Mepaku 目ぱち is a standard blink. It consists of three frames, two keys, and one inbetween.
In situations where eyes are partly covered, it's common practice to separate them onto a different layer.
The average blink is done timed on 2s or 3s (see timing).
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Variation in spacing and style tends to be more common since they're not timed to dialogue. Blinks can be animated through either the same-cel (gousei) method, where everything is on a single layer, or through the separate layer (x-1-2) method.
Inbetweens are biased towards the open eye to decelerate/accelerate the motion. Eyebrows may or may not move.
Creating the inbetween for the blink requires dropping the pupil along with the upper eyelid about 25% of the way to the closed position. All of the shapes and shadows will deform slightly in this process–some styles might have the eye go from completely open, with no upper eyelid visible, to partly closed.
In uncommon cases, Mepachi are done with 5 frames. In this case, two more frames are added in the ease-out of the animation.
Frame 2 is shown again, creating a smooth, slow motion of the eye opening. Frame 5 returns to the nearly opened eye before returning to frame 1.
This chart shows a 3 frame inbetween chart on the A cel, and a conventional single inbetween on B cel.