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HxCannyEdgeMap

Synopsis

HxImageRep HxCannyEdgeMap(HxImageRep img, double sigma)

Input

HxImageRep img

The image you want to determine the edges of.

double sigma

The standard deviation of the Gaussian kernel that is used to calculate the canny edge map.

Return value

HxImageRep

The output image is a 2D image, with HxVec2Double pixels. The first component of the pixel is the magnitude of the gradient in the X-direction, the second component of the pixel is the magnitude of the gradient in the Y-direction.

Description

The function HxCannyEdgeMap computes the magnitude of the gradient of img in the X- and Y-direction. For every position in img, the magnitude in the X-direction is put in the first element of the output-vector, while the magnitude in the Y-direction is put in the second element of the output-vector.

The magnitudes of the gradient in the X- and Y-direction are calculated by convolving img with the derivative of a 1D-Gaussian in both directions. The used Gaussians have a standard deviation of sigma.

Remarks

Valid input images

This function is only properly defined for 2D images with scalar pixels.

Valid values for sigma

This function is only properly defined for sigma greater than 0.

Border handling

This function uses MIRRORED border handling, see section Border handling.

Examples

Calculating the norm of the output of HxCannyEdgeMap

#include "HxImageRepGlobalFuncs.h"
#include "HxImageRep.h"

HxImageRep HxCannyEdgeMapExample1(HxImageRep img) {
   img = HxImageAsDouble(img);
   img = HxCannyEdgeMap(img, 1.0);
   img = HxNorm1(img);
   img = HxContrastStretch(img, 255);
   img = HxImageAsByte(img);

   return img;
}

int main(int argc, char* argv[])
{
    HxImageRep im1 = HxMakeFromFile(argv[1]);
    im1 = HxCannyEdgeMapExample1(im1);
    HxWriteFile(im1, argv[2]);

    return 0;
}

Input image for the HxCannyEdgeMap example.

Output image of the HxCannyEdgeMap example.

In this example we apply HxCannyEdgeMap on a grey value image. We take the size of the resulting vector pixels (HxNorm1), after which we stretch the image for proper visualisation (HxContrastStretch).

See also

HxCannyThreshold, HxCannyThresholdAlt,

Keywords

Edge detection, Filter, Canny,

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