ios - 在 Swift 中从 iOS 摄像头源获取像素值的最有效/实时方式

Question

这里有一些关于类似问题的讨论。喜欢this ，但它们似乎已经过时了，所以我想我应该在这里问一下。

我想从 swift 2.0 中的相机馈送中获得近乎实时的 RGB 像素值，甚至更好的是完整图像 RGB 直方图。我希望它尽可能快和最新(理想情况下约为 30 fps 或更高)

我可以直接从 AVCaptureVideoPreviewLayer 获取它还是我需要捕获每一帧(我假设是异步的，如果这个过程需要很长时间)然后从 jpeg/png 渲染中提取像素值？

一些示例代码，取自 jquave但针对 swift 2.0 进行了修改

import UIKit
import AVFoundation

class ViewController: UIViewController {

let captureSession = AVCaptureSession()
var previewLayer : AVCaptureVideoPreviewLayer?

var captureDevice : AVCaptureDevice?

override func viewDidLoad() {
    super.viewDidLoad()

    // Do any additional setup after loading the view, typically from a nib.
    captureSession.sessionPreset = AVCaptureSessionPresetHigh

    let devices = AVCaptureDevice.devices()

    // Loop through all the capture devices on this phone
    for device in devices {
        // Make sure this particular device supports video
        if (device.hasMediaType(AVMediaTypeVideo)) {
            // Finally check the position and confirm we've got the back camera
            if(device.position == AVCaptureDevicePosition.Back) {
                captureDevice = device as? AVCaptureDevice
                if captureDevice != nil {
                    print("Capture device found")
                    beginSession()
                }
            }
        }
    }
}

func focusTo(value : Float) {
    if let device = captureDevice {
        do {
            try device.lockForConfiguration()
                device.setFocusModeLockedWithLensPosition(value, completionHandler: { (time) -> Void in
                })
            device.unlockForConfiguration()
        } catch {
            //error message
            print("Can't change focus of capture device")
        }
    }
}

func configureDevice() {
    if let device = captureDevice {
        do {
            try device.lockForConfiguration()
                device.focusMode = .Locked
                device.unlockForConfiguration()
        } catch {
            //error message etc.
            print("Capture device not configurable")
        }
    }

}

func beginSession() {

    configureDevice()
    do {
        //try captureSession.addInput(input: captureDevice)
        try captureSession.addInput(AVCaptureDeviceInput(device: captureDevice))
        updateDeviceSettings(0.0, isoValue: 0.0)
    } catch {
        //error message etc.
        print("Capture device not initialisable")
    }
    previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
    self.view.layer.addSublayer(previewLayer!)
    previewLayer?.frame = self.view.layer.frame
    captureSession.startRunning()        
}

func updateDeviceSettings(focusValue : Float, isoValue : Float) {
    if let device = captureDevice {
        do {
            try device.lockForConfiguration()
            device.setFocusModeLockedWithLensPosition(focusValue, completionHandler: { (time) -> Void in
                //
            })

            // Adjust the iso to clamp between minIso and maxIso based on the active format
            let minISO = device.activeFormat.minISO
            let maxISO = device.activeFormat.maxISO
            let clampedISO = isoValue * (maxISO - minISO) + minISO

            device.setExposureModeCustomWithDuration(AVCaptureExposureDurationCurrent, ISO: clampedISO, completionHandler: { (time) -> Void in
                //
            })

            device.unlockForConfiguration()
        } catch {
            //error message etc.
            print("Can't update device settings")
        }

    }
}
}

Answer 1

您不需要 AVCaptureVideoPreviewLayer - 如果您想显示 视频，这就是您想要的。相反，您需要不同的输出:AVCaptureVideoDataOutput:

https://developer.apple.com/library/ios/documentation/AVFoundation/Reference/AVCaptureVideoDataOutput_Class/index.html#//apple_ref/occ/cl/AVCaptureVideoDataOutput

这使您可以直接访问样本缓冲区流，然后可以进入像素空间。

请注意:我不知道当前设备的吞吐量是多少，但我无法从 iPhone 4S 获得最高质量的实时流，因为 GPU<-->CPU 管道太慢了。