boundarymask

Find region boundaries of segmentation

Syntax

mask = boundarymask(L)

mask = boundarymask(BW)

mask = boundarymask(___,conn)

Description

mask = boundarymask(L) computes a mask that represents the region boundaries for the input label matrix L. The output, mask, is a logical image that is true at boundary locations and false at non-boundary locations.

mask = boundarymask(BW) computes the region boundaries for the input binary image BW.

mask = boundarymask(___,conn) computes the region boundaries using a connectivity specified by conn.

Examples

Create Rasterized Grid of Region Boundaries

Read an image into the workspace.

I = imread('kobi.png');

Create a superpixel representation of the image, returned as a label matrix.

L = superpixels(I,100);

Display the label matrix.

imshow(label2rgb(L))

Find the region boundaries of the label matrix.

mask = boundarymask(L);

Display the boundary mask over the original image by using the labeloverlay function. The region boundaries of the label matrix appear as 1-pixel wide cyan lines.

imshow(labeloverlay(I,mask,'Transparency',0))

Input Arguments

L — Label matrix

2-D numeric matrix | 2-D logical matrix

Label matrix, specified as a 2-D numeric matrix of nonnegative numbers or a 2-D logical matrix.

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

BW — Binary image

numeric matrix | logical matrix

Binary image, specified as a numeric or logical matrix of the same size as L.

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

conn — Pixel connectivity

8 (default) | 4

Pixel connectivity, specified as 4 or 8.

Value	Meaning
Two-Dimensional Connectivities
4	Pixels are connected if their edges touch. The neighborhood of a pixel are the adjacent pixels in the horizontal or vertical direction.	Current pixel is shown in gray.
8	Pixels are connected if their edges or corners touch. The neighborhood of a pixel are the adjacent pixels in the horizontal, vertical, or diagonal direction.	Current pixel is shown in gray.

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

Output Arguments

mask — Rasterized grid of region boundaries

2-D logical matrix

Rasterized grid of region boundaries, specified as a 2-D logical matrix of the same size as the input image. A pixel in mask is true when the corresponding pixel in the input image with value P has a neighboring pixel with a different value than P.

Data Types: logical

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• boundarymask supports the generation of C code (requires MATLAB^® Coder™). Note that if you choose the generic MATLAB Host Computer target platform, boundarymask generates code that uses a precompiled, platform-specific shared library. Use of a shared library preserves performance optimizations but limits the target platforms for which code can be generated. For more information, see Types of Code Generation Support in Image Processing Toolbox.

• When generating code, the input argument conn must be a compile-time constant.

Version History

Introduced in R2016a