system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do only some displays display HDR? Isn't a display just a series of pixels that display different color values? What makes an HDR display different?

To clarify, if my normal LCD display does not display HDR, what makes it different, hardware wise, from an HDR compatible one? I understand the HDR process when taking a picture, and the layering of differently exposed images, but then how can I view the HDR image on my non-HDR phone?
gpt
An HDR screen is a different concept to taking HDR photos. Although both relate to using a wider range of colours.

A non-HDR screen only has 256 different levels of red, green and blue. So there's only a certain range of colours and brightness it can display.

HDR screens increase this so there is a wider range of colours/brightness levels. True HDR screens are supposed to be capable of more brightness, but it's not just the maximum brightness that matters, it's how many levels of brightness each colour channel has.

So for example you could have a movie in HDR which for the most part looks the same as the non-HDR version, except explosions are brighter. If you just turned the brightness up on the non-HDR version, everything would just look washed out because the brightness goes up for everything. The HDR version has more brightness levels to work with.