RGB-CMYK Tutorial Needed

[BobRoosth]

One of my clients just asked for an explanation of what is required to convert digital camera images from RGB to CMYK for printing in his catalogue. I told him to talk with his printer's prepress department, but I'd also like to point him at a web site or book that might be of use. Since he does not have calibrated monitors, I suspect he would be better off taking RGB files to the prepress folk and having do the conversion, but they are asking for converted files.

Suggestions?

[Cristen Gillespie]

One of my clients just asked for an explanation of what is required to convert digital camera images from RGB to CMYK for printing in his catalogue. I told him to talk with his printer's prepress department, but I'd also like to point him at a web site or book that might be of use. Since he does not have calibrated monitors, I suspect he would be better off taking RGB files to the prepress folk and having do the conversion, but they are asking for converted files.

Suggestions?

Since your client doesn't want to bother to calibrate his monitors, books won't be of much use. Color management rather assumes a calibrated monitor. Get a printer profile to use from his printer and install it, use that to separate. Get from his printer which standard CMYK working space to select from the menu. Set it up as his working CMYK. Okay, there I'm assuming he has PS, but maybe that's too much to assume.

If he cares at all about color (don't see how he can if he doesn't try to calibrate his monitor), he can use gamut warning to check his RGB files before converting to CMYK. The gamut warning is a bit overly conservative, but it can help. Then convert to the CMYK working space that he's set up according to printer recommendations. If he hates the results (but how can he judge with an uncalibrated monitor, and I assume he doesn't know from numbers) he can try to help his file out a little bit, but he should be careful about futzing with a CMYK file if he doesn't know what he's doing.

If he does really care and wants to learn about color management, Fraser's Real World Color Mangement ought to help. Bruce is very good at explaining technical issues to the rest of us.

[mact]

Hi Bob, long time no type!

Calibrated monitors might be desireable, but IMHO not really necessary. Relying on them while being careless with (or un-appreciative of) other issues is apt to trip you up at an unfortunate time. My experience with trying to use a $$$$ Pressview monitor some years back (on a mac) was that freshly calibrated according to the book it was less predictive than a 7-year old Viewsonic on my PC. If you know what you are doing you can adjust colors on a monochrome monitor (I'm not claiming to be able to do so, but I have seen it done and for simple adjustments is actually pretty easy and in some cases can produce as good or better a result than that from someone with less understanding using the latest piece of kit).

Anyway:

Conversion to CMYK should be near the end of whatever tweaking and such is done. That way the cmyk can be created based upon what is actually going to be needed. What is needed for newsprint is a lot different from what would be needed for sheet fed on cast coated stock. A lot!

The major variables are:

A) the black generation. There is no separate "black" channel in RGB. One is created when converting by taking data out of the other channels. How much is taken and how heavy the resulting black becomes are factors that must be considered when doing the conversion.

An RGB value of 128,128,128 is a neutral grey. There are an almost infinite number of cmyk "equivalents" ranging from 0,0,0,50 to about 58,50,50,0. The difference between all of these equivalents is the black generation.

B) Total Ink Coverage (or TIC) is also an issue. In 4-color printing the maximum possible is 400%, flood coverage of all 4 colors. In practice this is unlikely, but depending on the conversion setup one can still get unsuitably high figures. The figures will depend entirely on the paper and press. Typical for newsprint is 240-260% coverage. For web-printed magazines, 290-300 might bbe typical. For sheetfed, 310-320. The TIC selected also affects how much of the CMY channels get converted to K.

With reference to Photoshop the setting I use most of the time is a custom setting that is suggested by Dan Margulis in his Professional Photoshop books.

!) Light black generation (produces a very light black channel that's pretty much only in the shadow areas). Photosop's default is much heavier and will often produce a black channel that looks great as a greyscale halftone all by itself, but these images are trouble on press because the pressman tries to "up" the black to get good type density. Along the way, the increased black ink darkens the image too much. Heavy or Maxiumum black generation ought be used mostly for converting screen shots not for most photos.

2) Maximum about 75% black (meaning there shuldn't be more than abut 75% K in any part of the image. In a properly neutral shadow area, C should be the heaviest, about 10 points above the others.)

3) Total ink...as described above. Note that a CMYK image converted for running on high quality stock on a sheet fed press as part of an ad might be rejected by a newspaper or even a magazine because the TIC would be out of their spec.

4) Gain. I use 17% I think most of thje conversions that I see already done use 20 (as a default). Neither of these are appropriate for newsprint or many web magazines.

