Bitmap decoder now can decode bitmap arrays (#930)

* Bitmap Decoder can now decode BitmapArray

* Add tests for bitmap metadata decoing. Fix an issue that a bitmap with a v5 header would be set in the metadata as an v4 header.

* Fixed issue with decoding bitmap arrays: color map size was not determined correctly. Added more test images.

* Refactor colormap size duplicate declaration.

* Fixed an issue, that when an unsupported bitmap is loaded the typ marker was not correctly shown in the error message

Author: brianpopow

src/ImageSharp/Formats/Bmp/BmpArrayFileHeader.cs

@@ -0,0 +1,53 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Runtime.InteropServices;
+
+namespace SixLabors.ImageSharp.Formats.Bmp
+{
+    [StructLayout(LayoutKind.Sequential, Pack = 1)]
+    internal readonly struct BmpArrayFileHeader
+    {
+        public BmpArrayFileHeader(short type, int size, int offsetToNext, short width, short height)
+        {
+            this.Type = type;
+            this.Size = size;
+            this.OffsetToNext = offsetToNext;
+            this.ScreenWidth = width;
+            this.ScreenHeight = height;
+        }
+
+        /// <summary>
+        /// Gets the Bitmap identifier.
+        /// The field used to identify the bitmap file: 0x42 0x41 (Hex code points for B and A).
+        /// </summary>
+        public short Type { get; }
+
+        /// <summary>
+        /// Gets the size of this header.
+        /// </summary>
+        public int Size { get; }
+
+        /// <summary>
+        /// Gets the offset to next OS2BMPARRAYFILEHEADER.
+        /// This offset is calculated from the starting byte of the file. A value of zero indicates that this header is for the last image in the array list.
+        /// </summary>
+        public int OffsetToNext { get; }
+
+        /// <summary>
+        /// Gets the width of the image display in pixels.
+        /// </summary>
+        public short ScreenWidth { get; }
+
+        /// <summary>
+        /// Gets the height of the image display in pixels.
+        /// </summary>
+        public short ScreenHeight { get; }
+
+        public static BmpArrayFileHeader Parse(Span<byte> data)
+        {
+            return MemoryMarshal.Cast<byte, BmpArrayFileHeader>(data)[0];
+        }
+    }
+}

src/ImageSharp/Formats/Bmp/BmpDecoderCore.cs

@@ -1053,18 +1053,11 @@ private void ReadInfoHeader()
             this.stream.Read(buffer, 0, BmpInfoHeader.HeaderSizeSize);
 
             int headerSize = BinaryPrimitives.ReadInt32LittleEndian(buffer);
-            if (headerSize < BmpInfoHeader.CoreSize)
+            if (headerSize < BmpInfoHeader.CoreSize || headerSize > BmpInfoHeader.MaxHeaderSize)
             {
                 BmpThrowHelper.ThrowNotSupportedException($"ImageSharp does not support this BMP file. HeaderSize is '{headerSize}'.");
             }
 
-            int skipAmount = 0;
-            if (headerSize > BmpInfoHeader.MaxHeaderSize)
-            {
-                skipAmount = headerSize - BmpInfoHeader.MaxHeaderSize;
-                headerSize = BmpInfoHeader.MaxHeaderSize;
-            }
-
             // Read the rest of the header.
             this.stream.Read(buffer, BmpInfoHeader.HeaderSizeSize, headerSize - BmpInfoHeader.HeaderSizeSize);
 
@@ -1169,15 +1162,13 @@ private void ReadInfoHeader()
             {
                 this.bmpMetadata.BitsPerPixel = (BmpBitsPerPixel)bitsPerPixel;
             }
-
-            // Skip the remaining header because we can't read those parts.
-            this.stream.Skip(skipAmount);
         }
 
         /// <summary>
         /// Reads the <see cref="BmpFileHeader"/> from the stream.
         /// </summary>
-        private void ReadFileHeader()
+        /// <returns>The color map size in bytes, if it could be determined by the file header. Otherwise -1.</returns>
+        private int ReadFileHeader()
         {
 #if NETCOREAPP2_1
             Span<byte> buffer = stackalloc byte[BmpFileHeader.Size];
@@ -1186,12 +1177,36 @@ private void ReadFileHeader()
 #endif
             this.stream.Read(buffer, 0, BmpFileHeader.Size);
 
