Radiance HDR

Radiance HDR, also known as RGBE or Radiance Picture, is raster image file format associated with the Radiance (or RADIANCE) lighting simulation software by Greg Ward. It supports high dynamic range imaging, and may have been one of the first formats to do so.

Format
Each pixel is encoded as four bytes: three color values (RGB or XYZ), and a shared exponent.

There are at least two versions of the format. The documentation for the ra_rgbe utility says "The file format for RADIANCE pictures was changed between release 1.4 and release 2.0."

Identifiers
The official filename extensions are .pic, .hdr, .rgbe, and .xyze. Some third-party applications use .rad, though that conflicts with Radiance Scene Description format. Some sources say that .img is also used.

Identification
Files are supposed to begin with an ASCII signature of " ". However, some apparently begin with " " instead, and some have no signature line at all. Note that some of Radiance's other file formats also use the " " signature.

Specifications

 * http://radsite.lbl.gov/radiance/refer/filefmts.pdf ("Picture" file format)

Software

 * Radiance source code
 * ImageMagick (format named "HDR")
 * Konvertor
 * XnView
 * pfstools
 * abydos
 * HDR Software

Sample files

 * HDR Image Gallery (also here)
 * http://radsite.lbl.gov/radiance/pub/pics/index.html
 * https://telparia.com/fileFormatSamples/image/radiance/

Links

 * Radiance web site
 * Wikipedia: RGBE image format
 * Wikipedia: Radiance
 * Media type registration