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I need to invert specific spot colors in a PDF. To be clear, I do not mean to simply turn a black spot color to white. I mean that I need a true negative. I have searched the manual and online for any reference to inverting spot colors in PitStop Pro, but have found nothing useful under "invert" "reverse" or "negative". I suspect this can't be done. Posting here just in case one of you fine folks knows how to do it. Thanks!

Could you explain a bit more about what you mean by a true negative? If we're talking about a negative of a print separation that would be independent of the colour - i.e. 100% ink would simply become 0% ink and vice versa, no matter what the colour of the ink is. If you want inverse colours the question becomes more complex since the "negative" of a colour can mean different things in different colour spaces. For example in RGB the negative of Red could be cyan (G+B) whereas in CMYK the same operation could result in dark blue (C+K).

Thanks for the reply. I mean that I do not simply want to shift the color to an "opposite" color, but to keep the same color and literally invert the channel, where 100% becomes 0%, 40% becomes 60%, etc. This needs to affect ONLY a specific spot color, so I can't simply flatten the layout in Photoshop and invert it. See below:

I don't think there's an easy way to do this currently, and nothing that will work in all cases. But depending on your specific needs you may get something like this to work:

* Select spot color by name
* Apply color curve, inverting the curve of the "other" channel
* Select the page
* Add rectangle the size of the media box, filled with 100% of the spot colour, behind the other objects

You'll probably have to experiment a lot and fiddle with object order and/or overprint.

I've played with this in the past and it can work, but it's tricky.
One of the issues is if there are other objects that come into play and knockout the color. Ensuring the same knockout is there when inverted can be challenging.
For instance here you have the egg knocking out. So your negative must be below the egg and overprint the rest of the page.

Having said that it's easier in PitStop version 2019 with the rasterize selection, so you can select the required objects and just rasterize those.
You can also do this with a copy of the original. I found that useful in the testing process.

Be interested how you get on.