How to calculate the average color of a UIImage?

Question

I want to build an app that lets the user select an image and it outputs the \"average color\".

For example, this image:

The average color would be a gr

Answer 1

I end up with this class extension:

extension UIImage {

func averageColor(alpha : CGFloat) -> UIColor {

    let rawImageRef : CGImageRef = self.CGImage!
    let  data : CFDataRef = CGDataProviderCopyData(CGImageGetDataProvider(rawImageRef))!
    let rawPixelData  =  CFDataGetBytePtr(data);

    let imageHeight = CGImageGetHeight(rawImageRef)
    let imageWidth  = CGImageGetWidth(rawImageRef)
    let bytesPerRow = CGImageGetBytesPerRow(rawImageRef)
    let stride = CGImageGetBitsPerPixel(rawImageRef) / 6

    var red = 0
    var green = 0
    var blue  = 0

    for row in 0...imageHeight {
        var rowPtr = rawPixelData + bytesPerRow * row
        for _ in 0...imageWidth {
            red    += Int(rowPtr[0])
            green  += Int(rowPtr[1])
            blue   += Int(rowPtr[2])
            rowPtr += Int(stride)
        }
    }

    let  f : CGFloat = 1.0 / (255.0 * CGFloat(imageWidth) * CGFloat(imageHeight))
    return UIColor(red: f * CGFloat(red), green: f * CGFloat(green), blue: f * CGFloat(blue) , alpha: alpha)
}

}