hdr-codec-support.md

Radiance HDR codec support

This document defines the implemented boundary of the first-party Radiance HDR codec.

Decode

• #?RADIANCE and #?RGBE signatures
• FORMAT=32-bit_rle_rgbe
• Standard per-channel scanline RLE, including 128-byte literal packets
• Legacy flat RGBE scanlines and legacy repeat packets
• +X, -X, +Y, and -Y resolution orientations
• Native rgbf32 output without 8-bit clipping
• Region decode with bounded scanline buffers
• XYZE pixel data
• Multiple pictures in one stream

Metadata

• Width, height, bit depth, floating-point sample format, and orientation text
• Multiplicative EXPOSURE fields
• GAMMA
• Automatic application of exposure, gamma, primaries, or color-correction fields

Encode

• Deterministic RGBE conversion from rgbf32 and normalized display pixels
• Standard scanline RLE for legal scanline widths
• Legacy flat output for widths outside the standard RLE range
• Optional EXPOSURE and GAMMA fields

Validation

• Header, dimension, allocation, scanline length, packet length, and truncation checks
• Real 1K Poly Haven CC0 HDR benchmark inputs
• Deterministic exponent-extreme and orientation tests