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.

example

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

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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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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.

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.

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.

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.

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 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.

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]

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.

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.

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.

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

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
reduceReduce density of points 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 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]);

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

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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.
    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.

Introduced in R2018b