Rob, for images that are colorful and not neutral, I agree with your statement of CMYK conversion can happen on PDF export, Photoshop, and in RIP.
But with B&W architectural images (as OP described) in RGB colorspace, is there any profile that will convert these neutral images into CMYK with a higher percentage of black, and lesser percentages of CMY (example: 40C 40M 40Y 90K)?
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