Потоки (Thread), не могу разобраться

procedure TQTest.AntiA(Sender: TObject; s:AnsiString; i:boolean);
var
   source,buffer:TBitmap;
   Jpg:TJPEGImage;
begin
     if i = true
      then
       begin
        (Sender as TImage).Picture:=nil;
        (Sender as TImage).Canvas.Brush.Color:=clBtnFace;
        (Sender as TImage).Canvas.Brush.Style:=bsSolid;
        (Sender as TImage).Canvas.Rectangle(-2,-2,(Sender as TImage).Width + 2,
                                                  (Sender as TImage).Height + 2);
       end;
 
     source:=TBitmap.Create;
     buffer:=TBitmap.Create;
     Jpg:=TJPEGImage.Create;
     Jpg.LoadFromFile(s);
 
     if ((Sender as TImage).Width / Jpg.Width * Jpg.Height >
         (Sender as TImage).Height / Jpg.Height * Jpg.Width)
      then
       begin
        buffer.Height:=(Sender as TImage).Height;
        buffer.Width:=Round(buffer.Height / Jpg.Height * Jpg.Width);
        if buffer.Width > (Sender as TImage).Width
         then
          begin
           buffer.Height:=Round((Sender as TImage).Width / buffer.Width * buffer.Height);
           buffer.Width:=(Sender as TImage).Width;
          end;
       end;
 
     if ((Sender as TImage).Width / Jpg.Width * Jpg.Height <=
         (Sender as TImage).Height / Jpg.Height * Jpg.Width)
      then
       begin
        buffer.Width:=(Sender as TImage).Width;
        buffer.Height:=Round(buffer.Width / Jpg.Width * Jpg.Height);
        if buffer.Height > (Sender as TImage).Height
         then
          begin
           buffer.Width:=Round((Sender as TImage).Height / buffer.Height * buffer.Width);
           buffer.Height:=(Sender as TImage).Height;
          end;
       end;
 
     source.Assign(Jpg);
     SetStretchBltMode(buffer.canvas.handle,HALFTONE);
     StretchBlt(buffer.canvas.handle,
                0,0,buffer.Width,buffer.Height,
                source.canvas.handle,
                0,0,source.width,source.height,
                SRCCOPY);
     (Sender as TImage).Canvas.Draw(((Sender as TImage).Width - buffer.Width) div 2,
                                    0,buffer);
     source:=nil;
     buffer:=nil;
     Jpg:=nil;
 
     if i = true
      then
       (Sender as TImage).Canvas.Brush.Color:=clWhite;
end;