When you output a file to grayscale (print or export) you only have black ink to work with. Rich black is darker than 100% K with no other colors mixed with it, so your 100% coverage on the printer or in the PDF would be mapped to the Rich Blacks, and your 100 K content, like text, would print or export as a tint of black in the mid-to-high 90s percentage range. By setting your handling of black to output all blacks as rich black, the 100 K will also output solid. This setting ONLY affects output to monochrome printers or output as grayscale PDF and will not make a difference in full color output.
Thanks for this reply. Do you mind if i check further?
Does this mean that I can ignore Rich Black if writing in colour? And having converted my [Black] text into Rich Black (50:40:40:100) swatch should i convert it back?
And in either case so do i take the option to Overprint Black Swatch at 100% (or is this irrelevant if printing colour)?
I guess I will need to understand this better.
Rich Black uses the 4 colours. So how does it work on a monochrome printer? And if you are printing a B&W image that varies of course from light do dark greys, how does Rich Black come into it? Is it the equivalent of converting a greyscale image to RGB?
When you print any color on a monochrome printer it is converted to a shade of gray (and this is why converting color photos to to grayscale can either really improve them when there is strong contrast but garish color combination, or make them nearly flat if the color values are all very similar). If your text is to be printed, making it rich black is likely to make it fuzzy when printed in color due to minor misregistration between the inks. The normal approach is to make black type overprint any background color to avoid trapping and registration problems.
If you set the preference to output all blacks accurately, as I said before, your 100% coverage on the monochrome printer will be reserved for objects that use rich black and your K-only objects will print as a dark gray (as they would appear in a full-color print when compared to a rich black object).