Input Lag Breakdown: Display Scaler Processing Delay vs Panel Scanout: Fundamental Mechanics and Deep Mathematical Modeling

[Caleb Rivera]

I’ve been drilling into how scaler processing latency and panel scanout time actually stack in the input lag chain, and I want to nail down the math before I trust any latency claims from panel manufacturers. Everyone cites the “fast mode” or “scaler bypass” figures, but I’m not seeing a clean derivation of how much delay survives once you remove the scaler. Specifically: when you’re in bypass mode, is the residual latency purely the line-buffer read/write overhead plus the top-to-bottom scanout time, or is there still a fixed floor from the panel’s own timing controller? And how does scanout time scale with refresh rate at a fixed resolution—is it strictly linear with the frame period, or does the gate-drain charging time of the TFT array introduce a nonlinear component at higher rates?

Second question: for someone chasing minimum input delay in competitive FPS titles, how do you isolate scaler delay from scanout in real-world measurement? I’ve read that you can’t fully eliminate scanout since the pixel has to physically complete its top-to-bottom sweep before the next frame is valid, but I want to confirm the proof. Does the scanout time represent an irreducible floor that adds directly to perceived latency, or does it only matter at the moment of a new frame actually landing on panel? Any references on the foundational derivation would help.

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