itextsharp - 使用 iTextsharp 从 PDF 中提取的图像格式不正确 - C#

Question

我正在使用 iTextsharp 从 PDF 文件中提取图像，我能够提取图像，但提取的图像格式不正确（即看起来像否定证明）。

代码：

string sFilePath = "Test3.pdf";
int pageNum = 1;

PdfReader pdf = new PdfReader(sFilePath);

PdfDictionary pg = pdf.GetPageN(pageNum);
PdfDictionary res = (PdfDictionary)PdfReader.GetPdfObject(pg.Get(PdfName.RESOURCES));
PdfDictionary xobj = (PdfDictionary)PdfReader.GetPdfObject(res.Get(PdfName.XOBJECT));
if (xobj == null) { return; }
int imageCount = 0;
foreach (PdfName name in xobj.Keys)
{
    PdfObject obj = xobj.Get(name);
    if (!obj.IsIndirect()) { continue; }
    PdfDictionary tg = (PdfDictionary)PdfReader.GetPdfObject(obj);
    PdfName type = (PdfName)PdfReader.GetPdfObject(tg.Get(PdfName.SUBTYPE));
    if (!type.Equals(PdfName.IMAGE)) { continue; }
    int XrefIndex = Convert.ToInt32(((PRIndirectReference)obj).Number.ToString(System.Globalization.CultureInfo.InvariantCulture));
    PdfObject pdfObj = pdf.GetPdfObject(XrefIndex);
    PdfStream pdfStrem = (PdfStream)pdfObj;
    byte[] bytes = PdfReader.GetStreamBytesRaw((PRStream)pdfStrem);
    if (bytes == null) { continue; }
    using (System.IO.MemoryStream memStream = new System.IO.MemoryStream(bytes))
    {
        try
        {
            memStream.Position = 0;
            System.Drawing.Image img = System.Drawing.Image.FromStream(memStream);

            if (!Directory.Exists(imgPath))
                Directory.CreateDirectory(imgPath);

            string path = Path.Combine(imgPath, String.Format(@"{0}.jpg", ++imageCount));
            System.Drawing.Imaging.EncoderParameters parms = new System.Drawing.Imaging.EncoderParameters(1);
            parms.Param[0] = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Compression, 0);
            var jpegEncoder = ImageCodecInfo.GetImageEncoders().ToList().Find(x => x.FormatID == ImageFormat.Jpeg.Guid);
            img.Save(path, jpegEncoder, parms);
        }
        catch (Exception ex)
        {

        }

    }
}