Elliptical region of interest
images.roi.Ellipse class creates an elliptical region-of-interest
(ROI) object. You call the
draw method of the object to begin drawing the
ROI interactively by using your mouse.
To draw the ROI interactively, position the pointer over the axes and click and drag to draw the ellipse. To finish drawing the ROI, release the pointer. To delete the ROI, position the pointer on the ellipse, right-click, and select Delete Ellipse from the context menu. For more information about interactive behaviors including keyboard shortcuts, see Tips.
images.roi.Ellipse class is a
creates an instance
h = images.roi.Ellipse
images.roi.Ellipse class with default properties.
creates the ROI on the axes specified by
h = images.roi.Ellipse(
modifies the appearance or behavior of the ROI by specifying values for one or more ROI
properties. You can set properties using name-value pairs with or without specifying an
h = images.roi.Ellipse(___,
ax— Parent of ROI
Parent of the ROI, specified as an
AspectRatio— Aspect ratio of ellipse
(1+sqrt(5))/2(default) | positive numeric scalar
Aspect ratio of the ellipse, specified as a numeric scalar. The value of this
property changes automatically when you draw or resize the ellipse, or by setting the
SemiAxes property. The
object calculates this value as
Center— Center of ROI
(default) | 1-by2 numeric array
Center of the ROI, specified as a 1-by-2 numeric array of the form
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.
Color— ROI color
ROI color, specified as a MATLAB®
[0 1 0]
Deletable— ROI can be interactively deleted via context menu
ROI can be interactively deleted via a context menu, specified as
false. When the value is
true (default), you
can delete the ROI via the context menu. To disable this context menu item, set this
false. When the value is set to
you can still delete the ROI by calling the
specifying the handle to the ROI as the input.
DrawingArea— Area of axes in which you can interactively place ROI
Area of the axes in which you can interactively place the ROI, specified as one of the values in this table.
|The drawing area is the current axes limits (default).|
|The drawing area has no boundary and ROIs can be drawn or dragged to extend beyond the axes limits.|
|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) | numeric scalar
Transparency of the ROI face, specified as a numeric scalar value in the range
1]. When the value is
1, the ROI face is fully opaque.
When the value is
0, the ROI face is completely transparent.
FaceSelectable— ROI face can capture clicks
ROI face can capture clicks, specified as
true (default), the ROI face
captures mouse clicks. When
false, the ROI face does not capture
FixedAspectRatio— Aspect ratio remains constant during interaction
Aspect ratio remains constant during interaction, specified as
false. When the value is
true, the ROI maintains the aspect ratio when you draw or resize
the ellipse. When the value is
false (default), you can change the
aspect ratio when drawing or resizing the ellipse. You can change the state of this
property using the default context menu.
HandleVisibility— Visibility of ROI handle in
Childrenproperty of parent
Visibility of the ROI handle in the
Children property of the parent,
specified as one of the values in this table.
|The object handle is always visible (default).|
|The object handle is hidden at all times.|
|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
Interactivity of the ROI, specified as one of the values in this table.
|The ROI is fully interactable (default).|
|The ROI is not interactable, and no drag points are visible.|
|The ROI can be translated (moved) within the drawing area but not
reshaped. This value is not available for use with
|The ROI can be reshaped but not translated. This value is not
available for use with |
Label— ROI label
''(default) | character vector | string
ROI label, specified as a character vector or string. By default, the ROI has no label
LineWidth— Width of ROI edge
Width of the ROI edge, specified as a positive numeric scalar in points. The default value is three times the number of points per screen pixel.
Parent— ROI parent
ROI parent, specified as an
Axes object. A
be the parent of the ROI.
RotationAngle— Angle around center of ROI
0(default) | nonnegative numeric scalar
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 property represents the
initial position of the ROI, before rotation. To determine the location of a rotated
ROI, use the
Selected— Selection state of ROI
Selection state of the ROI, specified as the logical value
false. You can also set this property interactively. For example,
clicking on the ROI selects the ROI and sets this property to
Similarly, pressing the Ctrl key and clicking the ROI deselects the ROI
and sets the value of this property to
SelectedColor— Color of ROI when selected
Color of the ROI when selected, specified as a MATLAB
ColorSpec (Color Specification). The
intensities must be in the range
'SelectedColor' is set to
'none', then the
Color defines the color of the ROI for all states,
selected or not.
[0 1 0]
SemiAxes— Lengths of semiaxes of ellipse
Lengths of the semiaxis of the ellipse, specified as a 1-by-2 array of the form
[semiaxis1 semiaxis2]. The
object assigns the length of the semiaxis that is closest to the x
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.
StripeColor— Color of ROI stripe
Color of the ROI stripe, specified as a MATLAB
ColorSpec (Color Specification) value.
By default, the edge of an ROI is solid colored. If you specify
StripeColor, the ROI edge is striped. The striping consists of a
combination of the value specified by
'Color' and this
[0 1 0]
Tag— Tag to associate with the ROI
''(default) | character vector | string scalar
Tag to associate with the ROI, specified as a character vector or string. Use the tag value to
find the ROI object in a hierarchy of objects using the
UIContextMenu— Context menu
Context menu, specified as a
ContextMenu object. Use this property to
display a custom context menu when you right-click the ROI. You
can create a custom context menu by using the
uicontextmenu function and then
configuring context menu properties.
UserData— Data to associate with ROI
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. MATLAB does not use this data.
Vertices— Locations of points that lie along perimeter of ellipse
Locations of points that lie along the perimeter of the ellipse, specified as an n-by-2 array. This property is read-only.
Visible— ROI visibility
ROI visibility, specified as one of the values in this table.
|Display the ROI (default).|
|Hide the ROI without deleting it. You still can access the properties of an invisible ROI.|
|Event Name||Trigger||Event Data||Event Attributes|
|ROI is about to be interactively deleted.|
|ROI is about to be interactively drawn.|
|ROI has been interactively drawn.|
|ROI shape or location is being interactively changed.|
|ROI shape or location has been interactively changed.|
|ROI has been clicked.|
Read an image into the workspace and display it.
I = imread('baby.jpg'); 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]);
The ROI supports the following interactivity, including keyboard shortcuts.
|Stop drawing the ROI.||Press Esc. The function returns a valid ROI object with an
|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.|
For information about using an ROI in an app created with App Designer, see Using ROIs in Apps Created with App Designer.