Tiff: Tiff format should not load thumbnail into collection

Author: mee-ironsoftware

IronSoftware.Drawing/IronSoftware.Drawing.Common.Tests/Data/example.tif

@@ -853,5 +853,18 @@ public void ExtractAlphaData_WithUnsupportedBppImage_ThrowsException()
             Assert.Equal($"Extracting alpha data is not supported for {bitmap.BitsPerPixel} bpp images.", exception.Message);
         }
 
+        [FactWithAutomaticDisplayName]
+        public void LoadImage_TiffImage_ShouldLoadWithoutThumbnail()
+        {
+            // Arrange
+            string imagePath = GetRelativeFilePath("example.tif");
+
+            // Act
+            var bitmap = new AnyBitmap(imagePath);
+
+            // Assert
+            bitmap.FrameCount.Should().Be(1);
+        }
+
     }
 }

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

@@ -2208,13 +2208,18 @@ private void OpenTiffToImageSharp(ReadOnlySpan<byte> bytes)
                 using MemoryStream tiffStream = new(bytes.ToArray());
 
                 // open a TIFF stored in the stream
-                using (var tif = Tiff.ClientOpen("in-memory", "r", tiffStream, new TiffStream()))
+                using (Tiff tif = Tiff.ClientOpen("in-memory", "r", tiffStream, new TiffStream()))
                 {
                     short num = tif.NumberOfDirectories();
                     for (short i = 0; i < num; i++)
                     {
                         _ = tif.SetDirectory(i);
 
+                        if (IsThumbnail(tif))
+                        {
+                            continue;
+                        }
+
                         var (width, height) = SetWidthHeight(tif, i, ref imageWidth, ref imageHeight);
 
                         // Read the image into the memory buffer
@@ -2281,6 +2286,22 @@ private void OpenTiffToImageSharp(ReadOnlySpan<byte> bytes)
             }
         }
 
+        /// <summary>
+        /// Determines if a TIFF frame contains a thumbnail.
+        /// </summary>
+        /// <param name="tif">The <see cref="Tiff"/> which set number of directory to analyze.</param>
+        /// <returns>True if the frame contains a thumbnail, otherwise false.</returns>
+        private bool IsThumbnail(Tiff tif)
+        {
+            FieldValue[] subFileTypeFieldValue = tif.GetField(TiffTag.SUBFILETYPE);
+
+            // Current thumbnail identification relies on the SUBFILETYPE tag with a value of FileType.REDUCEDIMAGE.
+            // This may need refinement in the future to include additional checks
+            // (e.g., FileType.COMPRESSION is NONE, Image Dimensions).
+            return subFileTypeFieldValue != null && subFileTypeFieldValue.Length > 0 
+                && (FileType)subFileTypeFieldValue[0].Value == FileType.REDUCEDIMAGE;
+        }
+
         private ReadOnlySpan<byte> PrepareByteArray(Image<Rgba32> bmp, int[] raster, int width, int height)
         {
             byte[] bits = new byte[GetStride(bmp) * height];