objective-c - 使 UIImage 变暗

Question

我已经搜索了很多，但是如果您按下按钮，我找不到如何使 UIImageView 变暗...

我已经尝试使用过滤器等，但它不起作用。

那么我该怎么做呢？

Answer 1

不完美但相当不错：

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 2

您可以在 imageView 中添加 CAGradientLayer。将以下代码添加到按钮按下事件中。

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

Answer 3

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 4

要使 UIImage 变暗，您应该尝试GPUImage，该框架有几个过滤器，例如 GPUImageBrightnessFilter、GPUImageContrastFilter 和 GPUImageSaturationFilter，它们可能有助于满足您的需要。

您还可以在此处找到一些有关如何使用此框架的示例。

Answer 5

在原始视图中添加黑色低不透明度覆盖子视图怎么样？

这里有几种可能的解决方案：

在 UIImageView 上添加不透明度为 0.3 的黑色叠加层

Answer 6

对于一个非常简单但愚蠢的方法，我建议您创建一个具有黑色背景颜色的新 UIView，将其 alpha 设置为 0.5 或更低，将其框架设置为您的 UIImageView.frame 并将其放在上面：

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