How do I create a UIImage from a CGImage in Swift?

Question

I'm trying to create a UIImage from the ALAssetsGroup#posterImage method. In Objective-C, I could simply call [UIImage imageWithCGImage:group.posterImage] but in Swift, UIImage(CGImage: group.posterImage) gives me a compiler error:

Could not find an overload for 'init' that accepts the supplied arguments

What am I doing wrong?

The real problem here is the "could not find an overload" message is not very informative. I suggest you file an enhancement request about that. Swift could do a lot better with its error messages. — matt, Jun 20 '14 at 04:31
@Fattie Check the date: this question was about the original version of Swift, not the current version. And there was no crash - it was a compiler error. — Bill, Feb 21 '23 at 19:40

Firo · Answer 1 · 2014-06-20T11:06:44.303

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If you look at the docs in Xcode6 you will see that posterImage() returns a Unmanaged<CGImage>! (in Swift, in ObjC it returns a CGImageRef). After some investigation from the docs I found this:

When you receive an unmanaged object from an unannotated API, you should immediately convert it to a memory managed object before you work with it.

So your solution would be:

UIImage(CGImage: group.posterImage().takeUnretainedValue())

edited Jun 20 '14 at 11:06

answered Jun 20 '14 at 04:13

Firo

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That doesn't help, but the error message I got from that code did: "no method for `() -> Unmanaged!`". So `posterImage` is a `func` rather than a property. Adding parens after posterImage did the trick. – Bill Jun 20 '14 at 11:00

score 12 · Answer 2 · edited Feb 20 '23 at 19:00

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Update for 2023 syntax:

someImage = UIImage(cgImage: someCGImage)

A typical example is taking the image from a CALayer:

someImage = UIImage(cgImage: donorLayer.contents as! CGImage)

Are you sure group.posterImage is not an optional?

have you tried

var img = UIImage(CGImage: group.posterImage!) // 2010s syntax

edited Feb 20 '23 at 19:00

Fattie

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answered Jun 20 '14 at 03:56

Albert James Teddy

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Yes, I'm sure. The above code gives the same compiler error. – Bill Jun 20 '14 at 10:57
This is the normal approach and works perfectly. – Fattie Feb 20 '23 at 18:56

score 3 · Answer 3 · answered May 22 '17 at 21:17

Here's an example that should work for you with Xcode 8.3:

    let frame = CGRect(origin: CGPoint(x: 0, y: 0), size: CGSize(width: 1920, height: 1080))
    let cgImage = CIContext().createCGImage(CIImage(color: .black()), from: frame)!
    let uiImage = UIImage(cgImage: cgImage)

score 2 · Answer 4 · answered Aug 02 '16 at 05:56

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Use init with CGIImage:

UIImage.init(CGImage: group.posterImage, scale: self.scale, orientation: .UpMirrored)

answered Aug 02 '16 at 05:56

Pichirichi

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if i have to increase the scale of the image how would be that possible ? – niks290192 Dec 23 '16 at 08:11
just set the scale you want with a CGFloat value – Pichirichi Jan 01 '17 at 09:00

How do I create a UIImage from a CGImage in Swift?

4 Answers4

Update for 2023 syntax: