#include <itkVectorGradientMagnitudeImageFilter.h>

Detailed Description

Computes a scalar, gradient magnitude image from a multiple channel (pixels are vectors) input.

Overview: This filter has two calculation modes. The first (default) mode calculates gradient magnitude as the difference between the largest two singular values in a singular value decomposition (SVD) of the partial derivatives [1]. The gradient is then based on the direction of maximal change, and is a characterization of how "elongated" the point-spread of the analysis is found to be.

The second, more heuristic, calculation mode finds gradient magnitude as the square-root of the sum of the * individual weighted vector component derivative sums squared. That is, * \( \mathbf{magnitude} = \left( \sum_{i=0}^n \sum_{j=0}^m \frac{\delta * \phi_j}{\delta \mathbf{x}_{i}}^2 \right)^{\frac{1}{2}} \), where \(\phi_j\) * is the \(j^{\mathbf{th}}\) channel of vector image \(\phi\) of dimension \(n\). * Weighting terms are applied to each vector component.

The second mode is computationally much faster than the first and has the advantage that it is automatically multi-threaded (some vnl functions used in the first mode are not thread-safe). The first mode, however, tends to give intuitively better results with less (or no) parameter tuning.

Template Parameters (Input and Output): This filter has one required template parameter which defines the input image type. The pixel type of the input image is assumed to be a vector (e.g., itk::Vector, itk::FixedArray). The scalar type of the vector components must be castable to floating point. Instantiating with an image of RGBPixel is not allowed but the image can be converted/adapted to Vector for processing.

The second template parameter, TRealType, can be optionally specified to define the scalar numerical type used in calculations. This is the component type of the output image. The default type of TRealType is float. For extra precision, you may safely change this parameter to double.

The third template parameter is the output image type. The third parameter will be automatically constructed from the first and second parameters, so it is not necessary (or advisable) to set this parameter explicitly. Given an M-channel input image with dimensionality N, and a numerical type specified as TRealType, the output image will be of type itk::Image<TRealType, N>.

Filter Parameters: The methods Set/GetUsePrincipleComponents and SetUsePrincipleComponentsOn/Off determine controls the calculation mode that is used.

The method UseImageSpacingOn will cause derivatives in the image to be scaled (inversely) with the pixel size of the input image, effectively taking derivatives in world coordinates (versus isotropic image space). UseImageSpacingOff turns this functionality off. Default is UseImageSpacingOn. The parameter UseImageSpacing can be set directly with the method SetUseImageSpacing(bool).

Weights can be applied to the derivatives directly using the SetDerivativeWeights method. Note that if UseImageSpacing is set to TRUE (ON), then these weights will be overridden by weights derived from the image spacing when the filter is updated. The argument to this method is a C array of TRealValue type.

Weights can be applied to each vector component of the image when the component derivative values are summed during computation. Specify these weights using the SetComponentWeights method. The argument to this method is a C array of TRealValue type. /**

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

itkVectorGradientMagnitudeImageFilter.h