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# subtractBlendMode()

Blends colors by subtracting color values from two images.

```
class func subtractBlendMode() -> any CIFilter & CICompositeOperation
```

## Return Value

The modified image.

## Discussion

This method applies the subtract-blend mode filter to an image. The effect calculates the colors in the output image by subtracting the color values that differ between the background image and the input image.

The subtract-blend mode filter uses the following properties:

- `inputImage`: An 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 image becoming darker with less detail:

```swift
func subtractBlendMode(inputImage: CIImage, backgroundImage: CIImage) -> CIImage {
    let colorBlendFilter = CIFilter.subtractBlendMode()
    colorBlendFilter.inputImage = inputImage
    colorBlendFilter.backgroundImage = backgroundImage
    return colorBlendFilter.outputImage!
}
```

![The image on the top left shows a beach with multiple palm trees and a rainbow arching across the blue sky.  The image below is a gradient image displaying a gradual color shift from purple to a dark orange. The image on the right shows the output from applying a subtract-blend mode filter. The result displays the sum of colors from both images, creating a darker image with dark red and purple colors.](images/com.apple.coreimage/media-3546402@2x.png)

---

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