C#快速获取JPG图片大小及英寸分辨率

//C#快速获取JPG图片大小及英寸分辨率
public static int getJpgSize(string
FileName, out Size JpgSize, out float Wpx, out float Hpx)

{//C#快速获取JPG图片大小及英寸分辨率
JpgSize = new Size(0, 0);

Wpx = 0; Hpx = 0;
int rx = 0;
if
(!File.Exists(FileName)) return rx;
FileStream F_Stream =
File.OpenRead(FileName);
int ff =
F_Stream.ReadByte();
int type =
F_Stream.ReadByte();
if (ff != 0xff || type !=
0xd8)
{//非JPG文件

F_Stream.Close();
return rx;
}

long ps = 0;
do
{

do
{
ff =
F_Stream.ReadByte();
if (ff < 0)
//文件结束
{

F_Stream.Close();
return rx;

}
} while (ff != 0xff);

do
{
type =
F_Stream.ReadByte();
} while (type == 0xff);

//MessageBox.Show(ff.ToString() + "," + type.ToString(),
F_Stream.Position.ToString());
ps =
F_Stream.Position;
switch (type)

{
case 0x00:
case
0x01:
case 0xD0:
case
0xD1:
case 0xD2:
case
0xD3:
case 0xD4:
case
0xD5:
case 0xD6:
case
0xD7:
break;
case 0xc0:
//SOF0段
ps = F_Stream.ReadByte() *
256;
ps = F_Stream.Position + ps +
F_Stream.ReadByte() - 2; //加段长度

F_Stream.ReadByte();
//丢弃精度数据
//高度

JpgSize.Height = F_Stream.ReadByte() * 256;

JpgSize.Height = JpgSize.Height +
F_Stream.ReadByte();
//宽度

JpgSize.Width = F_Stream.ReadByte() * 256;

JpgSize.Width = JpgSize.Width + F_Stream.ReadByte();

//后面信息忽略
if (rx!=1 && rx < 3) rx = rx +
1;
break;
case 0xe0:
//APP0段
ps = F_Stream.ReadByte() *
256;
ps = F_Stream.Position + ps +
F_Stream.ReadByte() - 2; //加段长度

F_Stream.Seek(5,SeekOrigin.Current);
//丢弃APP0标记(5bytes)

F_Stream.Seek(2,SeekOrigin.Current);
//丢弃主版本号(1bytes)及次版本号(1bytes)
int
units=F_Stream.ReadByte();
//X和Y的密度单位,units=0：无单位,units=1：点数/英寸,units=2：点数/厘米

//水平方向(像素/英寸)分辨率

Wpx=F_Stream.ReadByte()*256;

Wpx=Wpx+F_Stream.ReadByte();
if (units == 2) Wpx =
(float)(Wpx * 2.54); //厘米变为英寸

//垂直方向(像素/英寸)分辨率
Hpx = F_Stream.ReadByte() *
256;
Hpx = Hpx +
F_Stream.ReadByte();
if (units == 2) Hpx =
(float)(Hpx * 2.54); //厘米变为英寸

//后面信息忽略
if (rx!=2 && rx<3) rx = rx +
2;
break;

default:
//别的段都跳过////////////////
ps = F_Stream.ReadByte() *
256;
ps = F_Stream.Position + ps +
F_Stream.ReadByte() - 2; //加段长度

break;
}
if (ps + 1 >= F_Stream.Length)
//文件结束
{

F_Stream.Close();
return rx;

}
F_Stream.Position = ps; //移动指针
} while (type
!= 0xda); // 扫描行开始
F_Stream.Close();
return
rx;
}