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  "framework" : "CoreImage",
  "identifier" : "/documentation/CoreImage/CIFilter-swift.class/blendWithAlphaMask()",
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  "title" : "blendWithAlphaMask()"
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# blendWithAlphaMask()

Blends two images by using an alpha mask image.

```
class func blendWithAlphaMask() -> any CIFilter & CIBlendWithMask
```

## Return Value

The modified image.

## Discussion

This method applies the blend with alpha mask filter to an image. The effect uses values from the grayscale mask image to interpolate between the input and background images. The mask image consists of shades of gray that define the strength of the interpolation from zero (where the mask image is black) to the specified `radius` (where the mask image is white).

The blend with alpha mask filter uses the following properties:

- `inputImage`: An image with the type [`CIImage`](/documentation/CoreImage/CIImage).
- `maskImage`: An image that masks an area on the background image with the type [`CIImage`](/documentation/CoreImage/CIImage).
- `backgroundImage`: An image with the type [`CIImage`](/documentation/CoreImage/CIImage).

The following code creates a filter that results in the replacement of white in the mask image with the detail of the input image:

```swift
func blendWithAlphaMask(inputimage: CIImage, backgroundimage: CIImage, maskimage: CIImage) -> CIImage {
    let blendWithAlphaMaskFilter = CIFilter.blendWithAlphaMask()
    blendWithAlphaMaskFilter.inputImage = inputimage
    blendWithAlphaMaskFilter.maskImage = maskimage
    blendWithAlphaMaskFilter.backgroundImage = backgroundimage
    return blendWithAlphaMaskFilter.outputImage!
}
```

![A set of four photographs with two stacked on the left and two side by side on the right. The top photo on the left is of the New York City skyline taken from across the river on an overcast day, with a single boat in the center of the image. The bottom photo on the left is of multiple colorful rocks with moss covering them. The first photograph on the right is a transparent image with a five-point triangle, hexagon, circle, and square filled with white. The second photograph on the right is a blend with an alpha mask filter applied, resulting in the skyline photo with the detail of the moss covered rocks showing in the area that is white from the mask image.](images/com.apple.coreimage/media-3624591@2x.png)

---

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