How do I make an exact copy of a UIImage returned

问题:

I have divergent needs for the image returned from the iPhone camera. My app scales the image down for upload and display and, recently, I added the ability to save the image to the Photos app.

At first I was assigning the returned value to two separate variables, but it turned out that they were sharing the same object, so I was getting two scaled-down images instead of having one at full scale.

After figuring out that you can't do UIImage *copyImage = [myImage copy];, I made a copy using imageWithCGImage, per below. Unfortunately, this doesn't work because the copy (here croppedImage) ends up rotated 90º from the original.

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{   
    // Resize, crop, and correct orientation issues
    self.originalImage = [info valueForKey:@"UIImagePickerControllerOriginalImage"];
    UIImageWriteToSavedPhotosAlbum(originalImage, nil, nil, nil);
    UIImage *smallImage = [UIImage imageWithCGImage:[originalImage CGImage]]; // UIImage doesn't conform to NSCopy

    // This method is from a category on UIImage based on this discussion:
    // http://discussions.apple.com/message.jspa?messageID=7276709
    // It doesn't rotate smallImage, though: while imageWithCGImage returns
    // a rotated CGImage, the UIImageOrientation remains at UIImageOrientationUp!
    UIImage *fixedImage = [smallImage scaleAndRotateImageFromImagePickerWithLongestSide:480];
    ...
}

Is there a way to copy the UIImagePickerControllerOriginalImage image without modifying it in the process?

回答1:

Copy backing data and rotate it

This question asks a common question about UIImage in a slightly different way. Essentially, you have two related problems - deep copying and rotation. A UIImage is just a container and has an orientation property that is used for display. A UIImage can contain its backing data as a CGImage or CIImage, but most often as a CGImage. The CGImage is a struct of information that includes a pointer to the underlying data and if you read the docs, copying the struct does not copy the data. So...

Deep copying

As I'll get to in the next paragraph deep copying the data will leave the image rotated because the image is rotated in the underlying data.

UIImage *newImage = [UIImage imageWithData:UIImagePNGRepresentation(oldImage)];

This will copy the data but will require setting the orientation property before handing it to something like UIImageView for proper display.

Another way to deep copy would be to draw into the context and grab the result. Assume a zebra.

UIGraphicsBeginImageContext(zebra!.size)
zebra!.drawInRect(CGRectMake(0, 0, zebra!.size.width, zebra!.size.height))
let copy = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

Deep copy and Rotation

Rotating a CGImage has been already been answered. It also happens that this rotated image is a new CGImage that can be used to create a UIImage.

回答2:

This seems to work but you might face some memory problems depending on what you do with newImage:

CGImageRef newCgIm = CGImageCreateCopy(oldImage.CGImage);
UIImage *newImage = [UIImage imageWithCGImage:newCgIm scale:oldImage.scale orientation:oldImage.imageOrientation];

回答3:

This should work:

UIImage *newImage = [UIImage imageWithCGImage:oldImage.CGImage];

回答4:

UIImage *newImage = [UIImage imageWithData:UIImagePNGRepresentation(oldImage)];

回答5:

I think you need to create an image context (CGContextRef). Draw the UIImage.CGImage into the context with method CGContextDrawImage(...), then get the image from the context with CGBitmapContextCreateImage(...). With such routine, I'm sure you can get the real copy of the image you want. Hope it's helped you.