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Freehand

Freehand region of interest

Description

A Freehand object specifies the shape and position of a hand-drawn region of interest (ROI). You can customize the appearance and interactive behavior of the ROI.

For more information about using a freehand ROI, including keyboard shortcuts, see Tips.

Freehand ROI tracing the edge of an object in an image.

Creation

There are two ways to create a Freehand object. For more information, see Create ROI Shapes.

  • Use the drawfreehand function. Use this function when you want to create the ROI and set the appearance in a single command. You can specify the shape and position of the ROI interactively by drawing the ROI over an image using the mouse.

  • Use the images.roi.Freehand function described here. Use this function when you want to specify the appearance and behavior of the ROI before you specify the shape and position of the ROI. After creating the object, you can specify the shape and position interactively by using the draw function.

Description

example

roi = images.roi.Freehand creates a Freehand object 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 of the ROI using name-value arguments. You can specify multiple name-value arguments. Enclose each property name in single quotes.

Example: images.roi.Freehand('Color','y') creates a yellow colored Freehand object.

Input Arguments

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Parent of 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.

Properties

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Close the ROI, specified as a logical value true or false. When true, the Freehand object closes the ROI by connecting the last point drawn to the first point drawn.

ROI color, specified as an RGB triplet, a color name, or a short color name.

You can specify any color using an RGB triplet. An RGB triplet is a 3-element row vector whose elements specify the intensities of the red, green, and blue components of the color. The intensities must be in the range [0,1].

You can specify some common colors by name as a string scalar or character vector. This table lists the named color options and the equivalent RGB triplets.

Color NameShort NameRGB TripletAppearance
'red''r'[1 0 0]

A rectangle colored pure red

'green''g'[0 1 0]

A rectangle colored pure green

'blue''b'[0 0 1]

A rectangle colored pure blue

'cyan' 'c'[0 1 1]

A rectangle colored pure cyan

'magenta''m'[1 0 1]

A rectangle colored pure magenta

'yellow''y'[1 1 0]

A rectangle colored pure yellow

'black''k'[0 0 0]

A rectangle colored black

'white''w'[1 1 1]

A rectangle colored white

Here are the RGB triplets for the default colors that MATLAB® uses in many types of plots.

RGB TripletAppearance
[0 0.4470 0.7410]

A rectangle colored medium blue

[0.8500 0.3250 0.0980]

A rectangle colored reddish-orange

[0.9290 0.6940 0.1250]

A rectangle colored dark yellow

[0.4940 0.1840 0.5560]

A rectangle colored dark purple

[0.4660 0.6740 0.1880]

A rectangle colored light green

[0.3010 0.7450 0.9330]

A rectangle colored light blue

[0.6350 0.0780 0.1840]

A rectangle colored dark red

Example: 'Color','r'

Example: 'Color','green'

Example: 'Color',[0 0.4470 0.7410]

Context menu that displays when you right-click the ROI, specified as a ContextMenu object. You can create a custom context menu by using the uicontextmenu function and then configuring context menu properties.

Context menu provides an option to delete the ROI, specified as true or false. When the value is true, you can delete the ROI interactively using the context menu. When the value is false, the context menu option to delete the ROI is disabled.

In both cases, you can delete the ROI outside of the context menu by using the delete function.

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 number in the range [0, 1]. When the value is 1, the ROI face is completely 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 scalar. By default, the ROI has no label ('').

Transparency of the text background, specified as a number in the range [0, 1]. When set to 1, the text background is completely opaque. When set to 0, the text background is completely transparent.

Label text color, specified as an RGB triplet, a color name, or a short color name.

You can specify any color using an RGB triplet. An RGB triplet is a 3-element row vector whose elements specify the intensities of the red, green, and blue components of the color. The intensities must be in the range [0,1].

You can specify some common colors by name as a string scalar or character vector. This table lists the named color options and the equivalent RGB triplets.

Color NameShort NameRGB TripletAppearance
'red''r'[1 0 0]

A rectangle colored pure red

'green''g'[0 1 0]

A rectangle colored pure green

'blue''b'[0 0 1]

A rectangle colored pure blue

'cyan' 'c'[0 1 1]

A rectangle colored pure cyan

'magenta''m'[1 0 1]

A rectangle colored pure magenta

'yellow''y'[1 1 0]

A rectangle colored pure yellow

'black''k'[0 0 0]

A rectangle colored black

'white''w'[1 1 1]

A rectangle colored white

Here are the RGB triplets for the default colors that MATLAB uses in many types of plots.

RGB TripletAppearance
[0 0.4470 0.7410]

A rectangle colored medium blue

[0.8500 0.3250 0.0980]

A rectangle colored reddish-orange

[0.9290 0.6940 0.1250]

A rectangle colored dark yellow

[0.4940 0.1840 0.5560]

A rectangle colored dark purple

[0.4660 0.6740 0.1880]

A rectangle colored light green

[0.3010 0.7450 0.9330]

A rectangle colored light blue

[0.6350 0.0780 0.1840]

A rectangle colored dark red

Example: 'LabelTextColor','r'

Example: 'LabelTextColor','green'

Example: 'LabelTextColor',[0 0.4470 0.7410]

Label visibility, specified as one of these values.

ValueDescription
'on'Label is visible when the ROI is visible.
'hover'Label is visible only when the mouse is hovering over the ROI.
'off'Label is not visible.

