在图片框中显示 Jpeg 的元数据缩略图

Question

我需要显示图像的缩略图，该缩略图保存在图片框中的元数据中。我正在使用 VB.NET

http://msdn.microsoft.com/en-us/library/windows/desktop/ee719904%28v=vs.85%29.aspx#_jpeg_metadata

到目前为止，我想出了这个。添加断点会显示 GETQUERY 返回空，即使我知道该文件确实有缩略图

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
    Dim imagepath = "C:\xampp\htdocs\Downloads\IMG_1322.JPG" ' path to file
    Dim stream = New FileStream(imagepath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)
    Dim decoder = New JpegBitmapDecoder(stream, BitmapCreateOptions.None, BitmapCacheOption.None)
    Dim metadata = TryCast(decoder.Frames(0).Metadata, BitmapMetadata)

    Dim ms As New System.IO.MemoryStream

    Dim bm As Bitmap
    Dim arData() As Byte

    arData = metadata.GetQuery("/app0/{ushort=6}") '<--- Breakpoint here: Query returns nothing!


    ms.Write(arData, 78, arData.Length - 78)

    bm = New Bitmap(ms)

    PictureBox1.Image = bm
    stream.Close()

End Sub

Answer 1

你可以试试这样的：

Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
    Dim imagepath = "C:\xampp\htdocs\Downloads\IMG_1322.JPG" ' path to file
    Dim stream = New FileStream(imagepath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)
    Dim decoder = New JpegBitmapDecoder(stream, BitmapCreateOptions.None, BitmapCacheOption.None)
    Dim metadata = TryCast(decoder.Frames(0).Metadata, BitmapMetadata)

    Dim thumb As BitmapMetadataBlob
    thumb = metadata.GetQuery("/app1/thumb/")
    If Not (thumb Is Nothing) Then
        Dim src As New BitmapImage
        Dim ms As MemoryStream = New MemoryStream(thumb.GetBlobValue())
        src.BeginInit()
        src.StreamSource = ms
        src.EndInit()
        PictureBox1.Source = src
    End If
    stream.Close()

End Sub