ios - 用于输入和输出的不同摄像机 session 预设

Question

我正在创建一个自定义相机 View ，并尝试查看是否有办法为输入和输出设置不同的 session 预设。我希望能够向用户展示高分辨率，但以低分辨率捕获

var captureSession: AVCaptureSession!
var stillImageOutput: AVCapturePhotoOutput!
var videoPreviewLayer: AVCaptureVideoPreviewLayer!
@interface CameraViewController ()
@property (nonatomic) AVCaptureSession *session;
@property (nonatomic) AVCapturePhotoOutput *stillImageOutput;
@property (nonatomic) AVCaptureVideoPreviewLayer *videoPreviewLayer;
@end

captureSession = AVCaptureSession()
captureSession.sessionPreset = .high // <--show high resolution but capture at low

stillImageOutput = AVCapturePhotoOutput()

if captureSession.canAddInput(input) && 
captureSession.canAddOutput(stillImageOutput) {
    captureSession.addInput(input)
    captureSession.addOutput(stillImageOutput)
    setupLivePreview()
}

func setupLivePreview() {

    videoPreviewLayer = AVCaptureVideoPreviewLayer(session: captureSession)

    videoPreviewLayer.videoGravity = .resizeAspect
    videoPreviewLayer.connection?.videoOrientation = .portrait
    previewView.layer.addSublayer(videoPreviewLayer)
}

Answer 1

也许您可以将捕获的图片调整两次。首先减小图像尺寸，然后将其增大到相同尺寸。分辨率会降低。

示例函数；

func resizeImage(image: UIImage, targetSize: CGSize) -> UIImage {
    let size = image.size

    let widthRatio  = targetSize.width  / size.width
    let heightRatio = targetSize.height / size.height

    // Figure out what our orientation is, and use that to form the rectangle
    var newSize: CGSize
    if(widthRatio > heightRatio) {
        newSize = CGSize(width: size.width * heightRatio, height: size.height * heightRatio)
    } else {
        newSize = CGSize(width: size.width * widthRatio,  height: size.height * widthRatio)
    }

    // This is the rect that we've calculated out and this is what is actually used below
    let rect = CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height)

    // Actually do the resizing to the rect using the ImageContext stuff
    UIGraphicsBeginImageContextWithOptions(newSize, false, 1.0)
    image.draw(in: rect)
    let newImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return newImage!
}