Unity 使用IO流获取PNG/JPG/GIF/BMP的宽高【转】

原文链接：https://blog.csdn.net/flj135792468/article/details/107963280?utm_medium=distribute.pc_relevant.none-task-blog-baidulandingword-8&spm=1001.2101.3001.4242

读取图片流前8个字节

Png图片 8字节：89 50 4E 47 0D 0A 1A 0A = [1]:P[2]:N[3]:G

Jpg图片 2字节：FF D8

Gif图片 6字节：47 49 46 38 39|37 61 = G I F 8 9 7 a

Bmp图片 2字节：42 4D

根据字节判断所属是什么类型

public class FileUtility
{
public enum ImageType
{
Null,
Png,
Jpg,
Gif,
Bmp
}

/// <summary>
/// 获取图片格式
/// </summary>
private static ImageType GetImageType(byte[] bytes)
{
byte[] header = new byte[8];
Array.Copy(bytes, header, header.Length);
ImageType type = ImageType.Null;
//读取图片文件头8个字节
//Png图片 8字节：89 50 4E 47 0D 0A 1A 0A = [1]:P[2]:N[3]:G
if (header[0] == 0x89 && header[1] == 0x50 && header[2] == 0x4E && header[3] == 0x47 &&
header[4] == 0x0D && header[5] == 0x0A && header[6] == 0x1A && header[7] == 0x0A)
{
type = ImageType.Png;
}
//Jpg图片 2字节：FF D8
else if (header[0] == 0xFF && header[1] == 0xD8)
{
type = ImageType.Jpg;
}
//Gif图片 6字节：47 49 46 38 39|37 61 = GIF897a
else if (header[0] == 0x47 && header[1] == 0x49 && header[2] == 0x46 && header[3] == 0x38 &&
(header[4] == 0x39 || header[4] == 0x37) && header[5] == 0x61)
{
type = ImageType.Gif;
}
//Bmp图片 2字节：42 4D
else if (header[0] == 0x42 && header[1] == 0x4D)
{
type = ImageType.Bmp;
}
return type;
}

private static byte[] _header = null;
private static byte[] _buffer = null;

public static void FileInfo(string filePath, out byte[] bytes, out Vector2 size)
{
size = Vector2.zero;
FileStream stream = new FileStream(filePath, FileMode.Open, FileAccess.Read);
stream.Seek(0, SeekOrigin.Begin);
bytes = new byte[stream.Length];
stream.Read(bytes, 0, (int)stream.Length);

ImageType imageType = GetImageType(bytes);
switch (imageType)
{
case ImageType.Png:
{
stream.Seek(0, SeekOrigin.Begin);
_header = new byte[8];
stream.Read(_header, 0, 8);
stream.Seek(8, SeekOrigin.Current);

_buffer = new byte[8];
stream.Read(_buffer, 0, _buffer.Length);

Array.Reverse(_buffer, 0, 4);
Array.Reverse(_buffer, 4, 4);

size.x = BitConverter.ToInt32(_buffer, 0);
size.y = BitConverter.ToInt32(_buffer, 4);
}
break;
case ImageType.Jpg:
{
stream.Seek(0, SeekOrigin.Begin);
_header = new byte[2];
stream.Read(_header, 0, 2);
//段类型
int type = -1;
int ff = -1;
//记录当前读取的位置
long ps = 0;
//逐个遍历所以段，查找SOFO段
do
{
do
{
//每个新段的开始标识为oxff，查找下一个新段
ff = stream.ReadByte();
if (ff < 0) //文件结束
{
return;
}
} while (ff != 0xff);

do
{
//段与段之间有一个或多个oxff间隔，跳过这些oxff之后的字节为段标识
type = stream.ReadByte();
} while (type == 0xff);

//记录当前位置
ps = 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（图像基本信息）
case 0xc2: //JFIF格式的 SOF0段
{
//找到SOFO段，解析宽度和高度信息
//跳过2个自己长度信息和1个字节的精度信息
stream.Seek(3, SeekOrigin.Current);

//高度 占2字节 低位高位互换
size.y = stream.ReadByte() * 256;
size.y += stream.ReadByte();
//宽度 占2字节 低位高位互换
size.x = stream.ReadByte() * 256;
size.x += stream.ReadByte();
return;
}
default: //别的段都跳过
//获取段长度，直接跳过
ps = stream.ReadByte() * 256;
ps = stream.Position + ps + stream.ReadByte() - 2;
break;
}
if (ps + 1 >= stream.Length) //文件结束
{
return;
}
stream.Position = ps; //移动指针
} while (type != 0xda); // 扫描行开始
}
break;
case ImageType.Gif:
{
stream.Seek(0, SeekOrigin.Begin);
_header = new byte[6];
stream.Read(_header, 0, 6);

_buffer = new byte[4];
stream.Read(_buffer, 0, _buffer.Length);

size.x = BitConverter.ToInt16(_buffer, 0);
size.y = BitConverter.ToInt16(_buffer, 2);
}
break;
case ImageType.Bmp:
{
stream.Seek(0, SeekOrigin.Begin);
_header = new byte[2];
stream.Read(_header, 0, 2);
//跳过16个字节
stream.Seek(16, SeekOrigin.Current);
//bmp图片的宽度信息保存在第 18-21位 4字节
//bmp图片的高度度信息保存在第 22-25位 4字节
_buffer = new byte[8];
stream.Read(_buffer, 0, _buffer.Length);

size.x = BitConverter.ToInt32(_buffer, 0);
size.y = BitConverter.ToInt32(_buffer, 4);
}
break;
default:
break;
}

stream.Close();
stream.Dispose();
}

}