Monday, September 20, 2010

"CMYK" is Meaningless

For anyone working with print there is one key principal to keep in mind: "CMYK numbers" are meaningless. Far too often artists are lured into "working in CMYK" without actually understanding what it means, and fall into the trap of believing their work is more precise when the exact opposite is true. Saying "50% Cyan" does not actually specify any color, and will most likely result in many different colors being produced. The subtle yet critical difference between "untagged CMYK" vs. "unspecified CMYK" is the bottom line that will mean the difference between success and failure.

CMYK is a type of colorspace, but in and of itself does not actually specify anything. It just tells how one can define a specific colorspace. To actually make sense a specific device (either real or theoretical) needs to be targeted. Once the specifics are involved, however, working in a specific CMYK is a very helpful thing. It is good to try to not get caught up in distraction of focusing on the "how" of things and instead look to the "why" of doing things.

In this case, the distracting "how" is people "working in CMYK" while the "why" they should be focusing on is reliably creating and controlling color. Instead of an artist getting caught up in saying "I need to get exactly a 50% saturation of cyan ink onto the printing plate at this point", they need to shift to say "I need to get this point of the final print output to be exactly this shade of color." That is not to say that an artist should never be concerned about CMYK numbers and plate separations, but rather they need to keep in mind that the ink details are merely a means in reaching the ends of the final print. (There is one main exception to the focus on raw CMYK, but I'll cover that later)

So although 'raw CMYK' numbers might be meaningless and produce randomly shifting results in completely unpredictable ways, CMYK values in a specific context normally give very precise and controlled output. Be wary of anyone asking for or providing "generic CMYK". However, specifics such as "SWOP v2 CMYK" will allow for fairly exact control and results. If someone says "CMYK", the response should be "which CMYK?"

What does this all mean in practice? If one is producing artwork that will go to print, getting specifics nailed down is critical. When working with a good print house, they will provide either specific profiles for the output that will be run, or will say which industry standard profiles they will work from. The artist provides content targeting the specific CMYK profile and then the printed results comes back with the exact appearance that was intended. The print house gets this generally specified input and then does a specific conversion from what the artist supplied to the measured control needed for the specific press and the actual paper with that days inks and the current temperature, humidity, etc.

When such a good workflow is used one can get reprints run at any time later on and the output will match what was printed the past week, month or even year. Thus there is no need for the time nor the expense of multiple tweak-and-reprint runs to end up with acceptable results.

On the other hand, if a small shop is used that employs no color management in their own workflow, the burden falls squarely on the artist/customer to come up with ways to get consistent and desired output. Sometimes the print shop will provide some target profile, but make no guarantees as what the resulting run will look like.

This is the point where most will just think they're working directly with raw CMYK and just need to tweak things over and over until they are close enough. That's actually not what they should be doing. The critical need here is to understand that they are not working in "generic CMYK", but that they are working to a very specific CMYK. They really are working in "CMYK for fliers printed at the corner press". Sometimes that color will be consistent over time, but more often even that will vary from week to week or from day to day. If the artist was smart, he would have created his own profile for the local print shop and will work in an industry standard CMYK and convert to the specific local shop CMYK for delivery to them. He also should have done some simple calibrated output (perhaps in the margins of his run) so that if (or more likely when) the local print shop gives different colors for the same numbers he can call them on it and get things corrected.

For a shop with a good relationship, the artist can use his own management and tracking to get the print shop to correct their output. Some small shops might not even be employing much in the realm of color control but can happily match output to a reference proof they get handed along with the files for the job to be run that day.

