normalized the crops and optimized

LiloStitcher.cs

@@ -21,8 +21,8 @@ public readonly record struct PlateCoordinate(int Row, int Col)
         var colPart = new string(token.SkipWhile(char.IsLetter).ToArray());
 
         int row = 0;
-        foreach (var c in rowPart)
+        foreach (var character in rowPart)
-            row = row * 26 + (c - 'A' + 1);
+            row = row * 26 + (character - 'A' + 1);
 
         int.TryParse(colPart, out int col);
         return new PlateCoordinate(row, col);
@@ -33,9 +33,9 @@ public class TileCache(IMemoryCache cache)
 {
     private const long TileBytes = 720L * 720 * 3;
 
-    public Image<Rgba32>? Get(string key) => cache.TryGetValue(key, out Image<Rgba32>? img) ? img : null;
+    public Image<Rgb24>? Get(string key) => cache.TryGetValue(key, out Image<Rgb24>? img) ? img : null;
 
-    public void Set(string key, Image<Rgba32> img) =>
+    public void Set(string key, Image<Rgb24> img) =>
         cache.Set(key, img, new MemoryCacheEntryOptions
         {
             Size = TileBytes,
@@ -45,14 +45,14 @@ public class TileCache(IMemoryCache cache)
 
 public class TileLoader(TileCache cache, string assetDir)
 {
-    public async Task<Image<Rgba32>> LoadAsync(string name, CancellationToken ct)
+    public async Task<Image<Rgb24>> LoadAsync(string name, CancellationToken ct)
     {
         if (cache.Get(name) is { } hit)
             return hit;
 
         var path = Path.Combine(assetDir, $"{name}.png");
         await using var fs = File.OpenRead(path);
-        var image = await Image.LoadAsync<Rgba32>(fs, ct).ConfigureAwait(false);
+        var image = await Image.LoadAsync<Rgb24>(fs, ct).ConfigureAwait(false);
         cache.Set(name, image);
         return image;
     }
@@ -62,10 +62,17 @@ public class LiloStitcher(TileLoader loader)
 {
     private const int TileSize = 720;
 
+    private static readonly GraphicsOptions _copy = new()
+    {
+        Antialias = false,
+        AlphaCompositionMode = PixelAlphaCompositionMode.Src,
+        BlendPercentage = 1f
+    };
+
     public async Task<byte[]> CreateImageAsync(GenerateRequest req, CancellationToken ct)
     {
-        var parts = req.CanvasRect.ToUpperInvariant()
+        var parts = req.CanvasRect.ToUpperInvariant().Split(':', StringSplitOptions.TrimEntries |
-            .Split(':', StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries);
+                                                            StringSplitOptions.RemoveEmptyEntries);
         var part1 = PlateCoordinate.Parse(parts[0]);
         var part2 = PlateCoordinate.Parse(parts[1]);
 
@@ -82,34 +89,43 @@ public class LiloStitcher(TileLoader loader)
             .ToArray();
 
         var bitmaps = await Task.WhenAll(names.Select(n => loader.LoadAsync(n, ct))).ConfigureAwait(false);
-        var stitched = new Image<Rgba32>(cols * TileSize, rows * TileSize);
+        var stitched = new Image<Rgb24>(cols * TileSize, rows * TileSize);
 
-        int idx = 0;
+        stitched.Mutate(context =>
-        for (int r = 0; r < rows; r++)
         {
-            for (int c = 0; c < cols; c++, idx++)
+            int idx = 0;
+            for (int row = 0; row < rows; row++)
             {
-                stitched.Mutate(ctx => ctx.DrawImage(bitmaps[idx], new Point(c * TileSize, r * TileSize), 1f));
+                for (int col = 0; col < cols; col++, idx++)
+                {
+                    context.DrawImage(bitmaps[idx], new Point(col * TileSize, row * TileSize), 1f);
+                }
             }
-        }
+        });
 
         Validate(req.CropOffset, 2, nameof(req.CropOffset), inclusiveUpper: true);
         Validate(req.CropSize, 2, nameof(req.CropSize), inclusiveUpper: true);
 
-        int offsetX = (int)(req.CropOffset[0] * stitched.Width);
+        int offsetX = (int)Math.Truncate(req.CropOffset[0] * stitched.Width);
-        int offsetY = (int)(req.CropOffset[1] * stitched.Height);
+        int offsetY = (int)Math.Truncate(req.CropOffset[1] * stitched.Height);
-        int cropWidth = (int)(req.CropSize[0] * stitched.Width);
-        int cropHeight = (int)(req.CropSize[1] * stitched.Height);
 
