PQ, the perceptual quantizer, is the high dynamic range transfer function standardized as SMPTE ST 2084 and included in ITU-R BT.2100, which maps digital code values to absolute luminance levels from 0 to 10,000 cd/m², also called nits. In HDR video, PQ is the electro-optical transfer function behind HDR10, HDR10+ and Dolby Vision, and it replaces the traditional gamma curve used in standard dynamic range video.
PQ was designed around human contrast sensitivity, so that each step between adjacent code values stays close to or below the threshold of visible difference across the entire brightness range. That efficiency allows a 10-bit signal to cover HDR brightness without visible banding in most content.
How the PQ curve encodes brightness
PQ is an absolute, display-referred encoding. A given code value means a specific luminance on the display, for example about 100 nits at roughly 51 percent signal and about 1,000 nits at roughly 75 percent. This differs from SDR gamma, where a code value means a fraction of whatever peak brightness the display happens to have.
The curve is derived from a model of the just noticeable difference in luminance. Dark regions receive many fine steps, because the eye is very sensitive there, while the brightest regions receive fewer, coarser steps. In 12-bit, PQ steps stay below visibility across the full range; in 10-bit, they are close to the threshold and acceptable for nearly all delivery.
| Luminance | Approximate PQ signal | Significance |
|---|---|---|
| 0.005 nits | About 7 percent | Deep shadow near display black |
| 100 nits | About 51 percent | Traditional SDR peak white |
| 203 nits | About 58 percent | Reference diffuse white for HDR |
| 1,000 nits | About 75 percent | Common mastering peak |
| 4,000 nits | About 90 percent | High-end mastering peak |
| 10,000 nits | 100 percent | Maximum defined by the standard |
The table shows a key property of PQ: half of the signal range lies below about 100 nits, where most picture information, including skin tones and midtones, normally sits. The upper half is reserved for highlights.
PQ in HDR formats and metadata
PQ is the shared transfer function of the main consumer HDR formats, which differ mainly in their metadata. Because no consumer display reaches 10,000 nits, the metadata helps each display tone map the content to its own capability.
| Format | Bit depth | Metadata type | Tone mapping approach |
|---|---|---|---|
| HDR10 | 10-bit | Static: ST 2086, MaxCLL, MaxFALL | Display chooses its own curve for the whole program |
| HDR10+ | 10-bit | Dynamic, per scene or frame | Guided tone mapping that adapts over time |
| Dolby Vision | Up to 12-bit | Dynamic, with defined trims | Proprietary mapping following the colorist’s trims |
MaxCLL describes the brightest pixel in the program, and MaxFALL the highest frame-average light level. Incorrect values can cause displays to tone map too aggressively or too weakly, so they should be measured from the finished master.
PQ compared with HLG and SDR gamma
PQ and HLG are the two transfer functions defined in BT.2100, and they reflect different philosophies. PQ specifies exact brightness and suits mastered, metadata-driven content, while HLG is relative and backward compatible, which suits live broadcast.
| Property | PQ | HLG | SDR gamma (BT.1886) |
|---|---|---|---|
| Reference type | Absolute luminance | Relative to display peak | Relative to display peak |
| Range | 0 to 10,000 nits | Scales with display, often 1,000 nits | Typically up to 100 nits |
| Metadata | Recommended or required | Not required | Not used |
| SDR compatibility | Requires conversion | Usable directly on many SDR displays | Native |
| Typical use | Streaming, cinema-derived masters, discs | Live broadcast | Legacy SDR delivery |
Neither function is superior in every case. PQ offers predictable creative control in a mastered environment, while HLG avoids metadata and simplifies live production chains.
Mastering and grading in PQ
PQ grading requires a calibrated HDR reference monitor whose peak brightness matches the mastering target, most often 1,000 nits and sometimes 4,000 nits. The master is typically graded in a Rec. 2020 container while the actual colors are limited to the P3 gamut of current mastering displays.
A central practice is placing diffuse white near 203 nits, as recommended for HDR production, rather than pushing all bright areas toward peak. Specular highlights, the sun, lamps and reflections then use the range above it, which gives HDR its depth without making the whole picture uncomfortably bright.
| Decision | Common choice | Reason |
|---|---|---|
| Mastering peak | 1,000 nits | Widely supported by reference monitors and platforms |
| Reference white | About 203 nits | Consistent brightness with SDR expectations |
| Container gamut | Rec. 2020 with P3 content | Matches current mastering displays |
| Delivery bit depth | 10-bit or 12-bit | Prevents visible banding |
| SDR version | Separate trim pass or mapped derivative | Keeps intent on SDR screens |
Limitations and common mistakes
Because PQ is absolute, display capability and viewing conditions strongly affect the result. Several mistakes appear repeatedly in HDR production.
- Grading too bright overall, which makes the picture fatiguing and forces heavy tone mapping on consumer displays.
- Missing or wrong metadata, causing clipped or dull highlights on televisions that rely on it.
- Viewing PQ on an SDR monitor without conversion, where the image looks dark and flat.
- Delivering 8-bit PQ, which almost always shows banding in skies and gradients.
- Ignoring room brightness: PQ assumes a dim reference environment, so bright living rooms change perception.
Televisions in bright rooms may also apply ambient light adaptation that departs from the absolute intent of PQ. Colorists therefore check their masters on representative consumer displays in addition to the reference monitor.
In everyday language
PQ is the rule that tells an HDR television exactly how bright each part of the picture should be. Older video only said how bright something was compared with the maximum of the screen; PQ uses real brightness values instead.
It also spends its detail wisely. Our eyes notice small changes in dark areas much more than in very bright ones, so PQ uses fine steps in the shadows and larger steps in the highlights. That is why HDR video can show both a dark room and a bright lamp without ugly bands.
Seen in the real world
A streaming series is graded for HDR10 and Dolby Vision on a 1,000-nit reference monitor in PQ. The colorist places faces and white walls around 100 to 200 nits and lets sunlit windows, car headlights and fire reach 600 to 1,000 nits. After grading, the measured MaxCLL is 980 nits and MaxFALL is 190 nits, and these values are written into the HDR10 metadata.
On a high-end television that reaches about 1,000 nits, viewers see the image almost exactly as graded. On a mid-range model with a 400-nit peak, the television uses the metadata to compress the highlights smoothly. The midtones stay where the colorist placed them, so the scene keeps its intended mood on both screens.