AVIF and PQ Curve for HDR Master Storage

This article examines how the AV1 Image File Format (AVIF) integrates the SMPTE ST 2084 Perceptual Quantizer (PQ) transfer curve to serve as a robust, lightweight container for high dynamic range (HDR) master storage. It covers the underlying mechanics of PQ signaling, bit-depth requirements, color profile encapsulation, and the practical advantages AVIF offers over traditional archival formats for high-luminance visual assets.

The Role of the Perceptual Quantizer (PQ)

The Perceptual Quantizer, standardized as SMPTE ST 2084, is an electro-optical transfer function (EOTF) engineered to match the human visual system's contrast sensitivity, based on the Barten model. Unlike legacy gamma curves that distribute code values exponentially, PQ allocates code values perceptually across an absolute luminance range from 0.0001 nits to 10,000 nits. Because PQ is an absolute rather than a relative transfer function, code values represent definitive target brightness levels rather than a percentage of display capabilities.

Bit Depth and Compression Architecture

To represent the 10,000-nit range of the PQ curve without causing visual artifacts such as banding or posterization, higher bit depths are mandatory. AVIF utilizes the AV1 video codec's intra-frame compression capabilities within the ISO Base Media File Format (ISOBMFF) container:

• 10-bit and 12-bit Precision: AVIF supports the AV1 Main Profile (up to 10-bit 4:2:0) and Professional Profile (up to 12-bit 4:2:0, 4:2:2, or 4:4:4). When storing HDR masters, 10-bit is the baseline standard, but 12-bit PQ AVIF eliminates banding even in demanding gradient transitions and deep shadow regions.
• Lossless and Visually Lossless Compression: AVIF provides high-efficiency intra-frame encoding. For archival and mastering purposes, it supports mathematical lossless mode or near-lossless compression settings, significantly outperforming legacy formats like TIFF or DPX in storage efficiency while preserving high-frequency details.

Color Metadata Signaling via the NCLX Box

AVIF signals the PQ transfer function cleanly through container-level metadata using the Colour Information (colr) box with an nclx (Colour properties) profile:

• Colour Primaries: Set to ITU-R BT.2020 (value 9), which standardizes the wide color gamut necessary to accompany the PQ curve.
• Transfer Characteristics: Explicitly set to SMPTE ST 2084 (value 16), directing decoders to process luminance through the PQ EOTF.
• Matrix Coefficients: Typically set to BT.2020 non-constant luminance (value 9) for YUV representation, or identity (value 0) if preserving full-range RGB color planes.
• Full Range vs. Limited Range: AVIF files can explicitly flag full range (0–1023 for 10-bit; 0–4095 for 12-bit), ensuring the full code spectrum is allocated for mastering.

AVIF also supports embedded ICC profiles, allowing hybrid workflows where custom tone responses or non-standard primaries are required.

Mastering Display and Content Light Level Metadata

High dynamic range mastering demands explicit metadata to instruct target displays on proper tone-mapping. AVIF accommodates SMPTE ST 2086 and CTA-861-G metadata:

• Mastering Display Color Volume (MDCV): Specifies the chromaticity coordinates of the mastering monitor’s red, green, and blue primaries, white point, and the minimum/maximum mastering luminance.
• Content Light Level Information (CLLI): Carries the Maximum Content Light Level (MaxCLL) and Maximum Frame-Average Light Level (MaxFALL).

By integrating this metadata directly alongside the AV1 compressed bitstream, AVIF masters convey both the absolute visual data and the contextual mastering parameters required for accurate cross-platform reproduction.

Practical Benefits for HDR Master Storage

Using AVIF with the PQ curve provides distinct structural advantages for preservation and production workflows:

• Storage Footprint: While uncompressed 10-bit or 12-bit DPX, TIFF, or OpenEXR files require significant storage bandwidth, high-fidelity AVIF encodes achieve up to an 80–90% reduction in file size with zero perceptible degradation.
• Auxiliary Data Channels: AVIF supports alpha transparency and depth maps at identical bit depths, allowing layered master assets to be saved within a single container.
• Web and Production Readiness: Unlike raw intermediate formats, PQ-encoded AVIF files can simultaneously serve as modern web-ready delivery assets and master archives, as native decoding is standard in modern browsers, operating systems, and image processing pipelines.