Plus, I had to look up what on Earth is the "Halftone Phase" - it's from the Display Postscript extensions, was described in Postscript Level2 Manual, briefly mentioned in PDF 1.2 and gone without a trace in later references. I think there's no need nor support for it anymore. Rather (it goes to wishlist :) ) the 'SMask' ExtGState parameter would be implemented.
Steve Simms:
Feel free to send along a patch or a pull request that adds the SMask parameter. It doesn't look like it'll be too hard to add (you just need to check to see if the argument is a name or a dictionary, according to the spec).
Apr 02 07:37:37 2016 futuramedium [...] yandex.ru request, from RT 113514 (#33)
Steve Simms:
Feel free to send along a patch or a pull request that adds the SMask parameter. It doesn't look like it'll be too hard to add (you just need to check to see if the argument is a name or a dictionary, according to the spec).