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 ...

score 38 · Answer 1 · edited Jun 09 '19 at 21:12

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 09 '19 at 21:12

Eric

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answered Jan 03 '15 at 20:17

az_

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12

You can pass `nil` for `proposedRect` and get the same result. – rob mayoff Oct 27 '15 at 19:40
You should use `CGRect(origin: .zero, size: image.size)` instead of `CGRect(x: 0, y: 0, width: image.size.width, height: image.size.height)` – Peter Schorn Dec 19 '21 at 03:27

Jay Mehta · Answer 2 · 2021-03-17T06:45:57.737

18

Swift 5 code :-

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

edited Mar 17 '21 at 06:45

answered Dec 19 '17 at 13:33

Jay Mehta

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score 9 · Answer 3 · answered Jul 06 '14 at 12:48

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 06 '14 at 12:48

Lupurus

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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 structure. All indirectly returned Core Foundation objects are unmanaged as well.` Excerpt From: Apple Inc. “Using Swift with Cocoa and Objective-C.” iBooks. https://itunes.apple.com/ru/book/using-swift-cocoa-objective/id888894773?l=en&mt=11 – ovejka Jul 06 '14 at 12:52
5

what is takeUnretainedValue? there is no such thing on swift. – Duck Mar 01 '15 at 17:33
1

`takeUnretainedValue()` isn't available in Swift 5 (the code executes as expected by simply omitting it). – Todd Nov 06 '19 at 14:13

score 2 · Answer 4 · answered Apr 03 '18 at 11:03

2

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)
       }
    }
}

answered Apr 03 '18 at 11:03

Darkwonder

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This is very similar to the solution provided almost one year before: https://stackoverflow.com/a/62298762/1974224. Can you add details on why this answer is different from that one? – Cristik Aug 31 '21 at 09:58
@Cristik its more error-safe and shorer – Andrew_STOP_RU_WAR_IN_UA Jan 12 '22 at 04:11

score 1 · Answer 5 · answered Jun 10 '20 at 08:10

1

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
        }
    }
}

answered Jun 10 '20 at 08:10

madx

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Care to be taken when using `unsafelyUnwrapped`. Even Apple has a big red warning on the [documentation](https://developer.apple.com/documentation/swift/optional/1641793-unsafelyunwrapped) page for this feature. – Cristik Aug 31 '21 at 08:40
And also you're force unwrapping `tiffRepresentation`, which can lead to crashes in case of nil values. – Cristik Aug 31 '21 at 08:51

Swift NSImage to CGImage

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