icl::filter::CannyOp Class Reference

Class for the canny edge detector. More...

#include <CannyOp.h>

Inheritance diagram for icl::filter::CannyOp:

List of all members.

Public Member Functions
	CannyOp (icl32f lowThresh=0, icl32f highThresh=255, int preBlurRadius=0)
	Constructor.
	CannyOp (UnaryOp *dxOp, UnaryOp *dyOp, icl32f lowThresh=0, icl32f highThresh=255, bool deleteOps=true, int preBlurRadius=0)
	Constructor.
virtual	~CannyOp ()
	Destructor.
void	setThresholds (icl32f lowThresh, icl32f highThresh)
	changes the Thresholds
icl32f	getLowThreshold () const
	returns the lower threshold
icl32f	getHighThreshold () const
	returns the upper threshold
virtual void	apply (const core::ImgBase *src, core::ImgBase **dst)
	applies the Canny Operator
void	setPreBlurRadius (int preBlurRadius)
	sets the pre-blur-radius
bool	getPreBlurRadius () const
	returns current pre-blur feature state
Private Member Functions
void	setUpPreBlurOp ()
void	applyCanny32f (const core::ImgBase *dx, const core::ImgBase *dy, core::ImgBase *dst, int c)
	applies canny for one channel
void	applyCanny16s (const core::ImgBase *dx, const core::ImgBase *dy, core::ImgBase *dst, int c)
Private Attributes
std::vector< icl8u >	m_cannyBuf
	buffer for ippiCanny
core::ImgBase *	m_derivatives [2]
UnaryOp *	m_ops [2]
UnaryOp *	m_preBlurOp
icl32f	m_lowT
icl32f	m_highT
bool	m_ownOps
core::Img32f	m_buffer
int	m_preBlurRadius

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Detailed Description

Class for the canny edge detector.

Overview

The canny edge detector detects image borders from gray-scale images. It's result is an Img8u binary image containing thin borders.

Algorithm

The canny edge detector is a very common filter for edge detection, therefore it is already implemented in the IPP. The algorithm can be split into 3 major parts:

1. Image differentiation here, image x and y gradients are computed. Commonly this is done using sobel- X and -Y filters.
2. Non-Maximum suppression The image differentiation result is converted into an image intensity map and into a gradient direction map. Now all pixels are suppressed, that are not ridges in gradient intensity map mountain.
3. Thresholding Here a special threshold operation is used. Two threshold values (l=low threshold and h=high threshold) split the edge intensity scale into 3 parts:
   1. below the lower threshold pixels with such values are in any case no border pixels
   2. above the upper threshold these pixels are border pixels
   3. in the middle section these pixels are only border pixels if there's a connected chain of other pixels (each also in the middle section) that is connected in any way to a border pixel.

(please see IPP's canny edge detector documentation for more detail)

pre-blur features

In some cases (e.g. if input images are created synthetically) the border intensity image has too hard edges (e.g. from edges from black to white). In this case, the canny edge detector implementation overlooks these borders independent on the given threshold values.

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Constructor & Destructor Documentation

icl::filter::CannyOp::CannyOp	(	icl32f	lowThresh = 0,
		icl32f	highThresh = 255,
		int	preBlurRadius = 0
	)

Constructor.

With this Constructor the derivations are computed within the CannyOp. If you already have computed the derivations, use the other Constructor, due to performance reasons.

Parameters:

lowThresh	lower threshold
highThresh	upper threshold
preBlurRadius	if r> 0, gaussian kernel with masksize r*2+1 is applied to the input image first

icl::filter::CannyOp::CannyOp	(	UnaryOp *	dxOp,
		UnaryOp *	dyOp,
		icl32f	lowThresh = 0,
		icl32f	highThresh = 255,
		bool	deleteOps = true,
		int	preBlurRadius = 0
	)

Constructor.

Parameters:

dxOp	the x derivation of the src
dyOp	the y derivation of the src
lowThresh	lower threshold
highThresh	upper threshold
deleteOps	should the internaly created derivations be deleted?
preBlurRadius	if r> 0, gaussian kernel with masksize r*2+1 is applied to the input image first

virtual icl::filter::CannyOp::~CannyOp

(

)

[virtual]

Destructor.

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Member Function Documentation

virtual void icl::filter::CannyOp::apply	(	const core::ImgBase *	src,
		core::ImgBase **	dst
	)		[virtual]

applies the Canny Operator

Parameters:

src	the source image
dst	pointer to the destination image

Implements icl::filter::UnaryOp.

void icl::filter::CannyOp::applyCanny16s	(	const core::ImgBase *	dx,
		const core::ImgBase *	dy,
		core::ImgBase *	dst,
		int	c
	)		[private]

void icl::filter::CannyOp::applyCanny32f	(	const core::ImgBase *	dx,
		const core::ImgBase *	dy,
		core::ImgBase *	dst,
		int	c
	)		[private]

applies canny for one channel

icl32f icl::filter::CannyOp::getHighThreshold

(

)

const

returns the upper threshold

Returns:

the upper threshold

icl32f icl::filter::CannyOp::getLowThreshold

(

)

const

returns the lower threshold

Returns:

the lower threshold

bool icl::filter::CannyOp::getPreBlurRadius

(

)

const [inline]

returns current pre-blur feature state

void icl::filter::CannyOp::setPreBlurRadius

(

int

preBlurRadius

)

[inline]

sets the pre-blur-radius

if r> 0, gaussian kernel with masksize r*2+1 is applied to the input image first

void icl::filter::CannyOp::setThresholds	(	icl32f	lowThresh,
		icl32f	highThresh
	)

changes the Thresholds

Parameters:

lowThresh	lower threshold
highThresh	upper threshold

void icl::filter::CannyOp::setUpPreBlurOp

(

)

[private]

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Member Data Documentation

core::Img32f icl::filter::CannyOp::m_buffer [private]

std::vector<icl8u> icl::filter::CannyOp::m_cannyBuf [private]

buffer for ippiCanny

core::ImgBase* icl::filter::CannyOp::m_derivatives[2] [private]

icl32f icl::filter::CannyOp::m_highT [private]

icl32f icl::filter::CannyOp::m_lowT [private]

UnaryOp* icl::filter::CannyOp::m_ops[2] [private]

bool icl::filter::CannyOp::m_ownOps [private]

UnaryOp* icl::filter::CannyOp::m_preBlurOp [private]

int icl::filter::CannyOp::m_preBlurRadius [private]

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

• /home/jenkins/workspace/icl-manual-trunk/icl-manual/ICLFilter/src/ICLFilter/CannyOp.h