포토샵 레이어 마스크 개념 및 사용법

사용법 요약 :
1. 레이어마스크에 alt-click 하면 레이어마스크의 흑백이미지가 보임
2. 레이어마스크를 이미지에 overlap 해서 보려면 \ 누르면 됨
View Your Layer Mask As A Rubylith

다음 링크에 설명 잘 나와 있음
레퍼런스 : Understanding Layer Masks In Photoshop
As I mentioned at the beginning of this discussion, layer masks allow us to control the transparency of a layer, but unlike the Opacity option which controls overall transparency, layer masks allow us to set different levels of transparency for different areas of the layer (although technically, you could use them to control the overall opacity as well, but the Opacity option already handles that very well and layer masks are capable of so much more)...