MOST of the time when I get customer-generated CMYK the images are far too dark. Among the worst locally are the "Professional" photograpers who manage to generate images with 20% highlight dot, bright red faces, and too much TIC.

How I usually approach an image is to first look at it in RGB picking the true highlight and shadows (if there are any) and setting them to about 246,246,246 and 10,10,10 respectively. Look for neutral colors. A rock or clothing that is supposed to be a neutral grey should have RGB values that are about equal. Then after converting to process, I check for facial tones. Most of the time this is all that is needed. If the image is real dark, I might first take it into Lab and tweak the Lightness channel before anything else.

[ktinkel]

If he cares at all about color (don't see how he can if he doesn't try to calibrate his monitor)I get the impression you really, really believe in monitor calibration.

Does that mean you work in a space that is free of glare, out of ambient light? If not, how do you evaluate what you see on the screen?

Do you have a colorimeter that lets you check analog values? And how do you keep your calibration in tune?

Serious questions. I tested a couple of these devices on a fancy monitor, way back when, and realized that no matter what, I could never live with all the strictures of calibration. (And I also realized that I would never be a color retoucher, either — just not my thing.)

It seems to me that critical color needs to be adjusted by an expert, and evaluated by real hardcopy proofs, just as in the old days. (It would be nice if you could also have a date with a Scitex operator, as in the old days, as well, but c’est la vie!)

Less critical (“pleasing”) color can usually be managed by common-sense recipes (or by asking the printer to make the adjustments).

Adjusting gamma is one thing, but real calibration? Hard to believe there is much of that in typical design studios these days, but perhaps I am out of touch.

[terrie]

>>kt: Adjusting gamma is one thing, but real calibration? Hard to believe there is much of that in typical design studios these days, but perhaps I am out of touch.


Depends on who you talk to...are you in the Margulis camp or the Fraser/Blattner/Rodney camp??

Monitor calibration (among other color management tools) has come a long way in the last few years and I believe (at least if one reads the ColorSync users list) that more and more of it is being done...

To my mind, it's a question of consistency...using a color managed approach helps you to "know" not only where you are but where you are going. It gives a systematic basis for comparison.

Can it be a pain in the butt? Oh yeah...but the alternative can be more confusion...

Terrie

[ktinkel]

Monitor calibration (among other color management tools) has come a long way in the last few years and I believe (at least if one reads the ColorSync users list) that more and more of it is being done... So how do you control ambient lighting, glare, etc.? And how often do you re-calibrate your monitor, as they tend to change as they get warm, old, etc.?

I wasn’t willing to live in a cave, and hated those blinders used for full-time color-editing monitors.

You are an artist, so I can understand why you need to see what your colors are doing on-screen. But a designer is used to analog controls for this, and good work needs a color proof in any event (hang the cost!).

[terrie]

>>kt: So how do you control ambient lighting, glare, etc.?

I've always thought that the idea of working in a cave was not only not appealing but more than a bit of overkill. I will say that I don't have light glaring on my screen--who would...you can't see the screen then!? (oh where is that interobang key...'-}})--but my room is nicely lit by 3 lamps and my window is set back under an overhang so that while I get daylight into the room it's not bright light...

Basically, my room is well lit for my use and hasn't caused me any color problems...


>>And how often do you re-calibrate your monitor, as they tend to change as they get warm, old, etc.?

I recalibrate about once a month or so...some people do it more regularly--like weekly--but I've found that once a month works ok for me...the process takes about 10 minutes...if I had BIG BUCKS, I'd buy a Sony Artisan which is considered the creme de la creme of CRT monitors or if I had even BIGGER BUCKS I'd buy an Eizo LCD monitor both of which automatically calibrate when you turn them on...


>>I wasn’t willing to live in a cave, and hated those blinders used for full-time color-editing monitors.

See above...'-}}


>>You are an artist, so I can understand why you need to see what your colors are doing on-screen. But a designer is used to analog controls for this, and good work needs a color proof in any event (hang the cost!).

I understand your point but why shouldn't a designer get to see what they are doing too? As to proofs, lots and lots of people who color manage provide proofs...it's just when using a good color managed system, there are fewer surprises and when there are surprises, they can be easier to diagnose...

Terrie

[PeterArnel]

One of my clients just asked for an explanation of what is required to convert digital camera images from RGB to CMYK for printing in his catalogue. I told him to talk with his printer's prepress department, but I'd also like to point him at a web site or book that might be of use. Since he does not have calibrated monitors, I suspect he would be better off taking RGB files to the prepress folk and having do the conversion, but they are asking for converted files.

