Ellipse
R2026bDescription
An Ellipse object labels an interactive ellipse in a
Viewer object. The properties of the object control the appearance and
behavior of the ellipse annotation.
Interactive viewer-based ROIs enable you to draw, edit, and
measure regions of interest on images and volumes displayed using imageshow
and volshow. Interactive ROIs support dragging, resizing, event callbacks,
and measurement labels. Use interactive viewer-based ROIs to manually annotate an image, build
annotation workflows in apps, or respond to user interactions with ROI shapes. For a comparison
of interactive viewer-based ROIs with other ROIs, see Choose Approach to Annotate ROIs in Images.
Creation
You can create an Ellipse object in these ways. For more information,
see Create Interactive Viewer-Based ROIs.
Use the
uidrawfunction to interactively draw the ROI in a specified viewer and create the ROI object.Use the
images.ui.graphics.roi.Ellipsefunction described here. After you create the ROI, you can display it by adding the object to theAnnotationsproperty of aViewerobject.
Description
e = images.ui.graphics.roi.Ellipse creates an
Ellipse object with default property values. Use
e to query and modify properties of the
Ellipse object after you create it.
e = images.ui.graphics.roi.Ellipse(Name=Value) sets one or more
writable properties using
name-value arguments.
Example:
images.ui.graphics.roi.Ellipse(Position=[128 64 30 20)] creates an
ellipse annotation centered at the xy-coordinate (128, 64). The
ellipse has horizontal and vertical semiaxes of length 30 and
20, respectively.
Properties
Shape and Position
Position of the ROI, specified as a 5-element numeric vector of the form
[x y semix semiy theta] or a 4-element numeric vector of
the form [x y semix semiy]. The center of the ellipse is at
the xy-coordinate (x,
y). The ellipse has horizontal and vertical semiaxes of
lengths semix and semiy, respectively,
before rotation. If you specify Position as a 5-element
vector, the ellipse is rotated by theta degrees clockwise
about its center.
The object always stores this property value as a 5-element row vector.
Center coordinate of the ROI, specified as a 2-element numeric vector of the
form [x y].
Rotation angle around the center of the ellipse, specified as a numeric scalar. The angle is measured in degrees in a clockwise direction.
The value of RotationAngle does not impact the values
in the SemiAxes property. The
SemiAxes property represents the lengths of the
semiaxes before rotation.
Lengths of the semiaxes in the horizontal and vertical directions, specified
as a 2-element numeric vector of the form [semix
semiy].
This property is read-only.
Area covered by the ROI, represented as a numeric scalar.
This property is read-only.
Perimeter of the ROI, represented as a numeric scalar.
Color and Styling
ROI color, specified as an RGB triplet, a hexadecimal color code, a color name, or a short color name.
These are the RGB triplets for the default colors used in 2-D and 3-D
Viewer scenes.
| RGB Triplet | Appearance | Default Use |
|---|---|---|
[0 0.5610 1] |
| This is the default color when creating an ROI in a 2-D
Viewer object from the toolbar or by using the
uidraw function. |
[0.8660 0.3290 0] |
| This is the default color when creating an ROI in a 3-D
Viewer object from the toolbar or by using
uidraw. This color is also the default when you
create an ROI in any Viewer object by using an object
constructor function such as
images.ui.graphics.roi.Circle. |
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 from0toF. 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 the 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" |
|
This table lists the default color palettes for plots in the light and dark themes.
| Palette | Palette Colors |
|---|---|
Before R2025a: Most plots use these colors by default. |
|
|
|
You can get the RGB triplets and hexadecimal color codes for these palettes using the
orderedcolors and rgb2hex
functions. For example, get the RGB triplets for the "gem" palette
and convert them to hexadecimal color
codes.
RGB = orderedcolors("gem");
H = rgb2hex(RGB);Example: Color="r"
Example: Color="green"
Example: Color=[0 0.4470 0.7410]
Example: Color="#00FFFF"
Opacity of the ROI face, specified as a scalar 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 visibility, specified as "on" or "off", or as
. 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 can still access the properties of an invisible ROI. |
ROI label, specified as a string scalar or character vector. By default, the
label shows the lengths of the horizontal and vertical semiaxes. If the parent
Viewer has a nondefault value for the
SpatialUnits property, such as "mm",
then the label includes the specified units.
To display a custom label, specify the label to display as a string scalar
or character vector. To display no label, specify the
Label value as "".
Interactivity
Interactivity of the ROI, specified as one of the values in this table.
| Value | Description |
|---|---|
"all" | You can fully interact with the ROI. Reshape the ROI by changing the position of individual drag points on the boundary of the ROI, or translate (move) the entire ROI. |
"none" | You cannot interact with the ROI or access the context menu. No drag points are visible. |
"reshape" | You can reshape the ROI by changing the position of individual drag points on the boundary of the ROI. |
"translate" | You can translate the entire ROI within the drawing area. No drag points are visible, and you cannot reshape the ROI. |
"click" | You can click the ROI, but you cannot translate the ROI
interactively. After you click the ROI, the parent
Viewer broadcasts the
AnnotationMoved event.
|
ROI face supports interactions, specified as "on" or
"off", or as . 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" | The ROI face supports interactions. If
Interactions is "all" or
"translate", then you can interact with the
ROI by clicking the face and dragging the ROI. |
"off" | You cannot interact with the face of the ROI. |
Identifiers
Tag to associate with the ROI, specified as a character vector or string scalar. This property has no effect on the display, and the viewer does not use this property. You can use this property to track annotations for app building.
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. This property has no effect on the display, and the viewer does not use this property. You can use this property to append metadata to the ROI for app building.
Object Functions
createMask | Create binary mask image from ROI |
Examples
Display an image in a Viewer object. The viewer v is the parent of the image object created by imageshow.
img = imageshow("pears.png");
v = img.Parent;Create an elliptical ROI on the image, using the Position property to specify the position of the ROI in the form [x y semix semiy theta].
position = [446 204 103 75 292]; e = images.ui.graphics.roi.Ellipse(Position=position);
Display the ROI by adding it to the Annotations property of the Viewer object.
v.Annotations = [v.Annotations; e];
Tips
The ROI supports this interactivity, including keyboard shortcuts.
Behavior Interaction Add annotation To enable interactive drawing of an ellipse, call the
uidrawfunction and specify the second argument as"ellipse". To draw the ellipse, click to place a point on the perimeter of the ellipse, drag to the opposite point on the perimeter, and release. To adjust the center, hold Ctrl while you drag.Make semiaxes directions snap at 15 degree angles Hold Shift while drawing. Resize (reshape) annotation Pause on the edge of the ROI until one of the four vertices defining the semiaxes appears. Drag the vertex to reposition it. Moving the vertex closer to or further from the center changes the corresponding semiaxis value. Moving the point along the perimeter rotates the ellipse.
Move annotation Hold Ctrl and drag the ROI. Edit annotation label Right-click the edge of the ROI. From the context menu, select Edit label. When the label text highlights, type new text for the label. To finish editing, click outside the label. Remove annotation Right-click the edge of the ROI and choose Remove annotation from the context menu. Select Remove all annotations to remove all annotations in the viewer.
Version History
Introduced in R2026a
