Portable Float Map with 16-bit Half

Recently we saw some lively discussions about support of Half within the Tiff image format on the OpenEXR mailing list. That made me aware of the according oyHALF code paths inside Oyranos. In order to test easily, Oyranos uses the KISS format PPM. That comes with a three ascii lines header and then the uncompressed pixel data. I wanted to create some RGB images containing 16-bit floating point half channels, but that PFM format variant is not yet defined. So here comes a RFC.

A portable float map (PFM) starts with the first line identifier “Pf” or “PF” and contains 32-bit IEEE floating point data. The 16-bit IEEE/Nvidia/OpenEXR floating point data variant starts with a first line “Ph” or “PH” magic similar to PFM. “Ph” stands for grayscale with one sample. The “PH” identifier is used for RGB with three samples.

That’s it. Oyranos supports the format in git and maybe in the next 0.9.6 release.