11.31. ITK Gradient Magnitude Recursive Gaussian Image Filter

Computes the gradient magnitude (edge strength) of an image after Gaussian smoothing.

Group (Subgroup)

ITKImageGradient (ImageGradient)

Description

The gradient magnitude measures how fast intensity changes at each pixel — it is high along edges and near zero in flat regions, so the output is an edge-strength image. This filter first smooths the image with a Gaussian and then takes the gradient, combining the two steps so that the smoothing scale is controlled directly. Smoothing suppresses noise, so edges are detected more reliably than with a raw (un-smoothed) gradient.

The amount of smoothing is set by Sigma: a small Sigma responds to fine, sharp edges; a large Sigma blurs away fine detail and responds only to broad, large-scale edges.

Use this filter to produce an edge-strength map for edge detection, segmentation seeding (for example, as a speed image for level sets), or feature extraction.

Parameter Guidance

  • Sigma — the standard deviation (width) of the Gaussian smoothing kernel, measured in image-spacing (physical) units, not pixels. For example, with a pixel spacing of 0.5 µm, a Sigma of 1.0 corresponds to 2 pixels. Larger values smooth more and detect broader edges.

  • Normalize Across Scale — controls how the response is scaled when Sigma changes. Leave this off for ordinary edge detection. Enable it only when you compare gradient magnitudes computed at several different Sigma values (multi-scale analysis), so that the strongest response is not simply the smallest Sigma.

Required Input Sources

Operates on any scalar (grayscale) image — typically from Read Image, Read Images [3D Stack], or the output of a prior ITK image filter.

Input Parameter(s)

Parameter Name

Parameter Type

Parameter Notes

Description

Sigma

Scalar Value

Float64

Set/Get Sigma value. Sigma is measured in the units of image spacing.

Normalize Across Scale

Bool

Set/Get the normalization factor that will be used for the Gaussian. RecursiveGaussianImageFilter::SetNormalizeAcrossScale

Input Cell Data

Parameter Name

Parameter Type

Parameter Notes

Description

Image Geometry

Geometry Selection

Image

Select the Image Geometry Group from the DataStructure.

Input Cell Data

Array Selection

Allowed Types: int8, uint8, int16, uint16, int32, uint32, int64, uint64, float32, float64

The image data that will be processed by this filter.

Output Cell Data

Parameter Name

Parameter Type

Parameter Notes

Description

Output Image Data Array

DataObjectName

The result of the processing will be stored in this Data Array.

Example Pipelines

DREAM3D-NX Help

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