# convolutionRGB9Vertical() Applies a convolution 1 x 9 filter to the RGB components of an image. ``` class func convolutionRGB9Vertical() -> any CIFilter & CIConvolution ``` ## Return Value This method applies a 1 x 9 convolution to the `RGB` components of an image. The effect uses a 1 x 9 area surrounding an input pixel, the pixel itself, and those within a distance of 4 pixels vertically. The effect repeats this for every pixel within the image. Unlike the convolution filters, which use square matrices, this filter can only produce effects along a vertical axis. You can combine this filter with the [`convolutionRGB9Horizontal()`](/documentation/CoreImage/CIFilter-swift.class/convolutionRGB9Horizontal()) to apply separable 9 x 9 convolutions. This filter differs from the [`convolution9Vertical()`](/documentation/CoreImage/CIFilter-swift.class/convolution9Vertical()) filter, which processes all of the color components including the alpha component. ## Discussion The convolution-RGB-9-vertical filter uses the following properties: - `inputImage`: A [`CIImage`](/documentation/CoreImage/CIImage) containing the image to process. - `weights`: A [`CIVector`](/documentation/CoreImage/CIVector) representing the convolution kernel. - `bias`: A `float` representing the value that’s added to each output pixel. > Note: > When using a nonzero `bias` value, the output image has an infinite extent. You should crop the image before attempting to render it. The following code creates a filter that blurs the image in the vertical direction: ```swift func convolutionRGB9Vertical(inputImage: CIImage) -> CIImage { let convolutionFilter = CIFilter.convolutionRGB9Vertical() convolutionFilter.inputImage = inputImage let weights: [CGFloat] = [1, 1, 1, 1, 1, 1, 1, 1, 1].map { $0/9.0 } let kernel = CIVector(values: weights, 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)