OpenCv iOS 相机仅预览单一方向而无需拉伸

Question

我正在为 iOS 编写一个 OpenCv Cordova 插件。我需要相机预览为全屏并保持所有 iOS 设备（iPhone、iPad）的纵横比。

我能够实现人像模式（参见代码），它在 iPhone 6/plus 上完美运行，但相机预览在 iPad 上略有拉伸，可能是因为 AVCaptureSessionPresetHigh 的支持的分辨率为 1280x720 .有人对如何实现单一方向（仅限横向或纵向）并保持纵横比有任何想法吗？

我目前启动相机的代码是

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.

    // Initialize imageView to fullscreen
    imageView = [[UIImageView alloc] initWithFrame:[UIScreen mainScreen].bounds];
    [self.view addSubview:imageView];
    [imageView setContentMode:UIViewContentModeScaleAspectFill];
    [imageView setClipsToBounds:YES];

    self.videoCamera = [[FixedCvVideoCamera alloc] initWithParentView:imageView];
    self.videoCamera.delegate = self;
    self.videoCamera.defaultAVCaptureDevicePosition = AVCaptureDevicePositionBack;
    self.videoCamera.defaultAVCaptureSessionPreset = AVCaptureSessionPresetHigh;
    self.videoCamera.defaultAVCaptureVideoOrientation =  AVCaptureVideoOrientationPortrait;
    self.videoCamera.defaultFPS = 30;
    [self.videoCamera start];
}

请注意，我使用的是 FixedCvVideoCamera 而不是 OpenCv CvVideoCamera 类。原因是我继承并覆盖了 CvVideoCamera 的 layoutPreviewLayer 函数以保持纵向模式。

 - (void)layoutPreviewLayer;
{
    if (self.parentView != nil)
    {
        CALayer* layer = self->customPreviewLayer;
        CGRect bounds = self->customPreviewLayer.bounds;
        int rotation_angle = 0;

        switch (defaultAVCaptureVideoOrientation) {
            case AVCaptureVideoOrientationLandscapeRight:
                rotation_angle = 270;
                break;
            case AVCaptureVideoOrientationPortraitUpsideDown:
                rotation_angle = 180;
                break;
            case AVCaptureVideoOrientationLandscapeLeft:
                rotation_angle = 90;
                break;
            case AVCaptureVideoOrientationPortrait:
            default:
                break;
        }

        layer.position = CGPointMake(self.parentView.frame.size.width/2., self.parentView.frame.size.height/2.);
        layer.affineTransform = CGAffineTransformMakeRotation( DEGREES_RADIANS(rotation_angle) );
        layer.bounds = bounds;
    }
}

提前致谢。

Answer 1

我自己解决了。下面的代码将帮助那些只想要固定人像模式并支持前后摄像头的人。

视图控制器

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.

    // Initialize imageView to fullscreen
    imageView = [[UIImageView alloc] initWithFrame:[UIScreen mainScreen].bounds];
    [self.view addSubview:imageView];
    [imageView setContentMode:UIViewContentModeScaleAspectFill];
    [imageView setClipsToBounds:YES];

    self.videoCamera = [[FixedCvVideoCamera alloc] initWithParentView:imageView];
    self.videoCamera.delegate = self;
    self.videoCamera.defaultAVCaptureDevicePosition = AVCaptureDevicePositionBack;
    self.videoCamera.defaultAVCaptureSessionPreset = AVCaptureSessionPresetHigh;
    self.videoCamera.defaultAVCaptureVideoOrientation =  AVCaptureVideoOrientationPortrait;
    self.videoCamera.defaultFPS = 30;
    self.videoCamera.grayscaleMode = NO;

    [self.videoCamera start];
}

固定CvVideoCamera：CvVideoCamera

- (void)layoutPreviewLayer;
{
    if (self.parentView != nil)
    {
        CALayer* layer = self->customPreviewLayer;
        CGRect bounds = self->customPreviewLayer.bounds;
        NSLog(@"[FixedCvVideoCamera]Custom Preview Layer bounds %fx%f", bounds.size.width, bounds.size.height);

        float previewAspectRatio = bounds.size.height / bounds.size.width;
        NSLog(@"[FixedCvVideoCamera]Preview aspect ratio %f", previewAspectRatio);

        //int rotation_angle = 0;

        layer.position = CGPointMake(self.parentView.frame.size.width/2., self.parentView.frame.size.height/2.);
        //layer.affineTransform = CGAffineTransformMakeRotation( DEGREES_RADIANS(rotation_angle) );

        // Get video feed's resolutions
        NSArray* devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
        AVCaptureDevice* device = nil;
        for (AVCaptureDevice *d in devices) {
            // Get the default camera device - should be either front of back camera device
            if ([d position] == self.defaultAVCaptureDevicePosition) {
                device = d;
            }
        }

        // Set the default device if not found
        if (!device) {
            device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
        }

        CMVideoDimensions dimensions = CMVideoFormatDescriptionGetDimensions(device.activeFormat.formatDescription);
        CGSize resolution = CGSizeMake(dimensions.width, dimensions.height);
        if (self.defaultAVCaptureVideoOrientation == AVCaptureVideoOrientationPortrait || self.defaultAVCaptureVideoOrientation == AVCaptureVideoOrientationPortraitUpsideDown) {
            resolution = CGSizeMake(resolution.height, resolution.width);
        }
        NSLog(@"[FixedCvVideoCamera]Video feed resolution is %fx%f", resolution.width, resolution.height);

        float videoFeedAspectRatio = resolution.height / resolution.width;
        NSLog(@"[FixedCvVideoCamera]Video feed's aspect ratio is %f", videoFeedAspectRatio);

        // Set layer bounds to ASPECT FILL by expanding either the width or the height
        if (previewAspectRatio > videoFeedAspectRatio) {
            NSLog(@"[FixedCvVideoCamera] Preview is more rectangular than the video feed aspect ratio. Expanding width to maintain aspect ratio.");
            float newWidth = bounds.size.height / videoFeedAspectRatio;
            layer.bounds = CGRectMake(0, 0, newWidth, bounds.size.height);
        } else {
            NSLog(@"[FixedCvVideoCamera] Preview is equally or less rectangular (wider) than the video feed's aspect ratio. Expanding height bound to maintain aspect ratio.");
            float newHeight = bounds.size.width * videoFeedAspectRatio;
            layer.bounds = CGRectMake(0, 0, bounds.size.width, newHeight);
        }
    }
}