C# get thumbnail from file via windows api

Question

Windows explorer has the ability to show thumbnails of files. These thumbnails are provided by core and third-party shell extensions.

I know how to extend the shell to provide thumbnails to Windows.

What I want to do is retrieve the thumbnail image from any file on the system via the shell using C#. Is this possible?

Essentially, I'm writing a custom file browser and I want to show thumbnails, and can't possibly parse every file on the planet to make my own thumbnails.

Clarification: Many answers seem to be centered around web page thumbnails, or scaling an image. But that's not at all what I'm looking for. What I want is to ask Windows for the thumbnail representation of these file types: .DOC, .PDF, .3DM, .DWG... and mabye about a dozen more. I don't want to parse, render, and make thumbnails myself, because Windows already knows how.

The code I posted as an answer actually works... maybe it can be simplified and cleaned up a bit.

user_163921 · Answer

Microsoft Office Thumbnails in SharePoint at http://msdn.microsoft.com/en-us/library/aa289172(VS.71).aspx. is exactly what you want. (I had no trouble converting the VB.NET code into C# using http://www.developerfusion.com/tools/convert/vb-to-csharp/.)

Regarding the code you posted in your answer, Thumbnail Extraction Using the Shell at http://www.vbaccelerator.com/home/net/code/libraries/Shell_Projects/Thumbnail_Extraction/article.asp is the original article the code is from. I believe nearly all IExtractImage samples (you find searching) are based on this article's code, due to naming convention, comments, and so on, that are carried from the original. Since this article dates from April 2003, it carries some non-standard (non-.NET) coding conventions. I did some basic testing, and there are garbage collection issues, freeing unmanaged resource issues, and other clean-up issues. Therefore, I make a strong recommendation to avoid the code in that article. Moreover, the code is structured is such a way to make maintenance difficult.

There is a clean simplier version on MSDN, dated July 2005, called Microsoft Office Thumbnails in SharePoint at http://msdn.microsoft.com/en-us/library/aa289172(VS.71).aspx. This code and the article's code share similarities, which leads me to believe the Thumbnail Extraction Using the Shell article is the basis for the SharePoint article. The VB.NET version of GetThumbnailImage ignores the longestEdge parameter, but the C++ version uses it and documents the use of the ORIGSIZE and QUALITY flags. In addition, the code illustrates how to use .NET's FreeCoTaskMem instead of the Shell's IMalloc and SHGetMalloc.

IExtractImage works with files, folders, and other namespace objects. The MSDN code works with hidden files, whereas, the vbAccelerator code needs then SHCONTF_INCLUDEHIDDEN added to the EnumObjects call. In addition, the vbAccelerator enumerates over the shell folder's objects looking for the specified file, which seems a waste of time. This may have been needed to find the correct "relative" PIDL that is used for the GetUIObjectOf call.

ShellThumbnail (Work-In-Progress)

Complete sample project at http://cid-7178d2c79ba0a7e3.office.live.com/self.aspx/.Public/ShellThumbnail.zip.

Imports System.Runtime.InteropServices

Namespace Shell

    ''' 
    ''' Generates a thumbnail of a folder's picture or a file's image.
    ''' 
    ''' This is the "Folder's Picture" and not the "Folder's Icon"! Use SHGetFileInfo to generate the thumbnail for a folder's icon or for a file that does not have a thumbnail handler.
    ''' Microsoft Office Thumbnails in SharePoint at http://msdn.microsoft.com/en-us/library/aa289172%28VS.71%29.aspx.
    Public Class ShellThumbnail

        'TODO - Work out the details for image size and IEIFLAG handling.

#Region " Determining Thumbnail Size and Quality [documentation] "

        'http://support.microsoft.com/kb/835823
        'Determining Thumbnail Size and Quality
        'Browse to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer. Create or modify two DWORDs called ThumbnailSize and ThumbnailQuality. For ThumbnailSize set the value in pixels, with the default being 96. For ThumbnailQuality set the value as a number that represents the percentage quality between 50 and 100.


        'http://www.pctools.com/guides/registry/detail/1066/ (modified)
        '  User Key: [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer]
        'System Key: [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer]
        'Value Name: ThumbnailSize, ThumbnailQuality
        ' Data Type: REG_DWORD (DWORD Value)
        'Value Data: Size in pixels (32-255), Quality Percentage (50-100)


        'Microsoft® Windows® XP Registry Guide 
        'Jerry Honeycutt 
        '09/11/2002 
        'Microsoft Press
        'http://www.microsoft.com/mspress/books/sampchap/6232.aspx#118
        'ThumbnailsThe Thumbnails category controls the 
        'quality of thumbnails in Windows Explorer. Table 5-10 describes the values for 
        'Image Quality and Size. Create values that you don't see in the registry. The 
        'default value for ThumbnailQuality is 0x5A. The 
        'default value for ThumbnailSize is 0x60. Keep in mind 
        'that higher quality and larger thumbnails require more disk space, which is not 
        'usually a problem, but they also take longer to display. Changing the quality 
        'does not affect thumbnails that already exist on the file system.
        'Table 5-10 Values in Thumbnails
        '

