SoGradientOperatorProcessing2d Class Reference
[Gradient]

SoGradientOperatorProcessing2d engine provides different algorithms to extract the edges of a 2D image. More...

#include <ImageViz/Engines/EdgeDetection/Gradient/SoGradientOperatorProcessing2d.h>

Inheritance diagram for SoGradientOperatorProcessing2d:

Public Types
enum	GradientOperator { CANNY_DERICHE = 0, SHEN_CASTAN = 1, CANNY = 3, GAUSSIAN = 4, SOBEL = 5, PREWITT = 6 }
enum	GradientMode { AMPLITUDE_MAX_OF_MAGS = 0, AMPLITUDE_EUCLIDEAN = 1, AMPLITUDE_AND_ORIENTATION = 2, X_AND_Y_GRADIENTS = 3 }
Public Member Functions
	SoGradientOperatorProcessing2d ()
Public Attributes
SoSFImageDataAdapter	inImage
SoSFEnum	gradientOperator
SoSFEnum	gradientMode
SoSFFloat	standardDeviation
SoImageVizEngineOutput < SoSFImageDataAdapter, SoImageDataAdapter * >	outGradientXImage
SoImageVizEngineOutput < SoSFImageDataAdapter, SoImageDataAdapter * >	outGradientYImage
SoImageVizEngineOutput < SoSFImageDataAdapter, SoImageDataAdapter * >	outAmplitudeImage
SoImageVizEngineOutput < SoSFImageDataAdapter, SoImageDataAdapter * >	outOrientationImage

Detailed Description

SoGradientOperatorProcessing2d engine provides different algorithms to extract the edges of a 2D image.

For an introduction, see:

The SoGradientOperatorProcessing2d engine provides different algorithms to extract the edges of an image.

Note: You may normalize the filtered image, i.e. divide the output gray levels by the sum of absolute values of the kernel coefficients. If not, be aware that overflow may occur.

Canny-Deriche: It performs a recursive gradient computation to get the gradient in X and Y directions. It is an FIR (finite impulse response) filter. To minimize the effect of noise, it smooths the image before computing the gradient. A smoothing scale parameter determines the smoothing intensity. If the value is large, noise will be reduced but edges will be less sharp and only the most significant edges will survive. It is important to select the right coefficient to lower the noise just enough without defocusing the edges. Then it gets the maximum of these images with a gradient magnitude operation. For color images it calculates the maximum of intensity or the euclidian mean.

Shen-Castan: It calculates the gradient of Shen and Castan. It is a recursive and exponential filter that smooths an object and then extracts its edges. It is based on the Shen operator :

$f(x,y)=\frac{p^2}{4}\cdot e^{(-p(|x|+|y|))}$

The highest $p$ is, the more edges we get. For color images it calculates the maximum of intensity or the euclidian mean.

Canny: It performs an approximation to get the Canny-Deriche in X and Y directions using a convolution kernel 7x5 for X and 5x7 for Y. Result is nearly the same than Canny Deriche but process is much faster.

Gaussian: It performs a convolution with the derivatives of a Gaussian function along each image axis.

Sobel: It performs a convolution with the Sobel Kernel. $\mathbf{G_x} = \begin{bmatrix} -1 & 0 & +1 \\ -2 & 0 & +2 \\ -1 & 0 & +1 \end{bmatrix} \quad \mbox{and} \quad \mathbf{G_y} = \begin{bmatrix} -1 & -2 & -1 \\ 0 & 0 & 0 \\ +1 & +2 & +1 \end{bmatrix}$

Prewitt: It performs a convolution with the Prewitt Kernel. $\mathbf{G_x} = \begin{bmatrix} -1 & 0 & +1 \\ -1 & 0 & +1 \\ -1 & 0 & +1 \end{bmatrix} \quad \mbox{and} \quad \mathbf{G_y} = \begin{bmatrix} -1 & -1 & -1 \\ 0 & 0 & 0 \\ +1 & +1 & +1 \end{bmatrix}$

FILE FORMAT/DEFAULT

inImage	NULL
gradientOperator	CANNY_DERICHE
gradientMode	AMPLITUDE_MAX_OF_MAGS
standardDeviation	60.0f

Library references: gradient

See related examples:: BatchProcessing

Member Enumeration Documentation

enum SoGradientOperatorProcessing2d::GradientMode

Enumerator:

AMPLITUDE_MAX_OF_MAGS	This option computes the gradient maximal amplitude. Only the outAmplitudeImage output is set using this mode.
AMPLITUDE_EUCLIDEAN	This option computes the gradient euclidean amplitude. Only the outAmplitudeImage output is set using this mode.
AMPLITUDE_AND_ORIENTATION	This option computes euclidean amplitude and the orientation (between -128 and +128 degrees). Both outAmplitudeImage and outOrientationImage outputs are set using this mode.
X_AND_Y_GRADIENTS	This option computes gradient in X and Y directions. Both outGradientXImage and outGradientYImage outputs are set using this mode.

enum SoGradientOperatorProcessing2d::GradientOperator

Enumerator:

CANNY_DERICHE	The gradient is computed using the Canny-Deriche algorithm. Supported gradient output modes : AMPLITUDE_MAX_OF_MAGS, AMPLITUDE_EUCLIDEAN, AMPLITUDE_AND_ORIENTATION and X_AND_Y_GRADIENTS.
SHEN_CASTAN	The gradient is computed using the Shen and Castan algorithm. Supported gradient output modes : AMPLITUDE_MAX_OF_MAGS.
CANNY	The gradient is computed using the Canny algorithm. Supported gradient output modes : AMPLITUDE_MAX_OF_MAGS and AMPLITUDE_EUCLIDEAN.
GAUSSIAN	The gradient is computed using the Gaussian algorithm. Supported gradient output modes : AMPLITUDE_MAX_OF_MAGS, AMPLITUDE_EUCLIDEAN, AMPLITUDE_AND_ORIENTATION and X_AND_Y_GRADIENTS.
SOBEL	The gradient is computed using the Sobel algorithm. Supported gradient output modes : AMPLITUDE_MAX_OF_MAGS, AMPLITUDE_EUCLIDEAN, AMPLITUDE_AND_ORIENTATION and X_AND_Y_GRADIENTS.
PREWITT	The gradient is computed using the Prewitt algorithm. Supported gradient output modes : AMPLITUDE_MAX_OF_MAGS, AMPLITUDE_EUCLIDEAN, AMPLITUDE_AND_ORIENTATION and X_AND_Y_GRADIENTS.