Using Publisher (Windows version) to make books on MagCloud

[MikeA]

My first goal in learning Affinity Publisher is to make a few small books of photographs—my own, and friends' photographs. After seeing a photographer's enthusiastic endorsements of a service called MagCloud (a division of Blurb) I decided to give that company a try. They have packages that enable you to make very short books at low cost—a good way to experiment. From what I've seen of the photographer's samples on the MagCloud site, they do a good job, including with black and white images.

MagCloud doesn't offer a template in Publisher format, but creating probably wouldn't be difficult even for a newbie like me. My major point of confusion has to do with their color space requirements.

My source images will be exported as 8- or 16-bit TIFF files from a raw converter (Capture One), likely converted to sRGB—I don't know if Adobe RGB would be overkill in this case. Friends' photographs will all be JPEGs—again, sRGB.

MagCloud states that they expect RGB image files, but insist that all typography must be done "in CMYK color space" (their wording). I don't know why they insist on it. After all, they also say their process converts the entire PDF submitted to them to CMYK before they print the work.

How to proceed here? If I start with a new Affinity Publisher document set to CMYK, what happens to RGB images placed within it? Does Publisher immediately convert them to CMYK? Or do they remain in the RGB color space? (I know already that Publisher has an option, when exporting to PDF, to convert to CMYK while still preserving the images' existing color spaces.

Or would it be better to stick with RGB all the way through and simply blend colors using the CMYK sliders within Publisher*? MagCloud's own tech support people don't seem to be able to explain these things very well, so I haven't heard yet why they insist on CMYK for just the text within the source document. It might have to do with a need to specify something other than "hard" black for the typography. Apparently the four-color process doesn't like "hard" black. But the reasons for their requirement remain a bit murky. (They also say they don't support spot colors. This also makes me wonder what rendering intent I should choose, assuming Publisher has that option during exporting.)

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* But surely setting color values that way isn't the same as converting a document to CMYK.

[DWright]

In Publisher when you place a photo it will keep its own RGB colour profile so set up your document as a CMYK using the colour profile that MagCloud recommends then place your photos then export your PDF as a CMYK.

As CMYK uses 4 colour channels to make the correct colour if you only use 100% K (black) this will be printed as a dark grey colour, for a true black colour in CMYK you normally use the values of C75,M68,Y67,K90