如何使用dotnet只在jpg文件中散列图像数据？

Question

我有~20000 jpg图像,其中一些是重复的.遗憾的是,某些文件已使用EXIF元数据标记,因此简单的文件哈希无法识别重复的文件.

我试图创建一个Powershell脚本来处理这些,但却找不到只提取位图数据的方法.

system.drawing.bitmap只能返回一个位图对象,而不是字节.有一个GetHash()函数,但它显然作用于整个文件.

如何以排除EXIF信息的方式散列这些文件？如果可能的话,我宁愿避免外部依赖.

Answer 1

这是PowerShell V2.0高级功能实现.它有点长,但我已经验证它在同一张图片上提供了相同的哈希码(从位图像素生成),但具有不同的元数据和文件大小.这是一个支持管道的版本,它也接受通配符和文字路径:

function Get-BitmapHashCode
{
    [CmdletBinding(DefaultParameterSetName="Path")]
    param(
        [Parameter(Mandatory=$true, 
                   Position=0, 
                   ParameterSetName="Path", 
                   ValueFromPipeline=$true, 
                   ValueFromPipelineByPropertyName=$true,
                   HelpMessage="Path to bitmap file")]
        [ValidateNotNullOrEmpty()]
        [string[]]
        $Path,

        [Alias("PSPath")]
        [Parameter(Mandatory=$true, 
                   Position=0, 
                   ParameterSetName="LiteralPath", 
                   ValueFromPipelineByPropertyName=$true,
                   HelpMessage="Path to bitmap file")]
        [ValidateNotNullOrEmpty()]
        [string[]]
        $LiteralPath
    )

    Begin {
        Add-Type -AssemblyName System.Drawing
        $sha = new-object System.Security.Cryptography.SHA256Managed
    }

    Process {
        if ($psCmdlet.ParameterSetName -eq "Path")
        {
            # In -Path case we may need to resolve a wildcarded path
            $resolvedPaths = @($Path | Resolve-Path | Convert-Path)
        }
        else 
        {
            # Must be -LiteralPath
            $resolvedPaths = @($LiteralPath | Convert-Path)
        }

        # Find PInvoke info for each specified path       
        foreach ($rpath in $resolvedPaths) 
        {           
            Write-Verbose "Processing $rpath"
            try {
                $bmp    = new-object System.Drawing.Bitmap $rpath
                $stream = new-object System.IO.MemoryStream
                $writer = new-object System.IO.BinaryWriter $stream
                for ($w = 0; $w -lt $bmp.Width; $w++) {
                    for ($h = 0; $h -lt $bmp.Height; $h++) {
                        $pixel = $bmp.GetPixel($w,$h)
                        $writer.Write($pixel.ToArgb())
                    }
                }
                $writer.Flush()
                [void]$stream.Seek(0,'Begin')
                $hash = $sha.ComputeHash($stream)
                [BitConverter]::ToString($hash) -replace '-',''
            }
            finally {
                if ($bmp)    { $bmp.Dispose() }
                if ($writer) { $writer.Close() }
            }
        }  
    }
}

Answer 2

您可以将 JPEG 加载到 System.Drawing.Image 中并使用它的 GetHashCode 方法

using (var image = Image.FromFile("a.jpg"))
    return image.GetHashCode();

要获取字节，您可以

using (var image = Image.FromFile("a.jpg"))
using (var output = new MemoryStream())
{
    image.Save(output, ImageFormat.Bmp);
    return output.ToArray();
}

Answer 3

这是一个powershell脚本,它仅使用LockBits提取的图像字节生成SHA256哈希.这应该为每个不同的文件生成唯一的哈希.请注意,我没有包含文件迭代代码,但是使用foreach目录迭代器替换当前硬编码c:\ test.bmp应该是一个相对简单的任务.变量$ final包含最终哈希的十六进制 - ascii字符串.

[System.Reflection.Assembly]::LoadWithPartialName("System.Drawing")
[System.Reflection.Assembly]::LoadWithPartialName("System.Drawing.Imaging")
[System.Reflection.Assembly]::LoadWithPartialName("System.Security")


$bmp = [System.Drawing.Bitmap]::FromFile("c:\\test.bmp")
$rect = [System.Drawing.Rectangle]::FromLTRB(0, 0, $bmp.width, $bmp.height)
$lockmode = [System.Drawing.Imaging.ImageLockMode]::ReadOnly               
$bmpData = $bmp.LockBits($rect, $lockmode, $bmp.PixelFormat);
$dataPointer = $bmpData.Scan0;
$totalBytes = $bmpData.Stride * $bmp.Height;
$values = New-Object byte[] $totalBytes
[System.Runtime.InteropServices.Marshal]::Copy($dataPointer, $values, 0, $totalBytes);                
$bmp.UnlockBits($bmpData);

$sha = new-object System.Security.Cryptography.SHA256Managed
$hash = $sha.ComputeHash($values);
$final = [System.BitConverter]::ToString($hash).Replace("-", "");

也许等效的C#代码也可以帮助您理解:

private static String ImageDataHash(FileInfo imgFile)
{
    using (Bitmap bmp = (Bitmap)Bitmap.FromFile(imgFile.FullName))
    {                
        BitmapData bmpData = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), System.Drawing.Imaging.ImageLockMode.ReadOnly, bmp.PixelFormat);
        IntPtr dataPointer = bmpData.Scan0;
        int totalBytes = bmpData.Stride * bmp.Height;
        byte[] values = new byte[totalBytes];                
        System.Runtime.InteropServices.Marshal.Copy(dataPointer, values, 0, totalBytes);                
        bmp.UnlockBits(bmpData);
        SHA256 sha = new SHA256Managed();
        byte[] hash = sha.ComputeHash(values);
        return BitConverter.ToString(hash).Replace("-", "");                
    }
}