Victor Image Processing Library How-to Tips

Graphic Pen Drawing from an Image

To simulate a graphic pen drawing from a photographic image we create an ordered dither matrix of the same dimensions as the image, fill the matrix with diagonal lines, and apply the dither.

Original image		Graphic pen version

The steps used to create the graphic pen drawing are

• Create a grayscale version of the source image
• Brighten the grayscale image until the average gray is above 150
• Sharpen the grayscale image (optional, skip this step to generate more pen strokes)
• Create a graphic screen of same dimensions as the grayscale image
• Completely fill the graphic screen with random noise, pixels range from 0 to 255
• Blur the random noise along the direction of the graphic pen strokes (in this case, diagonal left to right)
• Apply the graphic screen to the grayscale image

The creategraphicpenscreen function below creates the screen and the graphicpendrawing function prepares the source image and applies the screen.

To save the image, call one of the Victor savefile functions in the Victor Library.

Graphic Pen Drawing of an Image - the C# Source Code

   public static int graphicpendrawing(ref vicwin.imgdes src, ref vicwin.imgdes result)
  {
      vicwin.imgdes tempimg1, tempimg2, tempimg3;
      int rcode;
      int redavg=0, grnavg=0, bluavg=0;
      int j;
      int swidth = 0, slength = 0;

      tempimg1 = new vicwin.imgdes();
      tempimg2 = new vicwin.imgdes();

      swidth = src.endx - src.stx + 1;
      slength = src.endy - src.sty + 1;
      rcode = vicwin.allocimage(ref tempimg1, swidth, slength, 8); // Allocate new 8-bit image to be src
      rcode = vicwin.allocimage(ref tempimg2, swidth, slength, 8); // Allocate new 8-bit image to be opr
      if (rcode == vicwin.NO_ERROR)
      {
          rcode = vicwin.colortogray(ref src, ref tempimg1);
          vicwin.calcavglevel(ref tempimg1, ref redavg, ref grnavg, ref bluavg);

          for (j = 0; j < 3; j++)
          {
              if (redavg < 150)
                  rcode = vicwin.gammabrighten(.8, ref tempimg1, ref tempimg1);
              vicwin.calcavglevel(ref tempimg1, ref redavg, ref grnavg, ref bluavg);
          }
          rcode = vicwin.sharpen(ref tempimg1, ref tempimg1);  // For more pen strokes and less detail, remove the sharpen
          if (rcode == vicwin.NO_ERROR)
          {
              rcode = creategraphicpenscreen(ref tempimg1, ref tempimg2); // Create the graphic screen
              rcode = vicwin.screen(ref tempimg1, ref tempimg2, ref tempimg2); // Apply the graphic screen

              if (rcode == vicwin.NO_ERROR)
              {    // Success, replace result with the new image
                  vicwin.freeimage(ref result);
                  vicwin.copyimgdes(ref tempimg2, ref result);
              }
              else
                  vicwin.freeimage(ref tempimg2);  // Failure, release the temp image, no harm done

          }

          vicwin.freeimage(ref tempimg1);  // Release the other temp image
      }
      return (rcode);
  }

   public static int creategraphicpenscreen(ref vicwin.imgdes src, ref vicwin.imgdes result)
  {
      vicwin.imgdes tempimg;
      int rcode;
      int swidth = 0, slength = 0;
      byte[] matrixkernel = new byte[81]{
   1,0,0,0,0,0,0,0,0,
   0,1,0,0,0,0,0,0,0,
   0,0,1,0,0,0,0,0,0,
   0,0,0,1,0,0,0,0,0,
   0,0,0,0,1,0,0,0,0,
   0,0,0,0,0,1,0,0,0,
   0,0,0,0,0,0,1,0,0,
   0,0,0,0,0,0,0,1,0,
   0,0,0,0,0,0,0,0,1};

      tempimg = new vicwin.imgdes();

      swidth = src.endx - src.stx + 1;
      slength = src.endy - src.sty + 1;
      rcode = vicwin.allocimage(ref tempimg, swidth, slength, 8); // Allocate new 8-bit image
      if (rcode == vicwin.NO_ERROR)
      {
          rcode = vicwin.addnoise(255, ref tempimg, ref tempimg);
          rcode = vicwin.matrixconvex(9, ref matrixkernel[0], 9, ref tempimg, ref result);
          vicwin.freeimage(ref tempimg);
      }
      return (rcode);
  }

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