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bwconvhull

Generate convex hull image from binary image

Syntax

CH = bwconvhull(BW)
CH = bwconvhull(BW,method)
CH = bwconvhull(BW,'objects',conn)

Description

example

CH = bwconvhull(BW) computes the convex hull of all objects in BW and returns CH, a binary convex hull image.

CH = bwconvhull(BW,method) specifies the desired method for computing the convex hull image.

CH = bwconvhull(BW,'objects',conn) specifies the desired connectivity used when defining individual foreground objects.

Examples

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Read a grayscale image into the workspace. Convert it into a binary image and calculate the union binary convex hull. Finally, calculate the objects convex hull and display all the images in one figure window.

subplot(2,2,1);
I = imread('coins.png');
imshow(I);
title('Original');

subplot(2,2,2);
BW = I > 100;
imshow(BW);
title('Binary');

subplot(2,2,3);
CH = bwconvhull(BW);
imshow(CH);
title('Union Convex Hull');

subplot(2,2,4);
CH_objects = bwconvhull(BW,'objects');
imshow(CH_objects);
title('Objects Convex Hull');

Input Arguments

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Input binary image, specified as a 2-D logical matrix.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical

Method used to compute the convex hull, specified as one of the following:

ValueDescription
'union'Compute the convex hull of all foreground objects, treating them as a single object
'objects'Compute the convex hull of each connected component of BW individually. CH contains the convex hulls of each connected component.

Data Types: char | string

Pixel connectivity, specified as one of these values The conn parameter is only valid when the method is 'objects'.

Value

Meaning

Two-Dimensional Connectivities

4-connected

Pixels are connected if their edges touch. Two adjoining pixels are part of the same object if they are both on and are connected along the horizontal or vertical direction.

8-connected

Pixels are connected if their edges or corners touch. Two adjoining pixels are part of the same object if they are both on and are connected along the horizontal, vertical, or diagonal direction.

Connectivity can also be defined in a more general way by specifying a 3-by-3 matrix of 0s and 1s. The 1-valued elements define neighborhood locations relative to the center element of conn. The matrix must be symmetric about its center element.

Data Types: double

Output Arguments

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Binary mask of the convex hull of all foreground objects in the input image, returned as a 2-D logical matrix.

Introduced in R2011a