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drawpolygon

Create customizable polygonal ROI

Syntax

h = drawpolygon
h = drawpolygon(ax)
h = drawpolygon(___,Name,Value)

Description

example

h = drawpolygon begins interactive placement of a polygonal region-of-interest (ROI) on the current axes. The function returns a handle to an images.roi.Polygon object. You can modify the ROI interactively using your mouse. The ROI object also supports a context menu that controls aspects of its appearance and behavior.

h = drawpolygon(ax) begins interactive placement of an ROI on the axes specified by ax.

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

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.

Examples

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Read an image into the workspace and display it.

imshow(imread('strawberries.jpg'))

Draw a polygonal ROI on the image. Use the 'FaceAlpha' name-value pair to make the face of the ROI transparent.

h = drawpolygon('FaceAlpha',0);

Change the color of the polygon outline by setting the 'Color' property of the ROI.

h.Color = 'yellow';

Read image into the workspace and display it.

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

Draw a polygonal ROI over the image, using the Position parameter to specify the location of vertices.

my_vertices = [500 500;400 600;400 700;500 800;600 800;700 700; 700 600];
h = drawpolygon('Position',my_vertices);

Input Arguments

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Parent axes of the ROI, specified as an axes 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: h = drawpolygon('FaceAlpha',0,'FaceSelectable',1);

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.

Area of the axes in which you can interactively place the ROI, specified as the comma-separated pair consisting of 'DrawingArea' and 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 rectangle beginning at (x,y), with width w and height h.

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.

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. This value is not available with the drawPoint function.
'reshape'ROI can be reshaped within the drawing area but not translated. This value is not available with the drawPoint function and the drawRectangle function.

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.

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 object. A UIAxes cannot be the parent of the ROI.

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]. Each row specifies the position of a vertex of the polygonal ROI. This value changes automatically when you draw or move the ROI.

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]

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 using the findobj function.

Context menu, specified as the comma-separated pair consisting of 'UIContextMenu' and a uicontextmenu object. Specify this name-value pair to display a custom context menu when you right-click on 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 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 an invisible ROI.

Output Arguments

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Polygonal ROI, returned as an images.roi.Polygon object.

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 ROI 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 (not on a vertex). The pointer changes to a fleur shape. Click and drag to move the ROI.

Introduced in R2018b