Darken an UIImage

Question

I've searched a lot, but i can't find how you can darken an UIImageView if you press a button...

I've tried it with filters etc, but it did not work.

So how can I do this?

What have you tried? Unless you tell us what you have tried we may just be pointing you back at it. Some sort of code that you have tried or tutorials you have tried would be good, than we would have a good please to start. Help us help you. — Popeye, Apr 29 '13 at 12:24
i've tried this : CIFilter *filter = [CIFilter filterWithName:@"CIExposureAdjust"]; [filter setDefaults]; [filter setValue:[NSNumber numberWithFloat:-2.0] forKey:@"inputEV"]; backgroundView.layer.filters = [NSArray arrayWithObject:filter]; — user2332018, Apr 29 '13 at 12:26
do you need to be able to save the darkened image or does it just need to appear darkened on the screen? — Michael Behan, Apr 29 '13 at 12:28

score 2 · Answer 1 · answered Nov 21 '19 at 18:58

Not perfect but pretty good:

public extension UIImage {

    private enum BlendMode {
        case multiply // This results in colors that are at least as dark as either of the two contributing sample colors
        case screen // This results in colors that are at least as light as either of the two contributing sample colors

    }

    // A level of zero yeilds the original image, a level of 1 results in black
    func darken(level: CGFloat = 0.5) -> UIImage? {
        return blend(mode: .multiply, level: level)
    }

    // A level of zero yeilds the original image, a level of 1 results in white
    func lighten(level: CGFloat = 0.5) -> UIImage? {
        return blend(mode: .screen, level: level)
    }

    private func blend(mode: BlendMode, level: CGFloat) -> UIImage? {
        let context = CIContext(options: nil)

        var level = level
        if level < 0 { level = 0 }
        else if level > 1 { level = 1 }

        let filterName: String
        switch mode {
        case .multiply: // As the level increases we get less white
            level = abs(level - 1.0)
            filterName = "CIMultiplyBlendMode"
        case .screen: // As the level increases we get more white
            filterName = "CIScreenBlendMode"
        }

        let blender = CIFilter(name: filterName)!
        let backgroundColor = CIColor(color: UIColor(white: level, alpha: 1))

        guard let inputImage = CIImage(image: self) else { return nil }
        blender.setValue(inputImage, forKey: kCIInputImageKey)

        guard let backgroundImageGenerator = CIFilter(name: "CIConstantColorGenerator") else { return nil }
        backgroundImageGenerator.setValue(backgroundColor, forKey: kCIInputColorKey)
        guard let backgroundImage = backgroundImageGenerator.outputImage?.cropped(to: CGRect(origin: CGPoint.zero, size: self.size)) else { return nil }
        blender.setValue(backgroundImage, forKey: kCIInputBackgroundImageKey)

        guard let blendedImage = blender.outputImage else { return nil }

        guard let cgImage = context.createCGImage(blendedImage, from: blendedImage.extent) else { return nil }
        return UIImage(cgImage: cgImage)
    }
}

score 1 · Answer 2 · answered Mar 01 '17 at 10:06

You can add CAGradientLayer in imageView.Add below code into button press event.

let  gradientLayer   = CAGradientLayer()
gradientLayer.frame  =  self.imageView.bounds
gradientLayer.colors = [UIColor.clearColor().CGColor,UIColor.blackColor().CGColor] 
self.imageView.layer.addSublayer(gradientLayer)

score 1 · Answer 3 · answered Jul 29 '20 at 18:55

Updated answer for Swift 5:

func addGradientOverlay() {
  let  gradientLayer   = CAGradientLayer()
  gradientLayer.frame  =  self.imageView.bounds
  gradientLayer.colors = [UIColor.clear.cgColor,UIColor.black.cgColor] 
  self.imageView.layer.addSublayer(gradientLayer)
}

score 0 · Answer 4 · answered Apr 29 '13 at 12:33

To darken an UIImage you should try GPUImage, this framework has several filters like GPUImageBrightnessFilter, GPUImageContrastFilter and GPUImageSaturationFilter which may help to do what you need.

You can also find few examples on how to use this framework here.

score 0 · Answer 5 · edited May 23 '17 at 10:29

0

How about adding a black low opacity overlay subview to your original view?

There are several possible solutions here:

adding black overlay with 0.3 opacity over UIImageView

edited May 23 '17 at 10:29

Community

1
1

answered Apr 29 '13 at 12:35

sunshineDev

323
3
10

score -1 · Answer 6 · answered Apr 29 '13 at 12:36

For a really easy but dumb approach I would suggest you create a new UIView with a black background colour, set its alpha to 0.5 or less, set its frame to your UIImageView.frame and put it on top of it:

UIView *tmpView = [[UIView alloc] initWithFrame:myImageView.frame.size.height];
tmpView.backgroundColor = [UIColor blackColor];
tmpView.alpha = 0.5
//add it on button press
[myImageView addSubview:tmpView];

Although I would not recommend to do this, it might be easier to grasp than all those GPUImage Filters

Darken an UIImage

6 Answers6