drawellipse

Create customizable elliptical ROI

Syntax

roi = drawellipse

roi = drawellipse(ax)

roi = drawellipse(___,Name=Value)

Description

The drawellipse function creates an Ellipse object that specifies the shape and position of an elliptical region of interest (ROI). You can create the ROI interactively by drawing the ROI over an image using the mouse, or programmatically by using name-value arguments. You can also specify the initial appearance and behavior of the ROI.

After you create the ROI, you can use object properties, object functions, and event notifications to customize the shape, position, appearance, and behavior of the ROI. For more information about using these capabilities, see Tips.

roi = drawellipse creates an Ellipse object and enables interactive drawing of an elliptical ROI on the current axes.

To draw the ROI, position the pointer on the image. The cursor changes to a fleur shape. Click and drag to draw the elliptical ROI. To finish the ROI, release the mouse button. For more information about using the ROI, including keyboard shortcuts and context menu options, see Tips.

roi = drawellipse(ax) creates the ROI in the axes specified by ax.

roi = drawellipse(___,Name=Value) modifies the appearance and behavior of the ROI using one or more name-value arguments.

Examples

Create Red Elliptical ROI

Read an image into the workspace and display it.

imshow(imread('llama.jpg'))

Interactively draw a red elliptical ROI.

h = drawellipse('Color','r');

Change the stripe color of the ROI to black, then increase the opacity of the ROI.

h.StripeColor = 'k';
h.FaceAlpha = 0.4;

Create Elliptical ROI Programmatically

Read an image into the workspace and display it.

I = imread('baby.jpg');
figure
imshow(I)

Draw an elliptical ROI on the image. Use the 'Center' name-value pair to specify the location of the ellipse and the 'SemiAxes' name-value pair to specify the shape of the ellipse. Set the edge of the ellipse to be a striped red line by specifying the 'StripeColor' name-value pair.

h = drawellipse('Center',[1000,1000],'SemiAxes',[500,250],'StripeColor','r');

Set Up Listener for Ellipse ROI Events

Read an image into the workspace.

I = imread('cameraman.tif'); 

Display the image.

imshow(I);

Draw a circular ROI on the image.

roi = drawellipse('Color','r');

Set up listeners for ROI moving events. When you move it, the ROI sends notifications of these events and executes the callback function you specify.

addlistener(roi,'MovingROI',@allevents);
addlistener(roi,'ROIMoved',@allevents);

The allevents callback function displays the previous position and the current position of the ROI.

function allevents(src,evt)
    evname = evt.EventName;
    switch(evname)
        case{'MovingROI'}
            disp(['ROI moving previous position: ' mat2str(evt.PreviousPosition)]);
            disp(['ROI moving current position: ' mat2str(evt.CurrentPosition)]);
        case{'ROIMoved'}
            disp(['ROI moved previous position: ' mat2str(evt.PreviousPosition)]);
            disp(['ROI moved current position: ' mat2str(evt.CurrentPosition)]);
    end
end

Input Arguments

ax — Parent of ROI

gca (default) | Axes object | UIAxes object

Parent of ROI, specified as an Axes object or a UIAxes object. For information about using an ROI in a UIAxes, including important limitations, see Using ROIs in Apps Created with App Designer.

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: roi = drawellipse(Color="y") creates a yellow colored Ellipse object.

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

Example: roi = drawellipse("Color","y") creates a yellow colored Ellipse object.

AspectRatio — Aspect ratio of ellipse

nonnegative number

Aspect ratio of the ellipse, specified as a nonnegative number. The aspect ratio is defined as SemiAxes(1)/SemiAxes(2).

Center — Center of ROI

1-by-2 numeric vector

Center of the ROI, specified as a 1-by-2 numeric vector of the form [x y].

Color — ROI color

[0 0.4470 0.7410] (default) | RGB triplet | color name | short color name

ROI color, specified as an RGB triplet, a color name, or a short color name.

You can specify any color using an RGB triplet. An RGB triplet is a 3-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].

You can specify some common colors by name as a string scalar or character vector. This table lists the named color options and the equivalent RGB triplets.

