added pixel-to-color conversion methods

Bitmap/AppKit/Helpers.swift

@@ -18,4 +18,19 @@ extension Pixel {
 	public init(_ cgColor: CGColor) {
 		self.init(NSColor(cgColor: cgColor)!)
 	}
+
+	/**
+	Creates a new `NSColor` from the pixel, taking alpha premultiplication into account.
+
+	There is some loss of information, e.g. a fully transparent red pixel loses information about its color due to alpha premultiplication. For fully transparent pixels, this method returns a fully transparent black color (`r=g=b=a=0`).
+	*/
+	var nsColor: NSColor {
+		guard self.alpha > 0 else { return #colorLiteral(red: 1, green: 1, blue: 1, alpha: 0) }
+		let alpha = CGFloat(self.alpha) // stupid premultiplication
+		let color = NSColor(red:   CGFloat(red)   / alpha,
+							green: CGFloat(green) / alpha,
+							blue:  CGFloat(blue)  / alpha,
+							alpha: alpha / 255)
+		return color
+	}
 }

Bitmap/UIKit/Helpers.swift

@@ -17,4 +17,19 @@ extension Pixel {
 	public init(_ cgColor: CGColor) {
 		self.init(UIColor(cgColor: cgColor))
 	}
+
+	/**
+	Creates a new `UIColor` from the pixel, taking alpha premultiplication into account.
+
+	There is some loss of information, e.g. a fully transparent red pixel loses information about its color due to alpha premultiplication. For fully transparent pixels, this method returns a fully transparent black color (`r=g=b=a=0`).
+	*/
+	var uiColor: UIColor {
+		guard self.alpha > 0 else { return #colorLiteral(red: 0, green: 0, blue: 0, alpha: 0) }
+		let alpha = CGFloat(self.alpha) // stupid premultiplication
+		let color = UIColor(red:   CGFloat(red)   / alpha,
+							green: CGFloat(green) / alpha,
+							blue:  CGFloat(blue)  / alpha,
+							alpha: alpha / 255)
+		return color
+	}
 }