Where are my blacks in CMYK?

So the assumption by some is that RGB is RGB and CMYK is CMYK, but that's not the case.  What RGB profile is in use is important.  What CMYK profile was used to convert to?  Was that the correct profile for the printing process?  If you choose an uncoated profile it prints with very low densities and will appear washed out, but if you convert to a coater paper profile it will not.   Just depends on how the job is going to be printed.   Some details about what you tried will go a long way in helping this community help you with this issue.  

Artur, What's really important here is WHY are you converting to CMYK.

IF you have been instructed to do that for an offset or maybe flexo print job, what CMYK ICC profile you have been asked to use.

There's is no "generic" CMYK, you need an exact ICC profile specification.

You ask about the K in the CMYK - that is created by the black generation curve in the CMYK ICC profile which will also contain info about GCR / UCR.

Areas which could be created with [effectively] equal densities of C,M&Y can also be made with part of that "grey component" replaced by K. Now less ink is used and the on press colour balance is more stable.

Making press ready CMYK is quite a responsibility.

There was a time when it was a job done by "scanner operators" with a very high level of skill and pay packet / holiday package. Then along came Photoshop and nowadays it's discussed by many as if making CMYK was as simple as switching on a light. 

You need a compelling reason to make the conversion, and if you have to do it you may need some training [or at least practice] on pre conversion optimisation (of the RGB) and then possibly on optimising the converted file too.

I hope this helps

thanks
neil barstow, colourmanagement.net :: adobe forum volunteer
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Yes, please read the indesign mag article, and answer the various questions asking you which profile you are coming from and to, and why do you convert to CMYK.

You keep in RGB for all these outputs:

Desktop printers use their own sofware to convert from RGB to CMYK or CMYK plus; Photo Bureax (mostly) want sRGB and commercial litho printers use (mostly) RGB images converted via PDF/X-4 to a CMYK that suits the substrate they'll be using.

(and if you also use these images for websites etc, they'll need to be in RGB)

Please set the Status Bar to »Document Profile« and post meaningful screenshots. 

Does the artwork feature fine black linework ot black type? 

You keep saying you »converted to CMYK« but you don’t seem to mention which CMYK. 

So: Which CMYK Space did you convert to and what was the image’s original RGB Color Cpace? 

You don't understand. CMYK is strictly for commercial offset presses (books, magazines etc. in large print runs). The only time you need to work in CMYK, is if you're preparing press-ready material that will go straight to press.

For anything else, work in RGB. Inkjet printers are RGB devices that expect RGB data. These printers have more than four inks, so a 4-ink separation makes no sense anyway.

Go back to your RGB originals.

How to bring blacks in CMYK for printing? When I converted RGB to CMYK its super dull and curves dont work.

Don't convert to CMYK, keep in RGB color mode and, probably for most purposes, choose sRGB color space.

(Note the RGB colour gamut is far larger than CMYK, so colours like bright greens and bright oranges will always be duller in CMYK)