drawellipse

Create customizable elliptical ROI

Description

example

roi = drawellipse creates an Ellipse object and enables interactive drawing of an elliptical region-of-interest (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.

Note

drawellipse is a convenience function for creating an Ellipse ROI object. If you create the ROI object directly, calling Ellipse, you must call the draw object function to enable interactive drawing of the ROI. In contrast, the drawellipse function creates the ROI object and calls the draw object function for you. Whichever way you create the ROI, you use object properties, object functions, and event notifications to customize its appearance and behavior. For more information about using these capabilities, see Tips.

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

example

roi = drawellipse(___,Name,Value) modifies the appearance and behavior of the ROI using one or more name-value pairs. Unspecified name-value pairs are set to the default value.

Examples

collapse all

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;

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');

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

collapse all

Parent axes of the 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 Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Example: roi = drawellipse('Color','k','Label','My Ellipse');

Aspect ratio of the ellipse, specified as the comma-separated pair consisting of 'AspectRatio' and a nonnegative numeric scalar, calculated as SemiAxes(1)/SemiAxes(2). This value changes automatically when you draw or resize the ROI, or change the value of the SemiAxes property.

Center of the ROI, specified as the comma-separated pair consisting of 'Center' and a 1-by-2 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 the comma-separated pair consisting of 'Color' and a MATLAB® ColorSpec (Color Specification) value.

Example: 'green'

Example: 'g'

Example: [0 1 0]

ROI can be interactively deleted via a context menu, specified as the comma-separated pair consisting of 'Deletable' and a logical value of 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 'Deletable' 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 the comma-separated pair consisting of 'DrawingArea' and 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 rectangle beginning at (x,y), with width w and height h.

Transparency of ROI face, specified as the comma-separated pair consisting of 'FaceAlpha' and a 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 the comma-separated pair consisting of 'FaceSelectable' and the value true or false. When true (default), the ROI face can capture clicks. When false, the ROI face cannot capture clicks.

Aspect ratio remains constant during interaction, specified as the comma-separated pair consisting of 'FixedAspectRatio' and the logical values true or false. When this value is true, the ROI maintains the aspect ratio when you draw or resize the ellipse. When this value is false (default), you can change the aspect ratio when drawing or resizing the ellipse. You can change this value by using the default context menu.

Visibility of the ROI handle in the Children property of the parent, specified as the comma-separated pair consisting of 'HandleVisibility' and 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 the comma-separated pair consisting of 'InteractionsAllowed' and 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'ROI can be translated (moved) within the drawing area but not reshaped.
'reshape'ROI can be reshaped within the drawing area but not translated.

ROI label, specified as the comma-separated pair consisting of 'Label' and a character vector or string. By default, this property is set to an empty array ('') and the ROI has no label.

Visibility of the ROI label, specified as the comma-separated pair consisting of 'LabelVisible' and 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 the comma-separated pair consisting of 'LineWidth' and a positive numeric scalar in points. The default value is three times the number of points per screen pixel.

ROI parent, specified as the comma-separated pair consisting of 'Parent' and 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 ellipse, specified as the comma-separated pair consisting of 'RotationAngle' and as a nonnegative numeric scalar. The angle is measured in degrees in a clockwise direction. This value changes automatically when you draw or move the ROI.

Selection state of the ROI, specified as the comma-separated pair consisting of 'Selected' and true or false. You can also set this value interactively. For example, clicking the ROI selects it and sets this value to true. Similarly, if you Ctrl-click the ROI, deselects it and sets this value to false.

Color of the ROI when selected, specified as the comma-separated pair consisting of 'SelectedColor' and a MATLAB ColorSpec (Color Specification). 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 the comma-separated pair consisting of 'SemiAxes' and a 1-by-2 array of the form [semiaxis1 semiaxis2]. The drawellipse function 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 the comma-separated pair consisting of 'StripeColor' and a MATLAB ColorSpec (Color Specification) value. 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 the comma-separated pair consisting of 'Tag' and a character vector or string scalar. Use the tag value to find the ROI object in a hierarchy of objects by using the findobj function.

Context menu, specified as the comma-separated pair consisting of 'UIContextMenu' and a ContextMenu object creating using the uicontextmenu function. Specify this name-value pair to display a custom context menu when you right-click the ROI. To create a custom context menu, create a ContextMenu object, by using the uicontextmenu function, and then configure context menu properties.

Data to associate with the ROI, specified as the comma-separated pair consisting of 'UserData' and 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 on the edge of the ROI, returned as the comma-separated pair consisting of 'Vertices' and an n-by-2 array.

This property is read-only.

ROI visibility, specified as the comma-separated pair consisting of 'Visible' and one of the values in this table.

ValueDescription
'on'Specify this value to display the ROI (default).
'off'Specify this value to hide the ROI without deleting it. You still can access the properties of a hidden ROI.

Output Arguments

collapse all

Elliptical ROI, returned as an Ellipse object.

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 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 object function.
  • The drawellipse function returns an Ellipse ROI object. After creation, use these capabilities of the object to customize the appearance and behavior of the ROI.

    • Object properties — ROI objects support properties that modify their appearance or behavior. For example, to change the color of the roi to yellow, set its Color property, roi.Color = 'yellow'.

    • Object functions — ROI objects support a set of object functions that operate on the ROIs. For example, if you want to pause the MATLAB command line after creating an ROI, call the wait object function.

    • Event notifications — ROI objects can notify your code when certain events, such as being moved or clicked, happen to the ROI. To receive these notifications, use the addlistener object function to set up listeners for specific events. In the listener, specify an event, such as 'ROIMoved', and a callback function that executes when the event occurs. 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.

    For an example of using event listeners with the Ellipse object, see Set Up Listener for Ellipse ROI Events. For more details about these capabilities, see the Ellipse object documentation.

Introduced in R2018b