在屏幕上显示从相机捕获的图像时的混乱答案

【问题标题】：Confusion when presenting captured image from camera on screen在屏幕上显示从相机捕获的图像时的混乱
【发布时间】：2013-10-26 10:21:37
【问题描述】：

我成功地从 iPhone 后置摄像头捕获图像并将其用作 UIImage。

图像可用后，我立即调用此方法：

- (void)putPhoto:(UIImage *)photo onTopOfPreview:(UIView *)preview {
    CALayer *photoLayer = [CALayer layer];
    photoLayer.frame = CGRectMake(10, 10, 300, 300);
    photoLayer.contents = (id)photo.CGImage;
    [self.view.layer addSublayer:photoLayer];
    //    [preview.layer addSublayer:photoLayer];
}

但图像旋转了 -90˚。因为这是我第一次使用 CALayers，所以我尝试使用 UIImageView 呈现图像，如下所示：

- (void)putPhotoOnScreen:(UIImage *)photo {
    UIImageView *imageView = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0, 300, 300)];
    imageView.image = photo;
    [self.view addSubview:imageView];
}

使用这种方法可以正确显示图像。所有这些都发生在纵向。

欢迎大家提出建议。

【问题讨论】：

标签： ios iphone objective-c uiimage calayer

【解决方案1】：

试试这个方法

 # pragma mark -
# pragma mark - Scale and Rotate according to Orientation

- (UIImage *)scaleAndRotateImage:(UIImage *)image
{
        int kMaxResolution = 640; // Or whatever

        CGImageRef imgRef = image.CGImage;
        CGFloat width = CGImageGetWidth(imgRef);
        CGFloat height = CGImageGetHeight(imgRef);

        CGAffineTransform transform = CGAffineTransformIdentity;
        CGRect bounds = CGRectMake(0, 0, width, height);
        if (width > kMaxResolution || height > kMaxResolution) {
        CGFloat ratio = width/height;
        if (ratio > 1) {
              bounds.size.width = kMaxResolution;
              bounds.size.height = roundf(bounds.size.width / ratio);
        }
        else {
            bounds.size.height = kMaxResolution;
             bounds.size.width = roundf(bounds.size.height * ratio);
        }
     }

CGFloat scaleRatio = bounds.size.width / width;
CGSize imageSize = CGSizeMake(CGImageGetWidth(imgRef), CGImageGetHeight(imgRef));
CGFloat boundHeight;
UIImageOrientation orient = image.imageOrientation;
switch(orient) {

    case UIImageOrientationUp: //EXIF = 1

        // landscape right
        transform = CGAffineTransformIdentity;
        break;

    case UIImageOrientationUpMirrored: //EXIF = 2
        transform = CGAffineTransformMakeTranslation(imageSize.width, 0.0);
        transform = CGAffineTransformScale(transform, -1.0, 1.0);
        break;

    case UIImageOrientationDown: //EXIF = 3

        // landscape left
        transform = CGAffineTransformMakeTranslation(imageSize.width, imageSize.height);
        transform = CGAffineTransformRotate(transform, M_PI);
        break;

    case UIImageOrientationDownMirrored: //EXIF = 4
        transform = CGAffineTransformMakeTranslation(0.0, imageSize.height);
        transform = CGAffineTransformScale(transform, 1.0, -1.0);
        break;

    case UIImageOrientationLeftMirrored: //EXIF = 5
        boundHeight = bounds.size.height;
        bounds.size.height = bounds.size.width;
        bounds.size.width = boundHeight;
        transform = CGAffineTransformMakeTranslation(imageSize.height, imageSize.width);
        transform = CGAffineTransformScale(transform, -1.0, 1.0);
        transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);
        break;

    case UIImageOrientationLeft: //EXIF = 6
        boundHeight = bounds.size.height;
        bounds.size.height = bounds.size.width;
        bounds.size.width = boundHeight;
        transform = CGAffineTransformMakeTranslation(0.0, imageSize.width);
        transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);
        break;

    case UIImageOrientationRightMirrored: //EXIF = 7
        boundHeight = bounds.size.height;
        bounds.size.height = bounds.size.width;
        bounds.size.width = boundHeight;
        transform = CGAffineTransformMakeScale(-1.0, 1.0);
        transform = CGAffineTransformRotate(transform, M_PI / 2.0);
        break;

    case UIImageOrientationRight: //EXIF = 8

        // Portrait Mode
        boundHeight = bounds.size.height;
        bounds.size.height = bounds.size.width;
        bounds.size.width = boundHeight;
        transform = CGAffineTransformMakeTranslation(imageSize.height, 0.0);
        transform = CGAffineTransformRotate(transform, M_PI / 2.0);
        break;

    default:
        [NSException raise:NSInternalInconsistencyException format:@"Invalid image orientation"];
}

UIGraphicsBeginImageContext(bounds.size);

CGContextRef context = UIGraphicsGetCurrentContext();

if (orient == UIImageOrientationRight || orient == UIImageOrientationLeft) {
    CGContextScaleCTM(context, -scaleRatio, scaleRatio);
    CGContextTranslateCTM(context, -height, 0);
}
else {
    CGContextScaleCTM(context, scaleRatio, -scaleRatio);
    CGContextTranslateCTM(context, 0, -height);
}

CGContextConcatCTM(context, transform);

CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, width, height), imgRef);
UIImage *imageCopy = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

return imageCopy;
}

【讨论】：

谢谢，我发现如果你将 UIImage 转换为 CGImage，关于方向的数据就会丢失。这也是解决方向问题的一种方法：stackoverflow.com/a/15039609/1378140
使用我的方法你还可以设置图片分辨率，如果你想调整图片大小以上传到服务器等。

【解决方案2】：

如果你想改变图像的方向，可以通过设置方向枚举在 UIImageView 中设置 UIImage 来改变它。

    UIImage *imageToDisplay =[UIImage imageWithCGImage:[originalImage CGImage]
                                      scale:1.0
                                      orientation: UIImageOrientationUp];

您可以将此图像设置为 UIImageView。

【讨论】：