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;
        }