So it looks like we're going to have 4 options. I opted for using integers instead of strings because that way if someone uses "colorGray": true it will give the same result as "colorGray": 1 which is the one I believe most will want. The instructions will say as much, but out off habit I expect some to put "colorGray": "1" which will result in it skipping the grayscale altogether. I think that's the best solution, but am happy to hear arguments saying otherwise & it'll be easy enough to change if people prefer the other.
The options I have now are:
1 -colorspace Grey
2 -colorspace LinearGray
3 -grayscale rec601luma
4 -grayscale rec709luma
Technically 2 & 4 should actually be the same thing, & they appear, to me, to be, but I figure some may want 1 or the other not knowing they are the same or maybe there are slight differences that I can't see in the images I tested with. Point in fact the rec601luma looks identical in most images but gives more distinction between a red & green item that look the same gray in 709/Gray & different in 601. It also preserves a gradient that fades from dark to light blue in a couple images better with more variance & a cleaner fade the same with red fades in another. I can't really say it's better, I just like the way it looks for these images better, maybe because they originated in a 601 colorspace, while 709, the current standard, may have the same thing in reverse for other books. As such I've left both options for users to pick.
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