Color shift…is it significant?

T
Posted By
tacitr
Oct 19, 2004
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332
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A printer said, after seeing the proof (or dummy, whatever), "now convert your images to CMYK, 20% dot gain, and give me the whole thing on a CD. Be sure to include the fonts."

So far, so good.

No, so far is not so good. There are many ways to convert an RGB color to a CMYK color. In order to give the printer something that is usable on press, you must know more information, and you must enter that information in Photoshop’s CMYK Setup dialog box. If you do not, then you may end up with a CMYK image that looks great on your computer screen but absolutely can not be printed.

The information you need to know includes:

– Black generation
– Total ink limit
– Separation technique (GCR or UCR)

Make the wrong choices, and your job can’t be printed. If you have never opened the Photoshop CMYK Setup dialog before, or if you have but you’re confused or intimidated by all the settings there, you should probably not be making CMYK separations yourself.

Moving right along:

But I then tried to make some prints from the converted files (CMYK) (using the li’l HP) and all those white backgrounds developed a slight cyan tint as did the whites in some of the other pics.

A home consumer-grade inkjet printer is not a proofing device and *can not* be used to make test prints of a CMYK image. The printer uses CMYK ink, but the CMYK the printer uses is not the same CMYK as a printing press. The software drivers of a home consumer-grade inkjet printer can only work with RGB data.

If you snd CMYK to a home inkjet printer, the driver converts the MYK to RGB, very badly–then converts the RGB back to the printer’s own peculiar brand of CMYK.

By the way, never, ever expect that something you run on a printing press is going to look like what you see on a home inkjet printer, in RGB or CMYK. It’s not going to happen. The printed piece absolutely will not match your inkjet printout. It’s not physically possible; the primary ink colors are different. Inkjet cyan ink is darker and bluer than the cyan ink used on a printing press.

1. Is this result normal? Typical? Does it really MEAN anything?

It means you’re using a home consumer-grade inkjet printer. If you want to know how the job will look on press, buy a contract proof. A contract proof will match the press output, and will cost you anywhere from $25 to $50.

2. Is it necessary to adjust the color balance again?

Never color correct based on what you see on a consumer inkjet printer. Only color correct based on what you see on a true contract proof, such as a MatchPrint.

3. How do I "test" the new CMYK files for proper color balance? Or, is it even necessary?

If you care about color, it’s very necessary. In the prepress industry, here is how it is normally done:

1. Scan the images. Not on a consumer desktop scanner; for best results, use a drum scanner. These cost anywhere from $17,000 US to $340,000 US. That’s why designers don’t make their own scans; they pay a trade shop or service bureau to do it.

2. Get a set of "random proofs", which are just contract proofs of all the scanned images. You’ll probably pay about $50 for this.

3. Color correct the images based on what you see on the randoms. If necessary, get some more randoms made to test your color corrections.

4. Put the job together.

5. Get a contract proof made of the finished brochure or book or whatever. Give the pressman the digital files and the finished contract proof. (Good printers will not accept a job without a contract proof, or will insist on making a contract proof before the job hits the press. It is called a "contract proof" because it represents the contract between you and the printer. the printer’s job is to make sure the printed piece matches the proof. The press operator uses the proof to set up the press.)

4. I’ve read that cyan is the "weak" color in 4-color printing. Is what I’m seeing just PS’s correction for a normal color adjustment?

No, it’s a consequence of the fact that consumer inkjet manufacturers use ink that’s blue, not cyan, because home users tend to expect and want images that are, from a professional prepress standpoint, too blue. Photoshop has nothing to do with it.

Now, some words on creating CMYK images in the first place:

You can just use Image->Mode->CMYK, and you’ll get a CMYK image.

However, depending on how that image will be printed on press, and what kind of paper is being used, the results may not be printable.

For best results, you MUST use File->Color Settings->CMYK Setup, and use the CMYK Setup dialog box to specify the separation parameters for your press and paper, EVERY time you create a CMYK separation.

Also, many colors in RGB can not be reproduced in CMYK. CMYK has a different range of colors, or "gamut," than RGB.

If your image contains out-of-gamut colors, these colors will be converted to their nearest approximation in CMYK. The result will be a color which is less saturated and somewhat flatter.

Often, a little bit of color tweaking is necessary in the CMYK image. After separating an RGB image to CMYK, you may wish to use the Curves command (Image->Adjust->Curves) to increase contrast in the midtones slightly, as the separation often becomes flatter in the midtones.

Specific colors can be tweaked with Image->Adjust->Selective Color. For example, if your blues have yellow in them, you can remove yellow from blues to make them more saturated and richer.

When you color corrrect the image, you should, of course, have your Info palette open. Look at the numbers in the out-of-gamut colors; see if your primary colors have any contaminating color that can be reduced to increase saturation. For example, yellow in your blues or cyan in your reds can be reduced, if present, to make the colors richer.

Vivid RGB blues often separate with too much magenta, making the colors appear more purple than blue. Using Selective Color to reduce magenta in blues will often solve this problem.

The range and depth of color you can expect to get depends on the settings in your CMYK setup, which themselves depend on the kind of paper and press you are going to be printing on.

As for setting up your CMYK separation:

If you just go Image->Mode->CMYK without changing the values in your CMYK setup, the result will look okay on most sheetfed presses and coated (glossy) color stocks, but will not be acceptable for, say, newspaper printing.

For best results, you should talk to your printer about what to do. Most importantly, make sure he gives you the values he needs for maximum ink and maximum black percentages; if you exceed these values, the image may smear on press.

As starter points:

For sheetfed presses printing on high-quality coated paper, you can usually use GCR, 100% black ink limit, 300% total ink limit, Light or Medium black generation.

For very high quality lithographic output, your total ink limit can go as high as 310%.

