如何从AVCapture中将图像裁剪到在显示器上看到的矩形

Question

这使我发疯，因为我无法使其工作。我有以下情况：

我使用AVCaptureSession和AVCaptureVideoPreviewLayer来创建我自己的相机界面。界面显示一个矩形。以下是填充整个屏幕的AVCaptureVideoPreviewLayer。

我希望以某种方式裁剪捕获的图像，使得生成的图像精确地显示在显示器上的矩形中显示的内容。

我的设置是这样的：

_session = [[AVCaptureSession alloc] init]; 
AVCaptureSession *session = _session; 
session.sessionPreset = AVCaptureSessionPresetPhoto; 

AVCaptureDevice *camera = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo]; 
if (camera == nil) { 
    [self showImagePicker]; 
    _isSetup = YES; 
    return; 
} 
AVCaptureVideoPreviewLayer *captureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:session]; 
captureVideoPreviewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill; 

captureVideoPreviewLayer.frame = self.liveCapturePlaceholderView.bounds; 
[self.liveCapturePlaceholderView.layer addSublayer:captureVideoPreviewLayer]; 

NSError *error; 
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:camera error:&error]; 
if (error) { 
    HGAlertViewWrapper *av = [[HGAlertViewWrapper alloc] initWithTitle:kFailedConnectingToCameraAlertViewTitle message:kFailedConnectingToCameraAlertViewMessage cancelButtonTitle:kFailedConnectingToCameraAlertViewCancelButtonTitle otherButtonTitles:@[kFailedConnectingToCameraAlertViewRetryButtonTitle]]; 
    [av showWithBlock:^(NSString *buttonTitle){ 
     if ([buttonTitle isEqualToString:kFailedConnectingToCameraAlertViewCancelButtonTitle]) { 
      [self.delegate gloameCameraViewControllerDidCancel:self]; 
     } 
     else { 
      [self setupAVSession]; 
     } 
    }]; 
} 
[session addInput:input]; 

NSDictionary *options = @{ AVVideoCodecKey : AVVideoCodecJPEG }; 
_stillImageOutput = [[AVCaptureStillImageOutput alloc] init]; 
[_stillImageOutput setOutputSettings:options]; 

[session addOutput:_stillImageOutput]; 

[session startRunning]; 
_isSetup = YES; 

我捕捉这样的形象：

[_stillImageOutput captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler: ^(CMSampleBufferRef imageSampleBuffer, NSError *error) 
{ 
    if (error) { 
     MWLogDebug(@"Error capturing image from camera. %@, %@", error, [error userInfo]); 
     _capturePreviewLayer.connection.enabled = YES; 
    } 
    else 
    { 
     NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer]; 
     UIImage *image = [[UIImage alloc] initWithData:imageData]; 

     CGRect cropRect = [self createCropRectForImage:image]; 
     UIImage *croppedImage;// = [self cropImage:image toRect:cropRect]; 
     UIGraphicsBeginImageContext(cropRect.size); 
     [image drawAtPoint:CGPointMake(-cropRect.origin.x, -cropRect.origin.y)]; 
     croppedImage = UIGraphicsGetImageFromCurrentImageContext(); 
     UIGraphicsEndImageContext(); 
     self.capturedImage = croppedImage; 
     [_session stopRunning];    
    } 
}]; 

在createCropRectForImage:方法我试过各种方法来计算矩形切出的形象，但迄今为止没有成功。

- (CGRect)createCropRectForImage:(UIImage *)image 
{ 
    CGPoint maskTopLeftCorner = CGPointMake(self.maskRectView.frame.origin.x, self.maskRectView.frame.origin.y); 
    CGPoint maskBottomRightCorner = CGPointMake(self.maskRectView.frame.origin.x + self.maskRectView.frame.size.width, self.maskRectView.frame.origin.y + self.maskRectView.frame.size.height); 

    CGPoint maskTopLeftCornerInLayerCoords = [_capturePreviewLayer convertPoint:maskTopLeftCorner fromLayer:self.maskRectView.layer.superlayer]; 
    CGPoint maskBottomRightCornerInLayerCoords = [_capturePreviewLayer convertPoint:maskBottomRightCorner fromLayer:self.maskRectView.layer.superlayer]; 
    CGPoint maskTopLeftCornerInDeviceCoords = [_capturePreviewLayer captureDevicePointOfInterestForPoint:maskTopLeftCornerInLayerCoords]; 
    CGPoint maskBottomRightCornerInDeviceCoords = [_capturePreviewLayer captureDevicePointOfInterestForPoint:maskBottomRightCornerInLayerCoords]; 

    float x = maskTopLeftCornerInDeviceCoords.x * image.size.width; 
    float y = (1 - maskTopLeftCornerInDeviceCoords.y) * image.size.height; 
    float width = fabsf(maskTopLeftCornerInDeviceCoords.x - maskBottomRightCornerInDeviceCoords.x) * image.size.width; 
    float height = fabsf(maskTopLeftCornerInDeviceCoords.y - maskBottomRightCornerInDeviceCoords.y) * image.size.height; 

    return CGRectMake(x, y, width, height); 
} 

这是我目前的版本，但没有得到正确的比例。有人可以帮助我！

- (UIImage*)cropImage:(UIImage*)originalImage toRect:(CGRect)rect{ 

    CGImageRef imageRef = CGImageCreateWithImageInRect([originalImage CGImage], rect); 

