## Documentation Center |

Label connected components in binary image

`L = bwlabeln(BW)[L, NUM] = bwlabeln(BW)[L, NUM] = bwlabeln(BW, conn)`

`L = bwlabeln(BW)` returns
a label matrix, `L`, containing labels for the connected
components in `BW`. The input image `BW` can
have any dimension; `L` is the same size as `BW`.
The elements of `L` are integer values greater than
or equal to 0. The pixels labeled `0` are the background.
The pixels labeled `1` make up one object; the pixels
labeled `2` make up a second object; and so on. The
default connectivity is 8 for two dimensions, 26 for three dimensions,
and `conndef(ndims(BW), 'maximal')` for higher dimensions.

`[L, NUM] = bwlabeln(BW)` returns
in `NUM` the number of connected objects found in `BW`.

`[L, NUM] = bwlabeln(BW, conn)` specifies
the desired connectivity. `conn` can have any of
the following scalar values.

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

| |

4-connected neighborhood | |

8-connected neighborhood | |

| |

6-connected neighborhood | |

18-connected neighborhood | |

26-connected neighborhood |

Connectivity can also be defined in a more general way for any
dimension by using for `conn` a 3-by-3-by- ...-by-3
matrix of `0`s and `1`s. The `1`-valued
elements define neighborhood locations relative to the central element
of `conn`. Note that `conn` must
be symmetric about its central element.

The functions `bwlabel`, `bwlabeln`,
and `bwconncomp` all compute connected components
for binary images. `bwconncomp` replaces the use
of `bwlabel` and `bwlabeln`. It
uses significantly less memory and is sometimes faster than the older
functions.

Function | Input Dimension | Output Form | Memory Use | Connectivity |
---|---|---|---|---|

bwlabel | 2-D | Double-precision label matrix | High | 4 or 8 |

bwlabeln | N-D | Double-precision label matrix | High | Any |

bwconncomp | N-D | CC struct | Low | Any |

Calculate the centroids of the 3-D objects.

BW = cat(3, [1 1 0; 0 0 0; 1 0 0],... [0 1 0; 0 0 0; 0 1 0],... [0 1 1; 0 0 0; 0 0 1]) bwlabeln(BW) ans(:,:,1) = 1 1 0 0 0 0 2 0 0 ans(:,:,2) = 0 1 0 0 0 0 0 2 0 ans(:,:,3) = 0 1 1 0 0 0 0 0 2

`bwconncomp` | `bwlabel` | `label2rgb` | `labelmatrix` | `regionprops`

Was this topic helpful?