C#实现根据图片的EXIF自动调整图片方向

梦里梦外; 2021-07-04 16:00 460阅读 0赞

## 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。  
![在这里插入图片描述][20200812120049896.png]

## 二、EXIF `Orientation` ##

Orientation  
The image orientation viewed in terms of rows and columns.  
按行和列查看的图像方向

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;
        }
    }

## .Net Core 通过`Exif`处理手机图片旋转问题 ##

获取图片 `exif` 的 `orientation` 信息核心代码，然后根据 `orientation` 进行图片不同方向的旋转

### 效果展示 ###

![在这里插入图片描述][20200812142412781.png]

### 核心代码 ###

private Image OrientationImage(Image image)
    { 
        if (Array.IndexOf(image.PropertyIdList, 274) > -1)
        { 
            var orientation = (int)image.GetPropertyItem(274).Value[0];
            switch (orientation)
            { 
                case 1:
                    // No rotation required.
                    break;
                case 2:
                    image.RotateFlip(RotateFlipType.RotateNoneFlipX);
                    break;
                case 3:
                    image.RotateFlip(RotateFlipType.Rotate180FlipNone);
                    break;
                case 4:
                    image.RotateFlip(RotateFlipType.Rotate180FlipX);
                    break;
                case 5:
                    image.RotateFlip(RotateFlipType.Rotate90FlipX);
                    break;
                case 6:
                    image.RotateFlip(RotateFlipType.Rotate90FlipNone);
                    break;
                case 7:
                    image.RotateFlip(RotateFlipType.Rotate270FlipX);
                    break;
                case 8:
                    image.RotateFlip(RotateFlipType.Rotate270FlipNone);
                    break;
            }
            image.RemovePropertyItem(274);
    
        }
        return image;
    }

### 文件转为`image`类型 ###

上传的图片文件（file（`IFormFile`） 或者 `base64(string)` 需转为 `image`，然后直接调用上面方法，输出新的 `image`  
保存(`save`方法)即可

`file` 的话

Image img = Bitmap.FromStream(file.OpenReadStream());

`base64` 的话

string base64string = HttpUtility.UrlDecode(base64);
     base64string = base64string.Replace(" ", "+").Split(',')[1];
     byte[] bt = Convert.FromBase64String(base64string);
     MemoryStream ms = new MemoryStream(bt);
     Image img = Image.FromStream(ms);

[20200812120049896.png]: /images/20210704/b938ad9b5e714023bab0380924b681c8.png
[20200812142412781.png]: /images/20210704/645936f2936f461bb623e55c7a85a69f.png