验证文件为JPEG [英] Verifying a file is JPEG

问题描述

我正在一个项目中，在该项目中，我使用文件夹对话框查找JPG文件并在列表中列出图像.

现在，我扩展了程序，以便用户可以将文件拖放到列表中.但是我希望图像是JPG.

我检查图像的大小，宽度和高度以及其他，如下所示....

I''m working on a project where I find JPG files using a folder dialog and list the images in a list.

Now, I''ve extended the program so the user can just drag and drop files in the list. But I want the images to be JPG.

I check for image size, width and height, and other as shown below....

public bool IsValid(string FileName)
       {
           Photo JPGFile = new Photo(FileName);

           //Check if the file exists.
           if (!System.IO.File.Exists(JPGFile.FullPath)) { return false; }

           //Check if the File is a JPG File.
           if (System.IO.Path.GetExtension(FileName).ToLower() != ".jpg")
           {
               //<-------------------------------Need a better validation------------>
               return false;
           }

           //Check if the FilePath Matches any other file in the List.
           foreach (Photo Picture in Photos)
           {
               if (FileName == Picture.FullPath)
               {
                   return false;
               }
               else
               {
                   continue;
               }
           }

           //Check if the File Size is greater than 450kb.

           if (JPGFile.GetRawSize() > 450)
           {
               return false;
           }

           //Check if the Height or width of the image is greater than that of the screen size.

           if (JPGFile.ImageWidth > SystemParameters.VirtualScreenWidth || JPGFile.ImageHeight > SystemParameters.VirtualScreenHeight)
           {
               return false;
           }

           return true;
       }

当我进行测试时，我只是将一个desktop.ini文件重命名为Desktop.jpg并通过了验证.任何人都可以帮助我如何真正检查图像是否为有效的jpg文件.

When I was testing, I just renamed a desktop.ini file to Desktop.jpg and it passed validation. Can anyone help please on how I can really check if the image is a VALID jpg file.

Thanks.

推荐答案

最简单的方法是将其作为图像打开，并在打开时检查其为JPG类型.但是，如果不是，那么您将获得一个异常，该异常可能并不总是可以捕获的.

一种更安全的方法是将文件作为二进制流打开，并检查开始和结束:JPG文件以两个字节0xFF和0xD8开始，并以两个字节0xFF和0xD9结尾. JPG文件中还有一些特定的ASCII字符串: http://en.wikipedia.org/wiki/Magic_number_ ％28programming％29#Magic_numbers_in_files [ ^ ]
如果存在这些内容，则可能是JPG.但是唯一可以确定的唯一真实方法是将其作为图像加载！

The easiest way is to open it as an image and check it''s a JPG type when it''s open. However, if it isn''t then you will get an exception which may not always be catchable.

A safer way is to open the file as a binary stream and check the start and end: JPG files start with the two bytes 0xFF and 0xD8, and end with the two bytes 0xFF and 0xD9. There are also some specific ASCII strings in JPG files: http://en.wikipedia.org/wiki/Magic_number_%28programming%29#Magic_numbers_in_files[^]
If these are present, it probably is a JPG. But the only true way to be absolutely sure is to load it as an image!

尝试以下操作:

try this:

public  bool IsJpegImage(string filename)
{
	try
	{
		System.Drawing.Image img = System.Drawing.Image.FromFile(filename);

					   
		return img.RawFormat.Equals(System.Drawing.Imaging.ImageFormat.Jpeg);
	}
	catch (OutOfMemoryException)
	{
		return false;
	}
} 

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