createMask

Create binary mask image from ROI

Syntax

bw = createMask(ROI)

bw = createMask(ROI,m,n)

bw = createMask(ROI,I)

bw = createMask(ROI,hImage)

Description

bw = createMask(ROI) returns a binary mask image with pixels inside the ROI set to true and pixels outside the ROI set to false. The mask is the same size as the image associated with the ROI.

bw = createMask(ROI,m,n) returns a binary mask image that is size [m,n].

bw = createMask(ROI,I) returns a binary mask image that is the size of the image I.

bw = createMask(ROI,hImage) returns a binary mask image that is the size of the Image object hImage.

Examples

Create Mask from Ellipse ROI in imshow Display

Read an image into the workspace and display it.

I = imread("pears.png");
imshow(I)

Draw an elliptical ROI on the image, using the Center name-value argument to specify the location of the ellipse and theSemiAxes name-value argument to specify the shape of the ellipse. Specify that the edge of the ellipse is a striped line.

h = drawellipse(Center=[447 204],SemiAxes=[78 72], ...
    RotationAngle=287,StripeColor="m");

Get a binary mask from the ROI. Pixels inside the ROI are true and pixels outside the ROI are false. Display the mask.

mask = createMask(h);
imshow(mask)

Create Mask From ROI in imageshow Display

Read an image into the workspace and display it by using the imageshow function.

I = imread("peppers.png");
imObj = imageshow(I);

Get a handle to the viewer window that contains the image.

viewer = imObj.Parent;

Draw a freehand ROI around the onion.

freehand = uidraw(viewer,"freehand");

Create a binary mask from the ROI. Pixels inside the ROI are true and pixels outside the ROI are false. Display the mask.

mask = createMask(freehand);
imageshow(mask)

Input Arguments

ROI — Region of interest

ROI object

Region of interest, specified as an ROI object associated with an imshow or imageshow display.

ROI shapes associated with an imshow display	AssistedFreehand Freehand Polyline Circle Line Rectangle Ellipse Polygon
ROI shapes associated with an imageshow display	Angle Circle Ellipse Freehand Line Point Polygon Polyline Rectangle

m — Row dimension of mask image

positive integer

Row dimension of the mask image, specified as a positive integer.

n — Column dimension of mask image

positive integer

Column dimension of the mask image, specified as a positive integer.

I — Input image array

numeric array

Input image array, specified as a numeric array.

hImage — Input image object

Image object

Input image object, specified as an Image object created by the imshow or imageshow function. For more details, see Image Properties for imshow displays or Image Properties for imageshow displays. If hImage corresponds to a multilevel blocked image, the finest resolution level determines the size of the mask image.

Output Arguments

bw — Binary mask image

logical array

Binary mask image, returned as a logical array.

Data Types: logical

Tips

• For more information about classifying pixels on the ROI boundary, see Classify Pixels That Are Partially Enclosed by ROI.

• If you specify a mask size that does not match the size of the image associated with the ROI object, then createMask crops or zero-pads the mask to the specified size. For imshow displays, the image associated with the ROI object is ROI.Parent.Children(2,1).CData. For imageshow displays, the image associated with the ROI object is ROI.Parent.Children.

Version History

Introduced in R2018b

R2026a: Support for viewer-based ROI objects

The function now supports creating a binary mask from these ROI annotation objects, which you can create within a Viewer object associated with an imageshow display. You can create an ROI annotation from the viewer toolstrip, by using the uidraw function, or by using the object creation function, such as images.ui.graphics.roi.Point.

• Angle

• Circle

• Ellipse

• Freehand

• Line

• Point

• Polygon

• Polyline

• Rectangle