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drawfreehand

Create customizable freehand ROI

Description

The drawfreehand function creates a Freehand object that specifies the shape and position of a freehand region of interest (ROI). You can create the ROI interactively by drawing the ROI over an image using the mouse, or programmatically by using name-value arguments. You can also specify the initial appearance and behavior of the ROI.

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

After you create the ROI, you can use object properties, object functions, and event notifications to customize the shape, position, appearance, and behavior of the ROI. For more information about using these capabilities, see Tips.

example

h = drawfreehand creates a Freehand 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.

h = drawfreehand(ax) creates the ROI in the axes specified by ax.

h = drawfreehand(___,Name,Value) modifies the appearance and behavior of the ROI using one or more name-value pairs.

Examples

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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;

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

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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.

Name-Value 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: 'Color','y' creates a yellow colored Freehand object

Close the freehand ROI, specified as the comma-separated pair consisting of 'Closed' and the logical value true or false. If true (default), drawfreehand closes the ROI by connecting the last waypoint drawn to the first waypoint 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.

Selection state of the ROI, specified as the logical value true or 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 number. The drawfreehand function uses the standard deviation of the Gaussian smoothing kernel to filter the x and y coordinates of the ROI. This argument defines the filter size using the equation: 2*ceil(2*Smoothing) + 1. 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 drawfreehand 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 an n-by-1 logical vector where n is the number of points defining the ROI. The length of Waypoints must match the number of rows of the Position name-value argument. Elements in Waypoints with the value true identify points in the Position matrix that are waypoints.

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.

Output Arguments

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Freehand ROI, returned as an Freehand 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 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.
  • The drawfreehand function creates a Freehand object. After you create the object, you can modify the shape, position, appearance, and behavior of the ROI by using these object capabilities.

    CapabilitySupport
    Object properties

    ROI objects have properties that specify their shape, position, appearance, and behavior. After you create the ROI object, change properties using dot notation.

    For example, to change the color of the roi to yellow, set its Color property:

    roi.Color = 'yellow'

    Object functionsROI objects have object functions that operate on the ROIs. For example, if you want to pause the MATLAB command line after creating an ROI, use the wait function.
    Event notifications

    ROI objects can notify your code when certain events occur, such as when the ROI is clicked or when the ROI is being moved. To receive event notifications, set up listeners. 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. You can specify a callback function that executes when an event occurs.

    For an example of using event listeners with the Freehand object, see Set Up Listener for Freehand ROI Events.

Compatibility Considerations

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Not recommended starting in R2020a

Introduced in R2018b