I have video of a stage with a bright screen behind it, and I thought it would be neat if I could (easily-enough) punch in another image on the screen. And not just a small section of it, but fill it out with a "projected" image that I'll animate using keyframe movement and zooming.
If I use the Luma Matte in Premiere, especially doing it before the Color Correction effect, it can find the bright screen pretty well. However, unlike the Chroma Key effect, the Luma Key effect doesn't seem to have anything for shifting the edge or feathering, so it leaves a white line around the figures (and it doesn't handle everything well, really).
The un-corrected footage is a bit dark with the screen being very bright; I not only raised the shadows but I knocked back the brightest whites on a curve adjustment. So using the un-corrected version it should be easy to make a matte from that, but the Luma Matte effect they included is just too lame and does not produce a clean image even though it can identify the screen.
Now I thought about using AE for this, but I don't know how to use it and it's not simple. The rotobrush has trouble with the white medallion at the head of the pipa and the gap that shows through the recurved neck of the instrument, and causes far more complications in the Premiere project in general.
So I'm wondering if there is a (free) add-on effect that does a better job of this and/or has more command over it, or a stand-alone tool to generate a traveling matte file, or some techniques and tips to make what comes with Premiere work out better.