private static Size DecodeBitmap(SequentialBinaryReader reader)
{
var magicNumber = reader.ReadUInt16();
// skip past the rest of the file header
reader.Skip(4 + 2 + 2 + 4);
int headerSize = reader.ReadInt32();
int width, height;
// We expect the header size to be either 40 (BITMAPINFOHEADER) or 12 (BITMAPCOREHEADER)
if (headerSize == 40)
{
// BITMAPINFOHEADER
width = reader.ReadInt32();
height = Math.Abs(reader.ReadInt32());
}
else if (headerSize == 12)
{
width = reader.ReadInt16();
height = reader.ReadInt16();
}
else
{
// Unexpected DIB header size
return(Size.Empty);
}
return(new Size(width, height));
}
private static Size DecodeEmf(SequentialBinaryReader reader)
{
// EMR_HEADER: Type + Size + Bounds
reader.Skip(4 + 4 + 16);
// Frame: specify the rectangular inclusive-inclusive dimensions,
// in .01 millimeter units, of a rectangle that surrounds the image stored in the metafile.
int left = reader.ReadInt32();
int top = reader.ReadInt32();
int right = reader.ReadInt32();
int bottom = reader.ReadInt32();
// Skip other headers:
// Signature (4) + Version (4) + Size (4) + Records (4) + Handles (2)
// + nReserved (2) + nDescription (4) + offDescription (4) + PalEntries (4)
reader.Skip(32);
// Next 8 bytes specify the size of the reference device, in pixels
int deviceSizeInPixelX = reader.ReadInt32();
int deviceSizeInPixelY = reader.ReadInt32();
// Then 8 more to specify the size of the reference device, in millimeters
int deviceSizeInMlmX = reader.ReadInt32();
int deviceSizeInMlmY = reader.ReadInt32();
int widthInPixel = (int)Math.Round(0.5 + ((right - left + 1.0) * deviceSizeInPixelX / deviceSizeInMlmX) / 100.0);
int heightInPixel = (int)Math.Round(0.5 + ((bottom - top + 1.0) * deviceSizeInPixelY / deviceSizeInMlmY) / 100.0);
return(new Size(widthInPixel, heightInPixel));
}
private static Size DecodePng(SequentialBinaryReader reader)
{
reader.IsBigEndian = true;
reader.ReadBytes(pngSignatureBytes.Length);
reader.Skip(8);
int width = reader.ReadInt32();
int height = reader.ReadInt32();
return(new Size(width, height));
}
private static Size DecodeGif(SequentialBinaryReader reader)
{
// 3 - signature: "GIF"
// 3 - version: either "87a" or "89a"
reader.Skip(6);
int width = reader.ReadInt16();
int height = reader.ReadInt16();
return(new Size(width, height));
}
/// <summary>
/// Examines the a file's first bytes and estimates the file's type.
/// </summary>
private static FileType DetectFileType(SequentialBinaryReader reader)
{
byte[] magicBytes = new byte[MaxMagicBytesLength];
for (int i = 0; i < MaxMagicBytesLength; i += 1)
{
magicBytes[i] = reader.ReadByte();
foreach (var kvPair in imageFormatDecoders)
{
if (StartsWith(magicBytes, kvPair.Key))
{
return(kvPair.Value);
}
}
}
return(FileType.Unrecognized);
}
private static Size DecodeJfif(SequentialBinaryReader reader)
{
reader.IsBigEndian = true;
var magicNumber = reader.ReadUInt16(); // first two bytes should be JPEG magic number
do
{
// Find next segment marker. Markers are zero or more 0xFF bytes, followed
// by a 0xFF and then a byte not equal to 0x00 or 0xFF.
byte segmentIdentifier = reader.ReadByte();
byte segmentType = reader.ReadByte();
// Read until we have a 0xFF byte followed by a byte that is not 0xFF or 0x00
while (segmentIdentifier != 0xFF || segmentType == 0xFF || segmentType == 0)
{
segmentIdentifier = segmentType;
segmentType = reader.ReadByte();
}
if (segmentType == 0xD9) // EOF?
{
return(Size.Empty);
}
// next 2-bytes are <segment-size>: [high-byte] [low-byte]
var segmentLength = (int)reader.ReadUInt16();
// segment length includes size bytes, so subtract two
segmentLength -= 2;
if (segmentType == 0xC0 || segmentType == 0xC2)
{
reader.ReadByte(); // bits/sample, usually 8
int height = (int)reader.ReadUInt16();
int width = (int)reader.ReadUInt16();
return(new Size(width, height));
}
else
{
// skip this segment
reader.Skip(segmentLength);
}
}while (true);
}
/// <summary>
/// Gets the dimensions of an image.
/// </summary>
/// <param name="stream">The content of the image.</param>
/// <returns>The dimensions of the specified image.</returns>
/// <exception cref="ArgumentException">The image was of an unrecognised format.</exception>
public static Size GetDimensions(Stream stream)
{
using (SequentialBinaryReader reader = new SequentialBinaryReader(stream))
{
FileType type = DetectFileType(reader);
stream.Seek(0L, SeekOrigin.Begin);
switch (type)
{
case FileType.Bitmap: return(DecodeBitmap(reader));
case FileType.Gif: return(DecodeGif(reader));
case FileType.Jpeg: return(DecodeJfif(reader));
case FileType.Png: return(DecodePng(reader));
default: return(Size.Empty);
}
}
}