Why we can’t replicate 0 input lag with monitor/TVs like we were able to do with CRTs

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Why we can’t replicate 0 input lag with monitor/TVs like we were able to do with CRTs

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CRTs are analog displays — that means that they don’t need to perform any calculations in order to display video, sort of like an [overhead projector](https://en.wikipedia.org/wiki/Overhead_projector).

Modern TVs and monitors have pixels, so some calculation needs to be done in order to figure out what color to make each pixel. It’s like trying to take a picture and drawing it onto graph paper, you have to do some thinking to figure out what boxes should be what color in order to get the closest representation of the original picture.

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CRT display works by shooting electron beam on a phospr surface on the display.
Where the beam hit the display would light up basically immediately and then go out.
Here is slow motion video of a CRT https://youtu.be/3BJU2drrtCM?t=104
The scanning you see in the vidseo happens so fast that human eye wouldn’t be able to see it at all and the screen would seem to be on constantly.

LCD (Liquid Crystal Display) works by having liquid crystals in it. Electricity is used to twist these crystals to change how much light gets through.
Twisting the crystal takes some time.
Some gaming displays have “overdrive” setting that uses stronger current/voltage to twist the crystals faster. But this can often result in overshooting. So if you try to go from white->gray the pixel overshoots white->dark gray->gray.

Let’s keep color out of it to make it simpler.

CRTs work like a hand moving a pen across paper from left to right without lifting it off the pape before you reach the right edge. You end up drawing the images as a set of horisontal lines, and it’s always the same amount of lines. The harder you press on the pen, the darker or lighter the line becomes. That means every movement you make has a direct effect on the drawing immediately, the relationship between your hand (the signal) and the drawing (the output) is analogous.
The analog signal is electric, and is sending tiny shocks to your arm, making you twitch and move. But it also requires you to always move your hand at the same speed across the paper on its own, otherwise the image looks wrong.
The wonderful thing is that even though the electric signal can be mangled, the automatic movement of your arm will ensure that at least something gets drawn, and it takes a lot to botch the image. There are some restrictions to the image though, like dimensions and framerate.

Pixel screens work like drawing an image using plastic beads on a grid.
For every bead you have to put down, you get a message with some numbers, one at a time. This message has to be interpreted as a color, before you can pick and place a bead. This means that there can be a delay, if you’re not quick enough to interpret the message.
Because the messages comes as a series of electric pulses that can be interpreted as numbers, like counting digits, it is a digital signal.
A digital signal is very flexible, both in terms of resolution and framerate, but it will always be a dependent on the signal and the interpreter to be aligned, and even small mistakes can botch the image.