        '
        '
        '
        '
        '
        '
        '
        '
        '
        '
        '
        '
        '
        '
        '
        '
        '
        '
        '
        '
        '
        'Setting Name Type Data
HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer    
Image Quality ThumbnailQuality REG_DWORD 0x32 - 0x64
Size (pixels) ThumbnailSize REG_DWORD 0x20 - 0xFF


#End Region

        Public Shared ReadOnly DefaultThumbnailSize As New System.Drawing.Size(96, 96)

        Public Const DefaultColorDepth As Integer = 32

        ''' 
        ''' Used to request an image from an object, such as an item in a Shell folder.
        ''' 
        ''' An absolute path to a file or folder.
        Public Shared Function ExtractImage(ByVal path As String) As Bitmap
            Return ExtractImage(path, System.Drawing.Size.Empty, DefaultColorDepth, 0)
        End Function

        ''' 
        ''' Used to request an image from an object, such as an item in a Shell folder.
        ''' 
        ''' An absolute path to a file or folder.
        ''' 
        Public Shared Function ExtractImage(ByVal path As String, ByVal size As System.Drawing.Size) As Bitmap
            Return ExtractImage(path, size, DefaultColorDepth, 0)
        End Function

        ''' 
        ''' Used to request an image from an object, such as an item in a Shell folder.
        ''' 
        ''' An absolute path to a file or folder.
        ''' 
        ''' The recommended color depth in units of bits per pixel. The default is 32.
        Public Shared Function ExtractImage(ByVal path As String, ByVal size As System.Drawing.Size, ByVal recommendedColorDepth As Integer) As Bitmap
            Return ExtractImage(path, size, recommendedColorDepth, 0)
        End Function

        ''' 
        ''' Used to request an image from an object, such as an item in a Shell folder.
        ''' 
        ''' An absolute path to a file or folder.
        ''' 
        ''' The recommended color depth in units of bits per pixel. The default is 32.
        Private Shared Function ExtractImage(ByVal path As String, ByVal size As System.Drawing.Size, ByVal recommendedColorDepth As Integer, ByVal flags As IEIFLAG) As Bitmap
            Dim oResult As Bitmap = Nothing

            Dim oDesktopFolder As IShellFolder = Nothing
            Dim hParentIDL As IntPtr
            Dim hIDL As IntPtr

            Dim oParentFolder As IShellFolder
            Dim hParentFolder As IntPtr
            Dim oExtractImage As IExtractImage
            Dim hExtractImage As IntPtr

            'Divide the file name into a path and file/folder name.
            Dim sFolderName As String = System.IO.Path.GetDirectoryName(path)
            Dim sBaseName As String = System.IO.Path.GetFileName(path)

            'Get the desktop IShellFolder.
            If SHGetDesktopFolder(oDesktopFolder) <> Missico.Win32.S_OK Then
                Throw New System.Runtime.InteropServices.COMException
            End If

            'Get the parent folder for the specified path.
            oDesktopFolder.ParseDisplayName(IntPtr.Zero, IntPtr.Zero, sFolderName, 0, hParentIDL, 0)
            oDesktopFolder.BindToObject(hParentIDL, IntPtr.Zero, ShellGUIDs.IID_IShellFolder, hParentFolder)
            oParentFolder = CType(Marshal.GetTypedObjectForIUnknown(hParentFolder, GetType(IShellFolder)), IShellFolder)

            'Get the file/folder's IExtractImage
            oParentFolder.ParseDisplayName(IntPtr.Zero, IntPtr.Zero, sBaseName, 0, hIDL, 0)
            oParentFolder.GetUIObjectOf(IntPtr.Zero, 1, New IntPtr() {hIDL}, ShellGUIDs.IID_IExtractImage, IntPtr.Zero, hExtractImage)

            'Free the pidls. The Runtime Callable Wrappers (RCW) should automatically release the COM objects.
            Marshal.FreeCoTaskMem(hParentIDL)
            Marshal.FreeCoTaskMem(hIDL)

            Marshal.FinalReleaseComObject(oParentFolder)
            Marshal.FinalReleaseComObject(oDesktopFolder)

            If hExtractImage = IntPtr.Zero Then

                'There is no handler for this file, which is odd. I believe we should default the file's type icon.
                Debug.WriteLine(String.Format("There is no thumbnail for the specified file '{0}'.", path), "ShellThumbnail.ExtractImage")

            Else

                oExtractImage = CType(Marshal.GetTypedObjectForIUnknown(hExtractImage, GetType(IExtractImage)), IExtractImage)

                'Set the size and flags
                Dim oSize As Missico.Win32.SIZE 'must specify a size
                Dim iFlags As IEIFLAG = flags Or IEIFLAG.IEIFLAG_ORIGSIZE Or IEIFLAG.IEIFLAG_QUALITY Or IEIFLAG.IEIFLAG_ASPECT

                If size.IsEmpty Then

                    oSize.cx = DefaultThumbnailSize.Width
                    oSize.cy = DefaultThumbnailSize.Height

                Else

                    oSize.cx = size.Width
                    oSize.cy = size.Height

                End If


                Dim hBitmap As IntPtr
                Dim sPath As New System.Text.StringBuilder(Missico.Win32.MAX_PATH, Missico.Win32.MAX_PATH)


                oExtractImage.GetLocation(sPath, sPath.Capacity, 0, oSize, recommendedColorDepth, iFlags)

                'if the specified path is to a folder then IExtractImage.Extract fails.

