Check if an image is dark in Swift.

imageDarkness.swift

func imageIsDark(image: CGImage) -> Bool {
    let redLum = 0.299
    let greenLum = 0.578
    let blueLum = 0.114
    let maxLum = 150.0
    guard let imageData = image.dataProvider?.data else { return false }
    guard let ptr = CFDataGetBytePtr(imageData) else { return false }
    let length = CFDataGetLength(imageData)
    let threshold = Int(Double(image.width * image.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 = (redLum * Double(r) + greenLum * Double(g) + blueLum * Double(b))
        if luminance < maxLum {
            darkPixels += 1
            if darkPixels > threshold {
                return true
            }
        }
    }
    return false
}