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RGB to CMYK : 2 different cases with 2 different results when printed

New Here ,
Oct 15, 2020 Oct 15, 2020

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Hello,

 

I have an image (a drawing) in RGB.

For printing purposes, I have to convert it to CMYK.

So here is what I did:

Case n °1
I open the RGB file and go to Image > Mode > and switch to CMYK.
I print it.

Case n °2
I create a blank CMYK file and paste the layers of the RGB drawing into it.

And I print.

While the 2 documents are now in CMYK, I have huge differences when printed.

Converting directly to CMYK (case 1) darkens the design a lot when printed, whereas importing the RGB layers into a blank CMYK document (case 2) leads to nearly the same color as the printed RGB.

I'm attaching 2 images:
- 1st one is to see the CMYK differences when printed (case 1 and case 2)
- the 2nd one is to see that RBG and case 2 printed out are very similar.

Can someone help me to understand those differences, and what should I do have perfect printed colors ?

Many thanks !

 

 

[Typo in subject line corrected from "RGB to CMJN" to "RGB to CMYK" by moderator.]

 

 

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Community Expert ,
Oct 15, 2020 Oct 15, 2020

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The short answer here is that CMYK is wrong. Don't do it. CMYK is for commercial offset printing only. Inkjet/desktop printers are RGB devices that expect RGB data.

 

Second, if you should ever need to work in CMYK, you need the actual CMYK profile. There is no such thing as a generic CMYK. Image > Mode just gives you whatever is set up as working CMYK, which most likely isn't the correct one. To work in CMYK, you really need to know what you're doing.

 

As for printer color management in general, you set this up in the Photoshop print dialog. Leave the document color space as it is. Pick the correct print profile for the printer and paper you're using. Then go into the printer driver and pick the correct media type there. Also turn printer color management off.

 

A simpler, but less accurate way, is to set "Printer manages color" instead of "Photoshop manages color". Then it's all handled in the printer driver, but you still have to pick the correct media type (paper).

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New Here ,
Oct 15, 2020 Oct 15, 2020

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Hello,

Thank you for your reply.

Yes, I should have been more precise.

The file will be send to a professional printer that needs CMYK.

Jacqyes

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LEGEND ,
Oct 15, 2020 Oct 15, 2020

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Darkening is correct. Paste is not colour managed so it cannot give accurate colour, even if by good luck it seems to be what you want. How is it printed, and what CMYK profile do you use?

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New Here ,
Oct 15, 2020 Oct 15, 2020

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Hello,

 

Thank you for your reply.

OK so now I know I should use Image > Mode to change to CMYK.

It will be printed at a professional offset printing company, and I use generic CMYK profile.

Now I've tested a new case 🙂
1. I open the RGB file
2. I flatten all visible layers
3. then Image > Mode > and I pick CMYK

I print this file, and it is very very close to the printed RGB, not dark as it was before.

I've seen on adobe website that they recommand to flatten the layers before changing the color mode:

in most cases, it is best to flatten a file before converting it. However, this is not required and in some cases it is not even desirable (when the file contains vector text layers, for example).


Do you think it is good if I do like it ?

Many thanks.

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New Here ,
Oct 15, 2020 Oct 15, 2020

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Here is the link on adobe:
https://helpx.adobe.com/photoshop/using/converting-color-modes.html

"Flatten the file before converting it. The interaction of colors between layer blending modes changes when the mode changes."

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Community Expert ,
Oct 15, 2020 Oct 15, 2020

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Again: there is no such thing as "generic CMYK". If you use Image > Mode, you get US Web Coated (SWOP) v2, because that just happens to be the default in Photoshop. There has to be some default, and they picked this. But chances are that's wrong. Don't use Image > Mode. Use Convert to Profile.

 

Outside the Americas, the SWOP standard doesn't apply. Presses are calibrated to different standards and different inks are used. And even inside North or South America, Web Coated SWOP isn't used everywhere.

 

In short, you need to know the specific CMYK profile that applies for the actual printing process. The printer should give you this. You can't really do anything until you know which one.

 

A CMYK profile is a description of an actual specific printing process. A press calibrated to a certain standard, using certain inks on certain paper stock. It's very specific.

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New Here ,
Oct 15, 2020 Oct 15, 2020

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Hi,


Thank you for all informations.

 

Yes, for the CMYK profile, I changed it from Edition > Colors

And here I've picked "Generic CMYK Profile" instead of US Web Coated (SWOP) v2".

So regarding the RGB to CMYK conversion, I found out that if I flatten the file before its conversion to CMYK, I get very similar tones than the RGB printed files (I'm printing on a laser printer for my test).

Is that good ?

Many thanks

 

 

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Community Expert ,
Oct 15, 2020 Oct 15, 2020

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Maybe I'm not explaining this well. What I'm trying to tell you is that there is a right way to do this: Ask the printer what CMYK profile to use.

