What Is HDR (High Dynamic Range)?

pcmag.com:

High dynamic range (HDR) video is one of the biggest 4K TV feature bullet points. It can push video content past the (now outdated) limitations to which broadcast and other media standards have adhered for decades. It's impressive to see on TVs that can handle it, but it can be a confusing technical feature thanks to several iterations each with differences that aren't well-defined. We're here to explain them to you.

TV contrast is the difference between how dark and how bright the picture can get. Dynamic range describes the extremes in that difference, and how much detail can be shown in between. Essentially, dynamic range is display contrast, and HDR represents broadening that contrast. However, just expanding the range between bright and dark is insufficient to improve a picture's detail. Whether a panel can reach 200 nits (relatively dim) or 2,000 nits (incredibly bright), and whether its black levels are 0.1cd/m^2 (washed-out, nearly gray) or 0 (completely dark), it can ultimately only show so much information based on the signal it's receiving.

Many popular video formats, including broadcast television and Blu-ray discs, are limited by standards built around the physical boundaries presented by older technologies. Black is set to only so black, because as Christopher Guest eloquently wrote, it could get "none more black." Similarly, white could only get so bright within the limitations of display technology. Now, with organic LED (OLED) and local dimming LED backlighting systems on newer LCD panels, that range is increasing. Both blacks and whites can reach further extremes, but video formats can't take advantage of it. Only so much information is presented in the signal, and a TV capable of reaching beyond those