Range
(HDR) format.  That means it doesn't have a concept of absolute color
and it can represent generic light intensity information rather than
just visual information like PPM does.  For example, two pixels that
are so close in intensity that the human eye cannot tell them apart
are not visually distinct, so a visual image format such as PPM would
have no reason to use different sample values for them.  But an HDR format
would.

<p>There are details of the PFM format in the <a href="pfm.html">PFM
Format D