[gendalf71]

Код:

var
  Form1: TForm1;
  ASrc, ADst :Tbitmap;
  K : Double;

procedure TForm1.btn1Click(Sender: TObject);
begin
  ADst := TBitmap.Create;
    ADst.Width := Screen.Width;
    ADst.Height := Screen.Height;
    BitBlt(ADst.Canvas.Handle, 0,0, Screen.Width, Screen.Height,
           GetDC(0), 0,0,SRCCOPY);
     If (ASrc = Nil) Or (ADst = Nil) Then
    Raise Exception.Create('Source or destination is Nil');
    ADst.Width := Round(ASrc.Width / Sqrt(K));
  ADst.Height := Round(ASrc.Height / Sqrt(K));
  ADst.Canvas.StretchDraw(Rect(0,0,ADst.Width,ADst.Height),ASrc);
    //ADst.Picture.Assign(ADst);
    ADst.SavetoFile('D:\123.jpg');
    ADst.Free;
end;

Выдает Source or destination is Nil. Извините, туплю =)