Light and shadow - though having the same source and the same origin, they are always in opposition.

光与影——虽然发源相同，起因一致，它们却往往背道而驰。

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When an object space normal map tells a face it's supposed to receive light coming from the left of the object it will always do so, even if the face is pointing away from the light source.

当一个物体空间的法线贴图告诉一个面，它被期望接受来自物体左边的光线，它就会这样做，即使这个面实际是指向光源的。

youdao

Face the light: Lights can dispel shadows and create soft features on your face, so always try to turn your face toward the main light source.

面朝光线：光线能驱散阴影，让五官显得柔和。所以，自拍时要尽量面朝主要光源。

youdao