High-definition is rapidly going mainstream.

Samsung has announced a new image sensor for notebook webcams that supports 720p HD video at 30 frames per second.

It’s too early to say how much HD-ready webcams will add to the cost of portable PCs, but given the sour economy and price pressures in the laptop market, it probably won’t be a lot. Mass production of the S5K4AW CMOS image sensor is slated to begin in the first half of 2009.

The Samsung announcement is another indication of how fast HD technology is going mainstream. In fact, it’s getting downright cheap. Bargain HD camcorders like the Flip MinoHD ($230) and the Kodak Zi6 ($180) are pocket-sized consumer gadgets that shoot 720p video. Trends indicate that most consumer video gadgets will soon be high-def. It won’t be long before the terms HD and high-definition sound as quaint as stereophonic and high fidelity.

But are we really ready for an all-HD world? The Samsung sensor, for instance, can improve image quality in low-light conditions, such as those late-night webcam sessions. And HD camcorders will likely capture more pimples, wrinkles, and gray hairs than most of us would care to save for posterity.

Maybe there’s something to be said for grainy, low-res video.