Image Processing Toolbox User's Guide |

**Finding the Area of the Foreground of a Binary Image **

The `bwarea`

function returns the area of a binary image. The area is a measure of the size of the foreground of the image. Roughly speaking, the area is the number of `on`

pixels in the image.

`bwarea`

does not simply count the number of pixels set to `on`

, however. Rather, `bwarea`

weights different pixel patterns unequally when computing the area. This weighting compensates for the distortion that is inherent in representing a continuous image with discrete pixels. For example, a diagonal line of 50 pixels is longer than a horizontal line of 50 pixels. As a result of the weighting `bwarea`

uses, the horizontal line has area of 50, but the diagonal line has area of 62.5.

This example uses `bwarea`

to determine the percentage area increase in `circbw.tif`

that results from a dilation operation.

BW = imread('circbw.tif'); SE = ones(5); BW2 = imdilate(BW,SE); increase = (bwarea(BW2) - bwarea(BW))/bwarea(BW); increase = 0.3456

See the reference page for `bwarea`

for more information about the weighting pattern.

Selecting Objects in a Binary Image | Finding the Euler Number of a Binary Image |

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