StringGrid->BMP

Jak zapisac zawartosc Stringgrida do bmp ?

próbowalem tak:
var Bmp:TBitMap;
begin
bmp:=Tbitmap.create;
bmp.Height:=50;
bmp.Width:=50;
bmp.Handle:=db.Canvas.Handle;
bmp.SaveToFile('c:\a.bmp');
bmp.Free;

var 
  Bmp:TBitMap;
begin
  bmp:=Tbitmap.create;
  bmp.Height:=50;
  bmp.Width:=50;
  bmp.Canvas.CopyRect(Rect(0,0,bmp.width,bmp.height), stringgrid.Canvas, Rect(0,0,stringgrid.width,stringgrid.height));
  bmp.SaveToFile('c:\a.bmp');
  bmp.Free;