swift图片颜色占比分析

extension UIImage {
    func scaleTo(size: CGSize) -> UIImage? {
        UIGraphicsBeginImageContextWithOptions(size, false, 1.0)
        self.draw(in: CGRect(x: 0, y: 0, width: size.width, height: size.height))
        let newImg = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return newImg
    }
    
    /// 一张图颜色占比 取十种颜色
    func colorRate() -> [Double] {
        // 把 UIImage 转换成 CGImage Data
        let provider = self.cgImage?.dataProvider
        let pixeData = provider?.data
        guard let pxData = pixeData else {
            return []
        }
        guard let data = CFDataGetBytePtr(pxData) else {
            return []
        }
        let dataLength = CFDataGetLength(pxData)
        let numberOfColorComponents = 4 // R,G,B, and A
        
        // 用来装 color ，key 为 R-G-B 字符串，value 为出现次数
        var colors = [String: Double]()
        var colorCount: Double = 0
        var i = 0
        while i < dataLength {
            i += numberOfColorComponents
            if data[i + 3] != 0 {//非透明
                colorCount += 1
                let red = data[i]
                let green = data[i + 1]
                let blue = data[i + 2]
                let result = "\(red)-\(green)-\(blue)"
                if !colors.keys.contains(result) {
                    colors[result] = 1
                } else {
                    colors[result] = colors[result]! + 1.0
                }
            }
        }
        
        let  colorValues = colors.values.sorted { $0 > $1 }
        var colorRates = [Double]()
        for (index, item) in colorValues.enumerated() {
            if index < 10 {
                let rate = item / colorCount
                colorRates.append(rate)
            }
        }
        return colorRates
    }
}