-            this.fileHeader = BmpFileHeader.Parse(buffer);
-
-            if (this.fileHeader.Type != BmpConstants.TypeMarkers.Bitmap)
+            short fileTypeMarker = BinaryPrimitives.ReadInt16LittleEndian(buffer);
+            switch (fileTypeMarker)
             {
-                BmpThrowHelper.ThrowNotSupportedException($"ImageSharp does not support this BMP file. File header bitmap type marker '{this.fileHeader.Type}'.");
+                case BmpConstants.TypeMarkers.Bitmap:
+                    this.fileHeader = BmpFileHeader.Parse(buffer);
+                    break;
+                case BmpConstants.TypeMarkers.BitmapArray:
+                    // The Array file header is followed by the bitmap file header of the first image.
+                    var arrayHeader = BmpArrayFileHeader.Parse(buffer);
+                    this.stream.Read(buffer, 0, BmpFileHeader.Size);
+                    this.fileHeader = BmpFileHeader.Parse(buffer);
+                    if (this.fileHeader.Type != BmpConstants.TypeMarkers.Bitmap)
+                    {
+                        BmpThrowHelper.ThrowNotSupportedException($"Unsupported bitmap file inside a BitmapArray file. File header bitmap type marker '{this.fileHeader.Type}'.");
+                    }
+
+                    if (arrayHeader.OffsetToNext != 0)
+                    {
+                        int colorMapSizeBytes = arrayHeader.OffsetToNext - arrayHeader.Size;
+                        return colorMapSizeBytes;
+                    }
+
+                    break;
+
+                default:
+                    BmpThrowHelper.ThrowNotSupportedException($"ImageSharp does not support this BMP file. File header bitmap type marker '{fileTypeMarker}'.");
+                    break;
             }
+
+            return -1;
         }
 
         /// <summary>
@@ -1203,7 +1218,7 @@ private int ReadImageHeaders(Stream stream, out bool inverted, out byte[] palett
         {
             this.stream = stream;
 
-            this.ReadFileHeader();
+            int colorMapSizeBytes = this.ReadFileHeader();
             this.ReadInfoHeader();
 
             // see http://www.drdobbs.com/architecture-and-design/the-bmp-file-format-part-1/184409517
@@ -1218,7 +1233,6 @@ private int ReadImageHeaders(Stream stream, out bool inverted, out byte[] palett
                 this.infoHeader.Height = -this.infoHeader.Height;
             }
 
-            int colorMapSize = -1;
             int bytesPerColorMapEntry = 4;
 
             if (this.infoHeader.ClrUsed == 0)
@@ -1227,35 +1241,38 @@ private int ReadImageHeaders(Stream stream, out bool inverted, out byte[] palett
                     || this.infoHeader.BitsPerPixel == 4
                     || this.infoHeader.BitsPerPixel == 8)
                 {
-                    int colorMapSizeBytes = this.fileHeader.Offset - BmpFileHeader.Size - this.infoHeader.HeaderSize;
+                    if (colorMapSizeBytes == -1)
+                    {
+                        colorMapSizeBytes = this.fileHeader.Offset - BmpFileHeader.Size - this.infoHeader.HeaderSize;
+                    }
+
                     int colorCountForBitDepth = ImageMaths.GetColorCountForBitDepth(this.infoHeader.BitsPerPixel);
                     bytesPerColorMapEntry = colorMapSizeBytes / colorCountForBitDepth;
 
                     // Edge case for less-than-full-sized palette: bytesPerColorMapEntry should be at least 3.
                     bytesPerColorMapEntry = Math.Max(bytesPerColorMapEntry, 3);
-                    colorMapSize = colorMapSizeBytes;
                 }
             }
             else
             {
-                colorMapSize = this.infoHeader.ClrUsed * bytesPerColorMapEntry;
+                colorMapSizeBytes = this.infoHeader.ClrUsed * bytesPerColorMapEntry;
             }
 
             palette = null;
 
-            if (colorMapSize > 0)
+            if (colorMapSizeBytes > 0)
             {
                 // Usually the color palette is 1024 byte (256 colors * 4), but the documentation does not mention a size limit.
                 // Make sure, that we will not read pass the bitmap offset (starting position of image data).
-                if ((this.stream.Position + colorMapSize) > this.fileHeader.Offset)
+                if ((this.stream.Position + colorMapSizeBytes) > this.fileHeader.Offset)
                 {
                     BmpThrowHelper.ThrowImageFormatException(
-                        $"Reading the color map would read beyond the bitmap offset. Either the color map size of '{colorMapSize}' is invalid or the bitmap offset.");
+                        $"Reading the color map would read beyond the bitmap offset. Either the color map size of '{colorMapSizeBytes}' is invalid or the bitmap offset.");
                 }
 
-                palette = new byte[colorMapSize];
+                palette = new byte[colorMapSizeBytes];
 
