一、什么是EXIF
Exif是英文Exchangeable Image File(可交换图像文件)的缩写，最初由日本电子工业发展协会(JEIDA --Japan Electronic Industry Development Association) 制订，目前的最新版本是发表于2002年04月的2.21 版。国际标准化组织(ISO)正在制订的相机文件设计标准（DCF -- Design role for Camera File system）可能以Exif2.1为基础。
所有的JPEG文件以字符串“0xFFD8”开头，并以字符串“0xFFD9”结束。文件头中有一系列“0xFF??”格式的字符串，称为“标识”，用来标记JPEG文件的信息段。“0xFFD8”表示图像信息开始，“0xFFD9”表示图像信息结束，这两个标识后面没有信息，而其它标识紧跟一些信息字符。
0xFFE0 -- 0xFFEF之间的标识符称为“应用标记”，没有被常规JPEG文件利用，Exif正是利用这些信息串记录拍摄信息如快门速度、光圈值等，甚至可以包括全球定位信息。其中拍摄方向的ID为“0x0112”，有1至8共8种值。而C#旋转图片可以通过EXIF来实现。
二、EXIF Orientation
- Orientation
- The image orientation viewed in terms of rows and columns.
- Tag = 274 (112.H)
- Type = SHORT
- Count = 1
- Default = 1
- 1 = The 0th row is at the visual top of the image, and the 0th column is the visual left-hand side.
- 2 = The 0th row is at the visual top of the image, and the 0th column is the visual right-hand side.
- 3 = The 0th row is at the visual bottom of the image, and the 0th column is the visual right-hand side.
- 4 = The 0th row is at the visual bottom of the image, and the 0th column is the visual left-hand side.
- 5 = The 0th row is the visual left-hand side of the image, and the 0th column is the visual top.
- 6 = The 0th row is the visual right-hand side of the image, and the 0th column is the visual top.
- 7 = The 0th row is the visual right-hand side of the image, and the 0th column is the visual bottom.
- 8 = The 0th row is the visual left-hand side of the image, and the 0th column is the visual bottom.
- Other = reserved
三、使用C#旋转图片
- public static void rotating(Bitmap img,ref int width, ref int height, int orien)
- {
- int ow = width;
- switch (orien)
- {
- case 2:
- img.RotateFlip(RotateFlipType.RotateNoneFlipX);//horizontal flip
- break;
- case 3:
- img.RotateFlip(RotateFlipType.Rotate180FlipNone);//right-top
- break;
- case 4:
- img.RotateFlip(RotateFlipType.RotateNoneFlipY);//vertical flip
- break;
- case 5:
- img.RotateFlip(RotateFlipType.Rotate90FlipX);
- break;
- case 6:
- img.RotateFlip(RotateFlipType.Rotate90FlipNone);//right-top
- width = height;
- height = ow;
- break;
- case 7:
- img.RotateFlip(RotateFlipType.Rotate270FlipX);
- break;
- case 8:
- img.RotateFlip(RotateFlipType.Rotate270FlipNone);//left-bottom
- width = height;
- height = ow;
- break;
- default:
- break;
- }
- }
至此，使用C#旋转图片的目的就达到了。
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