Rectangle

Rectangular region of interest

Description

The Rectangle object is a rectangular region-of-interest (ROI).

To draw the ROI, position the cursor on the axes and click and drag to create the shape. To finish the ROI, release the mouse button. For more information about using this ROI, including keyboard shortcuts, see Tips.

Creation

Description

To create a Rectangle object, use the images.roi.Rectangle creation function. After creating the object, call the draw object function to begin drawing the ROI. As a convenience, you can also use the drawrectangle function to create a Rectangle ROI. The drawrectangle function creates the ROI object and automatically calls the draw object function.

roi = images.roi.Rectangle creates an instance of the images.roi.Rectangle class with default properties.

roi = images.roi.Rectangle(ax) creates an ROI in the axes specified by ax.

roi = images.roi.Rectangle(___,Name,Value)sets properties using name-value pairs. For example, images.roi.Rectangle('Color','y') sets the color of the Rectangle object to yellow. You can specify multiple name-value pairs. Enclose each property name in single quotes.

Input Arguments

ax — Parent of ROI

gca (default) | Axes object | UIAxes object

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

AspectRatio — Aspect ratio of rectangle

1 (default) | positive numeric scalar

Aspect ratio of the rectangle, specified as a positive numeric scalar. The value of this property changes automatically when you draw or resize the rectangle. The images.roi.Rectangle object calculates this value as height/width

Color — ROI color

blue (default) | ColorSpec

ROI color, specified as a MATLAB^® ColorSpec (Color Specification).

Example: 'green'

Example: 'g'

Example: [0 1 0]

Deletable — ROI can be interactively deleted via context menu

true (default) | false

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.

DrawingArea — Area of axes in which you can interactively place ROI

'auto' (default) | 'unlimited' | [x,y,w,h]

Area of the axes in which you can interactively place the ROI, specified as one of the values in this table.

Value	Description
'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.

FaceAlpha — Transparency of ROI face

0.2 (default) | numeric scalar

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.

FaceSelectable — ROI face can capture clicks

true (default) | false

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.

FixedAspectRatio — Aspect ratio remains constant during interaction

false (default) | true

Aspect ratio remains constant during interaction, specified as true or false. When the value is true, the ROI maintains the aspect ratio when you draw or resize the rectangle. When the value is false (default), you can change the aspect ratio when drawing or resizing the rectangle. You can change the state of this property using the default context menu.

HandleVisibility — Visibility of ROI handle in Children property of parent

'on' (default) | 'off' | 'callback'

Visibility of the ROI handle in the Children property of the parent, specified as one of the values in this table.

Value	Description
'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.

InteractionsAllowed — Interactivity of ROI

'all' (default) | 'none' | 'translate'

Interactivity of the ROI, specified as one of the values in this table.

Value	Description
'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.

Label — ROI label

'' (default) | character vector | string

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

LabelVisible — Visibility of ROI label

'on' (default) | 'off' | 'hover'

Visibility of the ROI label, specified as one of these values:

Value	Description
'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.

LineWidth — Width of ROI edge

three times the number of points per screen pixel (default) | positive numeric scalar

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.

Parent — ROI parent

Axes object | UIAxes object

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 — Position of ROI

1-by-4 numeric array

Position of the ROI, specified as a 1-by-4 numeric array of the form [xmin, ymin, width, height]. xmin and ymin specify the location of the upper left corner of the rectangle. width and height specify the extent to the rectangle in two dimensions.

Rotatable — Ability of the rectangle to be rotated

false (default) | true

Ability of the rectangle to be rotated, specified as true or false. When the value is false (default), the rectangle cannot be rotated. When the value is true, you can rotate the rectangle by clicking near the markers at the corners.

RotationAngle — Angle around center of rectangle

0 (default) | numeric scalar

Angle around the center of the rectangle, specified as a numeric scalar. The angle is measured in degrees in a clockwise direction. The value of this property changes automatically when you draw or move the ROI.

