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imgradientxyz

Find the directional gradients of a 3-D image

Syntax

[Gx,Gy,Gz] = imgradientxyz(I)
[Gx,Gy,Gz] = imgradientxyz(I,method)

Description

example

[Gx,Gy,Gz] = imgradientxyz(I) returns the gradient along the x-axis, Gx, the y-axis, Gy and the z-axis, Gz, for the grayscale or binary 3-D image I.

[Gx,Gy,Gz] = imgradientxyz(I,method) calculates the directional gradients using the specified method.

Examples

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Read 3-D data and prepare it for processing.

volData = load('mri');
sz = volData.siz;
vol = squeeze(volData.D);

Calculate the directional gradients.

[Gx, Gy, Gz] = imgradientxyz(vol);

Visualize the directional gradients as a montage.

figure, montage(reshape(Gx,sz(1),sz(2),1,sz(3)),'DisplayRange',[])
title('Gradient magnitude along X')

 
figure, montage(reshape(Gy,sz(1),sz(2),1,sz(3)),'DisplayRange',[])
title('Gradient magnitude along Y')

 
figure, montage(reshape(Gz,sz(1),sz(2),1,sz(3)),'DisplayRange',[])
title('Gradient magnitude along Z')

Input Arguments

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Input image, specified as a nonsparse, numeric or logical, 3-D matrix

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical

Gradient operator, specified as one of the following values.

Value

Meaning

'sobel'

Sobel gradient operator (default)

'prewitt'

Prewitt gradient operator

'central' Central difference gradient. dI/dx = (I(x+1)- I(x-1))/ 2
'intermediate' Intermediate difference gradient. dI/dx = I(x+1) - I(x)

When applying the gradient operator at the boundaries of the image, imgradientxyz assumes values outside the bounds of the image are equal to the nearest image border value. This behavior is similar to the 'replicate' boundary option in imfilter.

Data Types: char

Output Arguments

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Directional gradient along x-axis (horizontal), returned as nonsparse matrix equal in size to image I. The X-axis points in the direction of increasing column subscripts. Gx is of class double, unless the input image I is of class single, in which case Gx is of class single.

Directional gradient along y-axis (vertical), returned as non-sparse matrix equal in size to image I. Y-axis points in the direction of increasing row subscripts. Gy is of class double, unless the input image I is of class single, in which case Gy is of class single.

Directional gradient along z-axis, returned as nonsparse matrix equal in size to image I. The Z-axis points in the direction of increasing third dimension subscripts. Gz is of class double, unless the input image I is of class single, in which case Gz is of class single.

Algorithms

imgradientxyz does not normalize the gradient output. If the range of the gradient output image has to match the range of the input image, consider normalizing the gradient image, depending on the method argument used. For example, with a Sobel kernel, the normalization factor is 1/44, for Prewitt, the normalization factor is 1/18.

Extended Capabilities

Introduced in R2016a

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