How much do I need to know about cmyk/prepress?

[Andymania]

As a beginner retoucher, I was wondering how well educated should I be about CMYK and the prepress process? I know substantially more about CMYK, GCR, dot gain, total ink coverage, etc but do I need to have as much knowledge about this stuff as a guy like Dan Margulis? How much of this stuff do pro retouchers really know and apply on a daily basis?

-Andy

[edgework]

Originally Posted by Andymania

As a beginner retoucher, I was wondering how well educated should I be about CMYK and the prepress process? I know substantially more about CMYK, GCR, dot gain, total ink coverage, etc but do I need to have as much knowledge about this stuff as a guy like Dan Margulis? How much of this stuff do pro retouchers really know and apply on a daily basis?

-Andy

If you do any work in print media, CMYK is still the only game in town. If, as is usually the case these days, you do all your retouching in RGB, only converting to CMYK when the file is sent to the RIP for proofing (or worse, passing your RGB masterpiece on to someone else to convert and proof), it would be a good idea to know what to expect out of the translation. Otherwise you and your client will be unpleasantly surprised when the ribs and shadows on your red sweater vanish into a red blob, or the subtle blues in that elaborate dress design turn to mud, or your skin looks like it was processed in a plutonium bath. CMYK is a pain in the ass, frankly, but accurate calibration and color management make it a lot easier to get the best out of the space than used to be the case, and avoid those nasty surprises.

[creativeretouch]

I would say if you wish to work within this industry you should continue learning. Also to be able see your results and compare them with your screen is also important.

Regards, Filip

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http://shotworldwide.com & http://photoapps.info

[eraanexact]

Originally Posted by edgework

If you do any work in print media, CMYK is still the only game in town. If, as is usually the case these days, you do all your retouching in RGB, only converting to CMYK when the file is sent to the RIP for proofing (or worse, passing your RGB masterpiece on to someone else to convert and proof), it would be a good idea to know what to expect out of the translation. Otherwise you and your client will be unpleasantly surprised when the ribs and shadows on your red sweater vanish into a red blob, or the subtle blues in that elaborate dress design turn to mud, or your skin looks like it was processed in a plutonium bath. CMYK is a pain in the ass, frankly, but accurate calibration and color management make it a lot easier to get the best out of the space than used to be the case, and avoid those nasty surprises.

Pretty much this.

[kav]

Edgework explained it better than me. CMYK is a little more finicky. While sometimes you will have to hand it off in RGB, there are some things you should remember to ensure that others don't mess it up. Saturated reds, greens, and blues can be problematic. Blues are one of the worst, but a red sweater or saturated green grass can produce a lot of problems. The thing is that if it's going to someone else for conversion, most of the time they're just going to hit convert and deal with any shifts from there. I don't care what they should do or examine. This is what actually happens. This matters because you don't want clipping or loss of detail in cyan, magenta, or yellow. Overall depending on output type, it can handle anywhere from around 240% total ink (say something like newsprint) to around 350%. If your blues have some blue values trending toward 100% cyan, 0% yellow, or anything that kills the detail in one of the two, this will cause problems. Red garments often tend to come close to maxing out magenta and sometimes yellow too. While you won't always see this stuff on your display when it's converted, they will cause problems when it's printed.

Skin also should retain 3% cyan or so regardless of profile within the lighter tones for detail and so that you don't run into detail problems. The reason I assigned an absolute value there is that things tend to sharpen slightly on press, and 1-2% is more likely to break. In practical terms, I try not to let my highlights exceed 245-250 in rgb values. Much of the perception is relative, so as long as there's enough difference between midtones and highlights, it won't look flat.

It's just little stuff, but you should seek to preserve details rather than absolute saturation, and even though you may make tweaks in cmyk, you should make sure that you don't introduce clipping in the conversion itself. If you have highly saturated objects, you should check for single channel clipping at the processing stage, and at the cmyk conversion stage. Worst case scenario is that you can lose details at both points.

[Andymania]

Good points fellas thanks. Kav, I am aware of the finicky behaviors of CMYK especially the cyan ink.

