Freehand

Freehand region of interest

Description

Freehand is a hand-drawn region-of-interest (ROI) object.

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

Creation

Description

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

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

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

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

Input Arguments

ax — Parent of ROI

gca (default) | Axes object | UIAxes object

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

Closed — Close freehand ROI

true (default) | false

Close the freehand ROI, specified as a logical value true or false. If true (default), images.roi.Freehand automatically closes the ROI by connecting the last point drawn to the first point drawn when you indicate that you are done drawing.

Color — ROI color

blue (default) | ColorSpec

ROI color, specified as a MATLAB^® ColorSpec (Color Specification).

Example: 'green'

Example: 'g'

Example: [0 1 0]

ContextMenu — Context menu

ContextMenu object

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.

Deletable — ROI can be interactively deleted via context menu

true (default) | false

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.

DrawingArea — Area of axes in which you can interactively place ROI

'auto' (default) | 'unlimited' | [x,y,w,h]

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

Value	Description
'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.

FaceAlpha — Transparency of ROI face

0.2 (default) | numeric scalar

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.

FaceSelectable — ROI face can capture clicks

true (default) | false

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.

HandleVisibility — Visibility of ROI handle in Children property of parent

'on' (default) | 'off' | 'callback'

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

Value	Description
'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.

InteractionsAllowed — Interactivity of ROI

'all' (default) | 'none' | 'reshape' | 'translate'

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

Value	Description
'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.

Label — ROI label

'' (default) | character vector | string

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

LabelVisible — Visibility of ROI label

'on' (default) | 'off' | 'hover'

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

Value	Description
'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.

LineWidth — Width of ROI edge

three times the number of points per screen pixel (default) | positive numeric scalar

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.

Multiclick — Control freehand drawing style during interactive placement

false (default) | true

Control the freehand drawing style during interactive placement, specified as the logical value true or false. When the value is false (the default), a single click and drag gesture completes the freehand ROI. When the value is true, multiple click and drag gestures can be combined with straight edges to make a more complex freehand ROI shape.

Parent — ROI parent

Axes object | UIAxes object

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.

Position — Position of ROI

n-by-2 numeric array

Position of the ROI, specified as an n-by-2 numeric array of the form [x1 y1;...;xn yn], where n is the number of points. Each row specifies the position of a point defining the ROI. Freehand generates these points as you draw the ROI shape. To work with fewer points, use the reduce object function.

Selected — Selection state of ROI

false (default) | true

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.

SelectedColor — Color of ROI when selected

'none' (default) | ColorSpec

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]

Smoothing — Smooth edge of ROI during interactive placement

1 (default) | positive numeric scalar

Smooth edge of ROI during interactive placement, specified as a non-negative scalar. The Freehand object uses the standard deviation of the Gaussian smoothing kernel to filter the x and y coordinates of the ROI. This parameter defines the filter size as in this equation: 2*ceil(2*Smoothing) + 1. You must set the parameter before drawing the ROI interactively. You can see the smoothing effect only after completing the drawing.

StripeColor — Color of ROI stripe

'none' (default) | ColorSpec value

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 — 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 findobj function.

UserData — Data to associate with ROI

any MATLAB data

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.

Visible — ROI visibility

'on' (default) | 'off' | on/off logical value

ROI visibility, specified as 'on' or 'off', or as numeric or logical 1 (true) or 0 (false). A value of 'on' is equivalent to true, and 'off' is equivalent to false. Thus, you can use the value of this property as a logical value. The value is stored as an on/off logical value of type matlab.lang.OnOffSwitchState.

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

Waypoints — Control points used to reshape ROI

[] (default) | n-by-1 logical array

Control points used to reshape ROI, specified as an n-by-1 logical array the same length as the Position property. Elements in Waypoints with the value true identify points in the Position array that are waypoints. By default, Freehand generates all the points that define the ROI and only makes points at locations of increased curvature into waypoints. You can turn all the points, or some subset of points, into waypoints by using code similar to roi.Waypoints(1:4:end) = true;.

