Add support for decoding tiff's with 32bit float gray pixel data with min is black

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/BlackIsZero32FloatTiffColor{TPixel}.cs

@@ -0,0 +1,69 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Numerics;
+using SixLabors.ImageSharp.Formats.Tiff.Utils;
+using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
+{
+    /// <summary>
+    /// Implements the 'BlackIsZero' photometric interpretation for 32-bit float grayscale images.
+    /// </summary>
+    internal class BlackIsZero32FloatTiffColor<TPixel> : TiffBaseColorDecoder<TPixel>
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        private readonly bool isBigEndian;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="BlackIsZero32FloatTiffColor{TPixel}" /> class.
+        /// </summary>
+        /// <param name="isBigEndian">if set to <c>true</c> decodes the pixel data as big endian, otherwise as little endian.</param>
+        public BlackIsZero32FloatTiffColor(bool isBigEndian) => this.isBigEndian = isBigEndian;
+
+        /// <inheritdoc/>
+        public override void Decode(ReadOnlySpan<byte> data, Buffer2D<TPixel> pixels, int left, int top, int width, int height)
+        {
+            // Note: due to an issue with netcore 2.1 and default values and unpredictable behavior with those,
+            // we define our own defaults as a workaround. See: https://github.com/dotnet/runtime/issues/55623
+            var color = default(TPixel);
+            color.FromVector4(TiffUtils.Vector4Default);
+            byte[] buffer = new byte[4];
+
+            int offset = 0;
+            for (int y = top; y < top + height; y++)
+            {
+                Span<TPixel> pixelRow = pixels.GetRowSpan(y).Slice(left, width);
+                if (this.isBigEndian)
+                {
+                    for (int x = 0; x < pixelRow.Length; x++)
+                    {
+                        data.Slice(offset, 4).CopyTo(buffer);
+                        Array.Reverse(buffer);
+                        float intensity = BitConverter.ToSingle(buffer, 0);
+                        offset += 4;
+
+                        var colorVector = new Vector4(intensity, intensity, intensity, 1.0f);
+                        color.FromVector4(colorVector);
+                        pixelRow[x] = color;
+                    }
+                }
+                else
+                {
+                    for (int x = 0; x < pixelRow.Length; x++)
+                    {
+                        data.Slice(offset, 4).CopyTo(buffer);
+                        float intensity = BitConverter.ToSingle(buffer, 0);
+                        offset += 4;
+
+                        var colorVector = new Vector4(intensity, intensity, intensity, 1.0f);
+                        color.FromVector4(colorVector);
+                        pixelRow[x] = color;
+                    }
+                }
+            }
+        }
+    }
+}

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/BlackIsZero32TiffColor{TPixel}.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
-using System.Numerics;
 using SixLabors.ImageSharp.Formats.Tiff.Utils;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.PixelFormats;

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/RgbFloat323232TiffColor{TPixel}.cs

@@ -57,7 +57,6 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
                         offset += 4;
 
                         var colorVector = new Vector4(r, g, b, 1.0f);
-                        Array.Reverse(buffer);
                         color.FromVector4(colorVector);
                         pixelRow[x] = color;
                     }

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/TiffColorDecoderFactory{TPixel}.cs

@@ -82,6 +82,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
                     DebugGuard.IsTrue(colorMap == null, "colorMap");
                     return new BlackIsZero32TiffColor<TPixel>(byteOrder == ByteOrder.BigEndian);
 
+                case TiffColorType.BlackIsZero32Float:
+                    DebugGuard.IsTrue(bitsPerSample.Channels == 1 && bitsPerSample.Channel0 == 32, "bitsPerSample");
+                    DebugGuard.IsTrue(colorMap == null, "colorMap");
+                    return new BlackIsZero32FloatTiffColor<TPixel>(byteOrder == ByteOrder.BigEndian);
+
                 case TiffColorType.Rgb:
                     DebugGuard.IsTrue(colorMap == null, "colorMap");
                     return new RgbTiffColor<TPixel>(bitsPerSample);

