Before jumping on the 120Hz wagon, it’s sort of important to understand why it’s being touted by manufactures. It may or may not be needed, and you may or may not like it. Its primary function is to combat the Sample and Hold Effect that occurs in our brain as a result of how it interprets what your eyes are seeing with some digital display types. Here’s a pretty good short version of what this is (not my words):
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“SAH (Sample and Hold) effect is due to how the eye-brain interprets the image perceived. Since light falling in the eye retina is persistent and the brain integrates light intensity over a short period of time, a certain amount of blanking time is required between frames for the brain to easily differentiate sequential images and interpret movements. Not doing so, the brain will integrate and join 2 subsequent frames and this will be perceived as fuzziness in the image. LCD/LCOS blanking time is almost nil since pixel state is always on for the duration of the whole frame. Single chip DLPs have some blanking time but definitely not as long as 3 Chip DLP due to its color wheel that turns several round per frame and display each color twice per round. 3 Chip DLP blanking time is directly proportional to pixel brightness intensity, and knowing the average pixel IRE hover in the 30s, add gamma to the equation and we’ll get on average very long blanking times with off state mirror time. CRTs have relatively long blanking times as well (about 14ms with 60fps material assuming 2ms phosphor decay time)”
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Frame interpolation and 120Hz are two different processes. 120Hz is just another type of frame rate doubling and will have mixed results depending on the source. For 24P film, it will do no good whatsoever and most likely just introduce judder. For 60Hz video, it will make it look more fluid.
Frame interpolation is when the display’s VP inserts extra frames that it ‘believes’ to be an accurate compromise between two sequential frames. For video, this appears to be working quite well. For film, all reports so far say is looks horrible. Dark frame insertion is Sony’s. DFI is where a frame of complete black is inserted between frames to mimic what you would see with 35 MM film projection. The dark frames represent the black (no image) area of the film between frames as it rolls past the beam. DFI is getting a lot of praise, but it comes at a price of loosing contrast.
At any rate, all that rambling aside, it would be a good idea to view a display before buying it. Watch film and video sources and see what you think. Some folks hate it, others love it.
DLP does not need any of these processes, but it’s not without its warts either.