Waypoints appear as circular shapes on the ROI edge. You can use waypoints to reshape the ROI by clicking and dragging the waypoint with the mouse. Moving waypoints modifies the freehand-drawn region between the waypoint you grabbed and the immediate neighboring waypoints.

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
reduce	Reduce density of points in ROI
wait	Block MATLAB command line until ROI operation is finished

Examples

Create Freehand ROI Non-interactively

Read an image into the workspace and display it.

I = imread('baby.jpg');
figure
imshow(I)

Create a freehand ROI on the image, using the Position property to specify the vertices of the ROI. 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.Freehand 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.Freehand(gca,'Position',[100 150;200 250;300 350;150 450]);

Set Up Listeners for Freehand ROI Events

Read an image into the workspace.

I = imread('cameraman.tif');

Display the image.

imshow(I);

Draw a freehand 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.Freehand(gca,'Position',[10 15;100 50;100 150;15 145]);

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 previous position and the current position of the Freehand 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

More About

Events

To receive notification from the ROI when certain events happen, set up listeners for these events. You can specify a callback function that executes when one of these events occurs. When the ROI notifies your application through the listener, it returns data specific to the event. Look at the event class for the specific event to see what is returned.

For an example, see Set Up Listeners for Freehand ROI Events.

Event Name	Trigger	Event Data	Event Attributes
DeletingROI	ROI is about to be interactively deleted.	event.EventData	NotifyAccess: private ListenAccess: public
DrawingStarted	ROI is about to be interactively drawn.	event.EventData	NotifyAccess: private ListenAccess: public
DrawingFinished	ROI has been interactively drawn.	event.EventData	NotifyAccess: private ListenAccess: public
MovingROI	ROI shape or location is being interactively changed.	images.roi.ROIMovingEventData	NotifyAccess: private ListenAccess: public
ROIMoved	ROI shape or location has been interactively changed.	images.roi.ROIMovingEventData	NotifyAccess: private ListenAccess: public
ROIClicked	ROI has been clicked.	images.roi.ROIClickedEventData	NotifyAccess: private ListenAccess: public
AddingWaypoint	A waypoint is about to be interactively added to the ROI.	event.EventData	NotifyAccess: private ListenAccess: public
WaypointAdded	A waypoint has been interactively added to the ROI.	event.EventData	NotifyAccess: private ListenAccess: public
RemovingWaypoint	A waypoint is about to be interactively removed from the ROI.	event.EventData	NotifyAccess: private ListenAccess: public
WaypointRemoved	A waypoint has been interactively removed from the ROI.	event.EventData	NotifyAccess: private ListenAccess: public

Tips

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

  Behavior	Keyboard shortcut
  Cancel drawing the ROI.	Press Esc. The function returns a valid ROI object with an empty Position field.
  Finish drawing (close) the ROI.	Double-click, which adds a point at the pointer position and draws a line connecting this point to the first point drawn, closing the ROI. Right-click, which draws a line connecting the last point to the first point drawn. Position the pointer over the first point and click. Press Enter, which draws a line connecting the last point to the first point drawn.
  Resize (reshape) the ROI.	Position pointer over a waypoint and then click and drag. No assistance (snapping to edges) is available in this mode.
  Add a waypoint.	Position the pointer on an edge of the ROI, right-click, and select Add Waypoint. You can also position the pointer on an edge of the ROI and double-click.
  Remove a waypoint.	Position the pointer on a waypoint, right-click, and select Remove Waypoint.
  Move the ROI.	Position the pointer over the ROI. The pointer changes to the fleur shape. Click and drag to move the ROI.
  Delete an ROI.	Position the pointer on the ROI (not on a vertex), right-click, and select Delete Freehand from the context menu. You can also delete the ROI programmatically using the delete object method.

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

Compatibility Considerations

UIContextMenu property is not recommended

Not recommended starting in R2020a

Starting in R2020a, using the UIContextMenu property to assign a context menu to a graphics object or UI component is not recommended. Use the ContextMenu property instead. The property values are the same.

There are no plans to remove support for the UIContextMenu property at this time. However, the UIContextMenu property no longer appears in the list returned by calling the get function on a graphics object or UI component.