UIImagePNGRepresentation问题？/图像旋转90度

Question

我想从UIImagePickerController加载图像,然后将选定的照片保存到我的应用程序的文档目录中.

UIImage *image = [info objectForKey:UIImagePickerControllerOriginalImage];
NSData *data1 = UIImagePNGRepresentation(image);

NSString *fileName = "1.png";
NSString *path = //get Document path, then add fileName
BOOL succ = [data1 writeToFile:path atomically:YES];

但是在我将图像保存到我的文档后,我发现,图像旋转了90度,然后我将方法UIImagePNGRepresentation更改为UIImageJPEGRepresentation,这次没关系,有谁知道问题是什么？

Answer 1

我遇到了同样的问题并且弄清楚了原因:从iOS 4.0开始,当相机拍照时它不会在保存之前旋转它,它只是在JPEG的EXIF数据中设置一个旋转标记.

如果将UIImage保存为JPEG,则会设置旋转标志.

PNG不支持旋转标志,因此如果将UIImage保存为PNG,它将被错误地旋转,并且没有设置标志来修复它.因此,如果你想要PNG,你必须自己旋转它们.

我会称这是PNG保存功能中的一个错误,但这只是一个意见(他们至少应该警告你这个).

Answer 2

试试这个:

func rotateImage(image: UIImage) -> UIImage? {
        if (image.imageOrientation == UIImage.Orientation.up ) {
            return image
        }
        UIGraphicsBeginImageContext(image.size)
        image.draw(in: CGRect(origin: CGPoint.zero, size: image.size))
        let copy = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return copy
    }

Answer 3

我用以下代码解决了这个问题.

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

    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 = bounds.size.width / ratio;
        }
        else {
            bounds.size.height = kMaxResolution;
            bounds.size.width = 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
            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
            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
            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;
}

Answer 4

下面的 swift 函数解决了这个问题。

func rotateImage(image: UIImage) -> UIImage? {
        if (image.imageOrientation == UIImage.Orientation.up ) {
            return image
        }
        UIGraphicsBeginImageContext(image.size)
        image.draw(in: CGRect(origin: CGPoint.zero, size: image.size))
        let copy = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return copy
    }

是的，就是这么简单，只是因为该drawInRect函数会考虑图像方向。