OpenXML插入图片，文件大小增加近150%

[LSSQXT]

VS2008 OpenXML2.0
按MSDN上的代码在一个大小不到2KB的docx文档中插入一张图片（大小607KB），发现文档大小变为（929KB），也就是说增加了所插入图片的差不多1.5倍，
但是
1、把扩展名改为.zip解压缩，解出来的文件夹总大小才608KB
2、用Word 2007打开并另存该文档为别的文件名，文件大小变为619KB（解压缩发现包里自动增加了一些页眉页脚样式之类的小xml文件）
有没有人知道问题出在哪里，请赐教！

代码如下：

Imports DocumentFormat.OpenXml
Imports DocumentFormat.OpenXml.Wordprocessing
Imports DocumentFormat.OpenXml.Packaging
Imports System.IO
Imports A = DocumentFormat.OpenXml.Drawing
Imports DW = DocumentFormat.OpenXml.Drawing.Wordprocessing
Imports PIC = DocumentFormat.OpenXml.Drawing.Pictures

Public Class Form1
    Dim docx_fn As String = "d:\TEMP\test2.docx"
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        '创建WordprocessingDocument实例doc，对应于TEST.docx文件
        Dim docx As WordprocessingDocument = WordprocessingDocument.Create(docx_fn, WordprocessingDocumentType.Document)

        Using docx
            '为doc添加MainDocumentPart部分
            Dim mp As MainDocumentPart = docx.AddMainDocumentPart()

            '为mainPart添加Document，对应于Word里的文档内容部分 
            mp.Document = New Document

            '为Document添加Body，之后所有于内容相关的均在此body中
            Dim body1 As Body = mp.Document.AppendChild(New Body)

            '添加段落P，P中包含一个文本
            Dim p As Paragraph = mp.Document.Body.AppendChild(New Paragraph)
            p.AppendChild(New Run(New Text("This is a Docx for test!")))

        End Using

    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Dim document As String = docx_fn
        Dim fileName As String = "Tulips.jpg"
        InsertAPicture(document, fileName)
    End Sub


    Public Sub InsertAPicture(ByVal document As String, ByVal fileName As String)
        Using wordprocessingDocument As WordprocessingDocument = wordprocessingDocument.Open(document, True)
            Dim mainPart As MainDocumentPart = wordprocessingDocument.MainDocumentPart

            Dim imagePart As ImagePart = mainPart.AddImagePart(ImagePartType.Jpeg)

            Using stream As New FileStream(fileName, FileMode.Open)
                imagePart.FeedData(stream)
            End Using

            AddImageToBody(wordprocessingDocument, mainPart.GetIdOfPart(imagePart))
        End Using
    End Sub

    Private Sub AddImageToBody(ByVal wordDoc As WordprocessingDocument, ByVal relationshipId As String)
        ' Define the reference of the image.
        Dim element = New Drawing( _
                              New DW.Inline( _
                          New DW.Extent() With {.Cx = 990000L, .Cy = 792000L}, _
                          New DW.EffectExtent() With {.LeftEdge = 0L, .TopEdge = 0L, .RightEdge = 0L, .BottomEdge = 0L}, _
                          New DW.DocProperties() With {.Id = CType(1UI, UInt32Value), .Name = "Picture1"}, _
                          New DW.NonVisualGraphicFrameDrawingProperties( _
                              New A.GraphicFrameLocks() With {.NoChangeAspect = True} _
                              ), _
                          New A.Graphic(New A.GraphicData( _
                                        New PIC.Picture( _
                                            New PIC.NonVisualPictureProperties( _
                                                New PIC.NonVisualDrawingProperties() With {.Id = 0UI, .Name = "Koala.jpg"}, _
                                                New PIC.NonVisualPictureDrawingProperties() _
                                                ), _
                                            New PIC.BlipFill( _
                                                New A.Blip( _
                                                    New A.BlipExtensionList( _
                                                        New A.BlipExtension() With {.Uri = "{28A0092B-C50C-407E-A947-70E740481C1C}"}) _
                                                    ) With {.Embed = relationshipId, .CompressionState = A.BlipCompressionValues.Print}, _
                                                New A.Stretch( _
                                                    New A.FillRectangle() _
                                                    ) _
                                                ), _
                                            New PIC.ShapeProperties( _
                                                New A.Transform2D( _
                                                    New A.Offset() With {.X = 0L, .Y = 0L}, _
                                                    New A.Extents() With {.Cx = 990000L, .Cy = 792000L}), _
                                                New A.PresetGeometry( _
                                                    New A.AdjustValueList() _
                                                    ) With {.Preset = A.ShapeTypeValues.Rectangle} _
                                                ) _
                                            ) _
                                        ) With {.Uri = "http://schemas.openxmlformats.org/drawingml/2006/picture"} _
                                    ) _
                                ) With {.DistanceFromTop = 0UI, _
                                        .DistanceFromBottom = 0UI, _
                                        .DistanceFromLeft = 0UI, _
                                        .DistanceFromRight = 0UI} _
                            )

        ' Append the reference to body, the element should be in a Run.
        wordDoc.MainDocumentPart.Document.Body.AppendChild(New Paragraph(New Run(element)))
    End Sub


End Class

PS:插入图片的代码来自https://msdn.microsoft.com/EN-US/library/office/bb497430(v=office.15).aspx?cs-save-lang=1&cs-lang=vb#code-snippet-5

[LSSQXT]

都没人遇到过吗???