Looks like you can do this with imagemagick

http://www.imagemagick.org/discourse-server/viewtopic.php?t=13359

From: Dennis Payne via WLUG <wlug@lists.wlug.org>
Sent: Sunday, November 15, 2020 8:22 PM
To: Worcester Linux Users' Group General Discussion <wlug@lists.wlug.org>
Cc: Dennis Payne <dulsi@identicalsoftware.com>
Subject: [EXT] [WLUG] CMYK jpeg
 
Anybody know of an easy tool to convert an image into a CMYK color
space jpeg? I found an online site that works but would like to do it
on my machine. Searching has only found how to do it for tiff files.

--
Dennis Payne
dulsi@identicalsoftware.com
https://nam03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsocial.freegamedev.net%2Fchannel%2Fdulsi&amp;data=04%7C01%7Cnjkrichevsky%40wpi.edu%7Cf3db634e4fe44534b4b808d889ce1501%7C589c76f5ca1541f9884b55ec15a0672a%7C0%7C0%7C637410865997176091%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=NChE0cJuwuXvXa4Fc7ZQrGPyGlH%2FIW8%2F0RpoeMIhP%2B0%3D&amp;reserved=0
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