# convolutionRGB3X3() Applies a convolution 3 x 3 filter to the `RGB` components of an image. ``` class func convolutionRGB3X3() -> any CIFilter & CIConvolution ``` ## Return Value The convolved image. ## 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()`](/documentation/CoreImage/CIFilter-swift.class/convolution3X3()) filter, which processes all of the color components including the alpha component. The convolution-RGB 3 x 3 filter uses the following properties: - `bias`: A `float` representing the value that’s added to each output pixel. - `weights`: A [`CIVector`](/documentation/CoreImage/CIVector) representing the convolution kernel. - `inputImage`: A [`CIImage`](/documentation/CoreImage/CIImage) containing the image to process. > 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: ```swift 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! } ```  --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)