-        if (offsetX + cropWidth > stitched.Width) cropWidth = stitched.Width - offsetX;
+        int restWidth  = stitched.Width  - offsetX;
-        if (offsetY + cropHeight > stitched.Height) cropHeight = stitched.Height - offsetY;
+        int restHeight = stitched.Height - offsetY;
 
-        var cropRect = new Rectangle(offsetX, offsetY, cropWidth, cropHeight);
+        int cropWidth  = Math.Max(1, (int)Math.Truncate(req.CropSize[0] * restWidth ));
+        int cropHeight = Math.Max(1, (int)Math.Truncate(req.CropSize[1] * restHeight));
 
-        using var cropped = stitched.Clone(ctx => ctx.Crop(cropRect));
+        int cropX = (int)Math.Truncate(offsetX / 2.0 + (restWidth - cropWidth) / 2.0);
+        int cropY = (int)Math.Truncate(offsetY / 2.0 + (restHeight - cropHeight) / 2.0);
+
+        var cropRect = new Rectangle(cropX, cropY, cropWidth, cropHeight);
+        using var cropped = stitched.Clone(context => context.Crop(cropRect));
 
         double scale = Math.Clamp(req.OutputScale, 0.0, 1.0);
-        Image<Rgba32> output;
+        if (scale <= 0 || scale > 1)
+            throw new ArgumentOutOfRangeException(nameof(req.OutputScale), "OutputScale must be > 0 and ≤ 1.0");
+
+        Image<Rgb24> output;
         if (scale < 1.0)
         {
             int width = Math.Max(1, (int)Math.Truncate(cropWidth * scale));
@@ -124,32 +140,33 @@ public class LiloStitcher(TileLoader loader)
         using var memStream = new MemoryStream();
         await output.SaveAsync(memStream, new PngEncoder
         {
+            CompressionLevel = PngCompressionLevel.Level1
         }, ct).ConfigureAwait(false);
         return memStream.ToArray();
+    }
 
-        static void Validate(double[] arr, int len, string name, bool inclusiveUpper)
+    static void Validate(double[] arr, int len, string name, bool inclusiveUpper)
+    {
+        if (arr is null || arr.Length < len)
+            throw new ArgumentException($"{name} must have length {len}");
+        double upper = inclusiveUpper ? 1.0 : 1.0 - double.Epsilon;
+        for (int i = 0; i < len; i++)
         {
-            if (arr is null || arr.Length < len)
+            var v = arr[i];
-                throw new ArgumentException($"{name} must have length {len}");
+            if (v < 0 || v > upper)
-            double upper = inclusiveUpper ? 1.0 : 1.0 - double.Epsilon;
+                throw new ArgumentOutOfRangeException($"{name}[{i}]= {v} outside [0,{upper}]");
-            for (int i = 0; i < len; i++)
-            {
-                var v = arr[i];
-                if (v < 0 || v > upper)
-                    throw new ArgumentOutOfRangeException($"{name}[{i}]= {v} outside [0,{upper}]");
-            }
-        }
-
-        static string RowName(int row)
-        {
-            var stringBuilder = new System.Text.StringBuilder();
-            while (row > 0)
-            {
-                row--;
-                stringBuilder.Insert(0, (char)('A' + row % 26));
-                row /= 26;
-            }
-            return stringBuilder.ToString();
         }
     }
+
+    static string RowName(int row)
+    {
+        var stringBuilder = new System.Text.StringBuilder();
+        while (row > 0)
+        {
+            row--;
+            stringBuilder.Insert(0, (char)('A' + row % 26));
+            row /= 26;
+        }
+        return stringBuilder.ToString();
+    }
 }

Program.cs

@@ -13,9 +13,9 @@ public static class Program
             var opt = new Options
             {
                 CanvasRect = "A1:AE55",
-                CropOffset = [0.0, 0.0],
+                CropOffset = [0.4, 0.4],
-                CropSize = [1.0, 1.0],
+                CropSize = [0.8, 0.8],
-                OutputScale = 1.0,
+                OutputScale = 0.5,
                 OutputPath = "stitched.png"
             };
 
@@ -40,7 +40,7 @@ public static class Program
             File.WriteAllBytes(opt.OutputPath!, pngBytes);
             Console.WriteLine($"Done. Wrote {opt.OutputPath}  ({pngBytes.Length / 1024.0:F1} KB)");
 
-            Console.WriteLine(begin - sw.ElapsedMilliseconds);
+            Console.WriteLine(sw.ElapsedMilliseconds - begin);
             return 0;
         }
         catch (Exception ex)

lilo-stitcher-console.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net9.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
     <RootNamespace>lilo_stitcher_console</RootNamespace>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>