kjb::Canny_edge_detector Class Reference

Implements the Canny edge detection algorithm. More...

#include <edge.h>

Public Member Functions
	Canny_edge_detector (float sigma=1, float begin_thresh=0, float end_thresh=0, size_t padding=0, bool use_fourier=true)
Canny_edge_detector &	operator= (const Canny_edge_detector &other)
void	swap (Canny_edge_detector &other)
Edge_set_ptr	operator() (const Image &img, bool noiseless_data=false) const
kjb::Edge_set *	detect_edges (const Image &img, bool noiseless_data=false)
	Detect edges in img. More...

Detailed Description

Implements the Canny edge detection algorithm.

See http://en.wikipedia.org/wiki/Canny_edge_detector.

We get rid of noise by first convolving the image with a Gaussian filter with standard deviation sigma. A gradient map is then computed using finite differences. The first threhsold is used to determine edge pixels and non edge pixels (non maxima suppression). We build edges by starting from edge pixels and following the gradient direction until we find a pixel whose gradient is lower than the second threshold (hysteresis).

Constructor & Destructor Documentation

kjb::Canny_edge_detector::Canny_edge_detector ( float  sigma = 1, float  begin_thresh = 0, float  end_thresh = 0, size_t  padding = 0, bool  use_fourier = true  )

inline

Parameters

sigma	Gaussian blurring sigma. Determines scale of edges to detect.
begin_thresh	Starting edge threshold hysteresis in the Canny edge detection algorithm. Lower value gives more edges.
end_thresh	Ending edge threshold for hysteresis in the Canny edge detection algorithm. Lower value gives longer edges. If it exceeds begin_thresh it isn't really hysteresis.
padding	Amount of padding to add to images before detecting edges. Images are padded by repeating the values occurring at image boundaries. Positive padding can prevent spurious edge detections on image boundary. If using, consider a value of around 2*sigma.
use_fourier	Specifies whether to use Fast Fourier transform for convolution or not.

Note that each argument has a default value.

Member Function Documentation

kjb::Edge_set* kjb::Canny_edge_detector::detect_edges ( const Image &  img, bool  noiseless_data = false  )

inline

Detect edges in img.

This returns a pointer. It is up to the user to clean up the memory to which it points.

Parameters

img.	The image to run the edge detection on
noiseless_data	Set to true if the image is noise free, meaning that each pixel whose intensity is bigger than zero is an edge point

Edge_set_ptr kjb::Canny_edge_detector::operator() ( const Image &  img, bool  noiseless_data = false  ) const

inline

Detect edges in img

The design decision to return a pointer is motivated by the fact that many objects may share this data.

Parameters

img	The image to run the edge detector on
noiseless_data	Set to true if the image is noise free, meaning that each pixel whose intensity is bigger than zero is an edge point

Canny_edge_detector& kjb::Canny_edge_detector::operator= ( const Canny_edge_detector &  other )

inline

void kjb::Canny_edge_detector::swap ( Canny_edge_detector &  other )

inline

Swaps the content of this edge detector with the edge detector provided in input

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The documentation for this class was generated from the following file:

• /work/kobus/src/lib/edge_cpp/edge.h