# bwconvhull

Generate convex hull image from binary image

## Description

## Examples

### Display Binary Convex Hull of Image

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

`BW`

— Input binary image

2-D logical matrix

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

**Data Types: **`single`

| `double`

| `int8`

| `int16`

| `int32`

| `int64`

| `uint8`

| `uint16`

| `uint32`

| `uint64`

| `logical`

`method`

— Method used to compute the convex hull

`'union'`

(default) | `'objects'`

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

Value | Description |
---|---|

`'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`

`conn`

— Pixel connectivity

`8`

(default) | `4`

| 3-by-3 matrix of `0`

s and `1`

s

Pixel connectivity, specified as one of these values The
`conn`

parameter is only valid when the
`method`

is `'objects'`

.

Value | Meaning | |
---|---|---|

| ||

| 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. |
Current pixel is shown in gray. |

| 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. |
Current pixel is shown in gray. |

Connectivity can also be defined in a more general way by specifying a
3-by-3 matrix of `0`

s and `1`

s. 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

`CH`

— Binary mask of the convex hull of all foreground objects in the input image

2-D logical matrix

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

## Version History

**Introduced in R2011a**

## See Also

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