本文是筆者用來記錄學(xué)習(xí) iOS 圖像處理相關(guān)的文章灵再，內(nèi)容可能有部分不對芽唇，可以通過評論或私信交流弛车。本文所有代碼都是 Swift 3.0

前言

在上一篇文章 iOS 圖像處理（一）：獲取某一點(diǎn)位置的像素 中有提到相機(jī)取色這么一個(gè)功能蛉鹿，其實(shí)這個(gè)功能在上篇文章的基礎(chǔ)上即可實(shí)現(xiàn)滨砍，現(xiàn)在來詳細(xì)講講；

實(shí)現(xiàn)

實(shí)現(xiàn)效果

因?yàn)橄鄼C(jī)功能需要用到真機(jī)，要獲取效果圖比較麻煩惋戏，就不上了领追。

筆者思路

方式一

通過相機(jī)獲取得到圖像數(shù)據(jù)，根據(jù)取色位置得到像素?cái)?shù)據(jù)响逢；

問題：因?yàn)檫@樣獲取得到的像素?cái)?shù)據(jù)是原數(shù)據(jù)绒窑，所以當(dāng)圖像進(jìn)行了一些變換操作（比如縮放），這時(shí)同樣要對位置進(jìn)行相應(yīng)的變換舔亭，實(shí)現(xiàn)起來相對麻煩些膨，所以不使用這種方式；

方式二

通過相機(jī)獲取得到圖像數(shù)據(jù)钦铺，將圖像數(shù)據(jù)渲染到 CALayer 上订雾，通過 CALayer 來獲取得到特定位置上的像素?cái)?shù)據(jù)，這跟上一篇文章的方式二是完全一樣的职抡；

初始化圖像預(yù)覽層：

let previewLayer = CALayer()

internal func setupUI() {
    previewLayer.bounds = view.bounds
    previewLayer.position = view.center
    previewLayer.contentsGravity = kCAGravityResizeAspectFill
    previewLayer.setAffineTransform(CGAffineTransform(rotationAngle: CGFloat(M_PI / 2.0)))
    view.layer.insertSublayer(previewLayer, at: 0)
}

初始化相機(jī)：

let session = AVCaptureSession()

// 相機(jī)數(shù)據(jù)幀接收隊(duì)列
let queue = DispatchQueue(label: "com.camera.video.queue")

// 取色位置
var center: CGPoint = .zero

internal func setupParameter() {
    
    session.beginConfiguration()
    session.sessionPreset = AVCaptureSessionPreset1280x720
    
    guard let device = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo),
        let deviceInput = try? AVCaptureDeviceInput(device: device) else {
        return
    }
    
    if session.canAddInput(deviceInput) {
        session.addInput(deviceInput)
    }
    
    let videoOutput = AVCaptureVideoDataOutput()
    videoOutput.videoSettings = [kCVPixelBufferPixelFormatTypeKey as AnyHashable: NSNumber(value: kCMPixelFormat_32BGRA)]
    videoOutput.alwaysDiscardsLateVideoFrames = true
    videoOutput.setSampleBufferDelegate(self, queue: queue)
    
    if session.canAddOutput(videoOutput) {
        session.addOutput(videoOutput)
    }
    
    session.commitConfiguration()
}

設(shè)置取色位置：

public override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    guard let touch = touches.first else {
        return
    }
    // 獲取用戶點(diǎn)擊位置在圖像上的相對位置
    let point = touch.location(in: self.view)
    center = point
    anchorButton.frame = CGRect(x: point.x - 20, y: point.y - 20 / 2, width: 40, height: 40)
}

獲取特定位置顏色：

public func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, from connection: AVCaptureConnection!) {
    
    guard let imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else {
        return
    }
    
    CVPixelBufferLockBaseAddress(imageBuffer, CVPixelBufferLockFlags(rawValue: CVOptionFlags(0)))
    
    guard let baseAddr = CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 0) else {
        return
    }
    let width = CVPixelBufferGetWidthOfPlane(imageBuffer, 0)
    let height = CVPixelBufferGetHeightOfPlane(imageBuffer, 0)
    let bytesPerRow = CVPixelBufferGetBytesPerRowOfPlane(imageBuffer, 0)
    let colorSpace = CGColorSpaceCreateDeviceRGB()
    let bimapInfo: CGBitmapInfo = [
        .byteOrder32Little,
        CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedFirst.rawValue)]
    
    guard let content = CGContext(data: baseAddr, width: width, height: height, bitsPerComponent: 8, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bimapInfo.rawValue) else {
        return
    }
    
    // 如果是從像素?cái)?shù)據(jù)中獲取特定位置像素葬燎，則是按以下被注釋的這部分代碼進(jìn)行獲取
    // 其中像素排序?yàn)椋築GRA，index 需要進(jìn)行要應(yīng)的變換
//        let data = baseAddr.assumingMemoryBound(to: UInt8.self)
//        let index = width * height * 2
//        let b = CGFloat(data.advanced(by: index + 0).pointee) / 255
//        let g = CGFloat(data.advanced(by: index + 1).pointee) / 255
//        let r = CGFloat(data.advanced(by: index + 2).pointee) / 255
//        let a = CGFloat(data.advanced(by: index + 3).pointee) / 255
//        let color = UIColor(red: r, green: g, blue: b, alpha: a)

    guard let cgImage = content.makeImage() else {
        return
    }
    
    DispatchQueue.main.async {
        self.previewLayer.contents = cgImage
        // self.previewLayer.pickColor 為 CALayer 的一個(gè)擴(kuò)展
        self.colorView.backgroundColor = self.previewLayer.pickColor(at: self.center)
    }
}

public extension CALayer {
    
    /// 獲取特定位置的顏色
    ///
    /// - parameter at: 位置
    ///
    /// - returns: 顏色
    public func pickColor(at position: CGPoint) -> UIColor? {
        
        // 用來存放目標(biāo)像素值
        var pixel = [UInt8](repeatElement(0, count: 4))
        // 顏色空間為 RGB缚甩，這決定了輸出顏色的編碼是 RGB 還是其他（比如 YUV）
        let colorSpace = CGColorSpaceCreateDeviceRGB()
        // 設(shè)置位圖顏色分布為 RGBA
        let bitmapInfo = CGImageAlphaInfo.premultipliedLast.rawValue
        guard let context = CGContext(data: &pixel, width: 1, height: 1, bitsPerComponent: 8, bytesPerRow: 4, space: colorSpace, bitmapInfo: bitmapInfo) else {
            return nil
        }
        // 設(shè)置 context 原點(diǎn)偏移為目標(biāo)位置所有坐標(biāo)
        context.translateBy(x: -position.x, y: -position.y)
        // 將圖像渲染到 context 中
        render(in: context)
        
        return UIColor(red: CGFloat(pixel[0]) / 255.0,
                       green: CGFloat(pixel[1]) / 255.0,
                       blue: CGFloat(pixel[2]) / 255.0,
                       alpha: CGFloat(pixel[3]) / 255.0)
    }
}

本文到此結(jié)束谱净！