Many of us have a love-hate relationship with the diamond keyer in image. We wish we could use the 3D Keyer or others. Was even featured in the Reverse User Group.
With 2026.1 we got one step closer, being able to put one matte channel in BFX for Image to use.
I recently discovered another way you could have your own keyer in Image. Let me explain.
There is an interesting, but not well known, detail about how Image routes all the connections internally. If you connect more than one Matchbox to a selective, there is a connection for both the image and the matte channel between them.
The image channel was obvious, because you create a processing chain. But the matte channel? Hello, that means if we had a matchbox that keys, it can provide a matte channel to a downstream Mastergrade.
Turns out there are already two Logik matchboxes that key. But they didn’t work out of the box. They weren’t written for this use case and didn’t export their matte channel correctly.
With a bit of coding work and the help of @FrancisBouillon we got a variation of crok_jt_key to work this way.
Here’s the example:
The setup - delete the default master grade in your selective (helps keep the priority order correct, or you’ll have to use the priority editor later to fix it).
Then add this custom version of crok_jt_key, for simplicity also add id_ShowAlpha, and then a Mastergrade.
crok_jt_key looks like it was originally conceived as a chroma keyer. The original version also has despill and some other features which are disabled in this custom version for now.
Sample the color (be sure to not use color management), look at the alpha channel, and adjust the x y z values to taste. Also the matte refinement.
It will look like this, because of id_ShowAlpha. When happy, just hide id_ShowAlpha so that the matte gets passed on to Mastergrade.
One more important change in Mastergrade - go into the ‘Shader tab’ and on the right, change the ‘Selective’ from ‘Selective’ to ‘Matte’. This tells image to pipe the matte into the shader, not the selective.
Then in Mastergrade you can grade away, and it will only impact the pixels that the key selected.
That opens new doors. Now we just need to write some Matchbox keyers 
Here’s the modified crok_jt_keyer if you want to experiment. I’ll clean it up a bit more in the coming days and submit to the portal with proper naming. Not sure yet if it should be posted as a compatible update to crok_jt_key, or become a new entry with reference to the original. Opinions welcome.
If you do endeavor of writing your own keyer, you have to write it as a selectiefx matchbox that supports Action, is a matte provider, and properly handles both the selective and matte channels. Pretty standard stuff, but need to look out for it.
cork_jt_image.zip (20.4 KB)