drawassisted

Create freehand ROI on image with assistance from image edges

Description

roi = drawassisted creates an AssistedFreehand object and enables interactive drawing of the hand-drawn region-of-interest (ROI) on the current axes. The AssistedFreehand ROI uses the edges in the underlying image to "assist" you as you draw the shape.

To draw the ROI, position the pointer on the image, click and release to place the first vertex (waypoint), and then move the pointer to draw a line. As you move the pointer to draw the shape, the line follows the contours of edges in the underlying image automatically. As you draw, click to place vertices along the line. To finish the ROI and close the shape, double-click. For more information about using the ROI, including keyboard shortcuts and context menu options, see Tips.

Note

drawassisted is a convenience function for creating an AssistedFreehand ROI object. If you create the ROI object directly, calling AssistedFreehand, you must call the draw object function to enable interactive drawing of the ROI. In contrast, the drawassisted 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.

roi = drawassisted(hImage) creates the ROI on the image specified by hImage.

roi = drawassisted(___,Name,Value) modifies the appearance and behavior of the ROI using one or more name-value pairs. Unspecified name-value pairs are set to default values.

Examples

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Read an image into the workspace and display it.

im = imread('peppers.png');
imshow(im)

Draw an assisted freehand ROI.

h = drawassisted;

Create a mask of the ROI.

bw = createMask(h);

Create an alpha matrix that specifies the transparency of the source image at each pixel.

alphamat = imguidedfilter(single(bw),im,'DegreeOfSmoothing',2);

Display a target image.

target = imread('fabric.png');
imshow(target)

Resize the source image and the alpha matrix to the same size as the target image.

alphamat = imresize(alphamat,[size(target,1),size(target,2)]);
im = imresize(im,[size(target,1),size(target,2)]);

Alpha blend the source ROI into the target image.

fused = single(im).*alphamat + (1-alphamat).*single(target);
fused = uint8(fused);
imshow(fused)

Read an image into the workspace.

I = imread('cameraman.tif');

Display the image. Use the imshow return value to get a handle to the image displayed. To create an AssistedFreehand ROI requires an underlying image.

img = imshow(I);

Draw an assisted freehand ROI on the image, with assistance from the underlying image.

roi = drawassisted(img,'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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Image object on which to draw ROI, specified as an image object.

Name-Value Pair 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: roi = drawassisted('LineWidth',5);

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

ROI color, specified as the comma-separated pair consisting of 'Color' and a MATLAB® ColorSpec (Color Specification) value.

Example: 'green'

Example: 'g'

Example: [0 1 0]

ROI can be interactively deleted via a context menu, specified as the comma-separated pair consisting of 'Deletable' and a logical value of 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 'Deletable' 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.

Transparency of ROI face, specified as the comma-separated pair consisting of 'FaceAlpha' and a 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 the comma-separated pair consisting of 'FaceSelectable' and the value true or false. When true (default), the ROI face can capture clicks. When false, the ROI face cannot capture clicks.

Visibility of the ROI handle in the Children property of the parent, specified as the comma-separated pair consisting of 'HandleVisibility' and 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.

Image on which to draw ROI, specified as the comma-separated pair consisting of 'Image' and a handle to an Image object.

Interactivity of the ROI, specified as the comma-separated pair consisting of 'InteractionsAllowed' and 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'ROI can be translated (moved) within the drawing area but not reshaped.
'reshape'ROI can be reshaped within the drawing area but not translated.

ROI label, specified as the comma-separated pair consisting of 'Label' and a character vector or string. By default, this property is set to an empty array ('') and the ROI has no label.

Visibility of the ROI label, specified as the comma-separated pair consisting of 'LabelVisible' and 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 the comma-separated pair consisting of 'LineWidth' and a positive numeric scalar in points. The default value is three times the number of points per screen pixel.

ROI parent, specified as the comma-separated pair consisting of 'Parent' and 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 the comma-separated pair consisting of 'Position' and an n-by-2 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. The AssistedFreehand object updates the value of this property as you move and reshape the ROI. To work with fewer points, use the reduce object function.

Selection state of the ROI, specified as the comma-separated pair consisting of 'Selected' and true or false. You can also set this value interactively. For example, clicking the ROI selects it and sets this value to true. Similarly, if you Ctrl-click the ROI, deselects it and sets this value to false.

Color of the ROI when selected, specified as the comma-separated pair consisting of 'SelectedColor' and a MATLAB ColorSpec (Color Specification). 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 the comma-separated pair consisting of 'Smoothing' and a non-negative scalar. The AssistedFreehand 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 using 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 the comma-separated pair consisting of 'StripeColor' and a MATLAB ColorSpec (Color Specification) value. 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 the comma-separated pair consisting of 'Tag' and a character vector or string scalar. Use the tag value to find the ROI object in a hierarchy of objects by using the findobj function.

Context menu, specified as the comma-separated pair consisting of 'UIContextMenu' and a ContextMenu object creating using the uicontextmenu function. Specify this name-value pair to display a custom context menu when you right-click the ROI. To create a custom context menu, create a ContextMenu object, by using the uicontextmenu function, and then configure context menu properties.

Data to associate with the ROI, specified as the comma-separated pair consisting of 'UserData' and 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 the comma-separated pair consisting of 'Visible' and one of the values in this table.

ValueDescription
'on'Specify this value to display the ROI (default).
'off'Specify this value to hide the ROI without deleting it. You still can access the properties of a hidden ROI.

Control points to reshape the ROI, specified as the comma-separated pair consisting of 'Waypoints' and an n-by-1 logical vector, the same length as Position. Elements in Waypoints with the value true indicate that the corresponding point in Position is a waypoint. Waypoints appear as circular shapes on the ROI edge. To reshape the ROI, click a waypoint and drag it. Dragging a waypoint modifies the contour of the freehand-drawn region between the waypoint and the immediate neighboring waypoints.

If you draw the ROI interactively, AssistedFreehand generates all the points in Position but 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;.

Output Arguments

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Assisted Freehand ROI, returned as an AssistedFreehand object.

Tips

  • This table describes how to perform common tasks with the AssistedFreehand ROI.

    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.
  • The drawassisted function returns an AssistedFreehand ROI 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 roi to yellow, set its Color property, 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 wait object 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 addlistener object 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 AssistedFreehand object, see Set Up Listener for AssistedFreehand Events. For more details about these capabilities, see the AssistedFreehand object documentation.

Introduced in R2018b