http://www.cineon.com/conv_10to8bit.php (as PDF) explains the maths to do the linear-to-log and log-to-linear transformations.

The PDF also explains the reasoning behind the log curve

Panalog is the exact same transformation, just with different white and black reference points (which are explained in the link malcom posted)

For practical purposes, you'd be better linearising the data in the Read node, or using a Colorspace node (which has a Panalog transfer), and using a sRGB viewer LUT (as Hugh suggests)..

You could also bake the transformation into a LUT file using the CMS Test Pattern and a Generate LUT node, with a Colorspace node in-between (Panalog in, sRGB out)

By: dbr [ Editor ]