    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef); 
    CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef); 
    CGContextRef bitmap = CGBitmapContextCreate(NULL, rect.size.width, rect.size.height, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo); 

    if (originalImage.imageOrientation == UIImageOrientationLeft) { 
     CGContextRotateCTM (bitmap, radians(90)); 
     CGContextTranslateCTM (bitmap, 0, -rect.size.height); 

    } else if (originalImage.imageOrientation == UIImageOrientationRight) { 
     CGContextRotateCTM (bitmap, radians(-90)); 
     CGContextTranslateCTM (bitmap, -rect.size.width, 0); 

    } else if (originalImage.imageOrientation == UIImageOrientationUp) { 
     // NOTHING 
    } else if (originalImage.imageOrientation == UIImageOrientationDown) { 
     CGContextTranslateCTM (bitmap, rect.size.width, rect.size.height); 
     CGContextRotateCTM (bitmap, radians(-180.)); 
    } 

    CGContextDrawImage(bitmap, CGRectMake(0, 0, rect.size.width, rect.size.height), imageRef); 
    CGImageRef ref = CGBitmapContextCreateImage(bitmap); 

    UIImage *resultImage=[UIImage imageWithCGImage:ref]; 
    CGImageRelease(imageRef); 
    CGContextRelease(bitmap); 
    CGImageRelease(ref); 

    return resultImage; 
} 

没有任何人有方法的“最佳组合”，使这项工作：

我也用这个方法来裁剪我的形象试过吗？ :)

Answer 1

我已经使用metadataOutputRectOfInterestForRect函数解决了这个问题。

它适用于任何方向。

[_stillImageOutput captureStillImageAsynchronouslyFromConnection:stillImageConnection 
               completionHandler:^(CMSampleBufferRef imageDataSampleBuffer, NSError *error) 
{ 
    if (error) 
    { 
     [_delegate cameraView:self error:@"Take picture failed"]; 
    } 
    else 
    { 

     NSData *jpegData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer]; 
     UIImage *takenImage = [UIImage imageWithData:jpegData]; 

     CGRect outputRect = [_previewLayer metadataOutputRectOfInterestForRect:_previewLayer.bounds]; 
     CGImageRef takenCGImage = takenImage.CGImage; 
     size_t width = CGImageGetWidth(takenCGImage); 
     size_t height = CGImageGetHeight(takenCGImage); 
     CGRect cropRect = CGRectMake(outputRect.origin.x * width, outputRect.origin.y * height, outputRect.size.width * width, outputRect.size.height * height); 

     CGImageRef cropCGImage = CGImageCreateWithImageInRect(takenCGImage, cropRect); 
     takenImage = [UIImage imageWithCGImage:cropCGImage scale:1 orientation:takenImage.imageOrientation]; 
     CGImageRelease(cropCGImage); 

    } 
} 
]; 

The takenImage is still imageOrientation dependent image。您可以删除进一步图像处理的方向信息。

UIGraphicsBeginImageContext(takenImage.size); 
[takenImage drawAtPoint:CGPointZero]; 
takenImage = UIGraphicsGetImageFromCurrentImageContext(); 
UIGraphicsEndImageContext(); 

Answer 2

看看this库，它可以帮你实现你想要的:)

Answer 3

AVMakeRectWithAspectRatioInsideRect 这个API是AVFoundation，它将返回裁剪区域给定作物尺寸的图像。

Answer 4

在斯威夫特3：

private func cropToPreviewLayer(originalImage: UIImage) -> UIImage { 
    let outputRect = previewLayer.metadataOutputRectOfInterest(for: previewLayer.bounds) 
    var cgImage = originalImage.cgImage! 
    let width = CGFloat(cgImage.width) 
    let height = CGFloat(cgImage.height) 
    let cropRect = CGRect(x: outputRect.origin.x * width, y: outputRect.origin.y * height, width: outputRect.size.width * width, height: outputRect.size.height * height) 

    cgImage = cgImage.cropping(to: cropRect)! 
    let croppedUIImage = UIImage(cgImage: cgImage, scale: 1.0, orientation: originalImage.imageOrientation) 

    return croppedUIImage 
}