To achieve a balance of getting closer to human perception within the bandwidth limitations of existing infrastructure and technologies, including chroma and luminance sampling, bit depth, and the strengths and weaknesses of Gamma vs Logarithmic curves, a better curve was needed.
Why was a better curve needed and what is the advantage of PQ*?
- Power functions waste bits at the high end of the luminance range
- Log functions waste bits at the low end of the luminance range
- Gamma fails at low luminance levels, even at higher bit depths
- Greatest efficiency would be to follow human perception
- PQ Shows balanced performance across the entire luminance range
* PQ is represented in practice by two approaches, HDR10 an open approach and Dolby® Vision, a proprietary system owned by Dolby Laboratories. Both are designed to make the most efficient use of bits throughout the range of luminance and contrast steps possible.
PQ is standardized in SMPTE ST 2084 and BT.2100 and PQ defines a curve that ensures banding is below the Just Noticeable Difference (JND). The PQ curve ensures the most efficient use of code words which minimizes the bit depth required.