"Toner/Ink Saver" implementation?

[garycarroll]

Neither the brightness or gamma functions do what I want, since each 
lightens grays but leaves dead black unchanged. I do think one or the 
other is in fact what most people would want, since most want to save 
toner on graphics but leave text black.

However, the documents I am trying to save toner/ink on are exclusively 
text, and so I need something that lightens text.

Your comment about the transfer function pointed me at what I needed.
added several modified transfer functions to the ppd so that the user 
can select the desired transfer function via the CUPS "modify printer" 
UI. The user selects the appropriate function to fit the printer 
(different printers react differently), the document type, and the 
degree of lightening that is acceptable. Rather than change the function 
for different runs we just set up several queues pointing to the same 
printer, each with a different function selected.

Preliminary results look very good. Fine detail is actually usually a 
little better than the printer defaults, and the desaturation of blacks 
is not noticable except in large blocks, which does not happen in the 
docs in question.

Thanks LOTS for your help.