PQ curve (SMPTE ST 2084)
PQ is the brightness curve behind HDR10, HDR10+ and Dolby Vision; each code value means an exact brightness.
PQ is the rulebook that tells a screen how bright each part of an HDR picture should be.
It works like a ruler with exact marks: a certain number always means the same brightness, from pitch black up to 10,000 nits.
HDR10, HDR10+ and Dolby Vision all use this rulebook.
Does the HDfury Vertex support PQ (SMPTE ST 2084) HDR?
YESYes. PQ HDR signals pass through and the OLED shows 'HDR: SMPTE ST 2084'. The Vertex does not change the PQ picture itself; it can only rewrite the HDR data that tells the display which curve to use.
How to use it with the Vertex:
- Check the RX info page on the OLED: it shows 'HDR: SMPTE ST 2084' for a PQ signal (p.19).
- In the USB GUI HDR INFOFRAME tab, the EOTF menu of the Custom HDR generator has SMPTE ST 2084 (p.32).
- Only tick Enable Custom HDR if you want to replace the source's HDR data (p.32).
- Switch it off with RS232 #set hdrcustom off (p.51) or IR vertex_hdrcustomoff (p.77).
What it is
Video is stored as numbers. An EOTF (electro-optical transfer function) is the rule that turns those numbers into light on the screen. SDR uses a gamma curve that is relative: the brightest number simply means 'as bright as this TV goes'.
PQ, short for Perceptual Quantizer, was developed by Dolby and standardised as SMPTE ST 2084 in 2014 and later in ITU-R BT.2100. It is absolute: each value stands for a fixed brightness between 0 and 10,000 nits. The steps are spread the way human eyes see differences, so 10 or 12 bits are enough to avoid visible banding.
No home TV reaches 10,000 nits, so a display has to fit brighter parts into what it can show. That is tone mapping. HLG is the other HDR curve; it is relative like SDR and needs no metadata.
On the Vertex
In the Custom HDR metadata generator, the EOTF menu offers SDR Luminance Range, HDR Luminance Range, HLG ITU-R BT.2100-0 and SMPTE ST 2084 (p.32). SMPTE ST 2084 is the PQ choice, and it is used in the factory example string (p.32).
When a PQ signal comes in, the RX info page of the OLED shows 'HDR: SMPTE ST 2084' (p.19), and the HDR pages show the decoded EOTF (p.42).
The Vertex does not change the PQ curve of the picture itself; it can only change the data that tells the display which curve and values to use (p.32).
Common questions
What does EOTF mean?
Electro-Optical Transfer Function: the rule a display uses to turn video numbers into light. PQ and HLG are the HDR EOTFs; gamma is the SDR one.
Is PQ the same as HDR10?
No. PQ is only the brightness curve. HDR10 is a full format that uses PQ plus BT.2020 colour, 10-bit and static metadata.
Why go up to 10,000 nits if no TV can?
It leaves room for the future. Films are usually mastered at 1,000 to 4,000 nits, and the display tone-maps to its own peak.