Kernel2D< ARITHTYPE > Class Template Reference

Generic 2 dimensional convolution kernel. More...

#include <vigra/stdconvolution.hxx>

Public Types
typedef BasicImage< value_type > ::Accessor	Accessor
typedef BasicImage< value_type > ::ConstAccessor	ConstAccessor
typedef BasicImage< value_type > ::const_traverser	ConstIterator
typedef BasicImage< value_type > ::traverser	Iterator
typedef ARITHTYPE	value_type

Public Member Functions
Accessor	accessor ()
ConstAccessor	accessor () const
BorderTreatmentMode	borderTreatment () const
Iterator	center ()
ConstIterator	center () const
int	height () const
void	initAveraging (int radius)
void	initDisk (int radius)
Kernel2D &	initExplicitly (Shape2 const &upperleft, Shape2 const &lowerright)
Kernel2D &	initExplicitly (BasicImage< value_type > const &image)
void	initGaussian (double std_dev, value_type norm)
void	initGaussian (double std_dev)
void	initSeparable (Kernel1D< value_type > const &kx, Kernel1D< value_type > const &ky)
template<class KernelIterator >
void	initSeparable (KernelIterator kxcenter, int xleft, int xright, KernelIterator kycenter, int yleft, int yright)
	Kernel2D ()
	Kernel2D (Kernel2D const &k)
Point2D	lowerRight () const
value_type	norm () const
void	normalize (value_type norm)
void	normalize ()
value_type &	operator() (int x, int y)
value_type	operator() (int x, int y) const
Kernel2D &	operator= (Kernel2D const &k)
InitProxy	operator= (value_type const &v)
value_type &	operator[] (Diff2D const &d)
value_type	operator[] (Diff2D const &d) const
void	setBorderTreatment (BorderTreatmentMode new_mode)
Point2D	upperLeft () const
int	width () const
	~Kernel2D ()

Detailed Description

template<class ARITHTYPE>
class vigra::Kernel2D< ARITHTYPE >

Generic 2 dimensional convolution kernel.

This kernel may be used for convolution of 2 dimensional signals.

Convolution functions access the kernel via an ImageIterator which they get by calling center(). This iterator points to the center of the kernel. The kernel's size is given by its upperLeft() (upperLeft().x <= 0, upperLeft().y <= 0) and lowerRight() (lowerRight().x >= 0, lowerRight().y >= 0) methods. The desired border treatment mode is returned by borderTreatment().

The different init functions create a kernel with the specified properties. The requirements for the kernel's value_type depend on the init function used. At least NumericTraits must be defined.

Usage:

#include <vigra/stdconvolution.hxx>
Namespace: vigra

MultiArray<2, float> src(w,h), dest(w,h);
...

// define horizontal Sobel filter
vigra::Kernel2D<float> sobel;
sobel.initExplicitly(Diff2D(-1,-1), Diff2D(1,1)) =  // upper left and lower right
                     0.125, 0.0, -0.125,
                     0.25,  0.0, -0.25,
                     0.125, 0.0, -0.125;

convolveImage(src, dest, sobel);

Required Interface:

value_type v = NumericTraits<value_type>::one();

See also the init functions.

Examples:

smooth_convolve.cxx.

Member Typedef Documentation

typedef ARITHTYPE value_type

the kernel's value type

typedef BasicImage<value_type>::traverser Iterator

2D random access iterator over the kernel's values

typedef BasicImage<value_type>::const_traverser ConstIterator

const 2D random access iterator over the kernel's values

typedef BasicImage<value_type>::Accessor Accessor

the kernel's accessor

typedef BasicImage<value_type>::ConstAccessor ConstAccessor

the kernel's const accessor

Constructor & Destructor Documentation

Kernel2D

(

)

Default constructor. Creates a kernel of size 1x1 which would copy the signal unchanged.

Kernel2D

(

Kernel2D< ARITHTYPE > const &

k

)

Copy constructor.

~Kernel2D

(

)

Destructor.

Member Function Documentation

Kernel2D& operator=

(

Kernel2D< ARITHTYPE > const &

k

)

Copy assignment.

InitProxy operator=

(

value_type const &

v

)

Initialization. This initializes the kernel with the given constant. The norm becomes v*width()*height().

Instead of a single value an initializer list of length width()*height() can be used like this:

vigra::Kernel2D<float> binom;

binom.initExplicitly(Diff2D(-1,-1), Diff2D(1,1)) =
0.0625, 0.125, 0.0625,
0.125,  0.25,  0.125,
0.0625, 0.125, 0.0625;

In this case, the norm will be set to the sum of the init values. An initializer list of wrong length will result in a run-time error.

void initSeparable	(	Kernel1D< value_type > const &	kx,
		Kernel1D< value_type > const &	ky
	)

Init the 2D kernel as the cartesian product of two 1D kernels of type Kernel1D. The norm becomes the product of the two original norms.

