public class CommonPaletteCreator
{
      Aurigma.GraphicsMill.Bitmap[] bitmaps = null;

      public CommonPaletteCreator()
      {

      }

      //Import RtlMoveMemory function for copying memory in unmanaged heap
      [DllImport("kernel32", EntryPoint="RtlMoveMemory")]
      private static extern int CopyMemory(IntPtr lpvDest, IntPtr lpvSrc, int cbCopy);

      public Aurigma.GraphicsMill.Bitmap[] Bitmaps
      {
            set
            {
                  bitmaps = value;
            }
            get
            {
                  return bitmaps;
            }
      }

      public Aurigma.GraphicsMill.ColorPalette CreatePalette()
      {                  
            //All source bitmaps should have the same pixel format
            Aurigma.GraphicsMill.PixelFormat commonPixelFormat =
                  Aurigma.GraphicsMill.PixelFormat.Format24bppRgb; //Aurigma.GraphicsMill.PixelFormat.Format32bppArgb

            //Total pixel count in all bitmaps
            int totalPixelCount = 0;
            foreach (Aurigma.GraphicsMill.Bitmap bitmap in bitmaps)
            {
                  if (bitmap.PixelFormat != commonPixelFormat)
                  {
                        //instead of exception throwing, we can also convert bitmap to required pixel format
                        throw new Exception("Only 24 bpp pixel format is supported.");
                  }
                  totalPixelCount += bitmap.Width * bitmap.Height;
            }
                  
            //Create common bitmap with width equals totalPixelCount and height equals 1
            using (Aurigma.GraphicsMill.Bitmap commonBitmap = new Aurigma.GraphicsMill.Bitmap(totalPixelCount, 1, commonPixelFormat))
            {
                  int bytesPerPixel = commonBitmap.BitsPerPixel / 8;
      
                  Aurigma.GraphicsMill.BitmapData commonBitmapData = commonBitmap.LockBits();

                  //Get pointer in unmanaged heap for common bitmap raw data
                  IntPtr commonBitmapPtr = commonBitmapData.Scan0;

                  //Copy data of source images to common image
                  foreach (Aurigma.GraphicsMill.Bitmap bitmap in bitmaps)
                  {
                        Aurigma.GraphicsMill.BitmapData bitmapData = bitmap.LockBits();

                        //Get pointer in unmanaged heap for bitmap raw data
                        IntPtr bitmapPtr = bitmapData.Scan0;

                        //Copy raw data from bitmap to common bitmap
                        for (int i = 0; i < bitmap.Height ; i++)
                        {
                              //Data actaully are not marshalled here, as we work in unmanaged heap only
                              CopyMemory(commonBitmapPtr, bitmapPtr,
                                    bitmapData.Width * bytesPerPixel);

                              //Pointer incrementing
                              bitmapPtr = (IntPtr)((int)(bitmapPtr) + bitmapData.Stride);
                              commonBitmapPtr = (IntPtr)((int)(commonBitmapPtr) + bitmapData.Width * bytesPerPixel);
                        }

                        bitmap.UnlockBits(bitmapData);
                  }

                  commonBitmap.UnlockBits(commonBitmapData);

                  //Create common palette
                  return new Aurigma.GraphicsMill.ColorPalette(commonBitmap, false);
            }
      }
}

class CommonPaletteTest
{
      ///

      /// The main entry point for the application.
      ///
      [STAThread]
      static void Main(string[] args)
      {
            //Load images
            Aurigma.GraphicsMill.Bitmap bitmap1 =
                  new Aurigma.GraphicsMill.Bitmap(@"C:\Flower.jpg");
            Aurigma.GraphicsMill.Bitmap bitmap2 =
                  new Aurigma.GraphicsMill.Bitmap(@"C:\Mountain.jpg");
            Aurigma.GraphicsMill.Bitmap bitmap3 =
                  new Aurigma.GraphicsMill.Bitmap(@"C:\Parrot.jpg");
      
            //Create common palette creator
            CommonPaletteCreator paletteCreator = new CommonPaletteCreator();
            
            //Set bitmaps for which we need to create common palette
            paletteCreator.Bitmaps = new Aurigma.GraphicsMill.Bitmap[]{bitmap1, bitmap2, bitmap3};

            //Create common palette
            Aurigma.GraphicsMill.ColorPalette commonPalette = paletteCreator.CreatePalette();

            //Reduce colors using common palette
            bitmap1.ColorManagement.ConvertToIndexed(8, Aurigma.GraphicsMill.ColorPaletteType.Custom,
                  commonPalette);
            bitmap2.ColorManagement.ConvertToIndexed(8, Aurigma.GraphicsMill.ColorPaletteType.Custom,
                  commonPalette);
            bitmap3.ColorManagement.ConvertToIndexed(8, Aurigma.GraphicsMill.ColorPaletteType.Custom,
                  commonPalette);

            //Save results
            bitmap1.Save(@"C:\Flower.png");
            bitmap2.Save(@"C:\Mountain.png");
            bitmap3.Save(@"C:\Parrot.png");
      }
}