PDFSharp 导出 JPG - ASP.NET

Question

我正在使用 ajaxfileupload 控件将 pdf 文件上传到服务器。在服务器端，我想将 pdf 转换为 jpg。使用PDFsharp Sample: Export Images 作为指导，我得到了以下信息：

Imports System
Imports System.Drawing
Imports System.Drawing.Imaging
Imports PdfSharp.Pdf
Imports System.IO
Imports PdfSharp.Pdf.IO
Imports PdfSharp.Pdf.Advanced

Namespace Tools

Public Module ConvertImage

Public Sub pdf2JPG(pdfFile As String, jpgFile As String)

        pdfFile = System.Web.HttpContext.Current.Request.PhysicalApplicationPath & "upload\" & pdfFile

        Dim document As PdfSharp.Pdf.PdfDocument = PdfReader.Open(pdfFile)

        Dim imageCount As Integer = 0
        ' Iterate pages
        For Each page As PdfPage In document.Pages
            ' Get resources dictionary
            Dim resources As PdfDictionary = page.Elements.GetDictionary("/Resources")
            If resources IsNot Nothing Then
                ' Get external objects dictionary
                Dim xObjects As PdfDictionary = resources.Elements.GetDictionary("/XObject")
                If xObjects IsNot Nothing Then
                    Dim items As ICollection(Of PdfItem) = xObjects.Elements.Values
                    ' Iterate references to external objects
                    For Each item As PdfItem In items
                        Dim reference As PdfReference = TryCast(item, PdfReference)
                        If reference IsNot Nothing Then
                            Dim xObject As PdfDictionary = TryCast(reference.Value, PdfDictionary)
                            ' Is external object an image?
                            If xObject IsNot Nothing AndAlso xObject.Elements.GetString("/Subtype") = "/Image" Then
                                ExportImage(xObject, imageCount)
                            End If
                        End If
                    Next
                End If
            End If
        Next
    End Sub

    Private Sub ExportImage(image As PdfDictionary, ByRef count As Integer)
        Dim filter As String = image.Elements.GetName("/Filter")
        Select Case filter
            Case "/DCTDecode"
                ExportJpegImage(image, count)
                Exit Select

            Case "/FlateDecode"
                ExportAsPngImage(image, count)
                Exit Select
        End Select
    End Sub

    Private Sub ExportJpegImage(image As PdfDictionary, ByRef count As Integer)
        ' Fortunately JPEG has native support in PDF and exporting an image is just writing the stream to a file.
        Dim stream As Byte() = image.Stream.Value
        Dim fs As New FileStream([String].Format("Image{0}.jpeg", System.Math.Max(System.Threading.Interlocked.Increment(count), count - 1)), FileMode.Create, FileAccess.Write)
        Dim bw As New BinaryWriter(fs)
        bw.Write(stream)
        bw.Close()
    End Sub

    Private Sub ExportAsPngImage(image As PdfDictionary, ByRef count As Integer)
        Dim width As Integer = image.Elements.GetInteger(PdfImage.Keys.Width)
        Dim height As Integer = image.Elements.GetInteger(PdfImage.Keys.Height)
        Dim bitsPerComponent As Integer = image.Elements.GetInteger(PdfImage.Keys.BitsPerComponent)

        ' TODO: You can put the code here that converts vom PDF internal image format to a Windows bitmap
        ' and use GDI+ to save it in PNG format.
        ' It is the work of a day or two for the most important formats. Take a look at the file
        ' PdfSharp.Pdf.Advanced/PdfImage.cs to see how we create the PDF image formats.
        ' We don't need that feature at the moment and therefore will not implement it.
        ' If you write the code for exporting images I would be pleased to publish it in a future release
        ' of PDFsharp.
    End Sub

End Module

End Namespace

当我调试时，它在 ExportImage 中的 Dim filter As String = image.Elements.GetName("/Filter") 上爆炸。消息是：

在线路336未处理的异常，柱21在〜：46138 /的ScriptResource.axd d = LGq0ri4wlMGBKd-1vxLjtxNH_pd26HaruaEG_1eWx-epwPmhNKVpO8IpfHoIHzVj2Arxn5804quRprX3HtHb0OmkZFRocFIG-7A-SJYT_EwYUd - x9AHktpraSBgoZk4VJ1RMtFNwl1mULDLid5o5U9iBcuDi4EQpbpswgBn_oI1＆T = ffffffffda74082d 0x800a139e - JavaScript 运行时错误：引发上传完成事件并开始新上传时出错

对问题可能是什么有任何想法？ ajaxfileupload 控件似乎有问题，但我不明白为什么它会在这里吠叫。它既不在这里也不在那里，但我知道我还没有使用 jpgFile。

Answer 1

PDFsharp 无法从 PDF 页面创建 JPEG 图像：
http://pdfsharp.net/wiki/PDFsharpFAQ.ashx#Can_PDFsharp_show_PDF_files_Print_PDF_files_Create_images_from_PDF_files_3

您参考的示例可以提取 PDF 文件中包含的 JPEG 图像。就这样。该示例并未涵盖所有可能的情况。

长话短说：您显示的代码似乎与错误消息无关。而且它似乎与您的预期目标无关。