When run on a ds phat, the bottom screen will still show the preprocessed video frames (no center and masking) since even with the backlight turned off the display can still show the contents.
The same happens on both DS Lite/DSi models, it's completely invisible in normal circumstances due to the different display types, only visible under a strong external light source.
When run on a ds phat, the bottom screen will still show the preprocessed video frames (no center and masking) since even with the backlight turned off the display can still show the contents.