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

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

@@ -47,6 +47,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
                     DebugGuard.IsTrue(colorMap == null, "colorMap");
                     return new WhiteIsZero32TiffColor<TPixel>(byteOrder == ByteOrder.BigEndian);
 
+                case TiffColorType.WhiteIsZero32Float:
+                    DebugGuard.IsTrue(bitsPerSample.Channels == 1 && bitsPerSample.Channel0 == 32, "bitsPerSample");
+                    DebugGuard.IsTrue(colorMap == null, "colorMap");
+                    return new WhiteIsZero32FloatTiffColor<TPixel>(byteOrder == ByteOrder.BigEndian);
+
                 case TiffColorType.BlackIsZero:
                     DebugGuard.IsTrue(bitsPerSample.Channels == 1, "bitsPerSample");
                     DebugGuard.IsTrue(colorMap == null, "colorMap");

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

@@ -83,6 +83,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
         /// </summary>
         WhiteIsZero32,
 
+        /// <summary>
+        /// Grayscale: 0 is imaged as black. The maximum value is imaged as white. Pixel data is 32-bit float.
+        /// </summary>
+        WhiteIsZero32Float,
+
         /// <summary>
         /// Palette-color.
         /// </summary>

src/ImageSharp/Formats/Tiff/PhotometricInterpretation/WhiteIsZero32FloatTiffColor{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 'WhiteIsZero' photometric interpretation for 32-bit float grayscale images.
+    /// </summary>
+    internal class WhiteIsZero32FloatTiffColor<TPixel> : TiffBaseColorDecoder<TPixel>
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        private readonly bool isBigEndian;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="WhiteIsZero32FloatTiffColor{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 WhiteIsZero32FloatTiffColor(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 = 1.0f - 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 = 1.0f - 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/WhiteIsZero8TiffColor{TPixel}.cs

@@ -27,7 +27,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff.PhotometricInterpretation
                 Span<TPixel> pixelRow = pixels.GetRowSpan(y).Slice(left, width);
                 for (int x = 0; x < pixelRow.Length; x++)
                 {
-                    byte intensity = (byte)(255 - data[offset++]);
+                    byte intensity = (byte)(byte.MaxValue - data[offset++]);
                     pixelRow[x] = TiffUtils.ColorFromL8(l8, intensity, color);
                 }
             }

src/ImageSharp/Formats/Tiff/TiffDecoderOptionsParser.cs

@@ -116,6 +116,12 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                     {
                         case 32:
                         {
+                            if (options.SampleFormat == TiffSampleFormat.Float)
+                            {
+                                options.ColorType = TiffColorType.WhiteIsZero32Float;
+                                return;
+                            }
+
                             options.ColorType = TiffColorType.WhiteIsZero32;
                             break;
                         }

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

@@ -251,6 +251,8 @@ namespace SixLabors.ImageSharp.Tests.Formats.Tiff
         [Theory]
         [WithFile(Flower32BitFloatGray, PixelTypes.Rgba32)]
         [WithFile(Flower32BitFloatGrayLittleEndian, PixelTypes.Rgba32)]
+        [WithFile(Flower32BitFloatGrayMinIsWhite, PixelTypes.Rgba32)]
+        [WithFile(Flower32BitFloatGrayMinIsWhiteLittleEndian, PixelTypes.Rgba32)]
         public void TiffDecoder_CanDecode_Float_96Bit_Gray<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel>
         {

tests/ImageSharp.Tests/TestImages.cs

@@ -607,6 +607,8 @@ namespace SixLabors.ImageSharp.Tests
             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 Flower32BitFloatGrayMinIsWhite = "Tiff/flower-miniswhite-float32_msb.tiff";
+            public const string Flower32BitFloatGrayMinIsWhiteLittleEndian = "Tiff/flower-miniswhite-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-miniswhite-float32_lsb.tiff

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:93e06533486f15e33f2435d081713fbecc3ba96c842058b7ba3a5d9116fe5f5c
+size 12814

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

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:800a101f4d23fa2a499fcef036ebfca7d9338ac71b06a32ad05e7eb1905ddae3
+size 12814