using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using pdftron.PDF;
using System.Drawing;
using System.IO;
using System.Drawing.Imaging;

namespace GrayscalePDFExample
{
    class Program
    {
        static void Main(string[] args)
        {
            ConvertPDF();
        }

        private static void ConvertPDF()
        {
            string pdfSource = @"C:\test\test.pdf";
            string destination = @"C:\test\test-gray.pdf";

            PDFDoc pdf = new PDFDoc(pdfSource);
            pdf.InitSecurityHandler();

            ElementWriter writer = new ElementWriter();
            ElementReader reader = new ElementReader();

            _imgCounter = 0;
            for (int i = 1; i <= pdf.GetPageCount(); ++i)
            {
                Page page = pdf.GetPage(i);
                reader.Begin(page);
                writer.Begin(page, ElementWriter.WriteMode.e_replacement, false);
                ConvertImagesToGrayscale(reader, writer, pdf);
                writer.End();
                reader.End();
            }

            writer.Dispose();
            reader.Dispose();

            pdf.Save(destination, pdftron.SDF.SDFDoc.SaveOptions.e_remove_unused);
            pdf.Close();
            pdf.Dispose();
        }

        private static int _imgCounter = 0;
        private static void ConvertImagesToGrayscale(ElementReader reader, ElementWriter writer, PDFDoc pdf)
        {
            Element element;
            while ((element = reader.Next()) != null) 	// Read page contents
            {
                bool written = false;
                switch (element.GetType())
                {
                    case Element.Type.e_image:
                    case Element.Type.e_inline_image:
                        _imgCounter++;
                        Bitmap bmp = MakeGrayscale(element.GetBitmap()); 
                        bmp.Save(@"C:\Test\gray" +  _imgCounter + ".bmp");
                        //byte[] imageData = null;
                        //using (MemoryStream ms = new MemoryStream())
                        //{
                        //    bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Bmp);
                        //    imageData = ms.ToArray();
                        //}
                        pdftron.PDF.Image img = pdftron.PDF.Image.Create(pdf, bmp);

                        //pdftron.PDF.Image img = pdftron.PDF.Image.Create(pdf, imageData, bmp.Width,
                        //   bmp.Height, 8, ColorSpace.CreateDeviceGray(), _JBIG2_hint);    
                        ElementBuilder b = new ElementBuilder();                    
                        element = b.CreateImage(img, element.GetGState().GetTransform());  //.GetCTM());

                        written = true;
                        writer.WriteElement(element);
                        break;
                    case Element.Type.e_form:				// Recursively process form XObjects
                        {
                            reader.FormBegin();
                            ConvertImagesToGrayscale(reader, writer, pdf);
                            reader.End();
                            break;
                        }
                    default:
                        break;
                }

                if (!written)
                {
                    writer.WriteElement(element);
                }
            }
        }

        // see http://tech.pro/tutorial/660/csharp-tutorial-convert-a-color-image-to-grayscale
        public static Bitmap MakeGrayscale(Bitmap original)
        {
            //create a blank bitmap the same size as original
            Bitmap newBitmap = new Bitmap(original.Width, original.Height, PixelFormat.Format24bppRgb);

            //get a graphics object from the new image
            Graphics g = Graphics.FromImage(newBitmap);

            //create the grayscale ColorMatrix
            ColorMatrix colorMatrix = new ColorMatrix(
               new float[][] 
              {
                 new float[] {.3f, .3f, .3f, 0, 0},
                 new float[] {.59f, .59f, .59f, 0, 0},
                 new float[] {.11f, .11f, .11f, 0, 0},
                 new float[] {0, 0, 0, 1, 0},
                 new float[] {0, 0, 0, 0, 1}
              });

            //create some image attributes
            ImageAttributes attributes = new ImageAttributes();

            //set the color matrix attribute
            attributes.SetColorMatrix(colorMatrix);

            //draw the original image on the new image
            //using the grayscale color matrix
            g.DrawImage(original, new Rectangle(0, 0, original.Width, original.Height),
               0, 0, original.Width, original.Height, GraphicsUnit.Pixel, attributes);

            //dispose the Graphics object
            g.Dispose();

            return newBitmap;
        }

    }
}