Finally in the case were the local print shop will give varying results and no help for color matching we reach the situation I mentioned where actually sending raw CMYK values is desired. However the reason for sending out a file with raw CMYK that is intended to go exactly to the end plates is in creating a test target output for measurement so that the artist can create his own target CMYK profile. The artist can send over a raw file to get a test output print, and then measure that test print. He then converts the real job files to using that locally created profile and sends the adjusted art files over to be printed. The net result is better output with lower costs due to avoiding reprints, etc. (so "raw CMYK values" should really only be used for printing test targets)

This last case helps illustrate the difference between "untagged CMYK" and "unspecified CMYK". The artists sends over art files that are not tagged with any embedded ICC profiles. However these are not raw nor "unspecified" CMYK values at all. Rather they are CMYK numbers in the specific profile that the artist himself has created to describe the characteristics of the local print shop. Although the files are not literally tagged with the profile, they have been created with an explicit ICC CMYK profile specified in the artists workflow.

And the bottom line? Be specific and you will save both time and money. And end up with happier clients.

18 comments:

ARBaboon said...

The point of working in CMYK is press readiness for four color process (as opposed to monotone or multitone) jobs. I would not recommend producing imagery originally in CMYK but when you are producing the final lay that will go to four color process there is debugging value in working in a CMYK space. If the mappings (color profile) were purely deterministic and completely abstracted to all subsystems a manual pre-conversion would be obsolete. If I had a dollar for every time an RGB element sneaked in when producing separations I would be rich.

ARBaboon said...

Sorry, I forgot to mention the importance of blending here. One reason why artist may push up the conversion to CMYK to earlier in a design is blending elements in different colorspaces is still a nightmare. When you overlay an element in a different colorspace did you mean to knock out the base one, to convert to the most expressive of the two, to overprint, or does it need to be manually resolved. Pre-press can be rather agitating when the in-house art department sends one of these franken files and then asks why they are being billed for 3 hours of extra pre-press art labor.

Stanley said...

i have a black/white HP Laser Jet printer P1006. It worked perfectly till I installed Google Apps and Google gmail. The printer kicks on, but it will not print.

Can you help? i have spent many hours on my home office computer. My office printer works perfectly too.

Markus said...

The main problem is that most print shops and even some offset printers don't know what you are talking about when it comes to profiles. There are even some shops that don't know how to calibrate their laser copy machines or printers and calibration is done every once in a while by the maintenance staff the drops in once a month.

Snaky Love said...

I do not quite understand what is your argument - this seems to be some addition to a longer discussion that I missed, so sorry if I do not understand the context.
However, I feel like you are not talking from a day-to-day printing experience - it is NOT the artists task to create a print profile - this has to be done by the company that prints your works, but they will of course use one of the established profiles and will absolutely avoid creating an own profile, because every single machine, every ink and every paper type used must be calibrated to this profile. Modern profiling systems are completely measured from input to output, every little step of the production is calibrated and measured.
So if you start making your own profile you are already doing it wrong.
If you want to print something that costs big money you do not go to a "print shop" but to some well known company that will help you with all problems regarding colors. If they do not know anything about calibrating their systems to a profile, they are doing it wrong and you should go and search for another company. A serious print company will have hundred-thousand-dollar color matching systems that only need one thing - your correct input.
This way you can produce correct color prints and will never have problems with wrong colors - and if the colors still are wrong and the whole thing starts to become a legal case, you will be happy to be able to prove that you have used the right colors (which the customers gave you).
This is the reason, why professional art work that has to do with color needs software, that supports CMYK and of course the industrial profiles that are used worldwide. A discussion about "cmyk not needed" is totally absurd, I read something like this in scribus world, this is like a farmer saying "water not needed".

Jon A. Cruz said...

There's a bit of ongoing discussion in the community, but my main point was to clarify where people most likely are hitting problems.

You mention that it is not an artists job to create a profile. However, in the cases where the print house does NOT do that, then the artist can't just punt. They have to know what's going on and correct in the situations where they need to. Yes, I know a service bureau should take care of that, but not all do.

Although different profiles can be used across the world, I have gotten a lot of feedback from those in other countries where none are used at all, even for things like hardback books where the assumption could be that things are done "right". Knowing what others are encountering in real life can be quite helpful.

mf said...

