Pseudogrey Script-fu in need of an update.

Software GIMP
15

A great article was posted here a few years ago.

https://discuss.pixls.us/t/digital-b-w-conversion-gimp/100

Mentioned in this article was some information about Pseudogrey:

https://discuss.pixls.us/t/digital-b-w-conversion-gimp/100#pseudogrey