Read raw data from TIFF IFDs

src/ImageSharp.Formats.Tiff/TiffConstants.cs

@@ -26,5 +26,15 @@ namespace ImageSharp.Formats
         /// Magic number used within the image file header to identify a TIFF format file.
         /// </summary>
         public const ushort HeaderMagicNumber = 42;
+
+        /// <summary>
+        /// Size (in bytes) of the TIFF file header.
+        /// </summary>
+        public const int SizeOfTiffHeader = 8;
+
+        /// <summary>
+        /// Size (in bytes) of each individual TIFF IFD entry
+        /// </summary>
+        public const int SizeOfIfdEntry = 12;
     }
 }

src/ImageSharp.Formats.Tiff/TiffDecoderCore.cs

@@ -59,6 +59,7 @@ namespace ImageSharp.Formats
             this.InputStream = stream;
 
             uint firstIfdOffset = ReadHeader();
+            TiffIfd firstIfd = ReadIfd(firstIfdOffset);
         }
 
         /// <summary>
@@ -70,8 +71,8 @@ namespace ImageSharp.Formats
 
         public uint ReadHeader()
         {
-            byte[] headerBytes = new byte[8];
-            ReadBytes(headerBytes, 8);
+            byte[] headerBytes = new byte[TiffConstants.SizeOfTiffHeader];
+            ReadBytes(headerBytes, TiffConstants.SizeOfTiffHeader);
 
             if (headerBytes[0] == TiffConstants.ByteOrderLittleEndian && headerBytes[1] == TiffConstants.ByteOrderLittleEndian)
                 IsLittleEndian = true;
@@ -88,7 +89,35 @@ namespace ImageSharp.Formats
             return firstIfdOffset;
         }
 
-        private byte[] ReadBytes(byte[] buffer, int count)
+        public TiffIfd ReadIfd(uint offset)
+        {
+            InputStream.Seek(offset, SeekOrigin.Begin);
+            
+            byte[] buffer = new byte[TiffConstants.SizeOfIfdEntry];
+
+            ReadBytes(buffer, 2);
+            ushort entryCount = ToUInt16(buffer, 0);
+
+            TiffIfdEntry[] entries = new TiffIfdEntry[entryCount];
+            for (int i = 0 ; i<entryCount; i++)
+            {
+                ReadBytes(buffer, TiffConstants.SizeOfIfdEntry);
+
+                ushort tag = ToUInt16(buffer, 0);
+                TiffType type = (TiffType)ToUInt16(buffer, 2);
+                uint count = ToUInt32(buffer, 4);
+                byte[] value = new byte[] { buffer[8], buffer[9], buffer[10], buffer[11] };
+
+                entries[i] = new TiffIfdEntry(tag, type, count, value);
+            }
+
+            ReadBytes(buffer, 4);
+            uint nextIfdOffset = ToUInt32(buffer, 0);
+
+            return new TiffIfd(entries, nextIfdOffset);
+        }
+
+        private void ReadBytes(byte[] buffer, int count)
         {
             int offset = 0;
 
@@ -102,8 +131,6 @@ namespace ImageSharp.Formats
                 offset += bytesRead;
                 count -= bytesRead;
             }
-
-            return buffer;
         }
 
         private Int16 ToInt16(byte[] bytes, int offset)

src/ImageSharp.Formats.Tiff/TiffIfd/TiffIfd.cs

@@ -0,0 +1,22 @@
+// <copyright file="TiffIfd.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageSharp.Formats
+{
+    /// <summary>
+    /// Data structure for holding details of each TIFF IFD
+    /// </summary>
+    internal struct TiffIfd
+    {
+        public TiffIfdEntry[] Entries;
+        public uint NextIfdOffset;
+
+        public TiffIfd(TiffIfdEntry[] entries, uint nextIfdOffset)
+        {
+            this.Entries = entries;
+            this.NextIfdOffset = nextIfdOffset;
+        }
+    }
+}

src/ImageSharp.Formats.Tiff/TiffIfd/TiffIfdEntry.cs

@@ -0,0 +1,26 @@
+// <copyright file="TiffIfdEntry.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageSharp.Formats
+{
+    /// <summary>
+    /// Data structure for holding details of each TIFF IFD entry
+    /// </summary>
+    internal struct TiffIfdEntry
+    {
+        public ushort Tag;
+        public TiffType Type;
+        public uint Count;
+        public byte[] Value;
+
+        public TiffIfdEntry(ushort tag, TiffType type, uint count, byte[] value)
+        {
+            this.Tag = tag;
+            this.Type = type;
+            this.Count = count;
+            this.Value = value;
+        }
+    }
+}