Suppose you print in two colors (black and cyan) to save money and time.
To do that you use only black and cyan plates of the final PDF, using only the colors that have no yellow nor magenta components.
That's not the situation for artistic works, but suppose you print a book or a review in two colors, with some vector and (gray) raster graphics too.

If you work with (S)RGB you may define colors that have yellow or magenta when converted to CMYK, and they would not be printed right, since only C and K plates are used.

Suppose you create your vector graphics with Inkscape. How would you solve this problem, Jon? (I mean: working with RGB and having only black and cyan to get things printed)

This is my solution, but I do not like it very much: I work with Inkscape, then import SVG in Corel Draw and manually convert all the objects' colors in CMYK with 0% magenta and 0% yellow.

Jon A. Cruz said...

Mf, for a close-enough solution you might try picking a CMYK profile that is close to the inks/papers you end up with. Then just assign that and pick colors in Inkscape via the CMS color tab and do the equivalent.

In the long run, this sounds like you might even have a generic duotone situation on hand that an extension would help with.

gespertino-gmail said...

@mf: Also you can create spot swatches in inkscape with the auto palette and work as you'd be using pantone colors (or whatever swatches you want) and mix them, overlap them, etc.
When you're done you can change the swatch colors for pure RGB secondary colors (for instance 100% G+B for cyan, 100% R+B for magenta. You can also create a layer with blacks) and export as PNG.
That PNG file can be taken to gimp, and there you can use the decompose tool to separate the image into clean CMY/K plates.
You can store those plates in a tiff with Separate+
I've done pretty complex duotones with that technique, but now it's easier with Inkscape 0.48 and Scribus 1.5 (still in development, but usable for that purpose).
Anyway, you're doing that with CMYK files because you don't have the right tool for creating duotones properly (with spot colors). I mean, it's a hack and it doesn't have to do with CMYK directly.

@jon: Speaking of spot colors. There's something really needed in inkscape for work with spot colors: Tint % of the spot inks.
Is something like that possible in SVG?
Also spot swatches should be usable as gradient stops, and with the current implementation that's impossible. Are you planning some change in that area?

gespertino-gmail said...

I forgot to mention: there are a couple of extensions created by the brazilian inkscape community that allow to export directly from Inkscape as CMYK PDF and CMYK tiff.
Using them you won't need the extra step of taking the PNG to GIMP and do the decompose and separate+ trick.

http://wiki.softwarelivre.org/InkscapeBrasil/CMYK

Te extensions work for what you intend to do, but they are not usable for full color prints, since they aren't color managed.

bigprinter said...

What needs to be pointed out is that CMYK is device dependent. So is RGB for that matter.

Every CMYK device has a limited range of colors it can produce. This range of colors is different from device to device. This range of colors can be affected by the inks used, media used, and even the environment the printer is in.

The use of profiles allows you to work within the range of colors that device can output and get repeatable color from said device.

Any artist who is creating output for CMYK has to and should under stand profiling.

Most print houses work within the SWOP v2 standard. Some don't. You need to find out from the print house what they are using.

And what you get off your little inkjet printer or laser printer is irrelevant unless it is setup as a proofer to match the final output from the print house.

By the way, color matching systems are not a hundred thousand dollars. We have one.

The best way to know what your color will be is to run a proof from the print house on the device and media the final job will be printed on.

Jon A. Cruz said...

You mention that "Most print houses work within the SWOP v2 standard", however that is only true for North America.

There are huge portions of the world that use different defaults. Shops in Europe use a different profile than SWOP; print shops in Japan use yet another different standard.

So an end user needs to take care and ensure they use the standards applicable to their specific location.

Mark said...

I have to say that this is a bit of a chicken-and-egg problem in the print industry. I was heavily involved for 14 years with print (from 1989-2003), and spoke at a number of regional and national conferences. Of course, color profiles were just emerging at the beginning of that period.

It makes me grin that we could roll the time stamps on these comments back by a decade, and they'd be a perfect mirror of the conversations happening in the late 90's (for the most part). What I have to wonder is, what is the cause of resistance from printers and designers to mastering color profiling? It is a bit confusing at first, but in my experience the rewards are fantastic.

