edge3

Find edges in 3-D grayscale volume

Syntax

BW = edge3(V,"approxcanny",thresh)

BW = edge3(V,"approxcanny",thresh,sigma)

BW = edge3(V,"Sobel",thresh)

BW = edge3(V,"Sobel",thresh,"nothinning")

Description

BW = edge3(V,"approxcanny",thresh) returns the edges found in the grayscale or binary volume V using the approximate Canny method. The approximate Canny method finds edges by looking for local maxima of the gradient of V. edge3 calculates the gradient using the derivative of a Gaussian smoothed volume.

The approximate Canny method uses two thresholds to detect strong and weak edges, and includes the weak edges in the output only if they are connected to strong edges. This method is more likely than the Sobel method to detect true weak edges.

BW = edge3(V,"approxcanny",thresh,sigma) returns the edges found in the intensity or binary volume V, where sigma specifies the standard deviation of the Gaussian smoothing filter. edge3 chooses the size of the filter automatically, based on sigma.

BW = edge3(V,"Sobel",thresh) accepts an intensity or a binary volume V and returns a binary volume BW with 1s where the function finds edges in V and 0s elsewhere.

The Sobel method finds edges using the Sobel approximation to the derivative. It returns edges at those points where the gradient of V is maximum. edge3 ignores all edges that are not stronger than thresh.

BW = edge3(V,"Sobel",thresh,"nothinning") speeds up the operation of the algorithm by skipping the additional edge-thinning stage. By default, or when "thinning" is specified, edge3 applies edge thinning.

Examples

Find Edges of MRI Volume Using Approximate Canny Method

Load volumetric data and remove any singleton dimensions.

load mri
V = squeeze(D);

Visualize original image.

montage(reshape(V,size(D)),map);

Detect edges in the volume.

BW = edge3(V,'approxcanny',0.6);

Visualize the detected edges. You can also view the result using the Volume Viewer app.

montage(reshape(BW,size(D)))

Input Arguments

V — Input volume

3-D numeric array

Input volume, specified as a 3-D numeric array.

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

thresh — Sensitivity threshold

numeric scalar | 2-element numeric row vector

Sensitivity threshold, specified as one of the following.

Method	Threshold value
Canny	Numeric scalar
Approximate Canny	2-element numeric row vector. The first element is the low threshold, and the second element is the high threshold, [lowthresh highthresh]
	Numeric scalar representing the high threshold. edge3 sets the low threshold as 0.4*thresh.
Sobel	Numeric scalar

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

sigma — Standard deviation of Gaussian filter

sqrt(2) | numeric scalar | 1-by-3 numeric vector

Standard deviation of the Gaussian filter, specified as a numeric scalar for isotropic volumes or a 1-by-3 numeric vector of the form [SigmaX SigmaY SigmaZ] for anisotropic volumes that have different scales in each direction.

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

Output Arguments

BW — Detected edges

3-D numeric array

Detected edges, returned as a 3-D numeric array of the same size as V. Pixel values of 1 indicate edges and pixel values of 0 indicate flat regions.

Extended Capabilities

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 R2017b

R2022b: Support for thread-based environments

edge3 now supports thread-based environments.