我正在使用AVFoundation类在我的应用中实现自定义相机。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作。
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！
答案 0 :(得分：21)
stillImageOutput captureStillImageAsynchronouslyFromConnection:...方法捕获的图像始终具有以下属性：
因此，向上旋转图像的解决方案是使用设备方向和CGImage大小来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 - 实施示例
我收到了许多关于此功能代码的请求。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;
}
答案 1 :(得分：7)
当设备的方向是UIDeviceOrientationLandscape 左时，为什么需要AVCaptureVideoOrientationLandscape 右，这是因为，出于某种原因，UIDeviceOrientationLandscape 左 == UIInterfaceOrientationLandscape 右，AVCaptureVideoOrientations遵循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。
答案 2 :(得分：0)
实际上，您的实施没有错误，您可以消除整个开关案例。
为什么切换案例可以消除：
设备和视频方向的相应值在数值上是相等的，即只要设备方向不是未知，面朝上或面朝下，就可以将UIDeviceOrientation和AVCaptureVideoOrientation等同起来
关于令人困惑的命名法：
设备方向LandscapeLeft =＆gt;手机顶部位于左侧。
所以，想象一下，视频的起点是.....那是正确的，TOP RIGHT corner =＆gt;风景正确。
同样在其他横向方向，视频方向远离手机顶部。 在纵向和颠倒的情况下，这不会造成混淆
<强>证明
捕获静止图像时，请检查方向EXIF值。 对于左侧的景观，EXIF方向为3（180度反转） 对于横向右侧，EXIF方向为1（无旋转）
当你显示时，你的exif方向被转换为相应的UIImageOrientation，所以不应该有反转。
在前置摄像头的情况下，我注意到了EXIF值，只需按照视频方向值（镜像效果没有处理）。仅使用1，3，6，8个EXIF值。
此外，镜子始终沿着从设备顶部到底部的线 因此，风景似乎是颠倒的，而肖像和颠倒的肖像只是镜像