Rec.2100 PQ vs sRGB: Why HDR White Can Look Brighter
sRGB describes standard-dynamic-range color relative to a display’s ordinary white, while Rec.2100 PQ can encode absolute display luminance up to 10,000 nits. That extra range lets a small HDR highlight render above normal UI white on capable hardware.
The short version
sRGB was designed for standard computer displays. Its brightest encoded value represents white, but the final luminance depends on the display and operating system. Rec.2100 is an HDR recommendation built around BT.2020 color primaries and either PQ or HLG.
PQ—standardized as SMPTE ST 2084—is the important part for brighter-than-white graphics. It describes light on an absolute scale. A highlight can therefore ask for a luminance well beyond the level used for menus, text, and ordinary web backgrounds.
Why #FFFFFF is still normal white
In an ordinary sRGB image or CSS color, #FFFFFF is the highest channel value. It is white, but it is not a command to drive an HDR panel to its physical peak. The operating system usually maps interface white to a comfortable reference level and reserves brighter output for HDR content.
That is why two patches that look numerically “white” can emit different amounts of light: one belongs to an SDR rendering context, while the other is interpreted through an HDR transfer curve and color profile.
Why the entire image should not be boosted
HDR headroom works best for selective highlights. If every pixel is pushed upward, the image can become uncomfortable, backgrounds can lift, and low-level JPEG noise becomes visible. A luminance threshold lets a converter raise near-white parts while keeping darker colors closer to their intended appearance.
What tone mapping does
When a screen or app cannot reproduce the encoded luminance, it compresses the signal into a smaller range. This is tone mapping. A good fallback keeps the composition readable and the mark recognizable even though the extra light is gone.
Frequently asked questions
Is Rec.2020 the same as Rec.2100?
Rec.2100 uses BT.2020 color primaries, but adds HDR system definitions including PQ and HLG transfer functions.
Does PQ always mean 10,000 nits on screen?
No. PQ can encode values up to 10,000 nits, but the display maps the signal to its own capabilities and may tone-map it.
Is #FFFFFF the brightest possible white?
It is the maximum channel value in an SDR sRGB context, but HDR media can describe luminance above the interface’s SDR white level.