What is HDR, anyway?

Original Article ↗ Hacker News Discussion ↗

Technical meanings of “HDR”

  • Commenters disagree on a precise definition:
    • Some use the strict imaging sense: scene‑referred data with higher dynamic range than SDR, often with absolute luminance encodings (e.g., PQ) and modern transfer functions.
    • Others use it loosely as “bigger range between darkest and brightest” for capture, formats, and displays.
  • Clarifications:
    • HDR video typically uses higher bit depth (10‑bit+), PQ or HLG transfer functions, and wide gamuts (BT.2020), not generic floating point.
    • PQ is absolute-luminance; HLG is relative. Gain‑map approaches (Apple/Google/Adobe) are SDR‑relative and considered more practical for consumer workflows.
    • Most consumer HDR displays actually show content in BT.2020-encoded pipelines but are physically closer to DCI‑P3 or even sRGB.

Tone mapping vs. HDR vs. dynamic range

  • Multiple people stress that:
    • HDR capture / storage, tone mapping, and HDR display are separate stages.
    • Early “HDR photography” was really tone mapping multiple exposures into SDR; film and negatives always had more range than paper or screens.
  • There’s pushback on calling historical analog work “HDR” in the modern technical sense, though others note that modern tone‑mapping research explicitly cites analog darkroom techniques.

Real‑world display and OS behavior

  • Many report that HDR on desktop OSes is a mess:
    • Windows HDR commonly causes washed‑out SDR content, broken screenshots, jarring mode switches, and inconsistent behavior across apps.
    • Linux HDR is just emerging; macOS does better on Apple displays but can still ignore users’ brightness expectations.
  • Cheap “HDR” monitors often only accept an HDR signal but lack contrast, local dimming, or brightness; enabling HDR can make things worse than SDR.
  • DisplayHDR 400 is widely criticized as damaging the “HDR” brand; real benefit generally starts around ~1000 nits plus good blacks or fine‑grained dimming.

Gaming and cinema experiences

  • Experiences are highly mixed:
    • Some games and films are cited as excellent, subtle HDR use; others are described as headache‑inducing, overly bright, or “washed‑out grey.”
    • A recurring complaint is misuse: bright UI elements or subtitles blasting peak nits, overdone bloom‑style aesthetics, and content mastered for ideal home‑theater conditions but watched on mediocre hardware in bright rooms.

Mobile, web, and feed usage

  • On phones and social feeds, HDR often feels like it overrides user brightness settings, with isolated highlights becoming uncomfortably bright.
  • Platforms rarely moderate HDR “loudness”; several suggest analogues to audio loudness normalization or browser‑level controls (e.g., CSS dynamic‑range‑limit).
  • Browser support is fragmented: Chrome shows the article’s images closer to intent; Firefox and some Android setups produce flat, grey, or posterized results, and some mobile browsers even crash on the page.