Image processing in Visual Studio C# .Net

Question

Hi!

I want to make an image filter in Visual Studio C# .The function of such filter is that redraw the original image only with its dark pixel.

I used following logic but its too slow and not efficient  

 for (int i = 0; i < 300; i++)

            {

                for (int j = 0; j < 200; j++)

                {               

                        p = new Pen(bitmap.GetPixel(i, j), 1);

                        for (int r1 = 0; r1 < 100; r1++)

                        {

                            for (int r2 =0; r2 < 100; r2++)

                            {

                                for (int r3 = 0; r3 < 100; r3++)

                                {

                                    if (p.Color ! = Color.FromArgb(255, r1, r2, r3))

                                    {

                                        p.Color = Color.Transparent;

                                     }

                                         g.DrawRectangle(p, 1 * i, 1 * j, 1, 1);

                                }

                            }

                        }

 

      My second question is that how we can manipulates the images in visual studio c# .net ,like convert the image in black &white color,grayscale etc etc

Please send the some code or hints +links