void __fastcall TForm1::Button3Click(TObject *Sender)
{
  int h=10, w=5;      // pixel assignment style: (easy but slow)
  Byte gray = 255;
  for (int row=10; row<10 h;   row)
     for (int col=10; col<10 w;   col)
        Image1->Picture->Bitmap->Canvas->Pixels[col][row] = RGB(gray, gray, gray);      // scanline assignment style: (fast but complex)
  Byte *ptr, red=0, green=0, blue=255;
  int index, fromX=20;
  Image1->Picture->Bitmap->PixelFormat = pf24bit; // for filling color properly.
  for (int row=10; row<10 h;   row)
     { ptr = (Byte*) Image1->Picture->Bitmap->ScanLine[row];
       index = fromX*3;
       for (int col=fromX; col bgr bgr bgr bgr bgr ......
            ptr[index 1] = green;
            ptr[index 2] = red;
            index  = 3;  // go to next right point
          }
     }
}