---
title: convolutionRGB3X3()
framework: coreimage
role: symbol
role_heading: Type Method
path: coreimage/cifilter-swift.class/convolutionrgb3x3()
---

# convolutionRGB3X3()

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

## Declaration

```swift
class func convolutionRGB3X3() -> any CIFilter & CIConvolution
```

## Return Value

Return Value The convolved image.

## Discussion

Discussion This method applies a 3 x 3 convolution to the RGB 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. This filter differs from the convolution3X3() filter, which processes all of the color components including the alpha component. The convolution-RGB 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 convolutionRGB3X3(inputImage: CIImage) -> CIImage {     let convolutionFilter = CIFilter.convolutionRGB3X3()     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

- [convolution3X3()](coreimage/cifilter-swift.class/convolution3x3().md)
- [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)
- [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)