 

"Generic CMYK profile" is obsolete and outdated. It's just legacy remains from old days before color management.

 

 

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New Here ,
Oct 15, 2020 Oct 15, 2020

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No no it is clear, problem is that the printer is not able to tell me 😞

Those drawings will printed as temporary tattoos.

They just say "we use CMYK" (which is an evidence), but that's all...

So once I have the information (if ever I manage to have it), is the method correct ? (flatten the file, change the mode) ?

Thank you

 

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Community Expert ,
Oct 15, 2020 Oct 15, 2020

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OK, if color is not critical...but if was, and they didn't give you a specific profile, you'd just have to ask somebody else in the company. Preferably the people actually operating the press. They always know. Sales/customer relations usually don't have a clue. I always avoid them and go straight to "the floor".

 

You have to flatten before changing profile, because the numbers will have a different meaning in another color space. Adjustment layers will change appearance. And RGB adjustments are obviously meaningless in CMYK.

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New Here ,
Oct 15, 2020 Oct 15, 2020

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Well, they say they use a Heidelberg printer.
Would this give me any help to find the CMYK profile needed ?

Many thanks.

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New Here ,
Oct 15, 2020 Oct 15, 2020

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Here are the 2 printers that will be used:

Heidelberg CD102-5+L five colour
Heidelberg SM74 4 colour printing machine.

 

 

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Community Expert ,
Oct 16, 2020 Oct 16, 2020

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Bonjour Jacques.

The printer used is only part of the equation, the inks used is another one, and way more important for the kind of profile needed, as the paper/support used...

 

But again, to print a preview on your inkjet is an approximation of a given set of ink/paper, and will go through a CYMK>RGB>whathever color mix your printer uses. One has to use a calibrated proofing printer to assess how a print might come out.

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Community Expert ,
Oct 16, 2020 Oct 16, 2020

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Using "generic CMYK" is a very poor way to work, its also risky to guess at Swop coated (Photoshop's default).

Printing press output depends on how the press is run - also on inks, substrate and the way the plates are made. These days there are ISO standard press conditions, described by ICC profiles such as those from GRACoL and from the ECI / FOGRA in Europe. 

 

If you are working with a printer who cannot give you an ICC profile to describe the process then you are effectively throwing a dart at a dartboard in the dark and hoping to hit the bullseye.

Guessing what CMYK to use is like sending a letter only knowing the town & guessing the street address and zipcode. 

 

You could ask the printer for their experience with received files., When files are received at the printers, they will predominantly have an embedded ICC CMYK profile.

Ask them this - looking at the files which were received and printed successfully, what was the ICC profile most commonly embedded. 

It seems you ideally need a better more modern printer - or the printer really needs to catch up with the way good standardized printing is done these days.

It's amazing the "just use generic CMYK" guys are still in business.

 

I hope this helps

thanks
neil barstow, colourmanagement.net :: adobe forum volunteer
[please do not use the reply button on a message within the thread, only use the blue reply button at the top of the page, this maintains the original thread title and chronological order of posts]

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New Here ,
Oct 17, 2020 Oct 17, 2020

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Hello,

Here is an update.

When I send my files to the printer, he has an inhouse designer that will set an .AI file with all my artworks organised on it and send it to print.

I finally got his file this morning and I have checked the CMYK profile he used, it is "Japan Color 2001 Coated CMYK profile" (the printer is in Asia).

So I suppose I have to pick the same profile ?

I won't be able to have more information on it, as the designer don't speak english at all 😞

How does it sound ?

Many thanks.

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Community Expert ,
Oct 17, 2020 Oct 17, 2020

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In that case I don't understand why the designer shouldn't do the final conversion to CMYK. That would be the normal and standard procedure, used everywhere else, and you'd just provide RGB originals.

 

A press-ready PDF is normally produced in InDesign, but I suppose it's possible with Illustrator as well.

 

A great advantage of doing it this way is flexibility. If press conditions change (new printer etc), it's just a matter of exporting a new PDF to new specifications.

 

I suspect there's a misunderstanding here, perhaps something lost in translation. Again, there is absolutely no reason you should send CMYK. One point to note is that CMYK to CMYK conversions should always be avoided, for many reasons.

 

Still, knowing the final profile is an advantage. That means you can soft proof to it, and so anticipate any gamut clipping in the print process. If you see any, you can try to compensate for it.

 

 

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Community Expert ,
Oct 17, 2020 Oct 17, 2020

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So I suppose I have to pick the same profile ?

 

Yes. If the designer has assigned Japan Color Coated to her AI file, then you should not convert to a conflicting CMYK profile.

