drawfreehand
Create customizable freehand ROI
Description
h = drawfreehandFreehand ROI object and enables interactive drawing of a
circular 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 line. 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
drawfreehand is a convenience function for creating a
Freehand ROI object. If you create the ROI object
directly, calling Freehand, you must call the draw object
function to enable interactive drawing of the ROI. In contrast, the
drawfreehand 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.
h = drawfreehand(___,Name,Value)
Examples
Create Freehand ROI That Is Not Selectable
Read an image into the workspace and display it.
imshow(imread('yellowlily.jpg'))
Draw a freehand ROI.
h = drawfreehand;
Fill in the face of the freehand ROI and disable the ability to select the ROI. The ROI does not move when you click and drag the mouse.
h.FaceAlpha = 1; h.FaceSelectable = false;
Set Up Listener 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.
roi = drawfreehand('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
Output Arguments
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 Positionfield.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 deleteobject method.The
drawfreehandfunction returns aFreehandROI 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
roito yellow, set itsColorproperty,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
waitobject 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
addlistenerobject 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
Freehandobject, see Set Up Listener for Freehand ROI Events. For more details about these capabilities, see theFreehandobject documentation.
Compatibility Considerations
See Also
drawassisted | drawcircle | drawcrosshair | drawcuboid | drawellipse | drawline | drawpoint | drawpolygon | drawpolyline | drawrectangle | Freehand