Xcode中CoreImage报错：找不到kCIImageAccurateMetadata与CIDetectorTypeColor

已正确关联CoreImage框架，尝试提取图片强调色作为背景时出现两个编译错误：

• Cannot find 'kCIImageAccurateMetadata' in scope
• Cannot find 'CIDetectorTypeColor' in scope
  清理Xcode缓存后问题仍存在，相关代码如下：

import SwiftUI
import UIKit
import CoreImage

class ColorExtractor {
    var dominantColor: UIColor?

    func extractColors(from image: UIImage, completion: @escaping ([UIColor]) -> Void) {
        guard let ciImage = CIImage(image: image) else {
            completion([])
            return
        }
        DispatchQueue.global(qos: .userInteractive).async {
            let accuracy = [kCIImageAccurateMetadata: true]
            let colorDetector = CIDetector(ofType: CIDetectorTypeColor, context: nil, options: accuracy)!
            let features = colorDetector.features(in: ciImage)
            let colors = features.compactMap { feature -> UIColor? in
                guard let color = feature.color else { return nil }
                return UIColor(ciColor: color)
            }
            self.dominantColor = colors.first
            DispatchQueue.main.async {
                completion(colors)
            }
        }
    }
}

问题原因 #

1. CIDetectorTypeColor并非CoreImage官方支持的检测器类型，CIDetector仅支持人脸、二维码、文本、矩形等检测场景，从未提供颜色检测的类型，你可能混淆了其他框架的API。
2. kCIImageAccurateMetadata是已废弃/移除的旧API键，当前CoreImage中检测器的精度选项使用CIDetectorAccuracy键，对应值为CIDetectorAccuracyHigh或CIDetectorAccuracyLow。

正确的图片主色调提取实现 #

如果需要提取图片的主色调，可以使用CoreImage的CIAreaAverage滤镜来实现，这是官方推荐的方式：

import SwiftUI
import UIKit
import CoreImage

class ColorExtractor {
    var dominantColor: UIColor?

    func extractColors(from image: UIImage, completion: @escaping ([UIColor]) -> Void) {
        guard let ciImage = CIImage(image: image) else {
            completion([])
            return
        }
        DispatchQueue.global(qos: .userInteractive).async {
            // 使用CIAreaAverage滤镜提取主色调
            let filter = CIFilter(name: "CIAreaAverage")!
            filter.setValue(ciImage, forKey: kCIInputImageKey)
            // 设置取样区域为整个图片
            let extent = ciImage.extent
            filter.setValue(CIVector(x: extent.origin.x, y: extent.origin.y, z: extent.size.width, w: extent.size.height), forKey: kCIInputExtentKey)
            
            guard let outputImage = filter.outputImage else {
                DispatchQueue.main.async {
                    completion([])
                }
                return
            }
            
            // 从输出图片中获取颜色值
            var bitmap = [UInt8](repeating: 0, count: 4)
            let context = CIContext(options: [.workingColorSpace: kCFNull!])
            context.render(outputImage, toBitmap: &bitmap, rowBytes: 4, bounds: CGRect(x: 0, y: 0, width: 1, height: 1), format: .RGBA8, colorSpace: nil)
            
            let color = UIColor(red: CGFloat(bitmap[0])/255, green: CGFloat(bitmap[1])/255, blue: CGFloat(bitmap[2])/255, alpha: CGFloat(bitmap[3])/255)
            self.dominantColor = color
            
            DispatchQueue.main.async {
                completion([color])
            }
        }
    }
}

说明 #

• CIAreaAverage滤镜会计算指定区域内的平均颜色，这里设置为整个图片，得到的就是图片的主色调。
• 通过CIContext将滤镜输出的1x1图片渲染到字节数组中，再转换为UIColor。

内容的提问来源于stack exchange，提问作者AYohannes