请问如何把Canvas中的图片存储下来?

var
  Bitmap: TBitmap;
  MyRect: TRect;
begin
  MyRect := Rect(10,10,100,100);//此处设置需要拷贝的区域
  Bitmap := TBitmap.Create;
  Bitmap.Height=MyRect.top-MyRect.Buttom;
  BitMap.Width=MyRect.Rigth-MyRect.Left;
  BitMap.Canvas.BrushCopy(MyRect, MyCanvas/*你要保存的Canvas*/, MyRect,clBlack);
  BitMap.Canvas.CopyRect(MyRect,MyCanvas,MyRect);
  BitMap.SaveToFile(MyFileName/*你要保存的文件名*/);
  Bitmap.Free;
end;