RGB Black to CMYK Black

[Colin30187875eszd]

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

[Jumpenjax]

Yes, you can, go image-adjustments- curves. See drop down channel and you can bump any color individually as you see fit.

[Colin30187875eszd]

Cheers Lee. And I presume that this will work for the blacks too even though they were originally coloured RGB?

[Colin30187875eszd]

Or more accurately, will this process lead to more of a rich black?

[Jumpenjax]

Yes and I hope this was helpful. You have more control with cmyk.

[Jumpenjax]

Since you are looking to print this at a local printer it should work fine. I use this method on a 48 page magazine every month. It is a great tool. My printer uses CMYK.

[Test Screen Name]

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?

[D Fosse]

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]

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.

[Colin30187875eszd]

Basically I draw pieces of art based on horror films and over the past few years they've started being published as magazine covers and I've also decided to try and set up my own website and sell physical copies of Mt work. However seeing the somewhat washed out nature of the end results and suddenly becoming cognisant of the whole RGB/CMYK thing, I'm just trying to find out the best way to handle all the work I've thus far completed in RGB upto press. Going forward of course I'll be working on Photoshop in CMYK  but in the meantime, I'm aware that certain changes might need to be made to my past RGB work in order for them to work when printed, hence the original query with regards black tones

[TheDigitalDog]

Unless you have an exact, specific recipe for CMYK, never convert from RGB to CMYK! Never. 

CMYK is a highly device-dependent color space. See:
http://digitaldog.net/files/CMYKPart1.pdf

http://digitaldog.net/files/CMYKPart2.pdf

GIVE your local printer tagged RGB and let them deal with any CMYK conversions from there on. Your life will be much easier and hassle-free. 

[Colin30187875eszd]

But every printer I've emailed concerning having prints made always insists on the pics being sent in CMYK; what should I do then?

[D Fosse]

Then you need to ask which CMYK, and don't settle until you get an answer. The customer relations people often don't know; ask the people operating the press, or the prepress operators.

Take your pick:

Don't edit in CMYK unless you have a clear understanding of ink limits and gamuts. Work in RGB and convert at the end if possible.

The only reason to work in CMYK is if you have text or black ink areas that you want to overprint the other inks.

[TheDigitalDog]

But every printer I've emailed concerning having prints made always insists on the pics being sent in CMYK; what should I do then?

By @Colin30187875eszd

Simple:

1. Find another printer.

2. Have printer supply you with their unique conversion process via an ICC CMYK profile. 

3. Make them do the conversions from tagged RGB. 

[Colin30187875eszd]

Thank you ever so much for supplying me with all this info; believe me, it's of great help and I really do appreciate it!

    Colin

[Colin30187875eszd]

Just out of interest, here's the tricky piece in question 

 

[D Fosse]

Depending on the paper stock and the associated CMYK profile, RGB 0-0-0, absolute black, will usually convert to something along the lines of 80-65-55-95. That's just under 300% total ink. That will be the deepest black possible in that print process. Don't exceed those percentages, you'll get in trouble - and most likely they'll send the file back to you and tell you to fix the problem.

The ink limit is built into the profile. If you work in RGB and convert at the end, you're safe.

The black ink alone is much lighter, more like charcoal.

The CMYK profile accounts for the ink limit. It does not account for diffuse paper reflectance. This can make the blacks appear even lighter.

CMYK is a representation of actual physical inks on paper. There are limits to how pure/saturated colors those inks can produce. That's the gamut limit, and it's a brick wall. You have to work inside this.

[Colin30187875eszd]

Thanks for this! So if I'm reading this right, even the kind of paper you print stuff onto can have a bearing on the kind of black you end up with?

[D Fosse]

That's right. Most obviously, coated vs. uncoated.

[Colin30187875eszd]

Just had another thought about this. When I originally sent my artpiece to a printer as an RGB to CMYK conversion, I'd converted it first on a free digital app called Medibang where I also did all the colouring too. Now although the only choice I had as a CMYK swap too option was Agfa the print that ensued was actually pretty good albeit with the black being ever so slightly too light (very very dark gray). But when I convert this same RGB piece to CMYK on Photoshop although the blacks look much blacker the rest of the colours looks vastly more washed out. What gives?

[D Fosse]

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.

[Zesty_wanderlust15A7]

Colin... Not an expert on this, but I think it helps to think of CMYK as a color mode that is heavily related to how we've printed on press for the longest time (and still). So it has to represent the limits of that system, thus changing your RGB colors if they are outside of the CMYK gamut. Surely you can understand a monitor can show fiercer color than ink on paper. Yes, there are some tricks to help on a press, like using more inks, certain paper, a gloss run (IIRC).

On desktop printers, people try to get closer by using even more different ink cartridges. 

D Fosee: "Every CMYK profile is a characterization of a specific print process."

You're going too B&W again... There are also Wide Gamut CMYK profiles that are probably intended for ease of editing, and (ideally) w/o losing the color. The Curvemeister plugin was a fan of that.

Others love the idea but claim it's not working...

Sef McCullough: "I have experimented with a wide-gamut CMYK profile which at first I was really excited about. After testing it out on a number of RGB images, I’m still seeing loss of quality somewhere around saturated 3/4 tones, kind of a flattening out and desaturation of the transitional areas into the Blacks. Enough that I would not work on an RGB image destined for web in that working space. I had high hopes at one time that this was a solution."

www.retouchist.org/blog/2018/1/11/retouching-in-cmyk-and-the-5-reasons-i-love-it

Or is he simply lacking the perfect profile...?

[D Fosse]

There are also Wide Gamut CMYK profiles that are probably intended for ease of editing, and (ideally) w/o losing the color.

By @Zesty_wanderlust15A7

I'm not sure what would be the purpose of that for images. Working in RGB and then converting to destination CMYK accomplishes exactly the same thing, and it is a much safer procedure because the profile handles ink limit (TAC) automatically, plus you get ideal GCR, UCR etc.

I could possibly see a use for it for print designers where you need to maintain overprinting K throughout. Not in Photoshop, but in Illustrator and InDesign. You might want to maintain master files for multiple press conditions.

Gamut clipping will happen regardless and you still have to deal with it. This is what soft proofing is for. Gamut remapping, if necessary, is much easier to do in RGB than in CMYK.

CMYK to CMYK conversions is something you normally don't want to do except by device link profiles.

[Colin30187875eszd]

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!)

[TheDigitalDog]

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!)

By @Colin30187875eszd

For all output, yes. 

The output quality can only be seen on the output. No matter the color model or color space.