visboundaries

Plot region boundaries

Syntax

visboundaries(BW)

visboundaries(B)

visboundaries(ax,___)

visboundaries(___,Name,Value)

h = visboundaries(___)

Description

visboundaries(BW) draws boundaries of regions in the binary image BW on the current axes. BW is a 2-D binary image where pixels that are logical true belong to the foreground region and pixels that are logical false constitute the background. visboundaries uses bwboundaries to find the boundary pixel locations in the image.

visboundaries(B) draws region boundaries specified by B, where B is a cell array containing the boundary pixel locations of the regions, similar in structure to the first output from bwboundaries.

visboundaries(ax,___) draws region boundaries on the axes specified by ax. Specify ax as the first input argument followed by any of the input argument combinations in the previous syntaxes.

visboundaries(___,Name,Value) uses name-value arguments to specify additional properties of the boundaries.

h = visboundaries(___) returns a handle h, for the boundaries.

Examples

Compute Boundaries and Plot on Image

Read image.

BW = imread('blobs.png');

Compute boundaries.

B = bwboundaries(BW);

Display image and plot boundaries on image.

imshow(BW)
hold on
visboundaries(B)

Visualize Segmentation Result

Read image and display it.

I = imread('toyobjects.png');
imshow(I)
hold on

Segment the image using the active contours (snakes) algorithm. First, specify the initial contour location close to the object that is to be segmented.

mask = false(size(I));
mask(50:150,40:170) = true;

Display the initial contour on the original image in blue.

visboundaries(mask,'Color','b');

Segment the image using the 'edge' method using 200 iterations.

bw = activecontour(I,mask,200,'edge');

Display the final contour on the original image in red.

visboundaries(bw,'Color','r');
title('Blue - Initial Contour, Red - Final Contour');

Input Arguments

BW — Binary image

logical array

Binary image, specified as a logical array.

Data Types: logical

B — Boundary pixel locations

cell array of Q-by-2 matrices

Boundary pixel locations, specified as a cell array. Each cell contains a Q-by-2 matrix, where Q is the number of boundary pixels for the corresponding region. Each row of these Q-by-2 matrices contains the row and column coordinates of a boundary pixel.

Data Types: cell

ax — Image on which to draw boundaries

current axes (default) | axes object

Image on which to draw boundaries, specified as an axes object.

Data Types: double

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: visboundaries(bw,'Color','b');

Color — Color of boundary

'red' (default) | RGB triplet | hexadecimal color code | color name | short color name

Color of the boundary, specified as an RGB triplet, a hexadecimal color code, a color name, or a short color name.

For a custom color, specify an RGB triplet or a hexadecimal color code.

• An RGB triplet is a three-element row vector whose elements specify the intensities of the red, green, and blue components of the color. The intensities must be in the range [0,1], for example, [0.4 0.6 0.7].

• A hexadecimal color code is a string scalar or character vector that starts with a hash symbol (#) followed by three or six hexadecimal digits, which can range from 0 to F. The values are not case sensitive. Therefore, the color codes "#FF8800", "#ff8800", "#F80", and "#f80" are equivalent.

Alternatively, you can specify some common colors by name. This table lists the named color options, the equivalent RGB triplets, and hexadecimal color codes.

Color Name	Short Name	RGB Triplet	Hexadecimal Color Code	Appearance
"red"	"r"	[1 0 0]	"#FF0000"
"green"	"g"	[0 1 0]	"#00FF00"
"blue"	"b"	[0 0 1]	"#0000FF"
"cyan"	"c"	[0 1 1]	"#00FFFF"
"magenta"	"m"	[1 0 1]	"#FF00FF"
"yellow"	"y"	[1 1 0]	"#FFFF00"
"black"	"k"	[0 0 0]	"#000000"
"white"	"w"	[1 1 1]	"#FFFFFF"
"none"	Not applicable	Not applicable	Not applicable	No color

Here are the RGB triplets and hexadecimal color codes for the default colors MATLAB^® uses in many types of plots.

RGB Triplet	Hexadecimal Color Code	Appearance
[0 0.4470 0.7410]	"#0072BD"
[0.8500 0.3250 0.0980]	"#D95319"
[0.9290 0.6940 0.1250]	"#EDB120"
[0.4940 0.1840 0.5560]	"#7E2F8E"
[0.4660 0.6740 0.1880]	"#77AC30"
[0.3010 0.7450 0.9330]	"#4DBEEE"
[0.6350 0.0780 0.1840]	"#A2142F"

Example: 'Color','r'

Example: 'Color','green'

Example: 'Color',[0 0 1]

Example: 'Color','#FF8800'

LineStyle — Style of boundary line

'-' (default) | '--' | ':' | '-.' | 'none'

Line style of boundary edge, specified as the comma-separated pair consisting of 'LineStyle' and any line specifier in the table below.

Line Style	Description	Resulting Line
"-"	Solid line
"--"	Dashed line
":"	Dotted line
"-."	Dash-dotted line
"none"	No line	No line

Example: 'LineStyle','-.'

LineWidth — Width of the line used for the boundary

2 (default) | positive number

Width of the line used for the boundary, specified as a positive number. Specify this value in points, where one point = 1/72 inch.

Example: 'LineWidth',4

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

EnhanceVisibility — Augment drawn boundary with contrasting features

true or 1 (default) | false or 0

Augment the drawn boundary with contrasting features to improve visibility on a varying background, specified as a numeric or logical 1 (true) or 0 (false).

Example: 'EnhanceVisibility',true

Data Types: logical

Output Arguments

h — Boundary lines

hggroup object

Boundary line, returned as an hggroup object. h is the child of the axes ax if specified, otherwise h is the child of the current axes.

Version History

Introduced in R2015a