使UIImage变暗

Question

我搜索了很多，但是如果你按一下按钮，我就找不到如何使UIImageView变暗......

我已尝试使用过滤器等，但它无效。

那我怎么能这样做呢？

Answer 1

Swift 5的更新答案：

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

Answer 2

要使UIImage变暗，你应该尝试GPUImage，这个框架有几个过滤器，如GPUImageBrightnessFilter，GPUImageContrastFilter和GPUImageSaturationFilter，可以帮助你做你需要的。

您还可以找到有关如何使用此框架here的几个示例。

Answer 3

如何在原始视图中添加黑色低不透明度叠加子视图？

这里有几种可能的解决方案：

adding black overlay with 0.3 opacity over UIImageView

Answer 4

您可以将以下代码中的imageView.Add中的CAGradientLayer添加到按钮事件中。

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

Answer 5

不完美，但还不错：

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)
    }
}

Answer 6

对于一个非常容易但又愚蠢的方法，我建议你创建一个黑色背景颜色的新UIView，将其alpha设置为0.5或更小，将其框架设置为UIImageView.frame并将其置于其上：

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];

虽然我不建议这样做，但它可能比所有那些GPUImage过滤器更容易掌握