators

zero_crossing_sub_pixzero_crossing_sub_pixZeroCrossingSubPixZeroCrossingSubPix (Operator)

Name

zero_crossing_sub_pixzero_crossing_sub_pixZeroCrossingSubPixZeroCrossingSubPix — Extract zero crossings from an image with subpixel accuracy.

Signature

zero_crossing_sub_pix(Image : ZeroCrossings : : )

Herror zero_crossing_sub_pix(const Hobject Image, Hobject* ZeroCrossings)

Herror T_zero_crossing_sub_pix(const Hobject Image, Hobject* ZeroCrossings)

void ZeroCrossingSubPix(const HObject& Image, HObject* ZeroCrossings)

HXLDCont HImage::ZeroCrossingSubPix() const

static void HOperatorSet.ZeroCrossingSubPix(HObject image, out HObject zeroCrossings)

HXLDCont HImage.ZeroCrossingSubPix()

Description

zero_crossing_sub_pixzero_crossing_sub_pixZeroCrossingSubPixZeroCrossingSubPixZeroCrossingSubPix extracts the zero crossings of the input image ImageImageImageImageimage with subpixel accuracy. The extracted zero crossings are returned as XLD-contours in ZeroCrossingsZeroCrossingsZeroCrossingsZeroCrossingszeroCrossings. Thus, zero_crossing_sub_pixzero_crossing_sub_pixZeroCrossingSubPixZeroCrossingSubPixZeroCrossingSubPix can be used as a sub-pixel precise edge extractor if the input image is a Laplace-filtered image (see laplacelaplaceLaplaceLaplaceLaplace, laplace_of_gausslaplace_of_gaussLaplaceOfGaussLaplaceOfGaussLaplaceOfGauss, derivate_gaussderivate_gaussDerivateGaussDerivateGaussDerivateGauss).

For the extraction, the input image is regarded as a surface, in which the gray values are interpolated bilinearly between the centers of the individual pixels. Consistent with the surface thus defined, zero crossing lines are extracted for each pixel and linked into topologically sound contours. This means that the zero crossing contours are correctly split at junction points. If the image contains extended areas of constant gray value 0, only the border of such areas is returned as zero crossings.

Execution Information

Parameters

ImageImageImageImageimage (input_object)  singlechannelimage objectHImageHImageHobject (int1 / int2 / int4 / real)

Input image.

ZeroCrossingsZeroCrossingsZeroCrossingsZeroCrossingszeroCrossings (output_object)  xld_cont-array objectHXLDContHXLDContHobject *

Extracted zero crossings.

Example (HDevelop)

* Detection zero crossings of the Laplacian-of-Gaussian
* of an aerial image
read_image(Image,'mreut')
derivate_gauss(Image,Laplace,3,'laplace')
zero_crossing_sub_pix(Laplace,ZeroCrossings)
dev_display(ZeroCrossings)

* Detection of edges, i.e, zero crossings of the Laplacian-of-Gaussian
* that have a large gradient magnitude, in an aerial image
read_image(Image,'mreut')
Sigma := 1.5
* Compensate the threshold for the fact that derivate_gauss(...,'gradient')
* calculates a Gaussian-smoothed gradient, in which the edge amplitudes
* are too small because of the Gaussian smoothing, to correspond to a true
* edge amplitude of 20.
Threshold := 20/(Sigma*sqrt(2*3.1415926))
derivate_gauss(Image,Gradient,Sigma,'gradient')
threshold(Gradient,Region,Threshold,255)
reduce_domain(Image,Region,ImageReduced)
derivate_gauss(ImageReduced,Laplace,Sigma,'laplace')
zero_crossing_sub_pix(Laplace,Edges)
dev_display(Edges)

Example (C)

/* Detection zero crossings of the Laplacian-of-Gaussian of aerial image */
read_image(&Image,"mreut");
derivate_gauss(Image,&Laplace,3,"laplace");
zero_crossing_sub_pix(Laplace,&ZeroCrossings);
disp_xld(ZeroCrossings,WindowHandle);

/* Detection of edges, i.e, zero crossings of the Laplacian-of-Gaussian
   that have a large gradient magnitude, in an aerial image */
read_image(&Image,"mreut");
Sigma = 1.5;
/* Compensate the threshold for the fact that derivate_gauss(...,'gradient')
   calculates a Gaussian-smoothed gradient, in which the edge amplitudes
   are too small because of the Gaussian smoothing, to correspond to a true
   edge amplitude of 20. */
Threshold = 20/(Sigma*sqrt(2*PI));
derivate_gauss(Image,&Gradient,Sigma,"gradient");
threshold(Gradient,&Region,Threshold,255);
reduce_domain(Image,Region,&ImageReduced);
derivate_gauss(ImageReduced,&Laplace,Sigma,"laplace");
zero_crossing_sub_pix(Laplace,&Edges);
disp_xld(Edges,WindowHandle);

