The toshiba, and most other RPTV's, actually still use the line doubler even if your source is progressive scan already. If you use a progressive scan dvd player to your Toshiba, you input 480p. The toshiba line doubler then upconverts this to 540p. Unfortunatly, it introduces some artificats in so doing, but from what I have read, this years toshiba's do a better job of it than last years. To my knowledge, the only sets that allow 480p to pass through without additional upconversion by the line doubler are Pioneer, Mitsubishi, and Panasonic. So yes, the line doubler is activly upconverting even if you are using a progressive scan dvd player.