Fixed corruption of true 3-byte Rgb24 input

Author: Sawraz-IS

IronSoftware.Drawing/IronSoftware.Drawing.Common.Tests/UnitTests/AnyBitmapFunctionality.cs

@@ -676,6 +676,37 @@ public void CreateMultiFrameTiffStream_Empty_Sequence_Throws()
             act.Should().Throw<ArgumentException>();
         }
 
+        [FactWithAutomaticDisplayName]
+        public void CreateMultiFrameTiff_Preserves_Rgb24_Pixels()
+        {
+            string jpgPath = GetRelativeFilePath("mountainclimbers.jpg");
+            using var expected = SixLabors.ImageSharp.Image.Load<Rgb24>(jpgPath);
+
+            using var result = AnyBitmap.CreateMultiFrameTiff(new List<string> { jpgPath });
+
+            result.Width.Should().Be(expected.Width);
+            result.Height.Should().Be(expected.Height);
+
+            var points = new[]
+            {
+                (1, 0),
+                (expected.Width - 1, 0),
+                (expected.Width / 3, expected.Height / 2),
+                (expected.Width / 2, expected.Height / 3),
+                (0, expected.Height - 1),
+                (expected.Width - 1, expected.Height - 1)
+            };
+
+            foreach (var (x, y) in points)
+            {
+                Rgb24 e = expected[x, y];
+                var a = result.GetPixel(x, y);
+                a.R.Should().Be(e.R, $"red channel at ({x},{y})");
+                a.G.Should().Be(e.G, $"green channel at ({x},{y})");
+                a.B.Should().Be(e.B, $"blue channel at ({x},{y})");
+            }
+        }
+
         private static AnyBitmap CreateSolidBitmap(int width, int height, Rgb24 color, int dpi)
         {
             var image = new SixLabors.ImageSharp.Image<Rgb24>(width, height, color);

IronSoftware.Drawing/IronSoftware.Drawing.Common/AnyBitmap.cs

@@ -3409,7 +3409,15 @@ private static void InternalSaveAsMultiPageTiff(IEnumerable<Image> images, Strea
                     switch (image)
                     {
                         case Image<Rgb24> imageAsFormat:
-                            imageAsFormat.CopyPixelDataTo(buffer);
+                            {
+                                // Rgb24 is 3 bytes/pixel, but the buffer/stride above and the
+                                // TIFF tags below are 4 samples/pixel (RGBA). Copying the 3-bpp
+                                // data directly would leave each row short by 'width' bytes,
+                                // shifting every subsequent row and corrupting the page. Convert
+                                // to Rgba32 so the bytes line up with the 4-bpp layout.
+                                using var rgba = imageAsFormat.CloneAs<Rgba32>();
+                                rgba.CopyPixelDataTo(buffer);
+                            }
                             break;
                         case Image<Abgr32> imageAsFormat:
                             imageAsFormat.CopyPixelDataTo(buffer);
@@ -3418,7 +3426,13 @@ private static void InternalSaveAsMultiPageTiff(IEnumerable<Image> images, Strea
                             imageAsFormat.CopyPixelDataTo(buffer);
                             break;
                         case Image<Bgr24> imageAsFormat:
-                            imageAsFormat.CopyPixelDataTo(buffer);
+                            {
+                                // Bgr24 is likewise 3 bytes/pixel; convert to Rgba32 for the
+                                // same reason as Rgb24 above (this also yields the correct
+                                // R,G,B sample order under PHOTOMETRIC.RGB).
+                                using var rgba = imageAsFormat.CloneAs<Rgba32>();
+                                rgba.CopyPixelDataTo(buffer);
+                            }
                             break;
                         case Image<Bgra32> imageAsFormat:
                             imageAsFormat.CopyPixelDataTo(buffer);