update drawGrid to save images with indexed pixels.

DeathSocket/ImageServices.fs

@@ -17,8 +17,11 @@
                Point ((interval * point), height)|]|]
 
     let drawGrid spec =
-        let img = Bitmap.FromFile spec.originalPath
+        // The originalImg is for images with indexed pixels.
+        let orignialImg = Bitmap.FromFile spec.originalPath
+        let img = new Bitmap (orignialImg.Width, orignialImg.Height)
         let graphics = Graphics.FromImage img
+        graphics.DrawImage (orignialImg, 0, 0)
         let pen = new Pen (spec.colour, width = spec.penWidth)
         let horizontalLines =
             createHorizontalLines (img.Size.Width) (img.Size.Height) (spec.rows)
@@ -27,6 +30,7 @@
         for line in horizontalLines do graphics.DrawLines (pen, line)
         for line in verticalLines do graphics.DrawLines (pen, line)
         img.Save (spec.savePath, ImageFormat.Png)
+        orignialImg.Dispose ()
         img.Dispose ()
         graphics.Dispose ()
         pen.Dispose ()