TPNGImage help

procedure TForm1.Button1Click(Sender: TObject);
var
  png: tpngobject;
  bmp: tbitmap;
  canvas: tcanvas;
  i: integer;
begin
  png := tpngobject.createblank(COLOR_PALETTE, 4, 150, 150);
  png.Canvas.Brush.Color := clBlack;
  png.Canvas.FillRect(Rect(0,0,png.width,png.height));
  png.canvas.pen.color := clRed;
  png.canvas.pen.width := 10;
  png.canvas.brush.Style := bsClear;
  png.canvas.Ellipse(20,20,png.width-20,png.width - 20);
  for i := 1 to 30 do
  begin
    case round(Random*5) of
      0: png.canvas.pen.color := clRed;
      1: png.canvas.pen.color := clBlue;
      2: png.canvas.pen.color := clWhite;
      3: png.canvas.pen.color := clGreen;
      4: png.canvas.pen.color := clYellow;
    end;
    png.canvas.Pen.Width := round(random*10);
    png.canvas.MoveTo(round(random*png.width),round(random*png.height));
    png.Canvas.LineTo(round(random*png.width),round(random*png.height));
  end;
  png.TransparentColor := clBlack;
  png.InterlaceMethod := imAdam7;
  png.MaxIdatSize := 100;
  png.AddztXt('Made using', 'PNG Delphi 1.56');
  png.AddztXt('Website', 'http://pngdelphi.sourceforge.net');
  with tchunktime(png.Chunks.Add(tchunktime)) do
  begin
    Year := 2006;
    Month := 5;
    Day := 5;
    Hour := 21;
    Minute := 24;
    Second := 21;
  end;

  png.savetofile('C:\new.png');
  png.free;
end;