diff --git a/src/Palette.cs b/src/Palette.cs
index e778597..15d35a3 100644
--- a/src/Palette.cs
+++ b/src/Palette.cs
@@ -45,6 +45,50 @@ namespace Palettizer2
 			GrayscaleCount += 1;
 		}
 
+		public void AddAlternateRowsFromOldPalette(StbImageSharp.ImageResult paletteImage)
+		{
+			// map row indices to original colors
+			var indexToGrayscaleMap = new Dictionary<int, byte>();
+
+			for (var i = 0; i < paletteImage.Height; i += 1)
+			{
+				var sourceColor = new Color
+				{
+					R = paletteImage.Data[i * paletteImage.Width * 4],
+					G = paletteImage.Data[i * paletteImage.Width * 4 + 1],
+					B = paletteImage.Data[i * paletteImage.Width * 4 + 2],
+					A = paletteImage.Data[i * paletteImage.Width * 4 + 3]
+				};
+
+				if (!ColorToGrayscaleMap.ContainsKey(sourceColor))
+				{
+					continue;
+					//throw new System.Exception("Color not found! " + sourceColor);
+				}
+
+				indexToGrayscaleMap[i] = ColorToGrayscaleMap[sourceColor];
+			}
+
+			// build the rows
+			for (var j = 1; j < paletteImage.Width; j += 1)
+			{
+				var paletteRow = new Color[256];
+
+				for (var i = 0; i < paletteImage.Height; i += 1)
+				{
+					if (!indexToGrayscaleMap.ContainsKey(i)) { continue; }
+					var grayscale = indexToGrayscaleMap[i];
+
+					paletteRow[grayscale].R = paletteImage.Data[(j + i * paletteImage.Width) * 4];
+					paletteRow[grayscale].G = paletteImage.Data[(j + i * paletteImage.Width) * 4 + 1];
+					paletteRow[grayscale].B = paletteImage.Data[(j + i * paletteImage.Width) * 4 + 2];
+					paletteRow[grayscale].A = paletteImage.Data[(j + i * paletteImage.Width) * 4 + 3];
+				}
+
+				AddAlternateColorRow(paletteRow);
+			}
+		}
+
 		public void AddAlternateColorRow(Color[] colors)
 		{
 			var byteArray = new byte[256 * 4];
diff --git a/src/Program.cs b/src/Program.cs
index d221459..7118e31 100644
--- a/src/Program.cs
+++ b/src/Program.cs
@@ -18,6 +18,11 @@ namespace Palettizer2
 				new Argument<string>(
 					"paletteName",
 					"The name of the palette sprite to output."
+				),
+				new Argument<FileInfo>(
+					"oldPalette",
+					() => null,
+					"For converting old-style palette to new"
 				)
 			};
 
@@ -26,11 +31,11 @@ namespace Palettizer2
 				palettize
 			};
 
-			palettize.Handler = CommandHandler.Create<DirectoryInfo, string>(HandlePalettize);
+			palettize.Handler = CommandHandler.Create<DirectoryInfo, string, FileInfo>(HandlePalettize);
 			return root.Invoke(args);
 		}
 
-		static void HandlePalettize(DirectoryInfo directory, string paletteName)
+		static void HandlePalettize(DirectoryInfo directory, string paletteName, FileInfo oldPalette)
 		{
 			var outputDir = Directory.CreateDirectory("output");
 			var palette = new Palette();
@@ -69,6 +74,15 @@ namespace Palettizer2
 				}
 			}
 
+			if (oldPalette != null)
+			{
+				using (var stream = File.OpenRead(oldPalette.FullName))
+				{
+					ImageResult paletteImage = ImageResult.FromStream(stream, ColorComponents.RedGreenBlueAlpha);
+					palette.AddAlternateRowsFromOldPalette(paletteImage);
+				}
+			}
+
 			// write palette sprite to PNG
 			var paletteOutputPath = Path.Combine(outputDir.FullName, paletteName + ".png");
 			using (var stream = File.OpenWrite(paletteOutputPath))