判断像素点是否是黑色

black_color.swift

let isBlackColor = { (x: Int, y: Int) -> Bool in
    let byteIndex = (bytesPerRow * y) + x * bytesPerPixel
    let r = CGFloat(rawData[byteIndex])
    let g = CGFloat(rawData[byteIndex + 1])
    let b = CGFloat(rawData[byteIndex + 2])
    // https://stackoverflow.com/a/12043228
    let luma = 0.2126 * r + 0.7152 * g + 0.0722 * b
    return luma < 40
}