What is the composition of an HDR signal and what makes it different from SDR signal I just don't really understand.

I mean does sdr signal contains just the values of each R,G and B between 0 to 256?

And does HDR contains the values of R,G and B between 0 to 1024 (if 10 bit panel)?

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But my question is if the HDR contains just the signal of the R, G and B value,  how can a monitor with local dimming adjust the backlight to represent the scene's brightness? does HDR signal also contain brightness?

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