thought that I've probably shared somewhere before: a beam index/aperture grille hybrid CRT

the problem with beam index CRTs is that they have to constantly run a minimum beam energy to illuminate the internal UV phosphor, for proper beam indexing

but... what if you didn't use beam indexing for *color* at all, using something like an aperture grille or slot/shadow mask for color... and instead used beam indexing for *geometry*?

then, the beam only need be active in the overscan area.

you could set up some sort of quadrature pattern or something like that so that the chassis knows exactly where the beam is, and can adjust geometry on the fly to maintain perfect geometry

the only real problem that this can't directly correct for is issues with geometry blooming because of brightness variation, and there's ways you could detect that happening (basically run in overscan at varying power levels to see what happens to geometry in a calibration cycle), and possibly compensate

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