Saving CGImageRef to a png file?

by

Using CGImageDestination and passing kUTTypePNG is the correct approach. Here’s a quick snippet:

@import MobileCoreServices; // or `@import CoreServices;` on Mac
@import ImageIO;

BOOL CGImageWriteToFile(CGImageRef image, NSString *path) {
    CFURLRef url = (__bridge CFURLRef)[NSURL fileURLWithPath:path];
    CGImageDestinationRef destination = CGImageDestinationCreateWithURL(url, kUTTypePNG, 1, NULL);
    if (!destination) {
        NSLog(@"Failed to create CGImageDestination for %@", path);
        return NO;
    }

    CGImageDestinationAddImage(destination, image, nil);

    if (!CGImageDestinationFinalize(destination)) {
        NSLog(@"Failed to write image to %@", path);
        CFRelease(destination);
        return NO;
    }

    CFRelease(destination);
    return YES;
}

You’ll need to add ImageIO and CoreServices (or MobileCoreServices on iOS) to your project and include the headers.

If you’re on iOS and don’t need a solution that works on Mac too, you can use a simpler approach:

// `image` is a CGImageRef
// `path` is a NSString with the path to where you want to save it
[UIImagePNGRepresentation([UIImage imageWithCGImage:image]) writeToFile:path atomically:YES];

In my tests, the ImageIO approach was about 10% faster than the UIImage approach on my iPhone 5s. In the simulator, the UIImage approach was faster. It’s probably worth testing each for your particular situation on the device if you’re really concerned with performance.

More Related Contents:

  1. NSObject subclass in Swift: hash vs hashValue, isEqual vs ==
  2. Is there a way to set associated objects in Swift?
  3. Create and export an animated gif via iOS?
  4. Input from the keyboard in command line application
  5. How to prevent circular reference when Swift bridging header imports a file that imports Hopscotch-Swift.h itself
  6. Convert String to URL (Why is resulting variable nil)
  7. Iterate through files in a folder and its subfolders using Swift’s FileManager
  8. Load local web files & resources in WKWebView
  9. Using Swift CFunctionPointer to pass a callback to CoreMIDI API
  10. Selecting global or object print function
  11. Front most window using CGWindowListCopyWindowInfo
  12. Saving WebView to PDF returns blank image?
  13. How to listen to global hotkeys with Swift in a macOS app?
  14. Why is the return value of String.addingPercentEncoding() optional?
  15. Is there a correct way to determine that an NSNumber is derived from a Bool using Swift?
  16. How do you use CGEventTapCreate in Swift?
  17. UITextField text change event
  18. How to create USDZ file using Xcode converter?
  19. Objective-C Introspection/Reflection
  20. How to test equality of Swift enums with associated values
  21. Swift constants: Struct or Enum
  22. Mixing C functions in an Objective-C class
  23. Swift async load image
  24. Cannot assign property in method of struct
  25. Are classes objects in Objective-C?
  26. Value of type ‘StorageMetadata’ has no member ‘downloadURL’
  27. How to pass one SwiftUI View as a variable to another View struct
  28. How to access NSWindow from @main App using only SwiftUI?
  29. What does the NS prefix mean?
  30. Use Cocoapods with an App Extension

Leave a Comment