Again the Trails FX

[Rene]

I've found again something strange related to the Trails FX. (btw. I love this FX!)

1) start a clip on any layer
2) apply the Trails FX on composition level
3) Feedback ca. 90%, Mode Luma ---> Bright regions are not faded out (nice feature anyway )
3) use the little cross on the upper left corner of the UI, to eject all layers.
4) bright regions are still visible

Is the Luma mode broken, or is it meant to be like this?

(OSX 10.6.7; GeForce GT 330M - 256MB)

[Joris]

Hey Rene

The trails effect uses an image buffer to create the trails. When you are in Luma mode and eject the content, the buffer is still filled (because the bright parts never erase), and it keeps adding itself to itself, so to say. When you decrease the feedback parameter, the buffer will clear.

Hope that explains things.

Joris

[Rene]

Hi Joris,

I'm not sure if I understood your reply...

the buffer is still filled (because the bright parts never erase), and it keeps adding itself to itself, so to say. When you decrease the feedback parameter, the buffer will clear.

never erase - That's exactly what happens, but I would expect even the white part to be faded out over time. When I set the Feedback to 1%, still a lot of space remains white (forever).

So I understand why the composition still displays something, even when I eject all layers, but with Feedback set to 1% it should fade out over time, shouldn't it?

[Joris]

Sorry if I wasn't clear

The Luma mode works much like the Luma Key blend mode. When in Luma mode, everything below a certain threshold will be erased, and anything above that threshold will stay and be added to the buffer. Even when you eject the source content, you're luma keying the buffer, which results in a small part of fully opaque white remaining.

The Alpha and Lighten modes work like their blend mode namesakes as well. The main difference is they don't work with a threshold, but an alpha or luminosity value respectively. The result of ejecting the source is a gradual fade out over time, because the buffer is composited over itself with ever decreasing alpha or luminosity levels.

Maybe someone could create a plugin that combines a luma key and a lighten blend mode to get the result you're after?

[Rene]

Thanks for clarification. Got it now