Samsung LN-T4671F LCD TV
In my new role here at UAV, one of my primary jobs is to review flat panels, so I decided to revisit the LN-T4671F and take a more in-depth look since it performed quite well overall in my original tests. One of the only drawbacks I identified at that time was mediocre shadow detail. As I worked with the TV for the UAV review, I came to realize that, in my haste to finish the work for Playback, I had set the brightness incorrectly, which impacted the shadow detail.
I'm really glad to have another go at this TV, which performed even better than it did during the evaluation for Playback (duh!). I regret any confusion this might cause, but in the interest of full disclosure, I thought it was important to come clean before presenting my review here.
The 46-inch LN-T4671F sits squarely between its 40- and 52-inch siblings in the 71 series, all with 1920x1080 native resolution. These sets employ a conventional fluorescent backlight, unlike the LN-T5281F and others in the 81 series, which feature LED backlighting.
Perhaps the most important feature of the LN-T4671F is its 120Hz operation, which is all the rage in LCD TVs these days. LCDs tend to suffer from what is commonly called "motion blur," which causes fast-moving objects in the image to appear blurry. These objects can also leave a ghostly trail in their wake. This occurs because LCD pixels are relatively slow to change their state from one brightness level to another, especially compared with plasma and DLP pixels.
To combat motion blur, someone had the bright idea of flashing frames on the screen at twice the rate of normal video—that is, at 120Hz instead of 60Hz. Because each frame lasts only half as long, motion blur should be reduced.
Actually, it's not quite that simple. (Is it ever?) First of all, how are 60 frames per second converted to 120? There are several ways to do it. Sometimes, a black frame is inserted between each real frame in a process called, logically enough, "black-frame insertion." A variation of this technique inserts a darkened copy of each frame immediately after the real one. This lowers the black level—another common bugaboo of LCDs—and masks any motion blur with darkness.
Another approach is to create new frames by "interpolating" between real frames—that is, analyzing any moving objects and calculating where they should be in the new frames. This can significantly smooth out onscreen motion, but it also carries the risk of introducing artifacts of its own unless it's done very carefully.
The LN-T4671F includes a feature called Auto Motion Plus (AMP), which can be set to Low, Medium, or High, or it can be turned off. If it's off, each frame in a 60Hz signal is simply doubled, and each frame in a 24Hz signal is repeated five times. In any event, the set's refresh rate is always 120Hz whether or not AMP is enabled.
If AMP is on, the set interpolates between actual frames; according to Samsung, "With AMP set to High, the full distance [traveled by an object from one actual frame to the next] is evenly interpolated. With AMP set to Low or Medium, only a portion of the distance is interpolated." I'm not sure why you'd want to interpolate only a portion of the distance. In any case, with a 60Hz signal, the processor is said to determine the original frame rate—converting it back to 24fps using inverse telecine if it encounters 3:2 pulldown—and then interpolate the new frames to get to 120Hz.