swift 获取相机 光亮度

要获取相机的光亮度，你可以使用AVCaptureDevice类和AVCaptureSession类来实现。下面是一个获取相机光亮度的示例代码：

import AVFoundation

// 创建一个AVCaptureSession对象
let captureSession = AVCaptureSession()

// 获取后置摄像头设备
guard let captureDevice = AVCaptureDevice.default(for: .video) else {
    print("无法获取后置摄像头")
    return
}

// 创建一个AVCaptureDeviceInput对象
guard let captureInput = try? AVCaptureDeviceInput(device: captureDevice) else {
    print("无法创建AVCaptureDeviceInput对象")
    return
}

// 将输入设备添加到会话
if captureSession.canAddInput(captureInput) {
    captureSession.addInput(captureInput)
}

// 创建一个AVCaptureVideoDataOutput对象
let captureOutput = AVCaptureVideoDataOutput()
captureOutput.alwaysDiscardsLateVideoFrames = true

// 设置代理并在后台队列中处理视频帧
let captureQueue = DispatchQueue(label: "com.example.captureQueue")
captureOutput.setSampleBufferDelegate(self, queue: captureQueue)

// 将输出设备添加到会话
if captureSession.canAddOutput(captureOutput) {
    captureSession.addOutput(captureOutput)
}

// 开始会话
captureSession.startRunning()

然后，你可以实现`AVCaptureVideoDataOutputSampleBufferDelegate`协议的方法来处理视频帧数据。在`captureOutput(_:didOutput:from:)`方法中，你可以获取每个视频帧的亮度信息：

extension YourViewController: AVCaptureVideoDataOutputSampleBufferDelegate {
    func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
        guard let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else {
            return
        }
        
        // 获取亮度信息
        let brightness = calculateBrightness(pixelBuffer: pixelBuffer)
        
        // 在主线程中更新UI或进行其他操作
        DispatchQueue.main.async {
            // 处理亮度值
            // ...
        }
    }
    
    func calculateBrightness(pixelBuffer: CVPixelBuffer) -> Float {
        CVPixelBufferLockBaseAddress(pixelBuffer, .readOnly)
        
        let baseAddress = CVPixelBufferGetBaseAddress(pixelBuffer)
        let bytesPerRow = CVPixelBufferGetBytesPerRow(pixelBuffer)
        let width = CVPixelBufferGetWidth(pixelBuffer)
        let height = CVPixelBufferGetHeight(pixelBuffer)
        
        var brightness: Float = 0.0
        
        if let baseAddress = baseAddress {
            let buffer = UnsafeMutableBufferPointer(start: baseAddress.assumingMemoryBound(to: UInt8.self), count: bytesPerRow * height)
            
            for row in 0..<height {
                for col in 0..<width {
                    let pixel = buffer[row * bytesPerRow + col]
                    brightness += Float(pixel)
                }
            }
            
            brightness /= Float(width * height)
        }
        
        CVPixelBufferUnlockBaseAddress(pixelBuffer, .readOnly)
        
        return brightness
    }
}

请注意，上面的代码只是一个基本示例，你可能需要根据自己的需求进行调整和优化。