-                this.stream.Read(palette, 0, colorMapSize);
+                this.stream.Read(palette, 0, colorMapSizeBytes);
             }
 
             this.infoHeader.VerifyDimensions();

src/ImageSharp/Formats/Bmp/BmpFileHeader.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -21,7 +21,7 @@ namespace SixLabors.ImageSharp.Formats.Bmp
     internal readonly struct BmpFileHeader
     {
         /// <summary>
-        /// Defines of the data structure in the bitmap file.
+        /// Defines the size of the data structure in the bitmap file.
         /// </summary>
         public const int Size = 14;
 
@@ -69,4 +69,4 @@ public unsafe void WriteTo(Span<byte> buffer)
             dest = this;
         }
     }
-}
+}

src/ImageSharp/Formats/Bmp/BmpImageFormatDetector.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -22,7 +22,9 @@ public IImageFormat DetectFormat(ReadOnlySpan<byte> header)
 
         private bool IsSupportedFileFormat(ReadOnlySpan<byte> header)
         {
-            return header.Length >= this.HeaderSize && BinaryPrimitives.ReadInt16LittleEndian(header) == BmpConstants.TypeMarkers.Bitmap;
+            short fileTypeMarker = BinaryPrimitives.ReadInt16LittleEndian(header);
+            return header.Length >= this.HeaderSize &&
+                   (fileTypeMarker == BmpConstants.TypeMarkers.Bitmap || fileTypeMarker == BmpConstants.TypeMarkers.BitmapArray);
         }
     }
-}
+}

src/ImageSharp/Formats/Bmp/BmpInfoHeader.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 using System;
 using System.Buffers.Binary;
@@ -51,10 +51,15 @@ internal struct BmpInfoHeader
         /// </summary>
         public const int SizeV4 = 108;
 
+        /// <summary>
+        /// Defines the size of the BITMAPINFOHEADER (BMP Version 5) data structure in the bitmap file.
+        /// </summary>
+        public const int SizeV5 = 124;
+
         /// <summary>
         /// Defines the size of the biggest supported header data structure in the bitmap file.
         /// </summary>
-        public const int MaxHeaderSize = SizeV4;
+        public const int MaxHeaderSize = SizeV5;
 
         /// <summary>
         /// Defines the size of the <see cref="HeaderSize"/> field.
@@ -272,7 +277,7 @@ public BmpInfoHeader(
         /// Parses the BITMAPCOREHEADER (BMP Version 2) consisting of the headerSize, width, height, planes, and bitsPerPixel fields (12 bytes).
         /// </summary>
         /// <param name="data">The data to parse.</param>
-        /// <returns>Parsed header</returns>
+        /// <returns>The parsed header.</returns>
         /// <seealso href="https://msdn.microsoft.com/en-us/library/windows/desktop/dd183372.aspx"/>
         public static BmpInfoHeader ParseCore(ReadOnlySpan<byte> data)
         {
@@ -289,7 +294,7 @@ public static BmpInfoHeader ParseCore(ReadOnlySpan<byte> data)
         /// are 4 bytes instead of 2, resulting in 16 bytes total.
         /// </summary>
         /// <param name="data">The data to parse.</param>
-        /// <returns>Parsed header</returns>
+        /// <returns>The parsed header.</returns>
         /// <seealso href="https://www.fileformat.info/format/os2bmp/egff.htm"/>
         public static BmpInfoHeader ParseOs22Short(ReadOnlySpan<byte> data)
         {
@@ -406,7 +411,7 @@ public static BmpInfoHeader ParseOs2Version2(ReadOnlySpan<byte> data)
         /// <seealso href="http://www.fileformat.info/format/bmp/egff.htm"/>
         public static BmpInfoHeader ParseV4(ReadOnlySpan<byte> data)
         {
-            if (data.Length != SizeV4)
+            if (data.Length < SizeV4)
             {
                 throw new ArgumentException(nameof(data), $"Must be {SizeV4} bytes. Was {data.Length} bytes.");
             }
@@ -457,4 +462,4 @@ internal void VerifyDimensions()
             }
         }
     }
-}
+}

tests/ImageSharp.Tests/Formats/Bmp/BmpDecoderTests.cs

@@ -343,7 +343,6 @@ public void BmpDecoder_ThrowsNotSupportedException_OnUnsupportedBitmaps<TPixel>(
         }
 
         [Theory]
-        [WithFile(Rgba32bf56AdobeV3, PixelTypes.Rgba32)]
         [WithFile(Rgb32h52AdobeV3, PixelTypes.Rgba32)]
         public void BmpDecoder_CanDecodeAdobeBmpv3<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : struct, IPixel<TPixel>
@@ -355,6 +354,18 @@ public void BmpDecoder_CanDecodeAdobeBmpv3<TPixel>(TestImageProvider<TPixel> pro
             }
         }
 