Рексервис said...

How to print a small only black (0M0Y0K100) letters?

Jon A. Cruz said...

To get black only letters in Inkscape, you have to select a CMYK profile, then use the CMS color picker to specify the black only value. The to print, going through something like Scribus is needed to gain a correct PDF.

Рексервис said...

Hmm, but then the whole image becomes black and white. So? I make comics. He is colorful, but the text in the balloon only 100% black. Due to the nature of newspaper printing, he looks so much better. I want to say that the arguments in the article are very far from the real needs of production.

toltec said...

As a former bureau operator in the UK I will add my piece. I am interested in Scribus now I no longer work there but have used Quark and InDesign commercially and am familiar with the ICC process. I will try to add more as I go along but have limited time today.

Any good printer will supply an ICC profile for his press, these can be hacked and re-entered if needed as they are simple files. Programs such as Quark or InDesign will load and use these. Failing that you will need to know the dot gain for his press and probably the paper he is using. They don't tend to change much.

In the UK we normally use Euroscale and most presses will be at around 15% dot gain.

Profiling is really for converting between screen RGB and CMYK between different printer types nad is the best way of getting precise colours. Get a book that shows CMYK colours printed as a colour chart. Corel actually used to print colour charts in the manual but books are available commercially.

They show exactly how each CMTK value colour will look and at a given dot gain value. Find out from your "professional" printer the dot gain for his press, enter the CMYK value you want, converting for his dot gain and hey presto, exact colour.

Profiles do not count as the CMYK is exactly as the press will print, as long as the paper is normal. Tell him what you have done.

toltec said...

Sorry

A couple of mistakes crept in as I was hurrying to finish before lunch.

I meants to say Inkscape, not Scribus, although I am interested in Scribus too.

As I said, or tried to, ICC profiling is all about making sure that what you see in RGB is similar to what you get when converted to CMYK on far more professional calibrated presses. Firstly CMYK simply cannot handle the range of colours in the RGB spectrum and converting from your pretty screen, proofing on a cheap bubblejet printer using copier paper and then expecting to convert to CMYK on a litho machine on gloss paper is going to end in tears.

The problem is, or was, is that people would use any program they had, Word, Corel Draw of something like Inkscape. View on their uncalibrated monitor, print on their uncalibrated inkjet printer using whatever cheap paper they had and wonder why the final result was not even close when returned from the litho press. Hence, the introduction of profiling in an atempt to allow printers to set up their various monitors and proofing presses (which vary quite a bit) to their presses (which do not). This can be extended for all of us.

CMYK is not a "colour space" but an exact value of ink on a piece of paper. You should not be using CMYK colour spaces on a computer unless the software and your monitor are a) very good and properly calibrated b) you never change between printing machines. Once you have saved in CMYK it cannot be changed from machine to machine. i.e you set it for one litho printer and paper type, then move to another paper type or print shop it will change. This will also be likely to cause problems if you get a proof made.

A press proofer will not match press output due to variations in the processes. If you set in CMYK, press profiling is fixed by these settings and cannot be fine tuned between the two processes. Using RGB colour space and ICC profilies would take care of this. Fine tuning being done between the software and the profiling.

If you need to print an exact colour get a colour chart, look at the CMYK value you want, look at the dot value used (it should say on the chart) set your CMYK colours to allow for this and your results will be exactly what you set. Although a proof from the printer may not be an exact match, (see above) the final output should be.

Failing that use ICC profiles with RGB colour space and rely on your printer to supply a proof and an accurate print. His profiling will convert between his CMYK proofer and his CMYK press so they match.

B.T.W. Ink manufacturers vary between countries which is why American, Japanese and European (Euroscale) processes vary slightly. SWOP should never be used unless you are printing on a Standard Web Offset Press. Web machines are for printing vast quantities, usually newspapers, on a huge roll of cheap paper and tend to have enormous dot gain values.