viscircles

Create circle

Syntax

viscircles(centers,radii)

viscircles(ax,centers,radii)

viscircles(___,Name=Value)

h = viscircles(___)

Description

viscircles(centers,radii) draws circles with specified centers and radii onto the current axes. You can use the imfindcircles function to find the centers and radii of circles in an image.

viscircles(ax,centers,radii) draws circles onto the axes specified by ax.

viscircles(___,Name=Value) uses name-value arguments to specify additional properties of the circles.

h = viscircles(___) returns a handle, h, to the drawn circles.

Examples

Draw Lines Around Bright and Dark Circles in Image

Read the image into the workspace and display it.

A = imread('circlesBrightDark.png');
imshow(A)

Define the radius range.

Rmin = 30;
Rmax = 65;

Find all the bright circles in the image within the radius range.

[centersBright, radiiBright] = imfindcircles(A,[Rmin Rmax],'ObjectPolarity','bright');

Find all the dark circles in the image within the radius range.

[centersDark, radiiDark] = imfindcircles(A,[Rmin Rmax],'ObjectPolarity','dark');

Draw blue lines around the edges of the bright circles.

viscircles(centersBright, radiiBright,'Color','b');

Draw red dashed lines around the edges of the dark circles.

viscircles(centersDark, radiiDark,'LineStyle','--');

Clear Axes Before Plotting Circles

The viscircles function does not clear the target axes before plotting circles. To remove circles that have been previously plotted in an axes, use the cla function. To illustrate, this example creates a new figure and then loops, drawing a set of circles with each iteration, clearing the axes each time.

figure
colors = {'b','r','g','y','k'}; 
 
for k = 1:5
    % Create 5 random circles to display,
    X = rand(5,1);
    Y = rand(5,1);
    centers = [X Y];
    radii = 0.1*rand(5,1);
 
    % Clear the axes.
    cla
 
    % Fix the axis limits.
    xlim([-0.1 1.1])
    ylim([-0.1 1.1])
 
    % Set the axis aspect ratio to 1:1.
    axis square
 
    % Set a title.
    title(['k = ' num2str(k)])
 
    % Display the circles.
    viscircles(centers,radii,'Color',colors{k});
              
    % Pause for 1 second.
    pause(1)
end

Input Arguments

centers — Coordinates of circle centers

two-column numeric matrix

Coordinates of circle centers, specified as a two-column numeric matrix. The x-coordinates of the circle centers are in the first column and the y-coordinates are in the second column.

radii — Circle radii

positive number | column vector

Circle radii, specified as a positive number or a column vector of positive numbers of the same length as centers. When radii is a positive number, viscircles draws all circles with the same radius. When radii is a column vector, viscircles draws each circle centers(j,:) with the corresponding radius radii(j).

ax — Axes in which to draw circles

handle

Axes in which to draw circles, specified as an Axes object returned by gca or axes.

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.

Example: viscircles(centers,radii,Color="b") specifies blue circle edges, using the short color name for blue.

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

Example: viscircles(centers,radii,"Color","b") specifies blue circle edges, using the short color name for blue.

EnhanceVisibility — Augment drawn circles with contrasting features to improve visibility

true or 1 (default) | false or 0

Augment drawn circles with contrasting features to improve visibility, specified as a numeric or logical 1 (true) or 0 (false). If you set the value to true, then viscircles draws a contrasting circle below the colored circle.

Data Types: logical

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: viscircles(centers,radii,Color="r");

Example: viscircles(centers,radii,Color="green");

Example: viscircles(centers,radii,Color=[0 0 1]);

Example: viscircles(centers,radii,Color="#FF8800");

LineStyle — Line style of circle edge

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

Line style of circle edge, specified as 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

LineWidth — Width of circle edge

2 (default) | positive number

Width of circle edge, specified a positive number. Line width is expressed in points, where each point equals 1/72 of an inch.

Data Types: double

Output Arguments

h — Circles drawn

hggroup object

Circles drawn, 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 R2012a

R2022b: Accepts scalar radii

viscircles accepts a scalar value for the radii argument. When radii is a scalar, viscircles draws all circles with the same radius.