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# areaMinimumAlpha()

Calculates the pixel within a specified area that has the smallest alpha value.

```
class func areaMinimumAlpha() -> any CIFilter & CIAreaMinimumAlpha
```

## Return Value

A 1 x 1 pixel image containing the color with the smallest alpha value.

## Discussion

This method applies the area minimum alpha filter to an image. This effect finds and returns the pixel with the lowest alpha value in the region defined by `extent`.

The area minimum alpha filter uses the following properties:

- `inputImage`: An image with the type [`CIImage`](/documentation/CoreImage/CIImage).
- `extent`:  A <doc://com.apple.documentation/documentation/CoreFoundation/CGRect> that specifies the subregion of the image that you want to process.

The following code creates a filter that results in a 1 x 1 pixel image containing the color with the lowest alpha value:

```swift
func areaMinimumAlpha(inputImage: CIImage) -> CIImage {
    let filter = CIFilter.areaMinimumAlpha()
    filter.inputImage = inputImage
    filter.extent = CGRect(
        x: inputImage.extent.width/2-250,
        y: inputImage.extent.height/2-250,
        width: 500,
        height: 500)
     return filter.outputImage!
}
```

![Two images side by side arranged horizontally. The left image is a photograph of a modern brick building. An outlined square highlights a 500 x 500 pixel region in the image. The right image contains the result of running the area minimum alpha filter. It contains the color from the highlighted square that has the minimum alpha value.](images/com.apple.coreimage/media-4332169@2x.png)

---

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