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

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  #1  
Old 05-25-2012, 07:34 PM
Andymania Andymania is offline
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How much do I need to know about cmyk/prepress?

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
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Old 05-25-2012, 11:09 PM
edgework edgework is offline
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Re: How much do I need to know about cmyk/prepress

Quote:
Originally Posted by Andymania View Post
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.
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Old 05-26-2012, 02:33 AM
creativeretouch creativeretouch is offline
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Re: How much do I need to know about cmyk/prepress

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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Old 05-27-2012, 01:53 PM
eraanexact eraanexact is offline
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Re: How much do I need to know about cmyk/prepress

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Originally Posted by edgework View Post
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.
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  #5  
Old 05-27-2012, 10:55 PM
kav kav is offline
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Re: How much do I need to know about cmyk/prepress

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.
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Old 05-29-2012, 06:19 AM
Andymania Andymania is offline
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Re: How much do I need to know about cmyk/prepress

Good points fellas thanks. Kav, I am aware of the finicky behaviors of CMYK especially the cyan ink.
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Old 05-29-2012, 08:03 AM
edgework edgework is offline
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Re: How much do I need to know about cmyk/prepress

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.
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Old 05-29-2012, 08:16 AM
Andymania Andymania is offline
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Re: How much do I need to know about cmyk/prepress

Edgework,

Good point. I forgot about the rendering intents.
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Old 05-29-2012, 08:26 AM
creativeretouch creativeretouch is offline
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Re: How much do I need to know about cmyk/prepress

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

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http://shotworldwide.com & http://photoapps.info
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Old 05-29-2012, 09:09 AM
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shift studio shift studio is offline
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Re: How much do I need to know about cmyk/prepress

Quote:
Originally Posted by edgework View Post
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!
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