UIImageWriteToSavedPhotosAlbum save as PNG with transparency?

Question

I\'m using UIImageWriteToSavedPhotosAlbum to save a UIImage to the user\'s photo album. The problem is that the image doesn\'t have transparency and is a JPG. I\'ve got the

Answer 1

As an alternative to creating a secondary UIImage for UIImageWriteToSavedPhotosAlbum the PNG data can be written directly using the PHPhotoLibrary.

Here is a UIImage extension named 'saveToPhotos' which does this:

extension UIImage {

    func saveToPhotos(completion: @escaping (_ success:Bool) -> ()) {

        if let pngData = self.pngData() {

            PHPhotoLibrary.shared().performChanges({ () -> Void in

                let creationRequest = PHAssetCreationRequest.forAsset()
                let options = PHAssetResourceCreationOptions()

                creationRequest.addResource(with: PHAssetResourceType.photo, data: pngData, options: options)

            }, completionHandler: { (success, error) -> Void in

                if success == false {

                    if let errorString = error?.localizedDescription  {
                        print("Photo could not be saved: \(errorString))")
                    }

                    completion(false)
                }
                else {
                    print("Photo saved!")

                    completion(true)
                }
            })
        }
        else {
            completion(false)
        }

    }
}

To use:

    if let image = UIImage(named: "Background.png") {
        image.saveToPhotos { (success) in
            if success {
                // image saved to photos
            }
            else {
                // image not saved
            }
        }
    }

Answer 2

As pointed out on this SO question there is a simple way to save pngs in your Photo Albums:

UIImage* image = ...;                                     // produce your image
NSData* imageData =  UIImagePNGRepresentation(image);     // get png representation
UIImage* pngImage = [UIImage imageWithData:imageData];    // rewrap
UIImageWriteToSavedPhotosAlbum(pngImage, nil, nil, nil);  // save to photo album

Answer 3

In Swift 5:

func pngFrom(image: UIImage) -> UIImage {
    let imageData = image.pngData()!
    let imagePng = UIImage(data: imageData)!
    return imagePng
}

Answer 4

This is a problem I have noticed before and reported on the Apple Developer Forums about a year ago. As far as I know it is still an open issue.

If you have a moment, please take the time to file a feature request at Apple Bug Report. If more people report this issue, it is more likely that Apple will fix this method to output non-lossy, alpha-capable PNG.

EDIT

If you can compose your image in memory, I think something like the following would work or at least get you started:

- (UIImage *) composeImageWithWidth:(NSInteger)_width andHeight:(NSInteger)_height {
    CGSize _size = CGSizeMake(_width, _height);
    UIGraphicsBeginImageContext(_size);

    // Draw image with Quartz 2D routines over here...

    UIImage *_compositeImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return _compositeImage;
}

//
// cf. https://developer.apple.com/iphone/library/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/FilesandNetworking/FilesandNetworking.html#//apple_ref/doc/uid/TP40007072-CH21-SW20
//

- (BOOL) writeApplicationData:(NSData *)data toFile:(NSString *)fileName {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    if (!documentsDirectory) {
        NSLog(@"Documents directory not found!");
        return NO;
    }
    NSString *appFile = [documentsDirectory stringByAppendingPathComponent:fileName];
    return ([data writeToFile:appFile atomically:YES]);
}

// ...

NSString *_imageName = @"myImageName.png";
NSData *_imageData = [NSData dataWithData:UIImagePNGRepresentation([self composeImageWithWidth:100 andHeight:100)];

if (![self writeApplicationData:_imageData toFile:_imageName]) {
    NSLog(@"Save failed!");
}

Answer 5

I created an extension of UIImage with safe unwrapping:

Extension

extension UIImage {
    func toPNG() -> UIImage? {
        guard let imageData = self.pngData() else {return nil}
        guard let imagePng = UIImage(data: imageData) else {return nil}
        return imagePng
    }
}

Usage:

let image = //your UIImage
if let pngImage = image.toPNG() {
     UIImageWriteToSavedPhotosAlbum(pngImage, nil, nil, nil)
}