Various ways to use C# to determine whether a file is an image

0. Common ways to judge picture files

There are three main ways to determine whether a file is an image:

Judging by file extension
Judging by the file header (Magic Number)
Try to load the file to judge (recommended: use ImageSharp)

1. Judging by file extension

This is the easiest way to determine whether it is an image by judging the extension of the file. Although the implementation is simple, it is not rigorous enough, because the file extension can be forged.

Code Example

public bool IsImageByExtension(string filePath) 
{ 
    // Supported image format extension    string[] validExtensions = { ".jpg", ".jpeg", ".png", ".bmp", ".gif", ".tiff", ".webp" }; 
    string extension = (filePath)?.ToLower(); // Get the file extension and convert it to lowercase    return (extension); 
}

Pros and cons

advantage: Simple implementation and high performance.
shortcoming: There is no guarantee that the content of the file is indeed a picture and may be forged.

2. Judgment through the file header (Magic Number)

Each file format has a unique binary header (Magic Number). The file type can be more accurately judged by reading the first few bytes of a file and matching it with the Magic Number in common image formats.

Code Example

public bool IsImageByHeader(string filePath)
{
    // Magic Number that defines common image formats    var imageHeaders = new Dictionary&lt;string, byte[]&gt;
    {
        { "jpg", new byte[] { 0xFF, 0xD8 } },
        { "png", new byte[] { 0x89, 0x50, 0x4E, 0x47 } },
        { "gif", new byte[] { 0x47, 0x49, 0x46 } },
        { "bmp", new byte[] { 0x42, 0x4D } },
        { "tiff", new byte[] { 0x49, 0x49, 0x2A, 0x00 } }
    };
 
    using (FileStream fs = new FileStream(filePath, , ))
    {
        byte[] buffer = new byte[4]; // Read the first 4 bytes of the file        (buffer, 0, );
 
        // Determine whether the file header matches a certain image format        foreach (var header in )
        {
            if (().SequenceEqual(header))
                return true;
        }
    }
    return false;
}

Pros and cons

advantage: More reliable, ensuring that the file header matches the image format.
shortcoming: You need to parse the file contents and take up resources slightly.

3. Use ImageSharp to determine whether the file is an image

As it is deprecated in .NET 6 and above, it is recommended to use the library to determine whether the file is an image. ImageSharp is a cross-platform image processing library that supports multiple image formats and can ensure that files not only match image extensions, but can indeed be parsed into image formats.

Install ImageSharp

Use the following command to installImageSharp：

dotnet add package

Or in the project.csprojAdded to the file:

<PackageReference Include="" Version="3.0.0" />

Code example: Detect file types using ImageSharp

using ;
 
public bool IsImageByImageSharp(string filePath)
{
    try
    {
        // Use to detect whether the file is a valid picture        using (var image = (filePath))
        {
            return true;
        }
    }
    catch ()
    {
        // The format is not supported or not the picture        return false;
    }
    catch (Exception)
    {
        // Other exceptions, such as the file does not exist, etc.        return false;
    }
}

Code parsing

: If the file is in a supported image format, it will be loaded successfully, otherwise an exception will be thrown.
UnknownImageFormatException: This exception is thrown when the file is not a picture or the format is not supported.
Other exceptions: Capture situations such as file path errors to avoid program crashes.

Pros and cons

advantage: Rigorous and reliable to ensure that the file content is indeed in the picture format.
shortcoming: It will take up resources slightly when loading the file.

Supported image formats

ImageSharpSupports common picture formats:

JPEG (.jpg, .jpeg)
PNG (.png)
GIF (.gif)
BMP (.bmp)
TIFF (.tiff)
WEBP (.webp)

4. Summary

The above is the detailed content of various methods of using C# to determine whether a file is a picture. For more information on whether a file is a picture, please pay attention to my other related articles!