Mask point with Active instance in Geo Comp

Beginners
1

Hi all,

I’m such a beginner in TouchDesigner, and I have a project I’m working on. It’s a bit hard to explain clearly, but I’ll try!

I’m working on a project where I’m transforming video into a point cloud. I’m trying to use a PNG as a mask to prevent certain particles from being generated.

My current setup works like this:

I use a Reorder POP to extract the RGB values from the video. The Blue channel is used to generate depth / point coordinates. These coordinates are sent directly to a Geo COMP through Translate OP for instancing the particles.

I added a white PNG logo on a black background. To prevent particles from appearing where the logo is, I’m using a Composite TOP to make the video black wherever the logo is, before sending it into the Reorder.

Capture d'écran 2026-09-27 221540
Capture d'écran 2026-09-27 2215402087×883 129 KB

This works in the sense that no particles are generated at the logo’s location.

However, I get a strange grid/mesh of particles behind the logo.

Capture d'écran 2026-09-27 221416
Capture d'écran 2026-09-27 221416641×837 302 KB

I think the reason is that the masked pixels are simply turned black, so their coordinates become 0,0,0 rather than the corresponding points actually being removed. All those points therefore end up at the same location, creating this strange grid.

What I would like to achieve is:

black/masked pixel → delete the corresponding point
non-black pixel → keep the point and its original coordinates

I read in the docs that Active instancing could be a way to create a mask. Could that work in this case?

What would be the best way to approach this in TouchDesigner?

Thanks!

edit : What I want to do is make sure that the points on my second screen that seem to be “arranged” and correspond to points in black areas are not arranged into a grid, but simply hidden. I hope that makes sense…

2

Hi @kaatarakt

when using instancing, there is a active channel you can use to control which data is used to instance the geometry. You can use a monochrome mask and assign it to the alpha channel of the texture that has the position values. Now reference the alpha channel in the active parameter on the instancing page.

If it’s a bit difficult to explain, please prepare and share a minimal reproducible example - this will help greatly when coming up with a workable solution.

cheers
Markus