Alpha Add weird behaviours and limitations
Hi,
I have noticed this weird behaviour of After Effects. I am not sure if it's a bug but it is certainly a lack of control and accuracy.
https://www.youtube.com/watch?v=-_HjZgTG7N8
As you can see in the video link above my goal is to use Track Matte inverted (it does the same using setMatte) on a layer above pointing to the layer below and making the masking layer visible so that the layer below looks to be above. Then I use the blending mode Alpha Add on the two layers to remove that visible edge.
form After Effects User Guide:
Alpha Add Composites layers normally but adds complementary alpha channels to create a seamless area of transparency. Useful for removing visible edges from two alpha channels that are inverted relative to each other or from the alpha channel edges of two touching layers that are being animated.
The weird thing is that it works just there is nothing under those layers.
The funny thing is if the layers with Alpha Add are pre-composed and you add a layer under the new composition the Alpha Add works properly. What is the science behind it? I am not understanding it.
My goal is to keep all the layers on the timeline allowing some other layers to pass below those with the Alpha Add without pre-composing any layer.
Please, let me know if you have a solution for that.
ps. For me, it's also very weird that Alpha Add is between the blending modes and not a switch or an effect so it's possible to choose Alpha Add and another Blending Mode if needed.
Many thanks.
Daniele
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