Layer opacity, defined between 0.0 and 1.0, is used as a merge factor when it has to be blended with another image.
In a layer-based compositing software like Autograph, this secondary image is usually the result of the stack underneath, and this factor is used by blend modes operations to define layer weight in blending. Opacity acts as a multiplier of the layer’s existing Alpha channel. The two are combined before the merge operation.
You have three ways to modify a layer's opacity:
- On the layer’s main line, with the Blend mode / Opacity dual controller
- By unfolding the layer parameters in the stack
- By inspecting the layer in the Properties Panel
Opacity can only be animated in the stack or the Properties Panel using the keyframe pie menu, or by adding a generator to this parameter. A layer's main line just offers quick access to this value, by replicating it to quickly set the transparency without unfolding the layer. If layer opacity is animated with a generator, the main line controller will be grayed out. If it is animated using keyframes, it will still be accessible. So, be careful to avoid accidentally adding animation keys by manipulating the slider.