I've always had trouble getting a Grayscale image to print as grayscale!
Sometimes on an RGB (non-postscript) printer it prints 'brownish'. Because the print machine is beside me, I can tinker and print till I get it right.
Sometimes when I send a Grayscale image off as CMYK or as Grayscale (whichever they ask for) to a commercial printer, the print is much darker than I had intended. And sometimes it's fine!
Is there a formula for getting it right every time?
A grayscale image converted to the grayscale color profile and exported as TIF is best for press. Of course the print shop could be awful.
If printing to a non-postscript printer you yet what've call here in the States Pot Luck. Some of those devices and the paper used are just awful.
If just running some on your desktop printer try desaturating a color image and sending as RGB. In my opinion that's you best chance with non-posrscript devices.
I see CorelDraw can convert to the 'default' Grayscale Dot Gain 15% on import.
Then it's just a matter of exporting to CMYK (with default ticked 'Map gray to CMYK black'). Right, so that keeps it all using black ink only.
Should a person check with the commercial printer what Dot Gain they use?
Re Desktop Printer, I'll try desaturating and sending to RGB.
I believe my wife's system still runs X8 and I'll have to check to make sure if the advanced conversion features are in X8.
With that said forget asking the printer odds are that they won't understand the question, however your assumptions are partially correct. Always keep the map gray to CMYK black on, export to native color.
Now when I get a chance I'll check if X8 has the advanced grayscale conversion capabilities and get back to you. Touching her computer is only allowed with her chastisement of my motives.
"WHAT? Are they doing another update? You know I HATE changes to my computer!
Ha ha! Very good!
So, if I 'export to native color' in the PDF, having 'Map gray to CMYK black' ticked ensures that when the print house makes the conversion to CMYK there will be no color cast?
If I export to CMYK in the PDF, is that the same thing? Or could there be a problem with that?
No, on press the grayscale objects will only print using black ink.
With that said, the black ink used for true CMYK printing often is not the same black ink used for spot color printing and the tone of the black may be more brown or blue depending on the ink set used.
If you are printing a CMYK job with grayscale images in it then the black with be from the ink set chosen for their CMYK work flow. Black for CMYK is a much more translucent ink.
If you're printing a file that is black only on white paper they may use a black ink for their single color presses and usually they are much more dense, (blue hued) but they will not look blue just really black.