A function to render a UIImage to grayscale

imageToGrayScale.swift

// Using it:
// imageview.image = imageToGrayScale(imageview.image!)

func imageToGrayScale(image: UIImage) -> UIImage {

    var imageRect = CGRectMake(0,0,CGFloat(CGImageGetWidth(image.CGImage)),CGFloat(CGImageGetHeight(image.CGImage)))
    
    var colorSpace = CGColorSpaceCreateDeviceGray()
    var context = CGBitmapContextCreate(nil, CGImageGetWidth(image.CGImage), CGImageGetHeight(image.CGImage), 8, 0, colorSpace, CGBitmapInfo.ByteOrderDefault)
    CGContextDrawImage(context, imageRect, image.CGImage)
    
    var imageRef = CGBitmapContextCreateImage(context)
    
    var newImage = UIImage(CGImage: imageRef!, scale: CGFloat(CGImageGetWidth(image.CGImage))/image.size.width, orientation: UIImageOrientation.Up)
    
    return newImage!;
}