While watching a standard-definition channel, search the HDTV's remote or its on-screen menus for a setting called Picture Size, P. Size, Aspect, AR, Format, Screen Size, Viewing Mode, or something similar. Of the options offered, the one you want is probably labeled 4:3, 4X3, standard, or normal.

Most HDTVs are smart enough to understand that your choice in this setting indicates how you want all of your SD channels--and only your SD channels--to look.

The same issues apply to DVDs, but they're resolved differently. Although DVDs are standard definition, they support both aspect ratios. On an anamorphic widescreen DVD, the disc-mastering process squeezes the wide, 16:9 image into a 4:3 frame; playback then stretches the image out again. (Movies on DVD often appear letterboxed within the 16:9 frame, because they were intended for even wider movie screens.)

By default your DVD player was set under the assumption that you have a 4:3 television. When you played an anamorphic disc on your standard TV, the player shrank and letterboxed the image, keeping the wide image and the proper proportions but throwing away 25 percent of the resolution.