imgradient3
Find gradient magnitude and direction of 3-D image
Syntax
Description
[
returns the gradient magnitude, Gmag
,Gazimuth
,Gelevation
]
= imgradient3(I
)Gmag
, gradient
direction, Gazimuth
, and gradient elevation
Gelevation
of the 3-D grayscale or
binary image I
.
[
calculates the gradient magnitude, direction, and elevation using
the specified Gmag
,Gazimuth
,Gelevation
]
= imgradient3(I
,method
)method
.
Examples
Compute 3-D Gradient Magnitude and Direction Using Sobel Method
Read 3-D data into the workspace and prepare it for processing.
volData = load('mri');
sz = volData.siz;
vol = squeeze(volData.D);
Calculate the gradients.
[Gmag, Gaz, Gelev] = imgradient3(vol);
Visualize the gradient magnitude as a montage.
figure, montage(reshape(Gmag,sz(1),sz(2),1,sz(3)),'DisplayRange',[]) title('Gradient magnitude')
Input Arguments
I
— Input image
3-D grayscale image | 3-D binary image
Input image, specified as a 3-D grayscale image or 3-D binary image.
method
— Gradient operator
"sobel"
(default) | "prewitt"
| "central"
| "intermediate"
Gradient operator, specified as one of the following values.
Value | Meaning | ||||||
---|---|---|---|---|---|---|---|
| Sobel gradient operator. The gradient of a pixel is a weighted sum of pixels in the 3-by-3-by-3 neighborhood. For example, in the depth (z) direction, the weights in the three planes are:
| ||||||
| Prewitt gradient operator. The gradient of a pixel is a weighted sum of pixels in the 3-by-3-by-3 neighborhood. For example, in the depth (z) direction, the weights in the three planes are:
| ||||||
"central" | Central difference gradient. The gradient of a pixel is a weighted difference of
neighboring pixels. For example, in the depth
(z) direction, | ||||||
"intermediate" | Intermediate difference gradient. The gradient of a pixel is the difference between an
adjacent pixel and the current pixel. For example,
in the depth (z) direction,
|
When applying the gradient operator at the boundaries of the image,
imgradient3
assumes values
outside the bounds of the image equal the nearest
image border value. This behavior is similar to the
"replicate"
boundary option in
imfilter
.
Data Types: char
| string
Gx
— Horizontal gradient
3-D numeric array
Horizontal gradient, specified as a 3-D numeric array.
The horizontal (x) axis points in
the direction of increasing column subscripts. You
can use the imgradientxyz
function to calculate
Gx
.
Gy
— Vertical gradient
3-D numeric array
Vertical gradient, specified as a 3-D numeric array of
the same size as Gx
. The
vertical (y) axis points in the
direction of increasing row subscripts. You can use
the imgradientxyz
function to calculate
Gy
.
Gz
— Depth gradient
3-D numeric array
Depth gradient, specified as a 3-D numeric array of
the same size as Gx
. The depth
(z) axis points in the
direction of increasing plane subscripts. You can
use the imgradientxyz
function to calculate
Gz
.
Output Arguments
Gmag
— Magnitude of the gradient vector
3-D numeric array
Gazimuth
— Azimuthal angle
3-D numeric array
Azimuthal angle, returned as a 3-D numeric array of the same size as the gradient magnitude,
Gmag
.
Gazimuth
contains angles in
degrees within the range [-180, 180] measured
between positive x-axis and the
projection of the point on the
x-y
plane.
Gazimuth
is of data type double
, unless the input
image or any of the directional gradients are of
data type single
. In this case,
Gmag
is of data type
single
.
Azimuth and Elevation
Gelevation
— Gradient elevation
3-D numeric array
Gradient elevation, returned as a 3-D numeric array of the same size as the gradient
magnitude, Gmag
.
Gelevation
contains angles in
degrees within the range [-90, 90] measured between
the radial line and the
x-y
plane.
Gelevation
is of data type double
, unless the input
image or any of the directional gradients are of
data type single
. In this case,
Gmag
is of data type
single
.
Algorithms
imgradient3
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 and for Prewitt,
the normalization factor is 1/18.
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.
Usage notes and limitations:
imgradient3
supports the generation of C code (requires MATLAB® Coder™). For more information, see Code Generation for Image Processing.When generating code, the input argument
method
must be a compile-time constant.
GPU Code Generation
Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.
Usage notes and limitations:
When generating code, the input argument
method
must be a compile-time constant.
Thread-Based Environment
Run code in the background using MATLAB® backgroundPool
or accelerate code with Parallel Computing Toolbox™ ThreadPool
.
This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.
Version History
Introduced in R2016aR2022b: Support for thread-based environments
imgradient3
now supports thread-based
environments.
See Also
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