The value of RotationAngle does not impact the values in Position. The Position property represents the initial position of the ROI, before rotation. To determine the location of a rotated ROI, use the Vertices property.

Selected — Selection state of ROI

false (default) | true

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.

SelectedColor — Color of ROI when selected

'none' (default) | ColorSpec

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]

StripeColor — Color of ROI stripe

'none' (default) | ColorSpec value

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 — Tag to associate with the ROI

'' (default) | character vector | string scalar

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.

UIContextMenu — Context menu

ContextMenu object

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.

UserData — Data to associate with ROI

any MATLAB data

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.

Vertices — Locations of points on edge of rectangle

n-by-2 array

Locations of points on the edge of the ROI, specified as an n-by-2 array.

This property is read-only.

Visible — ROI visibility

'on' (default) | 'off'

ROI visibility, specified as one of the values in this table.

Value	Description
'on'	Display the ROI (default).
'off'	Hide the ROI without deleting it. You still can access the properties of an invisible ROI.

Object Functions

addlistener	Create event listener bound to event source
beginDrawingFromPoint	Begin drawing ROI from specified point
bringToFront	Bring ROI to front of Axes stacking order
createMask	Create binary mask image from ROI
draw	Begin drawing ROI interactively
inROI	Query if points are located in ROI
wait	Block MATLAB command line until ROI operation is finished

Examples

Create Rectangular ROI Non-interactively

Read image into the workspace and display it.

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

Create a rectangular ROI on the image, using the Position parameter to specify its location and size. The example also specifies that the edge of the rectangle is a striped line. 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.Rectangle 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.Rectangle(gca,'Position',[500,500,1000,1000],'StripeColor','r');

Set Up Listeners for Rectangle ROI Events

Read an image into the workspace.

I = imread('cameraman.tif');

Display the image.

imshow(I);

Draw a Rectangle ROI on the image. Because this example specifies the length and location of the ROI, you do not have to call the draw method to enable interactive drawing.

roi = images.roi.Rectangle(gca,'Position',[80,45,80,100]);

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 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

Events

To receive notification from the ROI when certain events happen, set up listeners for these events. You can specify a callback function that executes when one of these events occurs. When the ROI notifies your application through the listener, it returns data specific to the event. Look at the event class for the specific event to see what is returned.

For an example, see Set Up Listeners for Rectangle ROI Events.

Event Name	Trigger	Event Data	Event Attributes
DeletingROI	ROI is about to be interactively deleted.	event.EventData	NotifyAccess: private ListenAccess: public
DrawingStarted	ROI is about to be interactively drawn.	event.EventData	NotifyAccess: private ListenAccess: public
DrawingFinished	ROI has been interactively drawn.	event.EventData	NotifyAccess: private ListenAccess: public
MovingROI	ROI shape or location is being interactively changed.	images.roi.RectangleMovingEventData	NotifyAccess: private ListenAccess: public
ROIMoved	ROI shape or location has been interactively changed.	images.roi.RectangleMovingEventData	NotifyAccess: private ListenAccess: public
ROIClicked	ROI has been clicked.	images.roi.ROIClickedEventData	NotifyAccess: private ListenAccess: public

Tips

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

  Behavior	Keyboard shortcut
  Cancel drawing the ROI.	Press Esc. The function returns a valid ROI object with an empty Position field.
  Resize (reshape) the ROI.	Position the cursor over a vertex and then click and drag. The rectangle has vertices at each corner and at the midpoint of each side. To preserve the aspect ratio while resizing, press the Shift key. To lock the aspect ratio, use the Fix Aspect Ratio in the right-click context menu.
  Move the ROI.	Position the cursor over the ROI. The cursor changes to the fleur shape. Click and drag the ROI.
  Delete the ROI.	Position the pointer on the rectangle, right-click, and choose Delete Rectangle from the context menu. You can also delete the ROI programmatically using the delete object method.

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