RGB Black to CMYK Black

Forum|Forum|2 years ago
May 31, 2023
4 replies
5795 views

Hello there

First time user here so go easy on me. Right this is more than likely a question that's been asked many a time on here but I'm having trouble with the black tones when I'm converting from RGB to CMYK. Basically up until about eight months ago, I'd no idea there were two different ways to work so I'd always just used the RGB one on Medibang. However on finding out about CMYK and then converting the art pieces I'd already completed to it, I could see that there was somewhat of a drabness to the colour tones thereafter.

Now on getting a local printer to try printing the converted art pieces, I must admit that I thought they looked really rather good. Okay the colours weren't quite as sharp as with the RGB images but still very good for all that. However, the black tones remained just a little too very, very dark gray; therefore I was wondering if it's possible, after the conversion to CMYK, to tweak the blacks at all to make them blacker still? Many thanks for reading this and I've got my fingers crossed someone out there might have the answer to my problems!

Colin

Windows

NB, colourmanagement

Community Expert

Colin, you can increase black density after conversion to CMYK using Photoshop tools but you have to be super careful not to violate the ink limits.

Black in offset print isn't just black ink it's made up of black and a mixture of the other inks. (i.e. CMY)

An ICC profile for a CMYK process includes information about the max ink a printing system can accept, we call that an inklimit, it might be 320 TAC (total area coverage) so converting to that from RGB is safe. Upping black density using, say, curve adjustments has its risks because you can push the ink ab mounts above the mac ink the machine can take, this can result in offset or even ink running.

If you have black in your RGB file that's reading 0,0,0 and a good CMYK profile for thew conversion that's going to give as much black density as allowed. Unless, of course, your (offset) printer isn't running optimal curves when making the printing plates.

I hope this helps
neil barstow, colourmanagement net - adobe forum volunteer - co-author: 'getting colour right'
google me "neil barstow colourmanagement" for lots of free articles on colour management

C

Colin30187875eszdAuthor

Known Participant

Yeah the black that I originally put down when colouring my art piece was 0
0 0 which at the time I thought was fine but of course since then I've
found out that in the RGB to CMYK conversion, the resulting black looks
very much like an extremely dark gray instead. But having access to
Photoshop now I'd always just supposed that you could do something like
rewrite the ink code so the incorrect black could then become the correct
kind of black for printing, especially once the art piece had been
converted to CMYK. I find I can tweak the other colours manually post
conversion such as all the flesh tones and what not to a satisfying degree
but essentially resetting the hard blacks to the correct kind of CMYK
blacks for satisfying printing remains a problem

D Fosse

Community Expert

It's pretty simple really: RGB 0-0-0 converts to the deepest possible black in the target CMYK profile.

Don't try to tweak this afterwards! You'll exceed the maximum ink limit, the inks will smear and not dry properly.

And again, you absolutely must have the correct CMYK profile.

That's all there is to it.

D Fosse

Community Expert

Don't do it!

First of all, CMYK is strictly for commercial offset print, books and magazines in large print runs. For small scale print jobs any printer will use inkjet printers, and inkjet printers are RGB devices expecting RGB data.

Don't use CMYK unless the printer specifically asks for it! Even then, you need to know which CMYK profile to use.

Second, even if CMYK was appropriate here, editing black levels is very risky. You need to know what you're doing. If you go over the total ink limit specified in the profile, you get ink smearing and drying problems. That's why the blacks are lighter in CMYK.

CMYK is a can of worms, not fit for the inexperienced. There's a lot of special considerations that have to do with how physical inks behave on physical paper, on a physical offset press.

Leslie Moak Murray

Community Expert

Came here to say this. For my work, it's usually CMYK, and every publisher has its own CMYK black they want you to use. My favorite, the one that looks the deepest black possible for CMYK, is 90-80-68-68, for instance. But you have to know what you are doing, and if this work of yours isn't for a specific job, you don't need to mess with it.

C

Colin30187875eszdAuthor

Known Participant

Again: there is no such thing as "CMYK". You have to know which CMYK profile is used!

Every CMYK profile is a characterization of a specific print process. It's a certain set of inks, on a certain paper stock, on an offset press calibrated to a certain standard (which varies in different parts of the world).

CMYK is not an "ideal" synthetic model. It's based on real world printing. It's dirty and imperfect.

So basically the quality of the image that Photoshop is showing me in the CMYK conversion will not necessarily by reflected in the quality of the image that a printer will ultimately print out? ( I think I've got that right!)

T

Test Screen Name

Legend

I think we may need to take a step back. If it was working before, why did you start converting to CMYK, specifically? Many art printers don't use CMYK, so you are potentially making things drab, when they could have printed perfectly before?