Orientation does not behave correctly with Photo in ALAsset

问题

I current have an app that uses ALAsssetsLibrary to fetch the photos. I have placed the photo to an image view and I am able to upload to the server. When I tested on the real device after taking some photos, I found out the photos that supposed to be taken in Portrait become a landscape.

Therefore, I called different function to get the CGImage like this:

UIImage *image = [UIImage imageWithCGImage:[representation fullResolutionImage] scale:1.0 orientation:(UIImageOrientation)[representation orientation]];

The first tried out, I used this :

UIImage *image = [UIImage imageWithCGImage:[representation fullResolutionImage]]

I thought the one with scale and orientation could give me the right orientation that the photo was taken. But it didn't give me the right solution.

Do I miss anything that is necessary to generate a correct orientation of photo?

回答1:

The correct orientation handling depends on the iOS version you are using. On iOS4 and iOS 5 the thumbnail is already correctly rotated, so you can initialize your UIImage without specifying any rotation parameters. However for the fullScreenImage, the behavior is different for each iOS version. On iOS 5 the image is already rotated on iOS 4 not.

So on iOS4 you should use:

ALAssetRepresentation *defaultRep = [asset defaultRepresentation];
UIImage *_image = [UIImage imageWithCGImage:[defaultRep fullScreenImage] 
                                                     scale:[defaultRep scale] orientation:(UIImageOrientation)[defaultRep orientation]];

On iOS5 the following code should work correctly:

ALAssetRepresentation *defaultRep = [asset defaultRepresentation];
UIImage *_image = [UIImage imageWithCGImage:[defaultRep fullScreenImage] scale:[defaultRep scale] orientation:0];

Cheers,

Hendrik

回答2:

Try this code:-

 UIImage* img = [UIImage imageWithCGImage:asset.thumbnail];
 img = [UIImage imageWithCGImage:img.CGImage scale:1.0 orientation:UIImageOrientationUp];

This may help you.

回答3:

My experience is limited to IOS 5.x but I can tell you that the thumbnail and fullscreen images are oriented properly. It's the fullresolutionimage that's horizontal when shot vertically. My solution is to use a category on uiimage that I got from here:

http://www.catamount.com/forums/viewtopic.php?f=21&t=967&start=0

It provides a nice rotating method on a UIImage like this:

        UIImage *tmp = [UIImage imageWithCGImage:startingFullResolutionImage];
        startingFullResolutionImage = [[tmp imageRotatedByDegrees:-90.0f] CGImage];

回答4:

For fullResolutionImage, I'd like to provide a solution as follows,

ALAssetRepresentation *rep = [asset defaultRepresentation];

// First, write orientation to UIImage, i.e., EXIF message.
UIImage *image = [UIImage imageWithCGImage:[rep fullResolutionImage] scale:rep.scale orientation:(UIImageOrientation)rep.orientation];
// Second, fix orientation, and drop out EXIF
if (image.imageOrientation != UIImageOrientationUp) {
   UIGraphicsBeginImageContextWithOptions(image.size, NO, image.scale);
   [image drawInRect:(CGRect){0, 0, image.size}];
   UIImage *normalizedImage = UIGraphicsGetImageFromCurrentImageContext();
   UIGraphicsEndImageContext();
   image = normalizedImage;
}
// Third, compression
NSData *imageData = UIImageJPEGRepresentation(image, 1.0);

imageData is what you want, and just upload it to your photo server.

By the way, if you think EXIF is useful, you can complement it to normalizedImage as you wish.

来源：https://stackoverflow.com/questions/8832547/orientation-does-not-behave-correctly-with-photo-in-alasset

标签

iphone

image

orientation

alassetslibrary