Add extension function to get dominant colors of an image

Package.swift

@@ -18,6 +18,7 @@ let package = Package(
         .target(name: "CyanConcurrency"),
         .target(name: "CyanSwiftUI", dependencies: ["CyanExtensions"]),
         .target(name: "CyanUI", dependencies: ["CyanSwiftUI"]),
+        .target(name: "CyanImage", dependencies: ["CyanExtensions"]),
         .target(
             name: "CyanKit",
             dependencies: [
@@ -27,6 +28,7 @@ let package = Package(
                 "CyanConcurrency",
                 "CyanSwiftUI",
                 "CyanUI",
+                "CyanImage",
             ]),
         .testTarget(
             name: "CyanConcurrencyTests",

Sources/CyanImage/Color.swift

@@ -0,0 +1,41 @@
+//
+//  Created by ktiays on 2022/10/17.
+//  Copyright (c) 2022 ktiays. All rights reserved.
+// 
+
+#if canImport(UIKit)
+
+import UIKit
+
+extension UIImage {
+
+    public convenience init?(with color: UIColor, size: CGSize = .init(width: 1, height: 1)) {
+        UIGraphicsBeginImageContextWithOptions(size, false, 0)
+        color.setFill()
+        UIRectFill(CGRect(origin: CGPoint.zero, size: size))
+        let image = UIGraphicsGetImageFromCurrentImageContext()
+        UIGraphicsEndImageContext()
+        guard let cgImage = image?.cgImage else {
+            return nil
+        }
+        self.init(cgImage: cgImage)
+    }
+
+}
+
+#elseif canImport(AppKit)
+
+import AppKit
+
+extension NSImage {
+
+    public convenience init(color: NSColor, size: NSSize = .init(width: 1, height: 1)) {
+        self.init(size: size)
+        lockFocus()
+        color.drawSwatch(in: NSRect(origin: .zero, size: size))
+        unlockFocus()
+    }
+
+}
+
+#endif

Sources/CyanImage/DominantColors.swift

@@ -0,0 +1,73 @@
+//
+//  Created by ktiays on 2022/10/11.
+//  Copyright (c) 2022 ktiays. All rights reserved.
+// 
+
+import CoreImage
+import CyanExtensions
+
+extension CIImage {
+
+    public func dominantColor(clusterCount: Int = 5) -> [PlatformColor] {
+        guard let kMeansFilter = CIFilter(name: "CIKMeans") else {
+            return []
+        }
+
+        kMeansFilter.setValue(self, forKey: kCIInputImageKey)
+        kMeansFilter.setValue(CIVector(cgRect: self.extent), forKey: kCIInputExtentKey)
+        kMeansFilter.setValue(clusterCount, forKey: "inputCount")
+        kMeansFilter.setValue(20, forKey: "inputPasses")
+
+        guard var outputImage = kMeansFilter.outputImage else {
+            return []
+        }
+
+        outputImage = outputImage.settingAlphaOne(in: outputImage.extent)
+
+        let context = CIContext()
+        var bitmap = [UInt8](repeating: 0, count: 4 * clusterCount)
+        context.render(outputImage,
+                       toBitmap: &bitmap,
+                       rowBytes: 4 * clusterCount,
+                       bounds: outputImage.extent,
+                       format: CIFormat.RGBA8,
+                       colorSpace: self.colorSpace!)
+
+        var dominantColors = [PlatformColor]()
+
+        for i in 0..<clusterCount {
+            let color = PlatformColor(red: CGFloat(bitmap[i * 4 + 0]) / 255.0, green: CGFloat(bitmap[i * 4 + 1]) / 255.0, blue: CGFloat(bitmap[i * 4 + 2]) / 255.0, alpha: CGFloat(bitmap[i * 4 + 3]) / 255.0)
+            dominantColors.append(color)
+        }
+
+        return dominantColors
+    }
+
+}
+
+#if canImport(UIKit)
+
+import UIKit
+
+extension UIImage {
+
+    @inlinable
+    public func dominantColors(clusterCount: Int = 5) -> [UIColor] {
+        CIImage(image: self)?.dominantColor(clusterCount: clusterCount) ?? []
+    }
+
+}
+
+#elseif canImport(AppKit)
+
+import AppKit
+
+extension NSImage {
+
+    public func dominantColors(clusterCount: Int = 5) -> [NSColor] {
+        ciImage?.dominantColor(clusterCount: clusterCount) ?? []
+    }
+
+}
+
+#endif

Sources/CyanImage/NSImage+CIImage.swift

@@ -0,0 +1,32 @@
+//
+//  Created by ktiays on 2022/10/14.
+//  Copyright (c) 2022 ktiays. All rights reserved.
+// 
+
+#if canImport(AppKit)
+
+import AppKit
+
+extension NSImage {
+
+    public var ciImage: CIImage? {
+        guard let data = self.tiffRepresentation,
+              let bitmap = NSBitmapImageRep(data: data) else {
+            return nil
+        }
+        return CIImage(bitmapImageRep: bitmap)
+    }
+
+}
+
+extension NSImage {
+
+    public convenience init(ciImage: CIImage) {
+        let imageRep = NSCIImageRep(ciImage: ciImage)
+        self.init(size: imageRep.size)
+        self.addRepresentation(imageRep)
+    }
+
+}
+
+#endif