Ellipse

Elliptical region of interest

Description

Ellipse is an elliptical region-of-interest (ROI) object.

To draw the ROI, position the cursor on the axes and click and drag to create the shape. To finish the ROI, release the mouse button. For more information about using this ROI, including keyboard shortcuts, see Tips.

To draw a circular ROI, use the Circle object.

Creation

Description

To create an Ellipse object, use the images.roi.Ellipse creation function. After creating the object, call the draw object function to begin drawing. As a convenience, you can also use the drawellipse function to create an Ellipse ROI. The drawellipse function creates the ROI object and calls the draw object function for you.

example

roi = images.roi.Ellipse creates an instance of the images.roi.Ellipse class with default properties.

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 pairs. For example, images.roi.Ellipse('Color','y') sets the color of the Ellipse object to yellow. You can specify multiple name-value pairs. Enclose each property name in single quotes.

Input Arguments

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

Properties

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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 images.roi.Ellipse object calculates this value as height/width.

Center of the ROI, specified as a 1-by-2 numeric array 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 a MATLAB® ColorSpec (Color Specification).

Example: 'green'

Example: 'g'

Example: [0 1 0]

ROI can be interactively deleted via a context menu, specified as true or false. When the value is true (default), you can delete the ROI via the context menu. To disable this context menu item, set this property to false. When the value is set to false, you can still delete the ROI by calling the delete function specifying the handle to the ROI as the input.

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 numeric scalar value in the range [0 1]. When the value is 1, the ROI face is fully opaque. When the value is 0, the ROI face is completely transparent.

ROI face can capture clicks, specified as true or false. When true (default), the ROI face captures mouse clicks. When false, the ROI face does not capture mouse clicks.

Aspect ratio remains constant during interaction, specified as true or 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.

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. By default, the ROI has no label ('').

Visibility of the ROI label, specified as one of these values:

ValueDescription
'on'Label is visible when the ROI is visible and the Label property is nonempty (default).
'hover'Label is visible only when the mouse hovers over the ROI.
'off'Label is not visible.

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.

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 the logical value true or false. 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 a MATLAB ColorSpec (Color Specification). The intensities must be in the range [0,1]. If 'SelectedColor' is set to 'none', then the value of Color defines the color of the ROI for all states, selected or not.

Example: 'green'

Example: 'g'

Example: [0 1 0]

Lengths of the semiaxis of the ellipse, specified as a 1-by-2 array of the form [semiaxis1 semiaxis2]. The images.roi.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 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 value.

Example: 'green'

Example: 'g'

Example: [0 1 0]

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 findobj function.

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.

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.

Locations of points that lie along the perimeter of the ellipse, specified as an n-by-2 array. This property is read-only.

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

ValueDescription
'on'Display the ROI (default).
'off'Hide the ROI without deleting it. You still can access the properties of an invisible ROI.

Object Functions

addlistenerCreate event listener bound to event source
beginDrawingFromPointBegin drawing ROI from specified point
bringToFrontBring ROI to front of Axes stacking order
createMaskCreate binary mask image from ROI
drawBegin drawing ROI interactively
inROIQuery if points are located in ROI
waitBlock MATLAB command line until ROI operation is finished

Examples

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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]);

Read an image into the workspace.

I = imread('cameraman.tif');

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.

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

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

More About

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Tips

  • 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 field.
    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 object function.
  • For information about using an ROI in an app created with App Designer, see Using ROIs in Apps Created with App Designer.

Introduced in R2018b