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# sharpenLuminance()

Applies a sharpening effect to an image.

```
class func sharpenLuminance() -> any CIFilter & CISharpenLuminance
```

## Return Value

The modified image.

## Discussion

This method applies the sharpen luminance filter to an image. The effect increases image detail by adjusting the luminance of each pixel within the `radius` property. Sharpening the luminance doesn’t effect the chroma data of each pixel.

The bicubic sharpen luminance filter uses the following properties:

- `inputImage`: An image with the type [`CIImage`](/documentation/CoreImage/CIImage).
- `radius`: A `float` representing the area of effect as an <doc://com.apple.documentation/documentation/Foundation/NSNumber>.
- `sharpness`: A `float` representing the desired strength of the effect as an <doc://com.apple.documentation/documentation/Foundation/NSNumber>.

The following code creates a filter that results in detail from the sign in the image to be more visible:

```swift
func sharpen (inputImage: CIImage) -> CIImage? {
    let sharpenLuminance = CIFilter.sharpenLuminance()
    sharpenLuminance.inputImage = inputImage
    sharpenLuminance.radius = 10
    sharpenLuminance.sharpness = 1
    return sharpenLuminance.outputImage!
}
```

![Two photographs of a downtown sidewalk with trees, a blue square highlighting the end of the sidewalk with a bike lane and street sign displayed. The photo on the left has no modifications to color. In the photo on the right a sharpen luminance filter has been applied resulting in the black of the bike lane sign becoming darker.](images/com.apple.coreimage/media-3595821@2x.png)

---

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