为什么AVCaptureVideoOrientation横向模式会导致静止图像颠倒？

Question

我正在使用AVFoundation类在我的应用程序中实现自定义相机.我只捕捉静止图像,而不是视频.我有一切工作,但我被一些东西困扰.我会在捕获静止图像时考虑设备方向,并适当地设置视频连接的videoOrientation.代码段:

    // set the videoOrientation based on the device orientation to
    // ensure the pic is right side up for all orientations
    AVCaptureVideoOrientation videoOrientation;
    switch ([UIDevice currentDevice].orientation) {
        case UIDeviceOrientationLandscapeLeft:
            // Not clear why but the landscape orientations are reversed
            // if I use AVCaptureVideoOrientationLandscapeLeft here the pic ends up upside down
            videoOrientation = AVCaptureVideoOrientationLandscapeRight;
            break;
        case UIDeviceOrientationLandscapeRight:
            // Not clear why but the landscape orientations are reversed
            // if I use AVCaptureVideoOrientationLandscapeRight here the pic ends up upside down
            videoOrientation = AVCaptureVideoOrientationLandscapeLeft;
            break;
        case UIDeviceOrientationPortraitUpsideDown:
            videoOrientation = AVCaptureVideoOrientationPortraitUpsideDown;
            break;
        default:
            videoOrientation = AVCaptureVideoOrientationPortrait;
            break;
    }

    videoConnection.videoOrientation = videoOrientation;

请注意我在景观案例中的评论.我必须反转方向映射或结果图像颠倒.我使用以下代码捕获并保存图像:

[self.stillImageOutput captureStillImageAsynchronouslyFromConnection:videoConnection 
    completionHandler:^(CMSampleBufferRef imageSampleBuffer, NSError *error)
    {
        NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer];
        self.stillImage = [UIImage imageWithData:imageData];
        // notify observers (image gets saved to the camera roll)                                                           
        [[NSNotificationCenter defaultCenter] postNotificationName:CaptureSessionManagerDidCaptureStillImageNotification object:self];
        self.stillImage = nil;
}];

没有其他图像处理或操纵.

我的应用程序使用上面的代码.我只是想了解为什么必须颠倒方向常数以适应景观方向.谢谢!

Answer 1

嘿,似乎没有人觉得在这个问题上有点兴趣.事实证明答案是直截了当的.通过该stillImageOutput captureStillImageAsynchronouslyFromConnection:...方法捕获的图像始终具有以下属性:

• 无论设备方向如何,UIImage方向=始终为UIImageOrientationRight
• UIImage尺寸= W x H(例如纵向宽度x纵向高度,取决于您的相机分辨率)
• CGImage尺寸=取决于设备方向(例如肖像或风景)

因此,向上旋转图像的解决方案是将设备方向与CGImage大小结合使用以应用适当的仿射变换.当我回答我自己的问题时,我不是代码中的解决方案,但我最终编写了一个名为的例程:

- (UIImage *)imageRotatedUpForDeviceOrientation:(UIDeviceOrientation)deviceOrientation

在包含各种图像处理增强功能的UIImage类别中.

编辑 - 实施例

我收到了许多关于功能代码的请求.我从一个有效的应用程序中提取了相关的实现.

// this method is implemented in your capture session manager (wherever AVCaptureSession is used)
// capture a still image and save the device orientation
- (void)captureStillImage
{
    UIDeviceOrientation currentDeviceOrientation = UIDevice.currentDevice.orientation;
      [self.stillImageOutput
      captureStillImageAsynchronouslyFromConnection:self.videoConnection
      completionHandler:^(CMSampleBufferRef imageSampleBuffer, NSError *error) {
          NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer];
          if (imageData) {
              UIImage *image = [UIImage imageWithData:imageData];
              NSDictionary *captureInfo = {
                  @"image" : image,
                  @"deviceOrientation" : @(currentDeviceOrientation)
              };
              // TODO: send image & orientation to delegate or post notification to observers
          }
          else {
              // TODO: handle image capture error
          }
    }];
}

// this method rotates the UIImage captured by the capture session manager based on the
// device orientation when the image was captured
- (UIImage *)imageRotatedUpFromCaptureInfo:(NSDictionary *)captureInfo
{
    UIImage *image = [captureInfo objectForKey:@"image"];
    UIDeviceOrientation deviceOrientation = [[captureInfo objectForKey:@"deviceOrientation"] integerValue];
    UIImageOrientation rotationOrientation = [self rotationNeededForImageCapturedWithDeviceOrientation:deviceOrientation];
    // TODO: scale the image if desired
    CGSize newSize = image.size;
    return [imageScaledToSize:newSize andRotatedByOrientation:rotationOrientation];
}

