How to set the alpha of an UIImage in SWIFT programmatically?

Question

I found a lot solutions here but not for Swift, and I know you can do this with a UIImageView, but in my case i need an programmatically set alpha transparent background image for an UIButton. Best would be an UIImage extension!

let img = UIImage(named: "imageWithoutAlpha")
var imgInsets = UIEdgeInsetsMake(0, 24, 0, 24)
image = image!.resizableImageWithCapInsets(imgInsets)

let myButton = UIButton(frame: CGRect(x: 50, y: 50, width: img!.size.width, height: img!.size.height))
myButton.setBackgroundImage(img, forState: UIControlState.Normal)
myButton.contentEdgeInsets = UIEdgeInsetsMake(0, 20, 0, 20)
myButton.setTitle("Startbutton", forState: UIControlState.Normal)
myButton.setTitleColor(UIColor.blackColor(), forState: UIControlState.Normal)
myButton.sizeToFit()
view.addSubview(myButton)

Current result:

Desired result:

Solution 1

Luckily I was able to help myself and would like to share with you my solution:

Swift 3

// UIImage+Alpha.swift

extension UIImage {  

    func alpha(_ value:CGFloat) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(size, false, scale)
        draw(at: CGPoint.zero, blendMode: .normal, alpha: value)
        let newImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return newImage!   
    }
}

The above new Swift extension I added to my project and then I changed the UIButton example as follows, to have an alpha transparent background image with a transparency of 50%.

let img = UIImage(named: "imageWithoutAlpha")!.alpha(0.5)
let myButton = UIButton()

myButton.setBackgroundImage(img, for: .normal)

Solution 2

The easiest way is to put your UIImage inside a UIImageView and set the alpha there.

let image = UIImage(named: "imageWithoutAlpha")
let imageView = UIImageView(image: image)
imageView.alpha = 0.5

myButton.setBackgroundImage(image, forState: UIControlState.Normal)

Solution 3

Swift 5, iOS 10+

If your app doesn't support operating systems prior to iOS 10 then you can take advantage of the more robust UIGraphicsImageRenderer UIKit drawing API.

extension UIImage {
    func withAlpha(_ a: CGFloat) -> UIImage {
        return UIGraphicsImageRenderer(size: size, format: imageRendererFormat).image { (_) in
            draw(in: CGRect(origin: .zero, size: size), blendMode: .normal, alpha: a)
        }
    }
}

Usage

let img = UIImage(named: "someImage")?.withAlpha(0.5)

Solution 4

I was able to set the alpha using the following code:

self.imageView.image = UIImageView(image: "image.png")
imageView.alpha = 0.5

View more solutions

Comments

[Peter Kreinz]

sorry, but that makes no sense!

[leonardo]

What exactly doesn't make sense?

[Peter Kreinz]

I tried your solution, but the transparency/opacity of the background image will not change

[leonardo]

Well, try again because it works 100%. Test properly before downvoting answers.

[dumbledad]

Not sure why this was down-voted: it proved an easy fix for me.

[ChucK]

In swift 2 I had to replace kCGBlendModeMultiply with CGBlendMode.Multiply, see stackoverflow.com/questions/31309521/…

[Add080bbA]

Answer to another question. Question is not "how to change opacity of UIImageView". Question is "how to change alpha of UIImage"

[Add080bbA]

Answer to another question. Question is not "how to change opacity of UIImageView". Question is "how to change alpha of UIImage"

[Patonz]

can you post an swift 3 version?

[Peter Kreinz]

swift 3 version added!

[Ethan G]

This seems to ignore color. I have an image with colors in it and when I apply this method, the resulting image is gray (but it does have the appropriate alpha).

[Ethan G]

In reading some of developer.apple.com/library/content/documentation/… it seems like .normal should work fine. Anyone else experiencing this "gray-scale" effect?

[gondo]

You are creating imageView but then never using it. You can't set UIView via UIButton.setBackgroundImage.

[Jan Nash]

I have to agree with gondo here.