Resources for Duotone Specification

[roniemartinez]

As described in the PSD File Format Specification:

"Duotone images: color data contains the duotone specification (the format of which is not documented). Other applications that read Photoshop files can treat a duotone image as a gray image, and just preserve the contents of the duotone information when reading and writing the file."

I do understand how duotones are created, the only problem is the structure of the file (and possible computation) which is not readily available. Anybody who tried to deal with duotones (monotone, duotone, tritone, quadtone)? Or possible links, sites, resources, etc. will be a big help.