/// <summary>
/// Reads the size of a BMP image from this stream at the current offset
/// Rewinds the stream to where it started when finished
/// </summary>
/// <param name="stream"></param>
/// <returns></returns>
public static Size GetBmpImageSize(Stream stream)
{
if (!ImageTypeHelper.IsBmp(stream))
{
throw new InvalidDataException("This is not a BMP stream");
}
var br = new BinaryReader(stream);
// jump over:
// 2: the magic number
// 4: size of the file
// 2: reserved
// 2: reserved
// 4: start of bmp data offset
// 4: header size
br.BaseStream.Seek(18, SeekOrigin.Begin);
var size = new Size(br.ReadInt32(), br.ReadInt32());
if (br.BaseStream.CanSeek)
{
br.BaseStream.Seek(-26, SeekOrigin.Current);
}
return(size);
}
/// <summary>
/// Tries to use the GNV fast image size checkers for JPEG, GIF, PNG, and BMP
/// Uses .NET newing-up an Image object as a fallback
/// </summary>
/// <param name="stream"></param>
/// <returns></returns>
public static Size GetImageSize(Stream stream)
{
var mimeType = stream.GetMimeFromBytes();
var imageFormat = ImageTypeHelper.GetImageFormatFromMimeType(mimeType);
if (imageFormat.Guid == ImageFormat.Jpeg.Guid)
{
return(GetJpegImageSize(stream));
}
if (imageFormat.Guid == ImageFormat.Gif.Guid)
{
return(GetGifImageSize(stream));
}
if (imageFormat.Guid == ImageFormat.Png.Guid)
{
return(GetPngImageSize(stream));
}
if (imageFormat.Guid == ImageFormat.Bmp.Guid)
{
return(GetBmpImageSize(stream));
}
using (var img = Image.FromStream(stream)) {
return(img.Size);
}
}
/// <summary>
/// Reads a JPEG image's dimensions and returns a <see cref="Size"/> object. Much faster
/// than using the built in <see cref="System.Drawing.Image"/> class which loads the entire image into memory
/// Rewinds the stream after reading.
/// </summary>
/// <param name="stream"></param>
/// <exception cref="InvalidDataException">Thrown when the Stream is not a JPEG image</exception>
/// <returns></returns>
public static Size GetJpegImageSize(Stream stream)
{
if (!ImageTypeHelper.IsJpeg(stream))
{
throw new InvalidDataException("This is not a JPEG stream");
}
try {
var br = new BinaryReader(stream);
// skip the 0xFFD8 marker
br.BaseStream.Seek(2, SeekOrigin.Current);
// keep reading packets until we find one that contains Size info
while (true)
{
ushort b1 = 0x00;
while (b1 != 0xFF)
{
b1 = br.ReadByte();
}
while (b1 == 0xFF)
{
b1 = br.ReadByte();
}
if (b1 >= 0xC0 && b1 <= 0xC3)
{
// this is the SOF (Start Of Frame) marker. skip 3 bytes
br.BaseStream.Seek(3, SeekOrigin.Current);
var h = br.ReadUInt16BE();
var w = br.ReadUInt16BE();
return(new Size(w, h));
}
else
{
// this isn't the SOF marker, skip to the next marker
br.BaseStream.Seek(br.ReadUInt16BE() - 2, SeekOrigin.Current);
}
}
}
catch (EndOfStreamException ex) {
throw new Exception("Hit the end of the stream without finding the dimensions. This file may be corrupt.", ex);
}
finally {
if (stream != null && stream.CanSeek)
{
stream.Seek(0, SeekOrigin.Begin);
}
}
}
/// <summary>
/// Reads the size of a PNG image from this stream at the current offset
/// Rewinds the stream to where it started when finished
/// </summary>
/// <param name="stream"></param>
/// <returns></returns>
public static Size GetPngImageSize(Stream stream)
{
if (!ImageTypeHelper.IsPng(stream))
{
throw new InvalidDataException("This is not a PNG stream");
}
var br = new BinaryReader(stream);
var position = br.BaseStream.Position;
// jump over the 8 byte signature, the 4 byte chunk length indicator, and the 4 byte IHDR marker
br.BaseStream.Seek(16, SeekOrigin.Begin);
var size = new Size((int)br.ReadUInt32BE(), (int)br.ReadUInt32BE());
if (br.BaseStream.CanSeek)
{
br.BaseStream.Seek(position, SeekOrigin.Begin);
}
return(size);
}
/// <summary>
/// Reads the size of a GIF image from this stream at the current offset
/// Rewinds the stream to where it started when finished
/// </summary>
/// <param name="stream"></param>
/// <returns></returns>
public static Size GetGifImageSize(Stream stream)
{
if (!ImageTypeHelper.IsGif(stream))
{
throw new InvalidDataException("This is not a GIF stream");
}
var br = new BinaryReader(stream);
// jump over:
// 3: GIF
// 3: version (87a, 89a, etc)
br.BaseStream.Seek(6, SeekOrigin.Current);
var size = new Size(br.ReadInt16(), br.ReadInt16());
if (br.BaseStream.CanSeek)
{
br.BaseStream.Seek(-10, SeekOrigin.Current);
}
return(size);
}
