UIImage from CALayer in iOS

Question

In my application, I have created a CALayer (with a few sublayers - the CALayer is composed of shapes added as sublayers).

I am trying to create a UIImage that I will be able to upload to a server (I have the code for this). However, I can't figure out how to add the CALayer to a UIImage.

Is this possible?

score 113 · Accepted Answer · edited Mar 06 '20 at 19:35

113

Sounds like you want to render your layer into a UIImage. In that case, the method below should do the trick. Just add this to your view or controller class, or create a category on CALayer.

Obj-C

- (UIImage *)imageFromLayer:(CALayer *)layer
{
  UIGraphicsBeginImageContextWithOptions(layer.frame.size, NO, 0);

  [layer renderInContext:UIGraphicsGetCurrentContext()];
  UIImage *outputImage = UIGraphicsGetImageFromCurrentImageContext();

  UIGraphicsEndImageContext();

  return outputImage;
}

Swift

func imageFromLayer(layer:CALayer) -> UIImage {
    UIGraphicsBeginImageContextWithOptions(layer.frame.size, layer.isOpaque, 0)
    layer.render(in: UIGraphicsGetCurrentContext()!)
    let outputImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return outputImage!
}

edited Mar 06 '20 at 19:35

Genki

3,055
2
29
42

answered Aug 11 '10 at 01:07

Todd Yandell

14,656
2
50
37

1

Exchange for `UIGraphicsBeginImageContextWithOptions(layer.frame.size, YES, 0);` – Jonny Aug 20 '13 at 07:56
11

I would recommend using `UIGraphicsBeginImageContextWithOptions(layer.frame.size, layer.opaque, 0);` – jfeldman Dec 04 '13 at 20:12
how would you update this to render a portion (given a rect in the layer) of the CALayer to an image and not the entire frame? – zumzum Jan 09 '20 at 18:39
UIGraphicsGetCurrentContext() returns nil – Hogdotmac Jan 12 '23 at 16:11

score 18 · Answer 2 · answered Apr 25 '13 at 09:48

18

Todd's answer is correct, however for retina screens there should be a little difference:

- (UIImage *)imageFromLayer:(CALayer *)layer
{

    if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)])
        UIGraphicsBeginImageContextWithOptions([layer frame].size, NO, [UIScreen mainScreen].scale);
    else
        UIGraphicsBeginImageContext([layer frame].size);

    [layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *outputImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return outputImage;
}

answered Apr 25 '13 at 09:48

Ömer Faruk Gül

965
1
10
22

4

Specifying `0` for `UIGraphicsBeginImageContextWithOptions()`'s `scale` arg defaults it to use `UIScreen.mainScreen.scale`. _(Per the docs, “The scale factor to apply to the bitmap. If you specify a value of 0.0, the scale factor is set to the scale factor of the device’s main screen.”)_ Your answer functionally offers no improvement over @Todd Yandell's. – Slipp D. Thompson Sep 16 '16 at 08:56

score 12 · Answer 3 · answered Aug 18 '16 at 00:42

I have created a Swift extension based for this:

extension UIImage {
    class func imageWithLayer(layer: CALayer) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(layer.bounds.size, layer.opaque, 0.0)
        layer.renderInContext(UIGraphicsGetCurrentContext()!)
        let img = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return img
    }
}

The usage:

var gradient = CAGradientLayer()
gradient.colors = [UIColor.redColor().CGColor, UIColor.blueColor().CGColor]
gradient.frame = CGRect(x: 0, y: 0, width: 200, height: 200)

let image = UIImage.imageWithLayer(gradient)

score 6 · Answer 4 · edited Feb 03 '18 at 14:42

6

Swift 3 version with a little bit of error checking for context.

extension UIImage {
  class func image(from layer: CALayer) -> UIImage? {
    UIGraphicsBeginImageContextWithOptions(layer.bounds.size, 
  layer.isOpaque, UIScreen.main.scale)

    defer { UIGraphicsEndImageContext() }

    // Don't proceed unless we have context
    guard let context = UIGraphicsGetCurrentContext() else {
      return nil
    }

    layer.render(in: context)
    return UIGraphicsGetImageFromCurrentImageContext()
  }
}

edited Feb 03 '18 at 14:42

Valérian

1,068
8
10

answered May 31 '17 at 18:49

Justin Wright

163
2
9

1

You can use `defer` to handle the `UIGraphicsEndImageContext()` – Valérian Feb 01 '18 at 10:27
Great suggestion. Updated to user defer. – Justin Wright Feb 02 '18 at 23:31

UIImage from CALayer in iOS

4 Answers4

Linked