procedure TFormMain.btnImageSelectionZoomClick(Sender: TObject);
begin
  ImageEnView1.MouseInteract := [miSelectZoom];
end;

ImageEnView1.DisplayOptions := ImageEnView1.DisplayOptions + [iedoDisableAutoFitWhenZoom];

procedure TFormMain.btnImageEnViewClick(Sender: TObject);
begin
  ImageEnView1.MouseInteract := [miSelectZoom];             
end;

procedure TFormMain.ImageEnView1MouseUp(Sender: TObject; Button:
    TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
  if ImageEnView1.MouseInteract = [miSelectZoom] then
  begin
    ImageEnView1.AutoShrink := False; 
    ImageEnView1.ZoomSelection();
  end;    
end;

procedure TFormMain.btnImageEnViewResetAutoShrinkClick(Sender: TObject);
begin
  ImageEnView1.AutoShrink := True;
  ImageEnView1.Update;
end;

procedure TForm1.Fit1Click(Sender: TObject);
begin
  if Fit1.Down then
    ImageEnView1.Fit(True) // this is the same as AutoShrink
  else
    ImageEnView1.Zoom := 100;
end;