Swift NSImage to CGImage

Question

How can I convert a NSImage to CGImage in Swift? In Objective-C I did it like this:

- (CGImageRef)CGImage { NSData *imageData = self.TIFFRepresentation; CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)imageData, NULL); CGImageRef maskRef = CGImageSourceCreateImageAtIndex(source, 0, NULL); return maskRef; }

Now I tried with:

extension NSImage { var CGImage: CGImageRef { get { let imageData = self.TIFFRepresentation let source = CGImageSourceCreateWithData(imageData as CFDataRef, nil) let maskRef = CGImageSourceCreateImageAtIndex(source, UInt(0), nil) return maskRef; } } }

I can't compile, I'm getting the error: Could not find an overload for 'init' that accepts the supplied arguments' at the line let maskRef ...

Eric · Accepted Answer · 2019-06-09 21:12:21Z

38

Here's what I'm using to convert NSImage to CGImage:

let image = NSImage(named:"image") if let image = image { var imageRect = CGRect(x: 0, y: 0, width: image.size.width, height: image.size.height) let imageRef = image.cgImage(forProposedRect: &imageRect, context: nil, hints: nil) }

edited Jun 9, 2019 at 21:12

Eric

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answered Jan 3, 2015 at 20:17

az_

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2 Comments

rob mayoff Over a year ago

You can pass nil for proposedRect and get the same result.

Peter Schorn Over a year ago

You should use CGRect(origin: .zero, size: image.size) instead of CGRect(x: 0, y: 0, width: image.size.width, height: image.size.height)

Jay Mehta · Accepted Answer · 2021-03-17 06:45:57Z

Swift 5 code :-

if let image = NSImage(named: "Icon"){ let cgImage = image.cgImage(forProposedRect: nil, context: nil, hints: nil) }

Lupurus · Accepted Answer · 2014-07-06 12:48:02Z

9

Ah, I found the solution. It's because in Swift you only the an unmanaged object (I just did not really understand, what this means). But this code now works:

extension NSImage { var CGImage: CGImageRef { get { let imageData = self.TIFFRepresentation let source = CGImageSourceCreateWithData(imageData as CFDataRef, nil).takeUnretainedValue() let maskRef = CGImageSourceCreateImageAtIndex(source, UInt(0), nil) return maskRef.takeUnretainedValue(); } } }

answered Jul 6, 2014 at 12:48

Lupurus

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3 Comments

ovejka Over a year ago

Right. It's from Apple's book:

When Swift imports APIs that have not been annotated, the compiler cannot automatically memory manage the returned Core Foundation objects. Swift wraps these returned Core Foundation objects in an Unmanaged<T> structure. All indirectly returned Core Foundation objects are unmanaged as well.

Excerpt From: Apple Inc. “Using Swift with Cocoa and Objective-C.” iBooks. itunes.apple.com/ru/book/using-swift-cocoa-objective/…

Duck Over a year ago

what is takeUnretainedValue? there is no such thing on swift.

Todd Over a year ago

takeUnretainedValue() isn't available in Swift 5 (the code executes as expected by simply omitting it).

Darkwonder · Accepted Answer · 2018-04-03 11:03:40Z

For Swift 4.0, XCode 9.2:

extension NSImage { @objc var CGImage: CGImage? { get { guard let imageData = self.tiffRepresentation else { return nil } guard let sourceData = CGImageSourceCreateWithData(imageData as CFData, nil) else { return nil } return CGImageSourceCreateImageAtIndex(sourceData, 0, nil) } } }

This is very similar to the solution provided almost one year before: stackoverflow.com/a/62298762/1974224. Can you add details on why this answer is different from that one?

madx · Accepted Answer · 2020-06-10 08:10:13Z

A Swift 5 implementation:

extension NSImage { var CGImage: CGImage { get { let imageData = self.tiffRepresentation! let source = CGImageSourceCreateWithData(imageData as CFData, nil).unsafelyUnwrapped let maskRef = CGImageSourceCreateImageAtIndex(source, Int(0), nil) return maskRef.unsafelyUnwrapped } } }

Care to be taken when using unsafelyUnwrapped. Even Apple has a big red warning on the documentation page for this feature.
And also you're force unwrapping tiffRepresentation, which can lead to crashes in case of nil values.

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