Handle white as zero based on photometric interpretation

src/ImageSharp/Formats/Tiff/Compression/T4TiffCompression.cs

@@ -16,16 +16,16 @@ namespace SixLabors.ImageSharp.Formats.Tiff.Compression
         /// Initializes a new instance of the <see cref="T4TiffCompression" /> class.
         /// </summary>
         /// <param name="allocator">The memory allocator.</param>
-        public T4TiffCompression(MemoryAllocator allocator)
-            : base(allocator)
+        /// <param name="photometricInterpretation">The photometric interpretation.</param>
+        public T4TiffCompression(MemoryAllocator allocator, TiffPhotometricInterpretation photometricInterpretation)
+            : base(allocator, photometricInterpretation)
         {
         }
 
         /// <inheritdoc/>
         public override void Decompress(Stream stream, int byteCount, Span<byte> buffer)
         {
-            // TODO: handle case when white is not zero.
-            bool isWhiteZero = true;
+            bool isWhiteZero = this.PhotometricInterpretation == TiffPhotometricInterpretation.WhiteIsZero;
             int whiteValue = isWhiteZero ? 0 : 1;
             int blackValue = isWhiteZero ? 1 : 0;
 

src/ImageSharp/Formats/Tiff/Compression/TiffBaseCompression.cs

@@ -14,10 +14,20 @@ namespace SixLabors.ImageSharp.Formats.Tiff
     {
         private readonly MemoryAllocator allocator;
 
+        private TiffPhotometricInterpretation photometricInterpretation;
+
         public TiffBaseCompression(MemoryAllocator allocator) => this.allocator = allocator;
 
+        public TiffBaseCompression(MemoryAllocator allocator, TiffPhotometricInterpretation photometricInterpretation)
+        {
+            this.allocator = allocator;
+            this.photometricInterpretation = photometricInterpretation;
+        }
+
         protected MemoryAllocator Allocator => this.allocator;
 
+        protected TiffPhotometricInterpretation PhotometricInterpretation => this.photometricInterpretation;
+
         /// <summary>
         /// Decompresses image data into the supplied buffer.
         /// </summary>

src/ImageSharp/Formats/Tiff/Compression/TiffCompressionFactory.cs

@@ -8,7 +8,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
 {
     internal static class TiffCompressionFactory
     {
-        public static TiffBaseCompression Create(TiffCompressionType compressionType, MemoryAllocator allocator)
+        public static TiffBaseCompression Create(TiffCompressionType compressionType, MemoryAllocator allocator, TiffPhotometricInterpretation photometricInterpretation)
         {
             switch (compressionType)
             {
@@ -21,7 +21,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 case TiffCompressionType.Lzw:
                     return new LzwTiffCompression(allocator);
                 case TiffCompressionType.T4:
-                    return new T4TiffCompression(allocator);
+                    return new T4TiffCompression(allocator, photometricInterpretation);
                 default:
                     throw TiffThrowHelper.NotSupportedCompression(nameof(compressionType));
             }

src/ImageSharp/Formats/Tiff/TiffDecoderCore.cs

@@ -276,7 +276,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                     stripBuffers[stripIndex] = this.memoryAllocator.AllocateManagedByteBuffer(uncompressedStripSize);
                 }
 
-                TiffBaseCompression decompressor = TiffCompressionFactory.Create(this.CompressionType, this.memoryAllocator);
+                TiffBaseCompression decompressor = TiffCompressionFactory.Create(this.CompressionType, this.memoryAllocator, this.PhotometricInterpretation);
 
                 RgbPlanarTiffColor<TPixel> colorDecoder = TiffColorDecoderFactory<TPixel>.CreatePlanar(this.ColorType, this.BitsPerSample, this.ColorMap);
 
@@ -313,7 +313,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
 
             Buffer2D<TPixel> pixels = frame.PixelBuffer;
 
-            TiffBaseCompression decompressor = TiffCompressionFactory.Create(this.CompressionType, this.memoryAllocator);
+            TiffBaseCompression decompressor = TiffCompressionFactory.Create(this.CompressionType, this.memoryAllocator, this.PhotometricInterpretation);
 
             TiffBaseColorDecoder<TPixel> colorDecoder = TiffColorDecoderFactory<TPixel>.Create(this.ColorType, this.BitsPerSample, this.ColorMap);