Pentax IS actuator shifts the sensor by 1 pixel in 4 directions. "The result is an image which has full color information at every pixel location -- and thus improved resolution and a greater resistance to false color artifacts -- but only a relatively modest increase in file size...
As an added bonus, images shot in the Pixel Shift Resolution mode should also have a cleaner, tighter noise pattern. The reason for this is twofold. First, since multiple exposures are involved, noise can be averaged out across those exposures. Secondly, in a Bayer-filtered sensor, two out of three colors at each pixel location must be interpolated (read: guessed) from the values of surrounding pixels. When that happens, noise from adjacent pixels is likewise spread across their neighbors, resulting in a less film-like and blotchier, more objectionable noise pattern. With full color information at each pixel, a Pixel Shift Resolution shot's high ISO grain pattern is finer, and we're guessing easier to clean up post-capture, too."
Pentax Youtube video calls this mode "Pixel Shift Resolution". It's somewhat similar to one appeared in the previous Pentax DSLR model, but then it used to be a high frequency 500Hz vibration, whereas now it's said to provide a higher resolution for static objects:
