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images.roi.Polygon class

Package: images.roi

Polygonal region of interest

Description

The images.roi.Polygon class defines a polygonal region-of-interest (ROI) over an image. You call the draw method of the object to begin drawing the ROI interactively by using your mouse.

To draw the ROI interactively, position the pointer over the axes, click and drag the pointer to draw the ROI. As you draw the line, click to create a vertex. Double-click to finish drawing and close the polygon. The ROI supports a right-click context menu that lets you add a vertex, delete a vertex, or delete the entire ROI, depending on where you right-click. To delete the ROI, position the pointer on the ROI, right-click, and choose Delete Polygon from the context menu. For more information about interactive behaviors including keyboard shortcuts, see Tips.

The images.roi.Polygon class is a handle class.

Creation

Description

example

h = images.roi.Polygon creates an instance of the images.roi.Polygon object with default properties.

h = images.roi.Polygon(ax) creates the ROI in the axes specified by ax.

h = images.roi.Polygon(___,Name,Value) modifies the appearance and behavior of the ROI using one or more name-value pairs to specify properties. You can set properties using name-value pairs with or without specifying ax.

Input Arguments

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Parent of the ROI, specified as an Axes object.

Properties

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Public Properties

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. This value is not available for use with images.roi.Point objects.
'reshape'The ROI can be reshaped but not translated. This value is not available for use with images.roi.Point objects or images.roi.Rectangle objects.

ROI label, specified as a character vector or string. By default, the ROI has no label ('').

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.

ROI parent, specified as an Axes object. A UIAxes cannot be the parent of the ROI.

Position of the ROI, specified as an n-by-2 numeric array of the form [x1 y1; ...;xn yn], where each row specifies the position of a vertex of the polygon.

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]

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.

Locations of points on the edge of the ROI, specified as an n-by-2 array. This property is read-only.

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.

Methods

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Events

Event NameTriggerEvent DataEvent Attributes
DeletingROIROI is about to be interactively deleted.event.EventData

NotifyAccess: private

ListenAccess: public

DrawingStartedROI is about to be interactively drawn.event.EventData

NotifyAccess: private

ListenAccess: public

DrawingFinishedROI has been interactively drawn.event.EventData

NotifyAccess: private

ListenAccess: public

MovingROIROI shape or location is being interactively changed.images.roi.ROIMovingEventData

NotifyAccess: private

ListenAccess: public

ROIMovedROI shape or location has been interactively changed.images.roi.ROIMovingEventData

NotifyAccess: private

ListenAccess: public

ROIClickedROI has been clicked.images.roi.ROIClickedEventData

NotifyAccess: private

ListenAccess: public

AddingVertexA vertex is about to be interactively added to the ROI.event.EventData

NotifyAccess: private

ListenAccess: public

VertexAddedA vertex has been interactively added to the ROI.event.EventData

NotifyAccess: private

ListenAccess: public

DeletingVertexA vertex is about to be interactively removed from the ROI.event.EventData

NotifyAccess: private

ListenAccess: public

VertexDeletedA vertex has been interactively removed from the ROI.event.EventData

NotifyAccess: private

ListenAccess: public

Examples

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Read an image into the workspace and display it.

I = imread('baby.jpg');
figure;
imshow(I)

Create a polygonal ROI on the image, using the Position property to specify the vertices of the ROI. Note that you must specify the axes where you want to draw the ROI as the first argument.

h = images.roi.Polygon(gca,'Position',[100 150; 200 250; 300 350; 150 450]);

Tips

  • The ROI supports the following interactivity, including keyboard shortcuts.

    BehaviorKeyboard shortcut
    Make drawn line snap at 15 degree angles.Hold the Shift key while drawing.
    Finish drawing (close) the ROI.

    Double-click, which adds a new vertex at the pointer position and draws a line to the first vertex to close the polygon.

    Press Enter, which adds a new vertex at the pointer position and draws a line to the first vertex to close the polygon.

    Right-click, which does not add a new vertex but closes the polygon from the previous vertex.

    Position pointer over the first vertex and click.

    Stop drawing the ROI.Press Esc. The function returns a valid ROI object with an empty Position field.
    Add a new vertex to the ROI.

    Position the pointer over the edge of the ROI and double-click.

    Position the pointer over the edge of the ROI, right-click, and select Add Vertex from the context menu.

    Remove the most recently added vertex but keep drawing.Press Backspace. The function redraws the line from the previous vertex to the current position of the pointer. You can only back up to the first vertex you drew.
    Resize (reshape) the ROI

    Position pointer over a vertex and then click and drag.

    Add a new vertex to the polygon and then click and drag.

    Remove a vertex. The ROI redraws the line connecting the two neighboring vertices.

    Move the ROI.Position the pointer over the ROI. Hover over the edge of the polygon (not on a vertex). The pointer changes to the fleur shape. Click and drag to move the ROI.
  • 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