Color Name	Short Name	RGB Triplet	Appearance
"red"	"r"	[1 0 0]
"green"	"g"	[0 1 0]
"blue"	"b"	[0 0 1]
"cyan"	"c"	[0 1 1]
"magenta"	"m"	[1 0 1]
"yellow"	"y"	[1 1 0]
"black"	"k"	[0 0 0]
"white"	"w"	[1 1 1]

Here are the RGB triplets for the default colors that MATLAB^® uses in many types of plots.

RGB Triplet	Appearance
[0 0.4470 0.7410]
[0.8500 0.3250 0.0980]
[0.9290 0.6940 0.1250]
[0.4940 0.1840 0.5560]
[0.4660 0.6740 0.1880]
[0.3010 0.7450 0.9330]
[0.6350 0.0780 0.1840]

Example: "Color","r"

Example: "Color","green"

Example: "Color",[0 0.4470 0.7410]

ContextMenu — Context menu

ContextMenu object

Context menu that displays when you right-click the ROI, specified as a ContextMenu object. You can create a custom context menu by using the uicontextmenu function and then configuring context menu properties.

Deletable — Context menu provides option to delete the ROI

true or 1 (default) | false or 0

Context menu provides an option to delete the ROI, specified as a numeric or logical 1 (true) or 0 (false). When the value is true, you can delete the ROI interactively using the context menu. When the value is false, the context menu option to delete the ROI is disabled.

In both cases, you can delete the ROI outside of the context menu by using the delete function.

DrawingArea — Area of axes in which you can interactively place ROI

"auto" (default) | "unlimited" | [x,y,w,h]

Area of the axes in which you can interactively place the ROI, specified as one of the values in this table.

Value	Description
"auto"	The drawing area is the current axes limits (default).
"unlimited"	The drawing area has no boundary and ROIs can be drawn or dragged to extend beyond the axes limits.
[x,y,w,h]	The drawing area is restricted to a rectangular region beginning at (x,y), and extending to width w and height h.

FaceAlpha — Transparency of ROI face

0.2 (default) | number in the range [0, 1]

Transparency of the ROI face, specified as a number in the range [0, 1]. When the value is 1, the ROI face is completely opaque. When the value is 0, the ROI face is completely transparent.

FaceSelectable — ROI face can capture clicks

true or 1 (default) | false or 0

ROI face can capture clicks, specified as a numeric or logical 1 (true) or 0 (false). When true, the ROI face captures mouse clicks. When false, the ROI face does not capture mouse clicks.

FixedAspectRatio — Aspect ratio remains constant

false or 0 (default) | true or 1

Aspect ratio remains constant during interaction, specified as a numeric or logical 0 (false) or 1 (true). When the value is true, the aspect ratio remains constant when you draw or resize the ROI. When the value is false, you can change the aspect ratio when drawing or resizing the ROI.

HandleVisibility — Visibility of ROI handle in Children property of parent

"on" (default) | "off" | "callback"

Visibility of the ROI handle in the Children property of the parent, specified as one of the values in this table.

Value	Description
"on"	The object handle is always visible (default).
"off"	The object handle is hidden at all times.
"callback"	The object handle is visible from within callbacks or functions invoked by callbacks, but not from within functions invoked from the command line.

InteractionsAllowed — Interactivity of ROI

"all" (default) | "none" | "reshape" | "translate"

Interactivity of the ROI, specified as one of the values in this table.

Value	Description
"all"	The ROI is fully interactable (default).
"none"	The ROI is not interactable, and no drag points are visible.
"translate"	The ROI can be translated (moved) within the drawing area but not reshaped.
"reshape"	The ROI can be reshaped but not translated.

Label — ROI label

'' (default) | character vector | string scalar

ROI label, specified as a character vector or string scalar. By default, the ROI has no label ('').

LabelAlpha — Transparency of text background

1 (default) | number in the range [0, 1]

Transparency of the text background, specified as a number in the range [0, 1]. When set to 1, the text background is completely opaque. When set to 0, the text background is completely transparent.

LabelTextColor — Label text color

"black" (default) | RGB triplet | color name | short color name

Label text color, specified as an RGB triplet, a color name, or a short color name.

You can specify any color using an RGB triplet. An RGB triplet is a 3-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].

You can specify some common colors by name as a string scalar or character vector. This table lists the named color options and the equivalent RGB triplets.