[edgework]

Sometimes, when converting from RGB, you might need to do more than one version, playing with the conversion intent. Photoshop's default method is Relative Colormetric, which converts precisely those tones that are in the CMYK gamut and crunches everything else at the edges, which is why subtle blues, saturated reds and most pastels go off the grid. Perceptual will attempt to move the entire color spectrum of the image inside a printable range, preserving the relationship between tones, while making no attempt to preserve actual color. Usually not a good solution, but if parts of your image will never convert precisely to CMYK, you can settle for an approximation that at least captures the look and feel of the original, then comp in the problem areas with masks.

[Andymania]

Edgework,

Good point. I forgot about the rendering intents.

[creativeretouch]

Usually I look at CMYK and RGB images like they did not come from the same source. When I convert them to CMYK I continue working on them and trying to get maximum even from this colour space.

Regards, Filip

-------------------------------------------------------
http://shotworldwide.com & http://photoapps.info

[shift studio]

Originally Posted by edgework

Usually not a good solution, but if parts of your image will never convert precisely to CMYK, you can settle for an approximation that at least captures the look and feel of the original, then comp in the problem areas with masks.

never thought of that (duh)
thanks!

[andrewrodney]

Originally Posted by Andymania

do I need to have as much knowledge about this stuff as a guy like Dan Margulis?

Nope! You only need a good ICC profile that actually defines the output process. That’s the hard part (getting that profile in many cases). The profile is the decoder ring that properly converts to CMYK from your source RGB data. You should soft proof and examine which rendering intent provides the most pleasing results (profiles don’t know squat about colors in context, humans do). The profile defines TAC, GCR, all the stuff necessary to ideally print on the device it (again hopefully) defines. There are literally thousands and thousands of differing CMYK print behaviors. Some would like you to believe you just pick any old generic profile (use SWOP V2) and all is fine. That would be true if the print conditions fully conformed to TR001 SWOP specifications that the V2 profile defines. If not, well then how far the print conditions differ, that’s how far off your output will be.

[edgework]

I worked in a studio that had just recently begun in-house proofing. The production manager set out on a true Grail quest for correct color. He pulled some past jobs that had gone into production, and sent the files out to all the prepress shops in town, and then compared the results when he got his 15 or so contract proofs back the next day. Every one was different, of course, and he was in serious danger of melting down and running out of hair to pull out of his head, crying to the universe "Which one is the right one?" I told him, "The one that gets the client's initials in the bottom right corner." I was just trying to be helpful but it wasn't what he wanted to hear.

Profiles will get you a good distance toward your goal, but if you're looking for a way to circumvent the time-tested method of running a proof, then making subjective decisions at the light box about what to tweak, and repeating the process until the client says "That's it!" we're probably talking about a parallel universe where all inks behave the same and all proofing devices are in perfect sync. Not this universe, unfortunately.

[andrewrodney]

Originally Posted by edgework

...he got his 15 or so contract proofs back the next day. Every one was different, of course, and he was in serious danger of melting down and running out of hair to pull out of his head, crying to the universe "Which one is the right one?"

Well the first question would be, did he get 15 ICC profiles for the process? It would be easier to evaluate which is ‘right’ (the answer is nearly always, the one you prefer). And the contract proof should match the press (that’s the point of the contract proof in the first place).

I told him, "The one that gets the client's initials in the bottom right corner."

Exactly. Now let’s hope that is what we see at the press check.

You start with the profile. Hopefully a good one that describes the process. But you have to proof. You have to get the proof signed off. Then the press has to match that proof really closely.

[Andymania]

Good feedback here folks. I do remember reading Margulis talking about how important contract proofs are. Andrew, you published a book on color management correct? (the one with the dog on the cover) If so, I'm gonna have to get it. Hopefully it will clear up any confusion I have on ICC profiles.

-Andy

[DJSoulglo]

I've recently gotten a new client who wants everything in 3 spotcolors. That was a thing I hadn't done in years. Good practise though.