Your poor, defenseless new HDTV has been the victim of sabotage. Factory conspirators have cranked up settings for brightness, contrast, color and sharpness so you can't miss the picture in the brilliance of the store's fluorescent-fired showroom.

You fall in love, reach for a credit card and bring home the TV. Now, in the softer lighting of your den, the picture looks as if it had spent the day at a Red Bull keg party. It's so fired up, hyper-bright, and the colors are so oversaturated that it's more than inaccurate: It's potentially dangerous, shortening the life of your plasma or the lamp in your DLP set. Even more alarming, you might even think this is the way an HDTV should look.

SpyderTV from Datacolor ($229) could be the most elaborate way for do-it-yourselfers to get the best picture - the best picture for your eyes and the best for your HDTV. It's a great tool if it fits your budget, the next best thing to a full-blown calibration by professionals trained by the Imaging Science Foundation. The pros charge about $500, lugging maybe $50,000 in test equipment into your home, for a full calibration.

SpyderTV uses a colorimeter, a sensor that attaches to the TV screen and sends readings from test patterns to a computer or laptop, then calculates ideal settings for your HDTV. It works with any TV, but not a projector.

I tested two televisions, a 60-inch Vizio plasma and a 50-inch Sony rear-projection HDTV, and quickly learned the SpyderTV provides excellent results - but only under optimum conditions.

It is ruthless in its honesty. If the room is not dim, the screen shielded from ambient light, results will be skewed. Same thing if a plasma screen is supposed to display a black test screen but instead retains a brighter image from a previous onscreen menu, as the Vizio did.

SpyderTV covers the basics: brightness, contrast, color, tint and color temperature, which is how the television displays white. (A cool color temperature accentuates blue; a warm color temperature accentuates red.) A separate test for sharpness that doesn't require the colorimeter is also available.

The package includes the colorimeter, called a Spyder for its long-legged design, and its USB cable, a test DVD, a software CD to load onto your laptop or nearby desktop computer (Windows 2000 or XP) and a storage bag. You'll also need a DVD player to display test patterns on the TV screen.

The software walks you through every step, starting with basic information about the TV's brand and model number. It also must know the minimum, maximum and current setting for brightness and other calibration points. Attach the SpyderTV to your TV screen midsection, pressing gently on the suction cups at the base of each leg, then attach the other end of the USB cable to your laptop. Then the testing begins.

My tests, timed by the SpyderTV software, took anywhere from 23 to 57 minutes. SpyderTV presumes you already have selected the TV's dullest-looking picture mode.

It's often called Cinema or Standard, but TVs often arrive from the factory in their hottest setting, Vivid. SpyderTV takes readings at minimum and maximum settings for brightness, contrast and all the rest, then requests multiple readings in between until it arrives at the optimum setting.

SpyderTV, not surprisingly, toned down the Vizio VM60P's factory settings for brightness, contrast, color and sharpness. It took two full tests to get it right, though. On the first, SpyderTV calculated a "1" setting for brightness - a chronically dark screen. So something wasn't right. That's when I noticed the Vizio had retained a brighter image from the test DVD's previous onscreen menu, creating a false reading.

SpyderTV never got the color temperature right. Flesh tones still looked too green. The Vizio had user-control settings for dialing in the correct blend of blue, green and red, but SpyderTV had no specific tests for it.

For that, I would need SpyderTV Pro ($300), a SpyderTV with advanced software for professionals and die-hard hobbyists. So I could only guess, then run through the test session again, start to finish.

Likewise, the Sony KDS-50A2000's initial readings were off, too, because I did not adequately shield the screen from daylight filtering through the edges of the room's shades. SpyderTV insists on a completely dark room.

Once you realize that, you're on your way to a better-looking picture. The SpyderTV's results were a huge improvement over the factory settings, with richer colors, deeper blacks, more natural flesh tones and lifelike images.

They were not, however, dramatically off those achieved with a $30 test DVD, the HDTV Calibration Wizard, produced by the ISF's Joel Silver and distributed by Monster Cable.

But after trying all of the major test DVDs - including the Avia Guide to Home Theater and Digital Video Essentials - and attending a two-day ISF training seminar, I still would say SpyderTV is better than anything except a professional calibration.

You, and your HDTV, will be saying, "Thanks, Spidey."

Hunt is The Courant's consumer electronics columnist.