Example (HDevelop)

* Detection zero crossings of the Laplacian-of-Gaussian
* of an aerial image
read_image(Image,'mreut')
derivate_gauss(Image,Laplace,3,'laplace')
zero_crossing_sub_pix(Laplace,ZeroCrossings)
dev_display(ZeroCrossings)

* Detection of edges, i.e, zero crossings of the Laplacian-of-Gaussian
* that have a large gradient magnitude, in an aerial image
read_image(Image,'mreut')
Sigma := 1.5
* Compensate the threshold for the fact that derivate_gauss(...,'gradient')
* calculates a Gaussian-smoothed gradient, in which the edge amplitudes
* are too small because of the Gaussian smoothing, to correspond to a true
* edge amplitude of 20.
Threshold := 20/(Sigma*sqrt(2*3.1415926))
derivate_gauss(Image,Gradient,Sigma,'gradient')
threshold(Gradient,Region,Threshold,255)
reduce_domain(Image,Region,ImageReduced)
derivate_gauss(ImageReduced,Laplace,Sigma,'laplace')
zero_crossing_sub_pix(Laplace,Edges)
dev_display(Edges)

Example (HDevelop)

* Detection zero crossings of the Laplacian-of-Gaussian
* of an aerial image
read_image(Image,'mreut')
derivate_gauss(Image,Laplace,3,'laplace')
zero_crossing_sub_pix(Laplace,ZeroCrossings)
dev_display(ZeroCrossings)

* Detection of edges, i.e, zero crossings of the Laplacian-of-Gaussian
* that have a large gradient magnitude, in an aerial image
read_image(Image,'mreut')
Sigma := 1.5
* Compensate the threshold for the fact that derivate_gauss(...,'gradient')
* calculates a Gaussian-smoothed gradient, in which the edge amplitudes
* are too small because of the Gaussian smoothing, to correspond to a true
* edge amplitude of 20.
Threshold := 20/(Sigma*sqrt(2*3.1415926))
derivate_gauss(Image,Gradient,Sigma,'gradient')
threshold(Gradient,Region,Threshold,255)
reduce_domain(Image,Region,ImageReduced)
derivate_gauss(ImageReduced,Laplace,Sigma,'laplace')
zero_crossing_sub_pix(Laplace,Edges)
dev_display(Edges)

Example (HDevelop)

* Detection zero crossings of the Laplacian-of-Gaussian
* of an aerial image
read_image(Image,'mreut')
derivate_gauss(Image,Laplace,3,'laplace')
zero_crossing_sub_pix(Laplace,ZeroCrossings)
dev_display(ZeroCrossings)

* Detection of edges, i.e, zero crossings of the Laplacian-of-Gaussian
* that have a large gradient magnitude, in an aerial image
read_image(Image,'mreut')
Sigma := 1.5
* Compensate the threshold for the fact that derivate_gauss(...,'gradient')
* calculates a Gaussian-smoothed gradient, in which the edge amplitudes
* are too small because of the Gaussian smoothing, to correspond to a true
* edge amplitude of 20.
Threshold := 20/(Sigma*sqrt(2*3.1415926))
derivate_gauss(Image,Gradient,Sigma,'gradient')
threshold(Gradient,Region,Threshold,255)
reduce_domain(Image,Region,ImageReduced)
derivate_gauss(ImageReduced,Laplace,Sigma,'laplace')
zero_crossing_sub_pix(Laplace,Edges)
dev_display(Edges)

Result

zero_crossing_sub_pixzero_crossing_sub_pixZeroCrossingSubPixZeroCrossingSubPixZeroCrossingSubPix usually returns the value 2 (H_MSG_TRUE). If necessary, an exception is raised.

Possible Predecessors

laplacelaplaceLaplaceLaplaceLaplace, laplace_of_gausslaplace_of_gaussLaplaceOfGaussLaplaceOfGaussLaplaceOfGauss, diff_of_gaussdiff_of_gaussDiffOfGaussDiffOfGaussDiffOfGauss, derivate_gaussderivate_gaussDerivateGaussDerivateGaussDerivateGauss

Alternatives

zero_crossingzero_crossingZeroCrossingZeroCrossingZeroCrossing

See also

threshold_sub_pixthreshold_sub_pixThresholdSubPixThresholdSubPixThresholdSubPix

Module

2D Metrology


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