Color Name	Short Name	RGB Triplet	Appearance
"red"	"r"	[1 0 0]
"green"	"g"	[0 1 0]
"blue"	"b"	[0 0 1]
"cyan"	"c"	[0 1 1]
"magenta"	"m"	[1 0 1]
"yellow"	"y"	[1 1 0]
"black"	"k"	[0 0 0]
"white"	"w"	[1 1 1]

Here are the RGB triplets for the default colors that MATLAB uses in many types of plots.

RGB Triplet	Appearance
[0 0.4470 0.7410]
[0.8500 0.3250 0.0980]
[0.9290 0.6940 0.1250]
[0.4940 0.1840 0.5560]
[0.4660 0.6740 0.1880]
[0.3010 0.7450 0.9330]
[0.6350 0.0780 0.1840]

Example: "LabelTextColor","r"

Example: "LabelTextColor","green"

Example: "LabelTextColor",[0 0.4470 0.7410]

LabelVisible — Label visibility

"on" (default) | "off" | "hover"

Label visibility, specified as one of these values.

Value	Description
"on"	Label is visible when the ROI is visible.
"hover"	Label is visible only when the mouse is hovering over the ROI.
"off"	Label is not visible.

LineWidth — Width of ROI border

positive number

Width of the ROI border, specified as a positive number in points. The default value is three times the number of points per screen pixel, such that the border is three pixels wide.

MarkerSize — Marker size

positive number

Marker size, specified as a positive number in points. The default value is eight times the number of points per screen pixel, such that markers are eight pixels in size.

Parent — ROI parent

Axes object | UIAxes object

ROI parent, specified as an Axes or UIAxes object. For information about using an ROI in a UIAxes, including important limitations, see Using ROIs in Apps Created with App Designer.

RotationAngle — Rotation angle

0 (default) | number

Rotation angle of the ROI, specified as a number. The angle is measured in degrees in a clockwise direction around the center of the ROI.

Selected — Selection state of ROI

false or 0 (default) | true or 1

Selection state of the ROI, specified as a numeric or logical 0 (false) or 1 (true).

SelectedColor — Color of ROI when selected

"none" (default) | RGB triplet | color name | short color name

Color of the ROI when selected, specified as an RGB triplet, a color name, a short color name, or "none". If you specify "none", then the value of Color defines the color of the ROI for all states, selected or not.

You can specify any color using an RGB triplet. An RGB triplet is a 3-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].

You can specify some common colors by name as a string scalar or character vector. This table lists the named color options and the equivalent RGB triplets.

Color Name	Short Name	RGB Triplet	Appearance
"red"	"r"	[1 0 0]
"green"	"g"	[0 1 0]
"blue"	"b"	[0 0 1]
"cyan"	"c"	[0 1 1]
"magenta"	"m"	[1 0 1]
"yellow"	"y"	[1 1 0]
"black"	"k"	[0 0 0]
"white"	"w"	[1 1 1]

Here are the RGB triplets for the default colors that MATLAB uses in many types of plots.

RGB Triplet	Appearance
[0 0.4470 0.7410]
[0.8500 0.3250 0.0980]
[0.9290 0.6940 0.1250]
[0.4940 0.1840 0.5560]
[0.4660 0.6740 0.1880]
[0.3010 0.7450 0.9330]
[0.6350 0.0780 0.1840]

Example: "SelectedColor","r"

Example: "SelectedColor","green"

Example: "SelectedColor",[0 0.4470 0.7410]

SemiAxes — Lengths of semiaxes of ellipse

1-by-2 numeric vector

Lengths of the semiaxis of the ellipse, specified as a 1-by-2 numeric vector of the form [semiaxis1 semiaxis2]. The drawellipse function assigns the length of the semiaxis that is closest to the x direction to semiaxis1.

StripeColor — Color of ROI stripe

"none" (default) | RGB triplet | color name | short color name

Color of the ROI stripe, specified as an RGB triplet, a color name, a short color name, or "none". If you specify "none", then the ROI edge is a solid color specified by Color. Otherwise, the edge of the ROI is striped, with colors alternating between the colors specified by Color and StripeColor.

You can specify any color using an RGB triplet. An RGB triplet is a 3-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].

You can specify some common colors by name as a string scalar or character vector. This table lists the named color options and the equivalent RGB triplets.