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

@@ -0,0 +1,111 @@
+// <copyright file="TiffDecoderIfdTests.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageSharp.Tests
+{
+    using System.IO;
+    using System.Linq;
+    using Xunit;
+
+    using ImageSharp.Formats;
+
+    public class TiffDecoderIfdTests
+    {
+        public static object[][] IsLittleEndianValues = new[] { new object[] { false },
+                                                                new object[] { true } };
+
+        [Theory]
+        [MemberData(nameof(IsLittleEndianValues))]
+        public void ReadIfd_ReadsNextIfdOffset_IfPresent(bool isLittleEndian)
+        {
+            Stream stream = new TiffGenIfd()
+                            {
+                                Entries =
+                                {
+                                    TiffGenEntry.Integer(TiffTags.ImageWidth, TiffType.Long, 150)
+                                },
+                                NextIfd = new TiffGenIfd()
+                            }
+                            .ToStream(isLittleEndian);
+
+            TiffDecoderCore decoder = new TiffDecoderCore(stream, isLittleEndian, null);
+            TiffIfd ifd = decoder.ReadIfd(0);
+
+            Assert.Equal(18u, ifd.NextIfdOffset);
+        }
+
+        [Theory]
+        [MemberData(nameof(IsLittleEndianValues))]
+        public void ReadIfd_ReadsNextIfdOffset_ZeroIfLastIfd(bool isLittleEndian)
+        {
+            Stream stream = new TiffGenIfd()
+                            {
+                                Entries =
+                                {
+                                    TiffGenEntry.Integer(TiffTags.ImageWidth, TiffType.Long, 150)
+                                }
+                            }
+                            .ToStream(isLittleEndian);
+
+            TiffDecoderCore decoder = new TiffDecoderCore(stream, isLittleEndian, null);
+            TiffIfd ifd = decoder.ReadIfd(0);
+
+            Assert.Equal(0u, ifd.NextIfdOffset);
+        }
+
+        [Theory]
+        [MemberData(nameof(IsLittleEndianValues))]
+        public void ReadIfd_ReturnsCorrectNumberOfEntries(bool isLittleEndian)
+        {
+            Stream stream = new TiffGenIfd()
+                            {
+                                Entries =
+                                {
+                                    TiffGenEntry.Integer(TiffTags.ImageWidth, TiffType.Long, 150),
+                                    TiffGenEntry.Integer(TiffTags.ImageLength, TiffType.Long, 210),
+                                    TiffGenEntry.Integer(TiffTags.Orientation, TiffType.Short, 1),
+                                    TiffGenEntry.Ascii(TiffTags.Artist, "Image Artist Name"),
+                                    TiffGenEntry.Ascii(TiffTags.HostComputer, "Host Computer Name")
+                                },
+                                NextIfd = new TiffGenIfd()
+                            }
+                            .ToStream(isLittleEndian);
+
+            TiffDecoderCore decoder = new TiffDecoderCore(stream, isLittleEndian, null);
+            TiffIfd ifd = decoder.ReadIfd(0);
+
+            Assert.NotNull(ifd.Entries);
+            Assert.Equal(5, ifd.Entries.Length);
+        }
+
+         [Theory]
+        [MemberData(nameof(IsLittleEndianValues))]
+        public void ReadIfd_ReadsRawTiffEntryData(bool isLittleEndian)
+        {
+            Stream stream = new TiffGenIfd()
+                            {
+                                Entries =
+                                {
+                                    TiffGenEntry.Integer(TiffTags.ImageWidth, TiffType.Long, 150),
+                                    TiffGenEntry.Integer(TiffTags.ImageLength, TiffType.Long, 210),
+                                    TiffGenEntry.Integer(TiffTags.Orientation, TiffType.Short, 1)
+                                },
+                                NextIfd = new TiffGenIfd()
+                            }
+                            .ToStream(isLittleEndian);
+
+            TiffDecoderCore decoder = new TiffDecoderCore(stream, isLittleEndian, null);
+            TiffIfd ifd = decoder.ReadIfd(0);
+            TiffIfdEntry entry = ifd.Entries[1];
+
+            byte[] expectedData = isLittleEndian ? new byte[] {210,0,0,0} : new byte[] {0,0,0,210};
+            Assert.NotNull(entry);
+            Assert.Equal(TiffTags.ImageLength, entry.Tag);
+            Assert.Equal(TiffType.Long, entry.Type);
+            Assert.Equal(4u, entry.Count);
+            Assert.Equal(expectedData, entry.Value);
+        }
+    }
+}