                Try

                    oExtractImage.Extract(hBitmap)

                Catch ex As System.Runtime.InteropServices.COMException

                    'clear the handle since extract failed
                    hBitmap = IntPtr.Zero

                    Debug.WriteLine(String.Format("There is no thumbnail for the specified folder '{0}'.", path), "ShellThumbnail.ExtractImage")

                Finally

                    Marshal.FinalReleaseComObject(oExtractImage)

                End Try

                If Not hBitmap.Equals(IntPtr.Zero) Then

                    'create the image from the handle
                    oResult = System.Drawing.Bitmap.FromHbitmap(hBitmap)

                    'dump the properties to determine what kind of bitmap is returned
                    'Missico.Diagnostics.ObjectDumper.Write(oResult)

                    'Tag={ }
                    'PhysicalDimension={Width=96, Height=96}
                    'Size={Width=96, Height=96}
                    'Width=96
                    'Height=96
                    'HorizontalResolution=96
                    'VerticalResolution=96
                    'Flags=335888
                    'RawFormat={ }
                    'PixelFormat=Format32bppRgb
                    'Palette={ }
                    'FrameDimensionsList=...
                    'PropertyIdList=...
                    'PropertyItems=...

                    Missico.Win32.DeleteObject(hBitmap) 'release the handle

                End If

            End If

            Return oResult
        End Function

    End Class

End Namespace

user_4344976 · Answer

Thanks to @Christian Nunciato, I want to explain more:

After you install WindowsAPICodePack-Shell by typing following command in Nuget console:

Install-Package WindowsAPICodePack-Shell -Version 1.1.1

first of all you should know that this cool solution needs you to install related program on the server, for instance if you want the shell to generate thumbnail for PDF files, you should install a PDF reader like Acrobat Reader or Foxit PhantomPDF or some thing like them on the server, it means server will create thumbnail for files which it recognizes them, and it makes sense.

Secondly, check to know which file extensions are generated thumbnail for, in the other words, check whether .psd or .msi file extensions have proper thumbnail or not, then prevent requesting server for generating thumbnail for them(check on both client end and server end).

Thirdly, you might need to get thumbnail through Ajax, personally I suggest you to give files some default thumbnails based on the file type at the first second, then request server for generating thumbnail, in that case you can use following code snippet (I receive the generated bitmap in Base64 format as image which is string actually):

Server side code:

[WebMethod]
public static string GetThumbnail(string path) {

    string thumb = string.Empty;

    path = @"D:\" + path.Replace("/", "\"); //Or Server.MapPath("/UploadedFiles");
    if (File.Exists(path))
    {
        try
        {
            Microsoft.WindowsAPICodePack.Shell.ShellFile shellFile = Microsoft.WindowsAPICodePack.Shell.ShellFile.FromFilePath(path);
            System.Drawing.Bitmap shellThumb = shellFile.Thumbnail.ExtraLargeBitmap;
            MemoryStream ms = new MemoryStream();
            shellThumb.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);//Jpeg is preferred, Png would make a bigger file size
            thumb = Convert.ToBase64String(ms.ToArray());
        }
        catch(Exception ex)
        {

        }
    }
    return thumb;
}

Client side code:

    var url = "Default.aspx/GetThumbnail",
        path = "Images/1.jpg",//For instance
        extension = path.split(".").pop().toLowerCase(),
        allowedExtensions = ["jpg", "jpeg", "png", "gif", "pdf", "mp4"];
    
    if (allowedExtensions.includes(extension)){
        $.ajax({
            type: 'POST',
            contentType: "application/json; charset=utf-8",
            url: url,
            data: "{'path':'" + path + "'}",
            async: true,
            xhrFields: {
                withCredentials: true
            },
            success: function (response) {
                if (!$.isEmptyObject(response.d))
                    $(elem).find("img").attr("src", "data:image/jpg;base64," + response.d);
            },
            error: function (err) {
                console.error(err);
            }
        });
    }

Take into consideration that since returned string might be a long text, you may run into an error saying:

Error during serialization or deserialization using the JSON JavaScriptSerializer. The length of the string exceeds the value set on the maxJsonLength property base64

in that case you have to add following code in web.config file:

maxJsonLength is an integer value and can be Int32.MaxValue, you can read more here.

C# get thumbnail from file via windows api

5 Answers

ShellThumbnail (Work-In-Progress)