+        [Theory]
+        [WithFile(Rgba32bf56AdobeV3, PixelTypes.Rgba32)]
+        public void BmpDecoder_CanDecodeAdobeBmpv3_WithAlpha<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            using (Image<TPixel> image = provider.GetImage(new BmpDecoder()))
+            {
+                image.DebugSave(provider);
+                image.CompareToOriginal(provider, new MagickReferenceDecoder());
+            }
+        }
+
         [Theory]
         [WithFile(WinBmpv4, PixelTypes.Rgba32)]
         public void BmpDecoder_CanDecodeBmpv4<TPixel>(TestImageProvider<TPixel> provider)
@@ -429,12 +440,35 @@ public void BmpDecoder_CanDecode4BytePerEntryPalette<TPixel>(TestImageProvider<T
         [InlineData(Bit4, 4)]
         [InlineData(Bit1, 1)]
         [InlineData(Bit1Pal1, 1)]
-        public void Identify(string imagePath, int expectedPixelSize)
+        public void Identify_DetectsCorrectPixelType(string imagePath, int expectedPixelSize)
         {
             var testFile = TestFile.Create(imagePath);
             using (var stream = new MemoryStream(testFile.Bytes, false))
             {
-                Assert.Equal(expectedPixelSize, Image.Identify(stream)?.PixelType?.BitsPerPixel);
+                IImageInfo imageInfo = Image.Identify(stream);
+                Assert.NotNull(imageInfo);
+                Assert.Equal(expectedPixelSize, imageInfo.PixelType?.BitsPerPixel);
+            }
+        }
+
+        [Theory]
+        [InlineData(Bit32Rgb, 127, 64)]
+        [InlineData(Car, 600, 450)]
+        [InlineData(Bit16, 127, 64)]
+        [InlineData(Bit16Inverted, 127, 64)]
+        [InlineData(Bit8, 127, 64)]
+        [InlineData(Bit8Inverted, 127, 64)]
+        [InlineData(RLE8, 491, 272)]
+        [InlineData(RLE8Inverted, 491, 272)]
+        public void Identify_DetectsCorrectWidthAndHeight(string imagePath, int expectedWidth, int expectedHeight)
+        {
+            var testFile = TestFile.Create(imagePath);
+            using (var stream = new MemoryStream(testFile.Bytes, false))
+            {
+                IImageInfo imageInfo = Image.Identify(stream);
+                Assert.NotNull(imageInfo);
+                Assert.Equal(expectedWidth, imageInfo.Width);
+                Assert.Equal(expectedHeight, imageInfo.Height);
             }
         }
 
@@ -465,8 +499,7 @@ public void BmpDecoder_CanDecode_Os2v2XShortHeader<TPixel>(TestImageProvider<TPi
             {
                 image.DebugSave(provider);
 
-                // TODO: Neither System.Drawing not MagickReferenceDecoder 
-                // can correctly decode this file.
+                // TODO: Neither System.Drawing or MagickReferenceDecoder can correctly decode this file.
                 // image.CompareToOriginal(provider);
             }
         }
@@ -486,5 +519,26 @@ public void BmpDecoder_CanDecode_Os2v2Header<TPixel>(TestImageProvider<TPixel> p
                 // image.CompareToOriginal(provider, new MagickReferenceDecoder());
             }
         }
+
+        [Theory]
+        [WithFile(Os2BitmapArray9s, PixelTypes.Rgba32)]
+        [WithFile(Os2BitmapArrayDiamond, PixelTypes.Rgba32)]
+        [WithFile(Os2BitmapArraySkater, PixelTypes.Rgba32)]
+        [WithFile(Os2BitmapArraySpade, PixelTypes.Rgba32)]
+        [WithFile(Os2BitmapArraySunflower, PixelTypes.Rgba32)]
+        [WithFile(Os2BitmapArrayMarble, PixelTypes.Rgba32)]
+        [WithFile(Os2BitmapArrayWarpd, PixelTypes.Rgba32)]
+        [WithFile(Os2BitmapArrayPines, PixelTypes.Rgba32)]
+        public void BmpDecoder_CanDecode_Os2BitmapArray<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            using (Image<TPixel> image = provider.GetImage(new BmpDecoder()))
+            {
+                image.DebugSave(provider);
+
+                // TODO: Neither System.Drawing or MagickReferenceDecoder can correctly decode this file.
+                // image.CompareToOriginal(provider);
+            }
+        }
     }
 }