Graphen aus der canvas wieder löschen

[Bummi]

Delphi-Quellcode:

procedure TForm1.btn_ZeichneClick(Sender: TObject);
var
  i,j:Integer;
  x,y,a,b,c: Double;
begin
  Initialize;
  a:= StrToFloat(edtEingabe.Text);
  b:= StrToFloat(edt_Bx.Text);
  c:= StrToFloat(edt_C.Text);
  i:=19;
  Image1.Canvas.pen.Color := clBlue;
  while i<660 do
  begin
    i:=i+1;
    x:=(i-450)/50; //50, da Koordinatensystem in 50er Schritten erstellt ist
    y:=a*sqr(x)+b*x+c;
    j:=round((450-y*50)); //450 Grenze von X-Achse
    if i= 20 then Image1.Canvas.MoveTo(i,j) else Image1.Canvas.LineTo(i,j)
  end;
end;


procedure TForm1.Initialize;
var
  i,j,k:Integer;
begin
  with Image1.Canvas do
  begin //X-Achse
    Brush.Color := clWhite;
    Fillrect(ClientRect);
    MoveTo(1125,450); //Graph
    LineTo(20,450);

    for i:= -8 to 13 do
    begin
      Image1.Canvas.TextOut(450+50*i,455,IntToStr(i)); //Beschriftung
      MoveTo(450+50*i,445); //Striche von Beschriftung
      LineTo(450+50*i,455);
      begin //Y-Achse
        MoveTo(450,20); //Graph
        LineTo(450,660);

        for j := -8 to -1 do
        begin
          Image1.Canvas.TextOut(455,450+50*j,IntToStr(-j)); //Beschriftung
          MoveTo(445,450+50*j); //Striche von Beschriftung
          LineTo(455,450+50*j);

          for k := 1 to 4 do
          begin
            Image1.Canvas.TextOut(455,450+50*k,IntToStr(-k)); //Beschriftung
            MoveTo(445,450+50*k); //Striche von Beschriftung
            LineTo(455,450+50*k);
          end;
        end;
      end;
    end;
  end;
end;


procedure TForm1.FormCreate(Sender: TObject);
begin
  Initialize;
end;