这是一个不改变原始图像颜色空间的解决方案。如果你想规范化一个灰度图像的方向，你不会幸运地使用所有基于UIGraphicsBeginImageContextWithOptions的解决方案，因为它在RGB颜色空间中创建了一个上下文。相反，你必须创建一个具有与原始图像相同属性的上下文并绘制:

extension UIImage {
    static let rotatedOrentations: [UIImage.Orientation] = [.left, .leftMirrored, .right, .rightMirrored]

    func normalizedImage() -> UIImage {
        if imageOrientation == .up {
            return self
        }

        let image = self.cgImage!
        let swapOrientation = UIImage.rotatedOrentations.contains(imageOrientation)
        let width = swapOrientation ? image.height : image.width
        let height = swapOrientation ? image.width : image.height
        let context = CGContext(data: nil, width: width, height: height, bitsPerComponent: image.bitsPerComponent, bytesPerRow: image.bytesPerRow, space: image.colorSpace!, bitmapInfo: image.bitmapInfo.rawValue)!
        let flipVertical = CGAffineTransform(a: 1, b: 0, c: 0, d: -1, tx: 0, ty: CGFloat(height));
        context.concatenate(flipVertical)
        UIGraphicsPushContext(context)
        self.draw(at: .zero)
        UIGraphicsPopContext()

        return UIImage(cgImage: context.makeImage()!)
    }
}

下面是Swift-4.2自动修正图像方向的代码 返回界面图像

func AutofixImageOrientation(_ image: UIImage)->UIImage {

    UIGraphicsBeginImageContext(image.size)

    image.draw(at: .zero)

    let newImage = UIGraphicsGetImageFromCurrentImageContext()

    UIGraphicsEndImageContext()

    return newImage ?? image
}

我想出了一个更简单的方法:

- (UIImage *)normalizedImage {
    if (self.imageOrientation == UIImageOrientationUp) return self; 

    UIGraphicsBeginImageContextWithOptions(self.size, NO, self.scale);
    [self drawInRect:(CGRect){0, 0, self.size}];
    UIImage *normalizedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return normalizedImage;
}

顺便说一句:@Anomie的代码没有考虑到比例，所以不适合2倍的图像。

如果你启用了编辑，那么编辑后的图像(与原始图像相反)将按照预期的方向:

UIImagePickerController *imagePickerController = [[UIImagePickerController alloc] init];
imagePickerController.allowsEditing = YES;
// set delegate and present controller

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {
    UIImage *photo = [info valueForKey:UIImagePickerControllerEditedImage];
    // do whatever
}

启用编辑功能允许用户在点击“使用照片”之前调整图像大小和移动图像

这是一个基于@Anomie接受的答案的Swift 2的UIImage扩展。它使用了更清晰的开关外壳。它还会考虑CGBitmapContextCreateImage()返回的可选值。

extension UIImage {
    func rotateImageByOrientation() -> UIImage {
        // No-op if the orientation is already correct
        guard self.imageOrientation != .Up else {
            return self
        }

        // We need to calculate the proper transformation to make the image upright.
        // We do it in 2 steps: Rotate if Left/Right/Down, and then flip if Mirrored.
        var transform = CGAffineTransformIdentity;

        switch (self.imageOrientation) {
        case .Down, .DownMirrored:
            transform = CGAffineTransformTranslate(transform, self.size.width, self.size.height)
            transform = CGAffineTransformRotate(transform, CGFloat(M_PI))

        case .Left, .LeftMirrored:
            transform = CGAffineTransformTranslate(transform, self.size.width, 0)
            transform = CGAffineTransformRotate(transform, CGFloat(M_PI_2))

        case .Right, .RightMirrored:
            transform = CGAffineTransformTranslate(transform, 0, self.size.height)
            transform = CGAffineTransformRotate(transform, CGFloat(-M_PI_2))

        default:
            break
        }

        switch (self.imageOrientation) {
        case .UpMirrored, .DownMirrored:
            transform = CGAffineTransformTranslate(transform, self.size.width, 0)
            transform = CGAffineTransformScale(transform, -1, 1)

        case .LeftMirrored, .RightMirrored:
            transform = CGAffineTransformTranslate(transform, self.size.height, 0)
            transform = CGAffineTransformScale(transform, -1, 1)

        default:
            break
        }

        // Now we draw the underlying CGImage into a new context, applying the transform
        // calculated above.
        let ctx = CGBitmapContextCreate(nil, Int(self.size.width), Int(self.size.height),
            CGImageGetBitsPerComponent(self.CGImage), 0,
            CGImageGetColorSpace(self.CGImage),
            CGImageGetBitmapInfo(self.CGImage).rawValue)
        CGContextConcatCTM(ctx, transform)
        switch (self.imageOrientation) {
        case .Left, .LeftMirrored, .Right, .RightMirrored:
            CGContextDrawImage(ctx, CGRectMake(0,0,self.size.height,self.size.width), self.CGImage)

        default:
            CGContextDrawImage(ctx, CGRectMake(0,0,self.size.width,self.size.height), self.CGImage)
        }

        // And now we just create a new UIImage from the drawing context
        if let cgImage = CGBitmapContextCreateImage(ctx) {
            return UIImage(CGImage: cgImage)
        } else {
            return self
        }
    }
}

这是一个不改变原始图像颜色空间的解决方案。如果你想规范化一个灰度图像的方向，你不会幸运地使用所有基于UIGraphicsBeginImageContextWithOptions的解决方案，因为它在RGB颜色空间中创建了一个上下文。相反，你必须创建一个具有与原始图像相同属性的上下文并绘制:

extension UIImage {
    static let rotatedOrentations: [UIImage.Orientation] = [.left, .leftMirrored, .right, .rightMirrored]

    func normalizedImage() -> UIImage {
        if imageOrientation == .up {
            return self
        }

        let image = self.cgImage!
        let swapOrientation = UIImage.rotatedOrentations.contains(imageOrientation)
        let width = swapOrientation ? image.height : image.width
        let height = swapOrientation ? image.width : image.height
        let context = CGContext(data: nil, width: width, height: height, bitsPerComponent: image.bitsPerComponent, bytesPerRow: image.bytesPerRow, space: image.colorSpace!, bitmapInfo: image.bitmapInfo.rawValue)!
        let flipVertical = CGAffineTransform(a: 1, b: 0, c: 0, d: -1, tx: 0, ty: CGFloat(height));
        context.concatenate(flipVertical)
        UIGraphicsPushContext(context)
        self.draw(at: .zero)
        UIGraphicsPopContext()

        return UIImage(cgImage: context.makeImage()!)
    }
}