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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. The conn parameter is only valid when the method is '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 array.

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

Connectivity, specified as either of the following scalar values. The conn parameter is only valid when the method is 'objects'.

ValueDescription
4Two-dimensional, four-connected neighborhood
8Two-dimensional, eight-connected neighborhood.

You can also define connectivity in a more general way by using a 3-by-3 matrix of 0s and 1s. The 1-valued elements define neighborhood locations relative to conn's center element. conn 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 array.

Introduced in R2011a

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