# Documentation

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# bwarea

Area of objects in binary image

## Syntax

```total = bwarea(BW) ```

## Description

`total = bwarea(BW)` estimates the area of the objects in binary image `BW`. `total` is a scalar whose value corresponds roughly to the total number of `on` pixels in the image, but might not be exactly the same because different patterns of pixels are weighted differently.

## Class Support

`BW` can be numeric or logical. For numeric input, any nonzero pixels are considered to be `on`. The return value `total` is of class `double`.

## Examples

collapse all

Read the image and display it.

```BW = imread('circles.png'); imshow(BW);```

Calculate the area of objects in the image.

`bwarea(BW)`
```ans = 1.4187e+04 ```

## Algorithms

`bwarea` estimates the area of all of the `on` pixels in an image by summing the areas of each pixel in the image. The area of an individual pixel is determined by looking at its 2-by-2 neighborhood. There are six different patterns, each representing a different area:

• Patterns with zero `on` pixels (area = 0)

• Patterns with one `on` pixel (area = 1/4)

• Patterns with two adjacent `on` pixels (area = 1/2)

• Patterns with two diagonal `on` pixels (area = 3/4)

• Patterns with three `on` pixels (area = 7/8)

• Patterns with all four `on` pixels (area = 1)

Keep in mind that each pixel is part of four different 2-by-2 neighborhoods. This means, for example, that a single `on` pixel surrounded by `off` pixels has a total area of 1.

## References

[1] Pratt, William K., Digital Image Processing, New York, John Wiley & Sons, Inc., 1991, p. 634.