What is "game mode" in modern TVs?

When watching speedrunners playing old console games, and even newer ones, it might be a bit surprising that many of them prefer a good old-fashioned chunky CRT TV over a modern LCD/LED TV (even though many of the latter support composite input, or in the worst case scenario, there exist converters).

Many people who don't know the reason might be a bit surprised by the reason: Input lag.

CRT TVs have essentially no input lag whatsoever. This means that the console is perfectly "in sync" with the cathode ray of the TV, ie. anything that the console is outputting for the current scanline is immediately shown on screen. The longest possible lag between eg. a controller button press and its effect happening on screen is 1/60th of a second (or 1/50th in the case of PAL), because that's how long the refreshing of the screen takes. This is more than sufficient for human reflexes (eg. in speedrunning).

This implies that LCD/LED TVs have some kind of input lag. That's often the case. Depending on the particular brand and model of TV, this input lag can vary all the way from one entire frame to half a dozen frames.

Modern TVs typically perform all kinds of post-processing to the image they are receiving for display. They might perform brightness/contrast adjustments, color correction, noise reduction, and all sorts of things. They buffer the input video signal they are taking, and perform these operations on the individual buffered images before displaying them. In some cases this might take several frames. (In other words, the image you are seeing might have been sent via the HDMI or whatever cable to it several frames prior, meaning something like 3/60ths or 4/60ths of a second ago.)

When watching TV or a DVD/BluRay this doesn't make any difference. It really doesn't matter if the BluRay player sent it the picture eg. 3/60ths of a second prior. It's impossible to even notice.

However, it can become noticeable when the TV is used to play a console game (or sometimes even a PC game). The more lag there is between you pressing a controller button, and its effect happening on screen, the more noticeable it becomes. For power-players (such as speedrunners and many online gamers) this input lag may be crucial. The better your reflexes are in a given game, the more you notice the input lag, and the more it hinders your gameplay.

Computer displays, even though in the modern day they use pretty much identical technology to TVs, generally eschew any such post-processing and display images as soon as they get it (meaning that the input lag is, optimally, at most that 1/60th of a second. Or even less if the display has a higher refresh rate.)

This is where the so-called "game mode" of many modern TVs comes in. Many people don't know what it means, and might think it's just a mode that adjusts brightness, contrast, color correction and other such things for games to look better (at least in the manufacturer's opinion). However, what it usually means is that the TV forgoes most of its post-processing steps in order to display the input image as soon as possible, reducing input lag.

With some TVs this might mean that it, for example, reduces the lag from something like 4/60ths of a second to just 2/60ths. A few TVs might even reach the computer monitor speed of 1/60ths of a second.

If you play with a console using a TV, it's recommended to use the "game mode" setting of the TV, if it has one, so that games will become more "responsive", without that input lag (or, at least, with a minimized input lag).