Fix an issue with grayscale images

CHANGELOG.md

@@ -15,6 +15,7 @@
 - Add an optimization that loads local resources with `file` and `data` schemes quickly without using `DataLoader` and `URLSession`. If you rely on the existing behavior, this optimization can be turned off using the `isLocalResourcesSupportEnabled` configuration option. https://github.com/kean/Nuke/pull/779
 - Deprecate `ImagePipeline.Configuration.dataCachingQueue` and perform data cache lookups on the pipeline's queue, reducing the amount of context switching
 - Update the infrastructure for coalescing image-processing tasks to use the task-dependency used for other operations
+- Fix [#782], an issue with grayscale images (8 bpp) not being rendered correctly when `Resize` processor is used
 
 ## Nuke 12.5
 

Sources/Nuke/Internal/Graphics.swift

@@ -160,7 +160,7 @@ extension PlatformImage {
 
 private extension CGContext {
     static func make(_ image: CGImage, size: CGSize, alphaInfo: CGImageAlphaInfo? = nil) -> CGContext? {
-        let alphaInfo: CGImageAlphaInfo = alphaInfo ?? (image.isOpaque ? .noneSkipLast : .premultipliedLast)
+        let alphaInfo: CGImageAlphaInfo = alphaInfo ?? preferredAlphaInfo(for: image)
 
         // Create the context which matches the input image.
         if let ctx = CGContext(
@@ -189,6 +189,17 @@ private extension CGContext {
             bitmapInfo: alphaInfo.rawValue
         )
     }
+
+    /// - See https://developer.apple.com/library/archive/documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_context/dq_context.html#//apple_ref/doc/uid/TP30001066-CH203-BCIBHHBB
+    private static func preferredAlphaInfo(for image: CGImage) -> CGImageAlphaInfo {
+        guard image.isOpaque else {
+            return .premultipliedLast
+        }
+        if image.bitsPerPixel == 8 {
+            return .none // The only pixel format supported for grayscale CS
+        }
+        return .premultipliedLast
+    }
 }
 
 extension CGFloat {