img.io.twainparams.xresolution.currentvalue:=72;
      img.io.twainparams.yresolution.currentvalue:=72;
      img.io.TwainParams.VisibleDialog:=false;

      img.IO.Acquire;

procedure Tmypreviewform.imgSelectionChanging(Sender: TObject);
var
  w,h:integer;
begin
  w:=img.SelectedRect.width;
  h:=img.SelectedRect.height;

  jfcform1.BeginAssign;
  try
    width_edit.Value:=(w/72)*2.54;
    height_edit.Value:=(h/72)*2.54;
  finally
    jfcform1.EndAssign;
  end;
end;

procedure Tmypreviewform.larghezza_editChange(Sender: TObject);
var
  x1,y1,x2,y2:integer;
begin
  x1:=img.SelectedRect.x;
  y1:=img.SelectedRect.y;

  x2:=x1+trunc(width_edit.asvalue*72/2.54);
  y2:=y1+trunc(height_edit.asvalue*72/2.54);

  img.SelectionBase := iesbBitmap;
  img.Select(x1,y1,x2,y2);
end;

var
  l,t,w,h:double;
    img.io.twainparams.xresolution.currentvalue:=300;
    img.io.twainparams.yresolution.currentvalue:=300;
    img.io.twainparams.bufferedtransfer:=true;

    if show_my_preview_form(l,t,w,h) then // this function open a form where a low dpi scan is made, allow the user to select the area to scan and returns left,top,width and height (in centimeters) of the selected area
    begin
      img.io.TwainParams.AcquireFrameEnabled:=true;
      img.IO.TwainParams.AcquireFrameLeft:=l/2.54; // cm are converted in inches
      img.IO.TwainParams.AcquireFrameTop:=t/2.54;
      img.IO.TwainParams.AcquireFrameRight:=(l+w)/2.54;
      img.IO.TwainParams.AcquireFrameBottom:=(t+h)/2.54;
      img.io.TwainParams.VisibleDialog:=false;
    end
    else abort;
  end;

  img.IO.Acquire;

    img.io.AcquireParams.AcquireFrameEnabled:=true;
    img.IO.AcquireParams.AcquireFrameLeft:=l/2.54;
    img.IO.AcquireParams.AcquireFrameTop:=t/2.54;
    img.IO.AcquireParams.AcquireFrameRight:=(l+w)/2.54;
    img.IO.AcquireParams.AcquireFrameBottom:=(t+h)/2.54;
    img.io.AcquireParams.VisibleDialog:=false;

    img.io.Acquire;