// return a scaled and rotated an image
- (UIImage *)imageScaledToSize:(CGSize)newSize andRotatedByOrientation:(UIImageOrientation)orientation
{
    CGImageRef imageRef = self.CGImage;    
    CGRect imageRect = CGRectMake(0.0, 0.0, newSize.width, newSize.height);
    CGRect contextRect = imageRect;
    CGAffineTransform transform = CGAffineTransformIdentity;

    switch (orientation)
    {
        case UIImageOrientationDown: { // rotate 180 deg
            transform = CGAffineTransformTranslate(transform, imageRect.size.width, imageRect.size.height);
            transform = CGAffineTransformRotate(transform, M_PI);
        } break;

        case UIImageOrientationLeft: { // rotate 90 deg left
            contextRect = CGRectTranspose(contextRect);
            transform = CGAffineTransformTranslate(transform, imageRect.size.height, 0.0);
            transform = CGAffineTransformRotate(transform, M_PI / 2.0);
        } break;

        case UIImageOrientationRight: { // rotate 90 deg right
            contextRect = CGRectTranspose(contextRect);
            transform = CGAffineTransformTranslate(transform, 0.0, imageRect.size.width);
            transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);
        } break;

        case UIImageOrientationUp: // no rotation
        default:
            break;
    }

    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
    CGColorSpaceRef colorSpaceRef = CGImageGetColorSpace(imageRef);

    // madify bitmapInfo to work with PNG if necessary
    if (bitmapInfo == kCGImageAlphaNone) {
        bitmapInfo = kCGImageAlphaNoneSkipLast;
    }
    else if (bitmapInfo == kCGImageAlphaLast) {
        bitmapInfo = kCGImageAlphaPremultipliedLast;
    }

    // Build a context that's the same dimensions as the new size
    CGContextRef context = CGBitmapContextCreate(NULL,
                                                 contextRect.size.width,
                                                 contextRect.size.height,
                                                 CGImageGetBitsPerComponent(imageRef),
                                                 0,
                                                 colorSpaceRef,
                                                 bitmapInfo);


    CGContextConcatCTM(context, transform);
    CGContextDrawImage(context, imageRect, imageRef);

    // Get the rotated image from the context and a UIImage
    CGImageRef rotatedImageRef = CGBitmapContextCreateImage(context);
    UIImage *rotatedImage = [UIImage imageWithCGImage:rotatedImageRef];

    // Clean up
    CGImageRelease(rotatedImageRef);
    CGContextRelease(context);

    return rotatedImage;
}

// return the UIImageOrientation needed for an image captured with a specific deviceOrientation
- (UIImageOrientation)rotationNeededForImageCapturedWithDeviceOrientation:(UIDeviceOrientation)deviceOrientation
{
    UIImageOrientation rotationOrientation;
    switch (deviceOrientation) {
        case UIDeviceOrientationPortraitUpsideDown: {
            rotationOrientation = UIImageOrientationLeft;
        } break;

        case UIDeviceOrientationLandscapeRight: {
            rotationOrientation = UIImageOrientationDown;
        } break;

        case UIDeviceOrientationLandscapeLeft: {
            rotationOrientation = UIImageOrientationUp;
        } break;

        case UIDeviceOrientationPortrait:
        default: {
            rotationOrientation = UIImageOrientationRight;
        } break;
    }
    return rotationOrientation;
}

Answer 2

至于为什么你需要AVCaptureVideoOrientationLandscape 权当设备的方向是UIDeviceOrientationLandscape 左,这是因为,出于某种原因,UIDeviceOrientationLandscape 左 == UIInterfaceOrientationLandscape 权和AVCaptureVideoOrientations遵循了UIInterfaceOrientation约定.

此外,UIDeviceOrientation包含其他选项,如UIDeviceOrientationFaceUp,UIDeviceOrientationFaceDown和UIDeviceOrientationUnknown.如果您的界面旋转以匹配设备的方向,您可以尝试从[UIApplication sharedApplication] .statusBarOrientation获取UIDeviceOrientation.