Add a background if the image is too dark and we are in dark mode.

iOS/UIKit Extensions/UIImage-Extensions.swift

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+//
+//  UIImage-Extensions.swift
+//  NetNewsWire
+//
+//  Created by Maurice Parker on 9/29/19.
+//  Copyright © 2019 Ranchero Software. All rights reserved.
+//
+
+import UIKit
+
+extension CGImage {
+
+	func isDark() -> Bool {
+		guard let imageData = self.dataProvider?.data else { return false }
+		guard let ptr = CFDataGetBytePtr(imageData) else { return false }
+		
+		let length = CFDataGetLength(imageData)
+		var visiblePixels = 0
+		var darkPixels = 0
+		
+		for i in stride(from: 0, to: length, by: 4) {
+			
+			let r = ptr[i]
+			let g = ptr[i + 1]
+			let b = ptr[i + 2]
+			let a = ptr[i + 3]
+			let luminance = (0.299 * Double(r) + 0.587 * Double(g) + 0.114 * Double(b))
+			
+			if Double(a) > 0.0 {
+				visiblePixels += 1
+				if luminance < 50 {
+					darkPixels += 1
+				}
+			}
+			
+		}
+		
+		return Double(darkPixels) / Double(visiblePixels) > 0.4
+	}
+	
+}
+
+extension UIImage {
+	func isDark() -> Bool {
+		return self.cgImage?.isDark() ?? false
+	}
+}