# kMeans() Applies the k-means algorithm to find the most common colors in an image. ``` class func kMeans() -> any CIFilter & CIKMeans ``` ## Return Value A one-dimensional [`CIImage`](/documentation/CoreImage/CIImage) containing the colors. ## Discussion This filter uses the k-means clustering algorithm to find the most common colors in an input image. The result is a [`CIImage`](/documentation/CoreImage/CIImage) with `count` x 1 dimensions. Each `RGBA` pixel in the result image represents the center of a k-means cluster. The `RGB` components contain the color and the alpha component represents the weight of the color. You typically use the [`kMeans()`](/documentation/CoreImage/CIFilter-swift.class/kMeans()) filter in conjunction with the [`palettize()`](/documentation/CoreImage/CIFilter-swift.class/palettize()) filter to produce an image with a reduced number of colors. - `inputImage`: A [`CIImage`](/documentation/CoreImage/CIImage) to process. - `extent`: A specifying the area of the image to analyze. - `means`: An optional [`CIImage`](/documentation/CoreImage/CIImage) containing a set of colors to use as seeds for the k-means clustering. - `count`: The number of k-means color clusters that should be created. Maximum is `128`, and default is `8`. - `passes`: The number of k-means passes that should run. Maximum is `20`, and default is `5`. - `perceptual`: Whether the k-means color palette should use a perceptual color space. > Tip: > The colors in the result of the ``doc://com.apple.coreimage/documentation/CoreImage/CIFilter-swift.class/kMeans()`` filter have an alpha component that indicates the weight of the color. You should set this value one using ``doc://com.apple.coreimage/documentation/CoreImage/CIImage/settingAlphaOne(in:)`` before using the palette. The following code example uses the [`kMeans()`](/documentation/CoreImage/CIFilter-swift.class/kMeans()) filter followed by the [`palettize()`](/documentation/CoreImage/CIFilter-swift.class/palettize()) filter to reduce the colors in the image to four: ```swift func kMeans(inputImage: CIImage) -> CIImage { let filter = CIFilter.kMeans() filter.inputImage = inputImage filter.extent = inputImage.extent filter.count = 4 filter.passes = 5 return filter.outputImage! } func palettize(inputImage: CIImage, paletteImage: CIImage) -> CIImage { let palettize = CIFilter.palettize() palettize.inputImage = inputImage palettize.paletteImage = paletteImage return palettize.outputImage! } let palette = kMeans(inputImage: image) let palettized = palettize(inputImage: image, palette.settingAlphaOne(in: palette.extent)) ```  --- 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)