Suggestions?
http://ecentral.creo.com/eCentral/training/online/online_classroom.asp

Bob have a look at this site - u may need to log on but the web training ( which is free is very good)
Its best not to leave RGB to CMYK to printer unless u want it to come straight out of the box -each system converts it differently

Peter

[ktinkel]

…why shouldn't a designer get to see what they are doing too? As to proofs, lots and lots of people who color manage provide proofs...it's just when using a good color managed system, there are fewer surprises and when there are surprises, they can be easier to diagnose...Designers do see! They get a photograph, and try to replicate it in print, through halftoning and all the rest. But the part I do not feel in control of is the on-screen part.

Besides that, perhaps because I have been a working graphic designer for (ulp!) nearly four decades, I have a sense of what is appropriate work for me, and what is not.

And because, further, I see so much truly awful imagery in print, much of it too soft, too blurry, too misshapen, I have a great caution about trying to work above my skill level.

But perhaps we are in a brave new world. Or perhaps we have once again taken a great leap downward in quality, and accepted it in the name of economy! <g>

[Franca]

Serious questions. I tested a couple of these devices on a fancy monitor, way back when, and realized that no matter what, I could never live with all the strictures of calibration. (And I also realized that I would never be a color retoucher, either — just not my thing.)Oh, thank goodness. I'm not alone in this. Phew! It is a *lot* of work to get your room set up just right and I came to the realization that it wouldn't be much good for anything else. Once you get the room set up you still have to do all the calibration, LOL! No, thanks.

[BobRoosth]

Thanks for the very thoughtful response. It has been a while. I have been busy enough with the rest of my life that reading replying here has not made it to the top of my list. I am two months behind reading some magazines I need to read to stay current. I will forward your remarks, along with the statement that the printer has to supply some of the values based on his press and paper.

--Bob

[terrie]

>>kt: Or perhaps we have once again taken a great leap downward in quality, and accepted it in the name of economy! <g>

Color management ain't magic...if you got a crappy design, color management isn't going to make it better...gigo...

Terrie

[terrie]

>>franca: Once you get the room set up you still have to do all the calibration, LOL! No, thanks.

I don't mean to belabor the point but while there is a relationship between how a room is lit and calibration in that glare on a monitor will impact the monitor calibration, just setting up a room as a cave, doesn't have anything to do with color management...

In my mind, color management is like having your car tuned...yes, the car will run if it's not tuned but it runs better if it *is* tuned...

My implementation of color management is fairly unsophisticated in that I have only calibrated my monitor (~$200 for the ColorVision Spyder) and have color management turned on in Photoshop with a defined working space...in doing that I provide a platform that allows my monitor, Photoshop (ID and Painter too) and my printer to speak a common language so that what I see on my screen is what I get when I print...

Works for me...

Terrie

[Franca]

Perhaps I will revisit the notion of "unsophisticated color management" at some point in the future. <g> Not doing much of any color work at the moment, and the last project wasn't a print on paper job anyhow. (Those sweatshirts and vinyl posters - kind of a cross the fingers and pray job!)

[terrie]

>>franca: Perhaps I will revisit the notion of "unsophisticated color management" at some point in the future. <g>

LOL!! Do let me know when you do...'-}}

Terrie

[Cristen Gillespie]

I get the impression you really, really believe in monitor calibration.

.

I believe in the numbers, but I think anyone can get their monitor (especially brightness/contrast) somewhat closer to being reliable without necessarily spending a lot of money, or any money if they dare work with Adobe Gamma, or what now works on OSX.

These are photographs (from his digital camera). He doesn't know how to convert to CMYK, or the best way, anyway, and that probably means he doesn't know how to read critical CMYK numbers for output. He doesn't need to, but he then needs a monitor that isn't totally lying to him (when ink hits paper, most of us experience a bit of surprise if we've been trusting our eyes and our monitor), and he needs to use gamut warning to make sure he isn't producing a delightfully saturated piece that can never make it to any printer.

Do I believe in the proper "light box" setup. Yes. If the color is really critical, that's best. With all the equipment that costs $$$$. I can't afford it, but my work isn't color critical. I don't suppose his is either, as most isn't. He can still get very good printing done if he gets a profile (I use Margulis', but that might not suit the actual printer doing the work--it's great for my Epson printer), and if he tries to learn to accommodate the output, not relying totally on what he sees on his monitor in RGB and then doing one of those "let the computer convert and I won't look at the results" jobs.

As Margulis has demonstrated, you can color correct on a B&W monitor. It's really when you start looking at monitor color that you get in trouble<G>