What is Radiance HDR?
Radiance HDR is a high-dynamic-range image format developed for the Radiance rendering system and commonly identified by the HDR extension. Its common RGBE pixel encoding represents each pixel with three color bytes and one shared-exponent byte.
How Radiance HDR works
Radiance HDR stores each pixel with three mantissa-like color bytes that share one exponent, providing a compact way to span luminance far beyond display-referred integer images. The file header carries descriptive variables, including a format line that declares the common RGBE encoding or the alternative XYZE encoding, plus a resolution-orientation line. Scanlines may use run-length coding to reduce repetition. The format is commonly read as scene-referred lighting data for renderers and environment maps, then tone-mapped or converted when preparing a conventional display asset.
Key facts
- 1RGBE allocates one byte to each color component and one shared exponent to the pixel. Channels with very different magnitudes therefore do not receive independent floating-point precision.
- 2The resolution string also states axis order and direction. A decoder that extracts only width and height can transpose or flip files whose orientation differs from its assumption.
- 3Radiance HDR has no alpha channel in its standard RGBE pixel representation. Transparency or masks must travel separately or be carried by another working format.
When Radiance HDR matters
Use Radiance HDR for lighting environments, rendering pipelines, or image-based illumination that requires a broad luminance range. Convert carefully when a destination lacks RGBE support or applies incompatible color handling.
Common use cases for file formats & compression
These examples cover file formats & compression broadly, not specifically Radiance HDR.
- Accepting heterogeneous uploads while producing a controlled set of delivery formats.
- Moving assets between cameras, editors, browsers, archives, and downstream APIs.
- Separating long-lived source files from compact derivatives optimized for a particular channel.
Working with file formats & compression
This guidance covers file formats & compression broadly, not just Radiance HDR.
A parser reads the file structure, identifies contained streams and metadata, and exposes them to a decoder or application. Conversion usually decodes the source representation and writes compatible information into a different structure or encoding.
This category covers file and bitstream formats, their structures, and the compression methods they use. A filename extension can be misleading, so evaluate the detected format, decoding support, metadata, transparency, color, timing, patents, and archival needs before choosing an output.
What you gain
- A suitable format preserves the properties a workflow actually needs.
- Standardized structures allow files to move between compatible tools and systems.
- Format conversion can improve delivery size, editability, or long-term accessibility.
What it costs
- Modern formats can save bandwidth but may need fallbacks for older clients and production tools.
- Converting to a simpler format can discard transparency, animation, metadata, color precision, or editability.
- Archival suitability, browser support, and editing support often favor different choices.
Before production
- 1Inspect the detected container, codec, MIME type, and magic bytes instead of trusting a suffix.
- 2Verify decoder support and preserve metadata, color, transparency, or timing when required.
- 3Retain the source when the chosen delivery format is lossy or tied to current software.