Color Name	Short Name	RGB Triplet	Appearance
"red"	"r"	[1 0 0]
"green"	"g"	[0 1 0]
"blue"	"b"	[0 0 1]
"cyan"	"c"	[0 1 1]
"magenta"	"m"	[1 0 1]
"yellow"	"y"	[1 1 0]
"black"	"k"	[0 0 0]
"white"	"w"	[1 1 1]

Here are the RGB triplets for the default colors that MATLAB uses in many types of plots.

RGB Triplet	Appearance
[0 0.4470 0.7410]
[0.8500 0.3250 0.0980]
[0.9290 0.6940 0.1250]
[0.4940 0.1840 0.5560]
[0.4660 0.6740 0.1880]
[0.3010 0.7450 0.9330]
[0.6350 0.0780 0.1840]

Example: "StripeColor","r"

Example: "StripeColor","green"

Example: "StripeColor",[0 0.4470 0.7410]

Tag — Tag to associate with ROI

'' (default) | character vector | string scalar

Tag to associate with the ROI, specified as a character vector or string scalar. Use the tag value to find the ROI object in a hierarchy of objects using the findobj function.

UserData — Data to associate with ROI

any MATLAB data

Data to associate with the ROI, specified as any MATLAB data. For example, you can specify a scalar, vector, matrix, cell array, string, character array, table, or structure. The drawellipse object does not use this data.

Visible — ROI visibility

"on" (default) | "off" | on/off logical value

ROI visibility, specified as "on" or "off", or as a numeric or logical 1 (true) or 0 (false). A value of "on" is equivalent to true, and "off" is equivalent to false. The value is stored as an on/off logical value of type OnOffSwitchState.

Value	Description
"on"	Display the ROI.
"off"	Hide the ROI without deleting it. You still can access the properties of an invisible ROI.

Output Arguments

roi — Elliptical ROI

Ellipse object

Elliptical ROI, returned as an Ellipse object.

Tips

• The ROI supports the following interactivity, including keyboard shortcuts.

  Behavior	Keyboard shortcut
  Cancel drawing the ROI.	Press Esc. The function returns a valid ROI object with an empty Position property.
  Fine-tune width of ellipse as you are drawing.	As you draw the ellipse, use the scroll wheel to make small changes to the width of the ellipse.
  Rotate the ROI.	Position the pointer near a vertex. The pointer changes to the rotate pointer. Click and rotate the ROI on its center. To make the rotation snap at 15 degree angles, press Shift as you rotate.
  Maintain aspect ratio while drawing.	Hold the Shift key as you draw. Creates a circular ROI. To lock the aspect ratio, position the pointer on the ROI, right-click, and select Fix Aspect Ratio from the context menu
  Resize (reshape) the ROI.	Position pointer over a vertex and then click and drag. To main the aspect ratio as you resize, Hold the Shift key.
  Move the ROI.	Position the pointer over the ROI. The pointer changes to the fleur shape. Click and drag to move the ROI.
  Delete the ROI.	Position the pointer over the ROI and right-click to view its context menu. Select Delete Ellipse from the menu. You can also delete the ROI using the delete function.

• The drawellipse function creates an Ellipse object. After you create the object, you can modify the shape, position, appearance, and behavior of the ROI by using these object capabilities.

  Capability	Support
  Object properties	ROI objects have properties that specify their shape, position, appearance, and behavior. After you create the ROI object, change properties using dot notation. For example, to change the color of the roi to yellow, set its Color property: roi.Color = 'yellow'
  Object functions	ROI objects have object functions that operate on the ROIs. For example, if you want to pause the MATLAB command line after creating an ROI, use the wait function.
  Event notifications	ROI objects can notify your code when certain events occur, such as when the ROI is clicked or when the ROI is being moved. To receive event notifications, set up listeners. When the ROI notifies your application through the listener, it returns data specific to the event. For example, with the ROIMoved event, the ROI object returns its previous position and its current position. You can specify a callback function that executes when an event occurs.

  For an example of using event listeners with the Ellipse object, see Set Up Listener for Ellipse ROI Events.

Version History

Introduced in R2018b

R2020a: UIContextMenu name-value argument is not recommended

Starting in R2020a, using the UIContextMenu name-value argument to assign a context menu to an ROI object is not recommended. Use the ContextMenu name-value argument instead. The values are the same.

There are no plans to remove support for the UIContextMenu name-value argument at this time.