Required Interface:

The kernel's value_type must be a linear algebra.

vigra::Kernel2D<...>::value_type v;
v = v * v;

void initSeparable	(	KernelIterator	kxcenter,
		int	xleft,
		int	xright,
		KernelIterator	kycenter,
		int	yleft,
		int	yright
	)

Init the 2D kernel as the cartesian product of two 1D kernels given explicitly by iterators and sizes. The norm becomes the sum of the resulting kernel values.

Required Interface:

The kernel's value_type must be a linear algebra.

vigra::Kernel2D<...>::value_type v;
v = v * v;
v += v;

Preconditions:

xleft <= 0;
xright >= 0;
yleft <= 0;
yright >= 0;

void initAveraging

(

int

radius

)

Init as a 2D box filter with given radius.

void initGaussian	(	double	std_dev,
		value_type	norm
	)

Init as a 2D Gaussian function with given standard deviation and norm.

void initGaussian

(

double

std_dev

)

Init as a 2D Gaussian function with given standard deviation and unit norm.

void initDisk

(

int

radius

)

Init the 2D kernel as a circular averaging filter. The norm will be calculated as NumericTraits<value_type>::one() / (number of non-zero kernel values). The kernel's value_type must be a linear space.

Required Interface:

value_type v = vigra::NumericTraits<value_type>::one();

double d;
v = d * v;

Precondition:

radius > 0;

Kernel2D& initExplicitly	(	Shape2 const &	upperleft,
		Shape2 const &	lowerright
	)

Init the kernel by an explicit initializer list. The upper left and lower right corners (inclusive) of the kernel must be passed either as Shape2 or Diff2D objects. A comma-separated initializer list for the kernel's weights is given after the assignment operator like this:

// define horizontal Sobel filter
vigra::Kernel2D<float> sobel;

sobel.initExplicitly(Diff2D(-1,-1), Diff2D(1,1)) =
0.125, 0.0, -0.125,
0.25,  0.0, -0.25,
0.125, 0.0, -0.125;

The norm is set to the sum of the initializer values. If the wrong number of values is given, a run-time error results. It is, however, possible to give just one initializer. This creates an averaging filter with the given constant:

vigra::Kernel2D<float> average3x3;

average3x3.initExplicitly(Shape2(-1,-1), Shape2(1,1)) = 1.0/9.0;

Here, the norm is set to value*width()*height().

Preconditions:

1. upperleft.x <= 0;
2. upperleft.y <= 0;
3. lowerright.x >= 0;
4. lowerright.y >= 0;
5. the number of values in the initializer list
is 1 or equals the size of the kernel.

Kernel2D& initExplicitly

(

BasicImage< value_type > const &

image

)

Init the kernel by providing a BasicImage with the kernel values.

The kernel's origin is placed at the center of the given image. The norm is set to the sum of the image values.

Preconditions:

odd image width and height;

Point2D upperLeft

(

)

const

Coordinates of the upper left corner of the kernel.

Point2D lowerRight

(

)

const

Coordinates of the lower right corner of the kernel.

int width

(

)

const

Width of the kernel.

int height

(

)

const

Height of the kernel.

Iterator center

(

)

ImageIterator that points to the center of the kernel (coordinate (0,0)).

ConstIterator center

(

)

const

ImageIterator that points to the center of the kernel (coordinate (0,0)).

value_type& operator()	(	int	x,
		int	y
	)

Access kernel entry at given position.

value_type operator()	(	int	x,
		int	y
	)		const

Read kernel entry at given position.

value_type& operator[]

(

Diff2D const &

d

)

Access kernel entry at given position.

value_type operator[]

(

Diff2D const &

d

)

const

Read kernel entry at given position.

value_type norm

(

)

const

Norm of the kernel (i.e. sum of its elements).

Accessor accessor

(

)

The kernels default accessor.

ConstAccessor accessor

(

)

const

The kernels default const accessor.

void normalize

(

value_type

norm

)

Normalize the kernel to the given value. (The norm is the sum of all kernel elements.) The kernel's value_type must be a division algebra or algebraic field.

Required Interface:

value_type v = vigra::NumericTraits<value_type>::one(); // if norm is not
                                                        // given explicitly

v += v;
v = v * v;
v = v / v;

void normalize

(

)

Normalize the kernel to norm 1.

BorderTreatmentMode borderTreatment

(

)

const

current border treatment mode

void setBorderTreatment

(

BorderTreatmentMode

new_mode

)

Set border treatment mode. Only BORDER_TREATMENT_CLIP and BORDER_TREATMENT_AVOID are currently allowed.

---

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

• vigra/stdconvolution.hxx