Ios 检查UIImage的分段是亮还是暗

我试图覆盖一个V形按钮，允许用户关闭当前视图。雪佛龙的颜色在深色图像上应为浅色，在浅色图像上应为深色。我附上了我描述的内容的截图

但是，在尝试计算图像的明暗度时，会对性能产生重大影响，我就是这样做的（在“CGImage”上操作）：

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在将图像安装到视图后，这里有两个选项可用于查找图像的大小：

一旦你得到了它，你就可以知道雪佛龙在哪里（你可能需要先转换它的框架）

如果性能仍然不足，我会考虑使用CoreImage来执行计算：

使用CoreImage有几种方法，但获得平均值是最简单的

var isDark: Bool {
    guard let imageData = dataProvider?.data else { return false }
    guard let ptr = CFDataGetBytePtr(imageData) else { return false }
    let length = CFDataGetLength(imageData)
    let threshold = Int(Double(width * height) * 0.45)
    var darkPixels = 0
    for i in stride(from: 0, to: length, by: 4) {
        let r = ptr[i]
        let g = ptr[i + 1]
        let b = ptr[i + 2]
        let luminance = (0.299 * Double(r) + 0.587 * Double(g) + 0.114 * Double(b))
        if luminance < 150 {
            darkPixels += 1
            if darkPixels > threshold {
                return true
            }
        }
    }
    return false
}

extension UIImage {
    var isDark: Bool {
        return cgImage?.isDark ?? false
    }
}

extension CGImage {
    var isDark: Bool {
        guard let imageData = dataProvider?.data else { return false }
        guard let ptr = CFDataGetBytePtr(imageData) else { return false }
        let length = CFDataGetLength(imageData)
        let threshold = Int(Double(width * height) * 0.45)
        var darkPixels = 0
        for i in stride(from: 0, to: length, by: 4) {
            let r = ptr[i]
            let g = ptr[i + 1]
            let b = ptr[i + 2]
            let luminance = (0.299 * Double(r) + 0.587 * Double(g) + 0.114 * Double(b))
            if luminance < 150 {
                darkPixels += 1
                if darkPixels > threshold {
                    return true
                }
            }
        }
        return false
    }

    func cropping(to rect: CGRect, scale: CGFloat) -> CGImage? {
        let scaledRect = CGRect(x: rect.minX * scale, y: rect.minY * scale, width: rect.width * scale, height: rect.height * scale)
        return self.cropping(to: scaledRect)
    }
}

extension UIImageView {
    func hasDarkImage(at subsection: CGRect) -> Bool {
        guard let image = image, let aspectSize = aspectFillSize() else { return false }
        let scale = image.size.width / frame.size.width
        let cropRect = CGRect(x: (aspectSize.width - frame.width) / 2,
                              y: (aspectSize.height - frame.height) / 2,
                              width: aspectSize.width,
                              height: frame.height)
        let croppedImage = image.cgImage?
            .cropping(to: cropRect, scale: scale)?
            .cropping(to: subsection, scale: scale)
        return croppedImage?.isDark ?? false
    }

    private func aspectFillSize() -> CGSize? {
        guard let image = image else { return nil }
        var aspectFillSize = CGSize(width: frame.width, height: frame.height)
        let widthScale = frame.width / image.size.width
        let heightScale = frame.height / image.size.height
        if heightScale > widthScale {
            aspectFillSize.width = heightScale * image.size.width
        }
        else if widthScale > heightScale {
            aspectFillSize.height = widthScale * image.size.height
        }
        return aspectFillSize
    }
}