高图表区域范围图形未以灰度显示PDF

Question

我有一个高图表区域范围图。当我使用itextsharp将其转换为灰度PDF（通过转换彩色PDF）时，该图未显示。这是什么原因？

我已经使用evo pdf通过html将其转换为彩色PDF，并且工作正常。当我使用itext将该PDF转换为灰度时，它并不显示高图表区域图。

PdfContentToGrayscaleConverter grayScaleConverter = new PdfContentToGrayscaleConverter();

            reader = new PdfReader(originalFileFullPath);

            using (FileStream fsOutput = new FileStream(grayFileFullPath, FileMode.Create, FileAccess.Write, FileShare.ReadWrite))
            {
                document = new iTextSharp.text.Document(reader.GetPageSizeWithRotation(1));
                writer = PdfWriter.GetInstance(document, fsOutput);

                document.Open();
                PdfContentByte cb = writer.DirectContent;

                int numberOfPages = reader.NumberOfPages;

                for (int pageNumber = 1; pageNumber <= numberOfPages; pageNumber++)
                {
                    Rectangle pageSizeWithRotation = reader.GetPageSizeWithRotation(pageNumber);

                    document.SetPageSize(pageSizeWithRotation);
                    document.NewPage();

                    // >>> CONVERT CURRENT PAGE TO GRAYSCALE
                    grayScaleConverter.Convert(reader, pageNumber);
                    // <<<<

                    PdfImportedPage pip = writer.GetImportedPage(reader, pageNumber);

                    if (pageSizeWithRotation.Rotation == 90 || pageSizeWithRotation.Rotation == 270)
                    {
                        cb.AddTemplate(pip, 0, -1f, 1f, 0, 0, pageSizeWithRotation.Height);
                    }
                    else
                    {
                        cb.AddTemplate(pip, 1f, 0, 0, 1f, 0, 0);
                    }
                }

                if (document != null)
                {
                    document.Close(); document.Dispose(); document = null;
                }
                if (writer != null)
                {
                    writer.Close(); writer.Dispose(); writer = null;
                }
                if (reader != null)
                {
                    reader.Close(); reader.Dispose(); reader = null;
                }
            }