After effects masking, grey line appears

[Sciencio5EC6]

I add a closed eye face layer on top of the opened eye face layer so if i want to do a blink effect i can move the mask path down. But i see the grey thing when i mask, Why does this happen actually? I did parenting so it can follow the opened eye face layer

 

[Mylenium]

That happens when your mask isn't exactly coinciding with full pixels and AE's sub-pixel sampling kicks in. The simple solution may be to switch layers to draft quality, effectively turning off sub-sampling. Otherwise you have to make an effort to place your masks more precisely.

Mylenium

[Sciencio5EC6 · Accepted solution]

I just fixed the issue. I have two layers the close and opened eye. Both has drop shadow and it cause the grey line to appear