---
title: convolution3X3()
framework: coreimage
role: symbol
role_heading: Type Method
path: coreimage/cifilter-swift.class/convolution3x3()
---

# convolution3X3()

Applies a convolution 3 x 3 filter to the RGBA components of an image.

## Declaration

```swift
class func convolution3X3() -> any CIFilter & CIConvolution
```

## Return Value

Return Value The modified image.

## Discussion

Discussion This method applies a 3 x 3 convolution to the RGBA components of an image. The effect uses a 3 x 3 area surrounding an input pixel, the pixel itself, and those within a distance of 1 pixel horizontally and vertically. The effect repeats this for every pixel within the image. The work area is then combined with the weight property vector to produce the processed image. This filter differs from the convolutionRGB3X3(), which only processes the RGB color components. The convolution 3 x 3 filter uses the following properties: note: When using a nonzero bias value, the output image has an infinite extent. You should crop the output image before attempting to render it. The following code creates a filter that sharpens the input image: func convolution3X3(inputImage: CIImage) -> CIImage? {     let convolutionFilter = CIFilter.convolution3X3()     convolutionFilter.inputImage = inputImage     let kernel = CIVector(values: [         0, -2, 0,         -2, 9, -2,         0, -2, 0     ], count: 9)     convolutionFilter.weights = kernel     convolutionFilter.bias = 0.0     return convolutionFilter.outputImage! }

## See Also

### Filters

- [convolution5X5()](coreimage/cifilter-swift.class/convolution5x5().md)
- [convolution7X7()](coreimage/cifilter-swift.class/convolution7x7().md)
- [convolution9Horizontal()](coreimage/cifilter-swift.class/convolution9horizontal().md)
- [convolution9Vertical()](coreimage/cifilter-swift.class/convolution9vertical().md)
- [convolutionRGB3X3()](coreimage/cifilter-swift.class/convolutionrgb3x3().md)
- [convolutionRGB5X5()](coreimage/cifilter-swift.class/convolutionrgb5x5().md)
- [convolutionRGB7X7()](coreimage/cifilter-swift.class/convolutionrgb7x7().md)
- [convolutionRGB9Horizontal()](coreimage/cifilter-swift.class/convolutionrgb9horizontal().md)
- [convolutionRGB9Vertical()](coreimage/cifilter-swift.class/convolutionrgb9vertical().md)