enable reading bmp with larger headers

src/ImageSharp/Formats/Bmp/BmpDecoderCore.cs

@@ -375,11 +375,18 @@ namespace ImageSharp.Formats
             // read header size
             this.currentStream.Read(data, 0, BmpInfoHeader.HeaderSizeSize);
             int headerSize = BitConverter.ToInt32(data, 0);
-            if (headerSize < BmpInfoHeader.HeaderSizeSize || headerSize > BmpInfoHeader.MaxHeaderSize)
+            if (headerSize < BmpInfoHeader.BitmapCoreHeaderSize)
             {
                 throw new NotSupportedException($"This kind of bitmap files (header size $headerSize) is not supported.");
             }
 
+            int skipAmmount = 0;
+            if (headerSize > BmpInfoHeader.MaxHeaderSize)
+            {
+                skipAmmount = headerSize - BmpInfoHeader.MaxHeaderSize;
+                headerSize = BmpInfoHeader.MaxHeaderSize;
+            }
+
             // read the rest of the header
             this.currentStream.Read(data, BmpInfoHeader.HeaderSizeSize, headerSize - BmpInfoHeader.HeaderSizeSize);
 
@@ -388,14 +395,23 @@ namespace ImageSharp.Formats
                 case BmpInfoHeader.BitmapCoreHeaderSize:
                     this.infoHeader = this.ParseBitmapCoreHeader(data);
                     break;
-
                 case BmpInfoHeader.BitmapInfoHeaderSize:
                     this.infoHeader = this.ParseBitmapInfoHeader(data);
                     break;
-
                 default:
-                    throw new NotSupportedException($"This kind of bitmap files (header size $headerSize) is not supported.");
+                    if (headerSize > BmpInfoHeader.BitmapInfoHeaderSize)
+                    {
+                        this.infoHeader = this.ParseBitmapInfoHeader(data);
+                        break;
+                    }
+                    else
+                    {
+                        throw new NotSupportedException($"This kind of bitmap files (header size $headerSize) is not supported.");
+                    }
             }
+
+            // skip the remaining header because we can't read those parts
+            this.currentStream.Skip(skipAmmount);
         }
 
         /// <summary>

tests/ImageSharp.Tests/TestImages.cs

@@ -117,7 +117,9 @@ namespace ImageSharp.Tests
             public const string F = "Bmp/F.bmp";
             public const string NegHeight = "Bmp/neg_height.bmp";
             public const string CoreHeader = "Bmp/BitmapCoreHeaderQR.bmp";
-            public static readonly string[] All = { Car, F, NegHeight, CoreHeader };
+            public const string V5Header = "Bmp/BITMAPV5HEADER.bmp";
+            
+            public static readonly string[] All = { Car, F, NegHeight, CoreHeader, V5Header };
         }
 
         public static class Gif

tests/ImageSharp.Tests/TestImages/Formats/Bmp/BITMAPV5HEADER.bmp

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:9d99f80a05e0ddb6309c84846dfac7d2ef4e9cdda6ed437646bc0edfee7d3130
+size 174026