Swift 3 Colour Space macOS not IOS - macos

Question

How can I convert an RGB image into its grayscaled colour space? I can find a lot of code for iOS but non for macOS.. And the Apple's documentations are all in objective C....
let width = image.size.width
let height = image.size.height
let imageRect = NSMakeRect(0, 0, width, height);
let colorSpace = CGColorSpaceCreateDeviceGray();
let bits = image.representations.first as! NSBitmapImageRep;
bitmap!.representationUsingType(NSBitmapImageFileType.NSPNGFileType, properties: nil)
let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue);
let context = CGContext(data: nil, width: Int(width), height: Int(height), bitsPerComponent: 8, bytesPerRow: 0, space: colorSpace, bitmapInfo: bitmapInfo.rawValue);
context.draw(image.cgImage!, in : imageRect);// and this line is wrong obviously..
This is what I have got so far..just copy and pasting from the internet.. but I have no idea on how to go further...

Answer 1

I have found an interesting way to do this.. My code are simply copied from the three sources below.
how to create grayscale image from nsimage in swift?
Greyscale Image using COCOA and NSImage
Changing the Color Space of NSImage: The second reply
My Code:
func saveImage(image:NSImage, destination:URL) throws{
let rep = greyScale(image);
var data = rep.representation(using: NSJPEGFileType, properties: [:]);
try data?.write(to: destination);
}
// rgb2gray
func greyScale(image: NSImage) -> NSBitmapImageRep{
let w = image.size.width
let h = image.size.height
let imageRect : NSRect! = NSMakeRect(0,0, w, h);
let colourSpace : ColourSpace! = CGColorSpaceCreateDeviceGray();
let context : CGContext! = CGContext(data: nil, width: Int(w),
height: Int(h), bitsPerComponent: 8,
bytesPerRow: 0, space: colorSpace,
bitmapInfo: CGImageAlphaInfo.none.rawValue);
context.draw(nsImageToCGImage(image: image), in: imageRect);
let greyImage : CGImage! = context.makeImage();
return NSBitmapImageRep(cgImage: greyImage);
}
func nsImageToCGImage(image: NSImage) -> CGImage{
if let imageData = image.tiffRepresentation as NSData! {
let imageSource : CGImageSource! = CGImageSourceCreateWithData(imageData,
nil);
let image = CGImageSourceCreateImageAtIndex(imageSource, 0, nil);
return image;
}
return nil;
}
I am still trying to understand the principle behind.

Answer 2

You can try CIFilter. The annoyance is that you have to convert back and forth between NSImage and CIImage:
import Cocoa
import CoreImage
let url = Bundle.main.url(forResource: "image", withExtension: "jpg")!
let image = CIImage(contentsOf: url)!
let bwFilter = CIFilter(name: "CIColorControls", withInputParameters: ["inputImage": image, "inputSaturation": 0.0])!
if let ciImage = bwFilter.outputImage {
let rep = NSCIImageRep(ciImage: ciImage)
let nsImage = NSImage(size: rep.size)
nsImage.addRepresentation(rep)
// nsImage is now your black-and-white image
}