# Ellipse

Elliptical region of interest

Since R2018b

## Description

An Ellipse object specifies the shape and position of an elliptical region-of-interest (ROI). You can customize the appearance and interactive behavior of the ROI.

For more information about using this ROI, including keyboard shortcuts, see Tips.

## Creation

There are two ways to create an Ellipse object. For more information, see Create ROI Shapes.

• Use the drawellipse function. Use this function when you want to create the ROI and set the appearance in a single command. You can specify the shape and position of the ROI interactively by drawing the ROI over an image using the mouse, or programmatically by using name-value arguments.

• Use the images.roi.Ellipse function described here. Use this function when you want to specify the appearance and behavior of the ROI before you specify the shape and position of the ROI. After creating the object, you can specify the shape and position interactively by using the draw function or programmatically by modifying properties of the object.

### Description

example

roi = images.roi.Ellipse creates an Ellipse object with default property values.

roi = images.roi.Ellipse(ax) creates the ROI on the axes specified by ax.

roi = images.roi.Ellipse(___,Name,Value) sets properties using name-value arguments. You can specify multiple name-value arguments.

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

### Input Arguments

expand all

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.

## Properties

expand all

Aspect ratio of the ellipse, specified as a positive number. The value of this property changes automatically when you draw or resize the ellipse, or by setting the SemiAxes property. The Ellipse object calculates this value as height/width. The default value is (1+sqrt(5))/2.

Center of the ROI, specified as a 1-by-2 numeric vector of the form [x y]. The values x and y are the coordinates of the center point of the ROI. The value of this property changes automatically when you draw or move the ROI.

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 NameShort NameRGB TripletAppearance
"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 TripletAppearance
[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]

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.

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.

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

ValueDescription
"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.

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.

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.

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. You can change the state of this property using the default context menu.

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

ValueDescription
"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.

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

ValueDescription
"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.

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

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.

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 NameShort NameRGB TripletAppearance
"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 TripletAppearance
[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]

Label visibility, specified as one of these values.

ValueDescription
"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.

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.

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.

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.

Angle around the center of the ROI, specified as a nonnegative numeric scalar. The angle is measured in degrees in a clockwise direction. The value of this property changes automatically when you draw or move the ROI.

The value of RotationAngle does not impact the value of Position. The Position property represents the initial position of the ROI, before rotation. To determine the location of a rotated ROI, use the Vertices property.

Selection state of the ROI, specified as a numeric or logical 0 (false) or 1 (true). You can also set this property interactively. For example, clicking on the ROI selects the ROI and sets this property to true. Similarly, pressing the Ctrl key and clicking the ROI deselects the ROI and sets the value of this property to false.

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 NameShort NameRGB TripletAppearance
"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 TripletAppearance
[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]

Lengths of the semiaxis of the ellipse, specified as a 1-by-2 numeric vector of the form [semiaxis1 semiaxis2]. The Ellipse object assigns the length of the semiaxis that is closest to the x direction to semiaxis1. Note however that the shape and orientation of the ellipse can change through interaction. The value of this property changes automatically when you draw or reshape the ROI.

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 NameShort NameRGB TripletAppearance
"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 TripletAppearance
[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 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.

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 Ellipse object does not use this data.

This property is read-only.

Locations of points on the perimeter of the ellipse, returned as an n-by-2 numeric matrix.

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.

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

## Object Functions

 addlistener Create event listener bound to event source beginDrawingFromPoint Begin drawing ROI from specified point bringToFront Bring ROI to front of Axes stacking order createMask Create binary mask image from ROI draw Begin drawing ROI interactively inROI Query if points are located in ROI wait Block MATLAB command line until ROI operation is finished

## Examples

collapse all

Read an image into the workspace and display it.

figure
imshow(I)

Create an elliptical ROI on the image, using the Center property to specify the location and the SemiAxes property to specify its shape. For programmatically created ROIs, if you want the ROI drawn in a specific axes, you must specify that axes as an input argument. Otherwise, an instance of the images.roi.Ellipse class is created but not displayed. In this example, specify the current axes (gca) to draw the ROI on the image in that axes.

h = images.roi.Ellipse(gca,'Center',[1000 1000],'Semiaxes',[350 150]);

Read an image into the workspace.

Display the image.

imshow(I);

Draw an elliptical ROI on the image. Because this example specifies the size and location of the ROI, you do not have to call the draw method to enable interactive drawing.

roi = images.roi.Ellipse(gca,'Center',[100 100],'Semiaxes',[50 80]);

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.

The allevents callback function displays at the command line the current center and the current semiaxes of the Ellipse ROI.

function allevents(src,evt)
evname = evt.EventName;
switch(evname)
case{'MovingROI'}
disp(['ROI moving Current Center: ' mat2str(evt.CurrentCenter)]);
disp(['ROI moving Current SemiAxes: ' mat2str(evt.CurrentSemiAxes)]);
case{'ROIMoved'}
disp(['ROI moved Current Center: ' mat2str(evt.CurrentCenter)]);
disp(['ROI moved Current SemiAxes: ' mat2str(evt.CurrentSemiAxes)]);
end
end

expand all

## Tips

• To draw the ROI interactively using the draw or drawellipse function, position the cursor on the axes and click and drag to create the shape. To finish the ROI, release the mouse button.

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

BehaviorKeyboard 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 anywhere in the ROI and right-click. Select Delete Ellipse from the context menu. You can also delete the ROI programmatically using the delete function.
• For information about using an ROI in an app created with App Designer, see Using ROIs in Apps Created with App Designer.

• To draw a circular ROI, use the Circle object.

## Version History

Introduced in R2018b

expand all