 

While keeping the file as RGB and delaying the conversion until export or output is a more flexible workflow, if it’s required you can still make the conversion to the final CMYK output space in Photoshop as long as you know the destination profile, which is apparently Japan Color 2001 Coated.

 

If you make the conversion via Image>Mode your current PS Color Settings are used to make the conversion. It might be better to use Edit>Convert to Profile where you can specify all the conversion options. Relative Colorimetric will attempt to maintain the color appearance when the color is inside of the CMYK gamut :

 

Screen Shot 14.png

 

If I place the AdobeRGB version and the Japan Color 2001 version in a CMYK AI file with Japan Color 2001 as the profile assignment, the output values of the 2 versions will be identical:

 

Screen Shot 15.png

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New Here ,
Oct 18, 2020 Oct 18, 2020

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Hello,

Thank you for your help.

So I've tried as you suggested (Edit > Convert to Profile).

Here I'm converting a CMYK Generic Profil file (the design has been created using this profile) to the Japan one:

Capture d’écran 2020-10-18 à 08.43.55.png

Flatten the image is ticked by default, so I guess I haven't to do it manually as I was doing before.
I click on OK and apparently it is converted to Japan Profile.
Now what is strange is that instead of having the Japan Profile set at the bottom of the screen, I just have CMYK without description (8bpc).
Capture d’écran 2020-10-18 à 08.52.15.png

And if I check the file detail, I don't have the profile anymore (I used the Mac details preview):

Capture d’écran 2020-10-18 à 08.56.26.png

Compared to my CMYK generic profile file:
Capture d’écran 2020-10-18 à 08.59.16.png

Is there a way to restore this ?

Many thanks again

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New Here ,
Oct 18, 2020 Oct 18, 2020

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Ok, I switched my photoshop in English, it will be easier.

So after the conversion, I have this untagged CMYK:
Capture d’écran 2020-10-18 à 12.29.07.png


Instead of the converted Japan profile 😞

And here are my color settings:
Capture d’écran 2020-10-18 à 12.29.58.png


And here my Convert to Profile:
Capture d’écran 2020-10-18 à 12.35.45.png

What would be wrong this time ?

Many thanks

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Community Expert ,
Oct 18, 2020 Oct 18, 2020

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Why do you have color management policies set to "off"? Never do that, ever. It is guaranteed to get you in trouble. It should always be "preserve embedded profiles".

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New Here ,
Oct 18, 2020 Oct 18, 2020

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I have no idea, it was photoshop default settings.

Ok so I've put preserve embedded profile, and I can see the Japan one at the bottom, thanks !

And now I guess a very last question.

When I generally flatten an image, the transparent background is always filled by white.

When I convert to profile, flatten is ticked, but it still gives the transparent background, it is normal ? Or should I flatten the image prior to convert to profile ?

I mean for me it is good to keep the transparent background, just want to make sur I'm doing the whole thing the correct way.

Thanks.

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Community Expert ,
Oct 18, 2020 Oct 18, 2020

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The conversion you are showing is from Generic CMYK to Japan Color Coated (a CMYK-to-CMYK conversion).

 

Do you have the original RGB version of the artwork? The ideal would be to make one conversion—RGB-to-CMYK—rather than your RGB-to-CMYK1-to-CMYK2. A conversion directly from the original RGB space using Releative Colorimetric will maintain the original color, which is what I assume you are looking for.

 

You don’t have to flatten on the conversion, but if you are using certain color blending modes they will function differently if they are not flattened, and you might get an unwanted a color shift.

 

For example the Difference blend mode works differently in CMYK mode than it does in RGB:

 

Screen Shot 19.pngScreen Shot 20.png

 

 

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Community Expert ,
Oct 18, 2020 Oct 18, 2020

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And also any adjustment layers will change appearance, as the numbers get a new meaning in the new color space.

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New Here ,
Oct 18, 2020 Oct 18, 2020

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To sum up, I have:
- Generic CMYK file designs (very few)
- RGB file designs (approx 99% of my designs)

So all designs will be printed, so I guess I should have asked the designer to create the design in CMYK directly, and export a RGB version to put on my website.

Would you have done this way ? (I'm a "web man", with no experience at all with the whole printing things).

Problem is also that some RGB files have colored designs, and when converting it to CMYK, the colors change a lot, so I'm asking my designer to redo colored design in CMYK...

For RBG design, if I don't flatten the file before converting it, it gets darker.
I've noticed that if I flatten the image and convert it to CMYK, I'm very close to the RGB (when printed on my own printer), but I don't have the transparent background which is a problem too.

So I'm really lost on what I should really do, and how it will look like when printed in real.

I'm also testing the output on my HP laserjet, but if I understood, personal printer won't print as a CMYK but as RGB, so I can't really see the result neither.

Also, I can't ask the printer to do samples, as it would cost a fortune.

The whole project seems now very complicated for me...

Thanks


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