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/TiffColorType.cs

@@ -43,6 +43,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
         /// </summary>
         BlackIsZero32,
 
+        /// <summary>
+        /// Grayscale: 0 is imaged as black. The maximum value is imaged as white. Pixel data is 32-bit float.
+        /// </summary>
+        BlackIsZero32Float,
+
         /// <summary>
         /// Grayscale: 0 is imaged as white. The maximum value is imaged as black.
         /// </summary>

src/ImageSharp/Formats/Tiff/TiffDecoderOptionsParser.cs

@@ -177,6 +177,12 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                     {
                         case 32:
                         {
+                            if (options.SampleFormat == TiffSampleFormat.Float)
+                            {
+                                options.ColorType = TiffColorType.BlackIsZero32Float;
+                                return;
+                            }
+
                             options.ColorType = TiffColorType.BlackIsZero32;
                             break;
                         }
@@ -234,18 +240,18 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                         TiffThrowHelper.ThrowNotSupported("Only BitsPerSample with equal bits per channel are supported.");
                     }
 
-                    if (options.SampleFormat == TiffSampleFormat.Float)
-                    {
-                        options.ColorType = TiffColorType.RgbFloat323232;
-                        return;
-                    }
-
                     if (options.PlanarConfiguration == TiffPlanarConfiguration.Chunky)
                     {
                         ushort bitsPerChannel = options.BitsPerSample.Channel0;
                         switch (bitsPerChannel)
                         {
                             case 32:
+                                if (options.SampleFormat == TiffSampleFormat.Float)
+                                {
+                                    options.ColorType = TiffColorType.RgbFloat323232;
+                                    return;
+                                }
+
                                 options.ColorType = TiffColorType.Rgb323232;
                                 break;
 

tests/ImageSharp.Tests/Formats/Tiff/TiffDecoderTests.cs

@@ -248,6 +248,17 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
             image.DebugSave(provider);
         }
 
+        [Theory]
+        [WithFile(Flower32BitFloatGray, PixelTypes.Rgba32)]
+        [WithFile(Flower32BitFloatGrayLittleEndian, PixelTypes.Rgba32)]
+        public void TiffDecoder_CanDecode_Float_96Bit_Gray<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            // Note: because the MagickReferenceDecoder fails to load the image, we only debug save them.
+            using Image<TPixel> image = provider.GetImage();
+            image.DebugSave(provider);
+        }
+
         [Theory]
         [WithFile(GrayscaleDeflateMultistrip, PixelTypes.Rgba32)]
         [WithFile(RgbDeflateMultistrip, PixelTypes.Rgba32)]

tests/ImageSharp.Tests/TestImages.cs

@@ -605,6 +605,8 @@ namespace SixLabors.ImageSharp.Tests
             public const string Flower24BitGrayLittleEndian = "Tiff/flower-minisblack-24_lsb.tiff";
             public const string Flower32BitGray = "Tiff/flower-minisblack-32.tiff";
             public const string Flower32BitGrayLittleEndian = "Tiff/flower-minisblack-32_lsb.tiff";
+            public const string Flower32BitFloatGray = "Tiff/flower-minisblack-float32_msb.tiff";
+            public const string Flower32BitFloatGrayLittleEndian = "Tiff/flower-minisblack-float32_lsb.tiff";
             public const string Flower32BitGrayMinIsWhite = "Tiff/flower-miniswhite-32.tiff";
             public const string Flower32BitGrayMinIsWhiteLittleEndian = "Tiff/flower-miniswhite-32_lsb.tiff";
 

tests/Images/Input/Tiff/flower-minisblack-float32_lsb.tiff

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:af82e07e6298082c91d60a97acb29b67ecabf386bc14371fcb698b248cfd3b40
+size 12814

tests/Images/Input/Tiff/flower-minisblack-float32_msb.tiff

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:5c918b8aa9968c03c12d85b3bcacd35ae57663a19f5490fc1c351521ed835f30
+size 12814