Width of the ROI border, specified as a positive number in points. The default value is three times the number of points per screen pixel, such that the border is three pixels wide.

Marker size, specified as a positive number in points. The default value is eight times the number of points per screen pixel, such that markers are eight pixels in size.

Control the freehand drawing style during interactive placement, specified as the logical value true or false. When the value is false, 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 matrix where n is the number of vertices or points defining the ROI. Each row represents the [x y] coordinates of a vertex or point. The Freehand object generates these points as you draw the ROI shape interactively. To work with fewer points, use the reduce 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 an RGB triplet, a color name, a short color name, or 'none'. If you specify 'none', then the value of Color defines the color of the ROI for all states, selected or not.

You can specify any color using an RGB triplet. An RGB triplet is a 3-element row vector whose elements specify the intensities of the red, green, and blue components of the color. The intensities must be in the range [0,1].

You can specify some common colors by name as a string scalar or character vector. This table lists the named color options and the equivalent RGB triplets.

Color NameShort NameRGB TripletAppearance
'red''r'[1 0 0]

A rectangle colored pure red

'green''g'[0 1 0]

A rectangle colored pure green

'blue''b'[0 0 1]

A rectangle colored pure blue

'cyan' 'c'[0 1 1]

A rectangle colored pure cyan

'magenta''m'[1 0 1]

A rectangle colored pure magenta

'yellow''y'[1 1 0]

A rectangle colored pure yellow

'black''k'[0 0 0]

A rectangle colored black

'white''w'[1 1 1]

A rectangle colored white

Here are the RGB triplets for the default colors that MATLAB uses in many types of plots.

RGB TripletAppearance
[0 0.4470 0.7410]

A rectangle colored medium blue

[0.8500 0.3250 0.0980]

A rectangle colored reddish-orange

[0.9290 0.6940 0.1250]

A rectangle colored dark yellow

[0.4940 0.1840 0.5560]

A rectangle colored dark purple

[0.4660 0.6740 0.1880]

A rectangle colored light green

[0.3010 0.7450 0.9330]

A rectangle colored light blue

[0.6350 0.0780 0.1840]

A rectangle colored dark red

Example: 'SelectedColor','r'

Example: 'SelectedColor','green'

Example: 'SelectedColor',[0 0.4470 0.7410]

Smooth edge of ROI after interactive placement, specified as a nonnegative 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 specify the property before drawing the ROI interactively. You can see the smoothing effect only after completing the drawing.

Color of the ROI stripe, specified as an RGB triplet, a color name, a short color name, or 'none'. If you specify 'none', then the ROI edge is a solid color specified by Color. Otherwise, the edge of the ROI is striped, with colors alternating between the colors specified by Color and StripeColor.

You can specify any color using an RGB triplet. An RGB triplet is a 3-element row vector whose elements specify the intensities of the red, green, and blue components of the color. The intensities must be in the range [0,1].

You can specify some common colors by name as a string scalar or character vector. This table lists the named color options and the equivalent RGB triplets.

Color NameShort NameRGB TripletAppearance
'red''r'[1 0 0]

A rectangle colored pure red

'green''g'[0 1 0]

A rectangle colored pure green

'blue''b'[0 0 1]

A rectangle colored pure blue

'cyan' 'c'[0 1 1]

A rectangle colored pure cyan

'magenta''m'[1 0 1]

A rectangle colored pure magenta

'yellow''y'[1 1 0]

A rectangle colored pure yellow

'black''k'[0 0 0]

A rectangle colored black

'white''w'[1 1 1]

A rectangle colored white

Here are the RGB triplets for the default colors that MATLAB uses in many types of plots.

RGB TripletAppearance
[0 0.4470 0.7410]

A rectangle colored medium blue

[0.8500 0.3250 0.0980]

A rectangle colored reddish-orange

[0.9290 0.6940 0.1250]

A rectangle colored dark yellow

[0.4940 0.1840 0.5560]

A rectangle colored dark purple

[0.4660 0.6740 0.1880]

A rectangle colored light green

[0.3010 0.7450 0.9330]

A rectangle colored light blue

[0.6350 0.0780 0.1840]

A rectangle colored dark red

Example: 'StripeColor','r'

Example: 'StripeColor','green'

Example: 'StripeColor',[0 0.4470 0.7410]

Tag to associate with the ROI, specified as a character vector or string scalar. Use the tag value to find the ROI object in a hierarchy of objects using the findobj function.

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. The Freehand object does not use this data.

ROI visibility, specified as 'on' or 'off', or as a numeric or logical 1 (true) or 0 (false). A value of 'on' is equivalent to true, and 'off' is equivalent to false. The value is stored as an on/off logical value of type OnOffSwitchState.

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

Position point is waypoint, specified as a logical vector of the same length as the Position property. Elements in Waypoints with the value true identify points in the Position matrix that are waypoints. By default, the Freehand object 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 that you clicked and the adjacent 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)

Figure contains an axes object. The axes object contains an object of type image.

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]);

Figure contains an axes object. The axes object contains 2 objects of type image, images.roi.freehand.

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

  • To draw the ROI interactively using the draw or drawfreehand function, position the cursor on the image and click and drag to draw the ROI shape. To finish drawing the ROI, release the mouse button.

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

Compatibility Considerations

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Not recommended starting in R2020a

Introduced in R2018b