暂时将PDF转换为图像以便读取QR码

Question

我需要能够从PDF文件中读取QR码.我正在使用thinkworks.QRCode,它接受图像并返回QR码中保存的数据.我有那个部分在工作.

但是,我需要能够接受多页PDF文件并将每页作为图像发送到QR阅读器.然后,我需要将原始PDF的每个页面保存为以QR码中包含的数据命名的单页PDF.

您建议我在这个项目中使用哪个库？我见过的许多人创造了永久性的图像,但我只想要临时图像.有什么东西可以轻易让我这样做吗？是否有另一个QR阅读器可以阅读pdfs？

感谢您提供的任何建议!

Answer 1

我使用itextsharp和libtiff.NET从PDF文件中提取tiff图像到内存中.底线是itextsharp将允许您访问图像,但如果它们被编码,您需要自己进行编码或使用另一个库,这是libtiff.NET的用武之地.

根据我提出的问题的答案修改了以下代码:PDF添加文本和展平

Private Shared Function ExtractImages(ByVal pdf As Byte()) As List(Of Byte())
    Dim images As New List(Of Byte())
    Dim reader As New PdfReader(pdf)

    If (reader IsNot Nothing) Then
        ' Loop through all of the references in the PDF.
        For refIndex = 0 To (reader.XrefSize - 1)
            ' Get the object.
            Dim obj = reader.GetPdfObject(refIndex)

            ' Make sure we have something and that it is a stream.
            If (obj IsNot Nothing) AndAlso obj.IsStream() Then
                ' Cast it to a dictionary object.
                Dim pdfDict = DirectCast(obj, iTextSharp.text.pdf.PdfDictionary)

                ' See if it has a subtype property that is set to /IMAGE.
                If pdfDict.Contains(iTextSharp.text.pdf.PdfName.SUBTYPE) AndAlso (pdfDict.Get(iTextSharp.text.pdf.PdfName.SUBTYPE).ToString() = iTextSharp.text.pdf.PdfName.IMAGE.ToString()) Then
                    ' Grab various properties of the image.
                    Dim filter = pdfDict.Get(iTextSharp.text.pdf.PdfName.FILTER).ToString()
                    Dim width = pdfDict.Get(iTextSharp.text.pdf.PdfName.WIDTH).ToString()
                    Dim height = pdfDict.Get(iTextSharp.text.pdf.PdfName.HEIGHT).ToString()
                    Dim bpp = pdfDict.Get(iTextSharp.text.pdf.PdfName.BITSPERCOMPONENT).ToString()

                    ' Grab the raw bytes of the image
                    Dim bytes = PdfReader.GetStreamBytesRaw(DirectCast(obj, PRStream))

                    ' Images can be encoded in various ways. 
                    ' All of our images are encoded with a single filter.
                    ' If there is a need to decode another filter, it will need to be added.
                    If (filter = iTextSharp.text.pdf.PdfName.CCITTFAXDECODE.ToString()) Then
                        Using ms = New MemoryStream()
                            Using tiff As Tiff = tiff.ClientOpen("memory", "w", ms, New TiffStream())
                                tiff.SetField(TiffTag.IMAGEWIDTH, width)
                                tiff.SetField(TiffTag.IMAGELENGTH, height)
                                tiff.SetField(TiffTag.COMPRESSION, Compression.CCITTFAX4)
                                tiff.SetField(TiffTag.BITSPERSAMPLE, bpp)
                                tiff.SetField(TiffTag.SAMPLESPERPIXEL, 1)

                                tiff.WriteRawStrip(0, bytes, bytes.Length)
                                tiff.Flush()
                                images.Add(ms.ToArray())
                                tiff.Close()
                            End Using
                        End Using
                    Else
                        Throw New NotImplementedException("Decoding this filter has not been implemented")
                    End If
                End If
            End If
        Next
    End If

    Return images
End Function