For web-fed presses on glossy paper, or sheetfed presses using high-quality uncoated paper at a 110-line halftone or above, use GCR, 100% black ink limit, 280% total ink limit, Light or Medium black generation.

Newsprint is a different story entirely. For newsprint, appropriate settings might be UCR, 240% to 260% total ink limit, 85% black ink limit. When you convert the image to CMYK, it will look washed-out and flat, but newsprint darkens *considerably* on press so this reduction in density is necessary.

Hope that helps.


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J
jjs
Oct 19, 2004
"Pixmaker" wrote in message
[…]
The printed results were just fine…in fact surprisingly good.
A printer said, after seeing the proof (or dummy, whatever), "now convert your images to CMYK, 20% dot gain, and give me the whole thing on a CD. Be sure to include the fonts."

Your printer is incapable of being HIS printer. You cannot proof using your printer. It’s a totally different thing (RGB, for one.)

In this case, you might get a pre-press professional who can talk to the printer to discern _exactly_ what CMYK settings are neccessary. Those two professionals speak the language. In the meantime, study up. If you are very lucky you can get a pre-press pro to teach you the inside story. Good luck on that; my mate is a pre-press pro and to keep peace in the family we don’t talk shop. 🙂
P
pixmaker
Oct 19, 2004
I’m a long-time photographer but a relative newbie at pre-press. For some time, I have been proofing (and sometimes displaying) pics printed on a simple HP inkjet (932C) with very nice results. In fact, I’m amazed at how well these images look. (For really nice stuff, I use an Epson 2200.)

I use a calibrated Diamond Pro monitor, PS7 and work in the Adobe RGB color space.

Recently, using Pagemaker, I created a brochure (11 x 17, singlefold) for a small company and printed it out on the HP. The pics were of aluminum fabricated parts on a white background (and some other, establishing shots.). To be certain that the side-by-side images would print about the same, I balanced the white background in PS by equalizing the RGB levels, using curves.

The printed results were just fine…in fact surprisingly good.

A printer said, after seeing the proof (or dummy, whatever), "now convert your images to CMYK, 20% dot gain, and give me the whole thing on a CD. Be sure to include the fonts."

So far, so good.

But I then tried to make some prints from the converted files (CMYK) (using the li’l HP) and all those white backgrounds developed a slight cyan tint as did the whites in some of the other pics.

Questions:

1. Is this result normal? Typical? Does it really MEAN anything?

2. Is it necessary to adjust the color balance again? It seems to me that I’m now using a different process and what I see out of the printer may no longer bear a true (or even reasonable) resemblance to what may come off the press.

3. How do I "test" the new CMYK files for proper color balance? Or, is it even necessary?

4. I’ve read that cyan is the "weak" color in 4-color printing. Is what I’m seeing just PS’s correction for a normal color adjustment?

5. I understand that my li’l printer wants to receive RGB and that another conversion is probably taking place when I print from CMYK files. So, is what I’m seeing irrelevant?

Any commentary will be gratefully received as I stumble along this path toward understanding.

Pixmaker in FLL
==========================
It’s not the heat, it’s the humidity!
==========================
(…Think the humidity’s bad?
You should watch us vote!)
P
pixmaker
Oct 19, 2004
Hello, Tacit:

YES! It helps. . . a lot! I greatly appreciate the time you spent outlining what for you must be elementary stuff. . .sort of like "Prepress 101."

I am especially impressed with your ability to drive directly to the important points of my questions without any attempt to "dazzle me with footwork." What a refreshing approach! I suspect that it simply illustrates the difference between "them as can and <G> them as writes instruction books."

Inasmuch as your brief explanation is worth more than I found in the four (count ’em, four) PS books I have purchased to aid my understanding of this subject, I heartily suggest you consider publishing, yourself!

I’m a photographer, not a graphic designer or prepress expert, and, early on with PS, I bought a book to help learn this program. And then, I bought another…and another. It wasn’t until I got Scott Kelby’s book that I found someone who could say, "do this, do it again until you develop your skills, and you’ll get this!"

That’s an example of how I view your explanation. Thank you.

After too many years using everything from a Speed Graphic to an F4 and years in a darkroom, I began to believe I was "gettin’ kinda good." Now, with digital, I’m starting all over again and, in truth, I’m very impatient with the learning process. That’s OK, though because I probably went through the same thing years ago…just forgot all that!

I’ve talked with 7 different printing companies and have not found one that tells me much more than I mentioned in my first post. Is that because they really don’t know? Or, perhaps there’s more to be made from correcting mistakes from folks like me?

Maybe, they’re just tired of trying to explain a fairly complex process to people who aren’t in their trade and have come to the conclusion that they’re going to have to do it themselves eventually, so why waste the time trying to teach amateurs. I can understand that!

Thanks!

Pixmaker in FLL
==========================
It’s not the heat, it’s the humidity!
==========================
(…Think the humidity’s bad?
You should watch us vote!)
EC
Ed Clarke
Oct 21, 2004
In article , Tacit wrote:

A home consumer-grade inkjet printer is not a proofing device and *can not* be used to make test prints of a CMYK image. The printer uses CMYK ink, but the CMYK the printer uses is not the same CMYK as a printing press. The software drivers of a home consumer-grade inkjet printer can only work with RGB data.

There’s a CMYK RIP for the Epson 1280. Can this be used as a pre-press proof printer? Actually, after reading your posting, it sounds like you have to get a proof from the actual printing press to be sure the colors come out right. Is that true?
T
tacitr
Oct 21, 2004
There’s a CMYK RIP for the Epson 1280. Can this be used as a pre-press proof printer?

Not with Epson’s RIP, no.

There are RIPs which are designed to drive Epson printers and produce output that’s color-accurate to a printing press, such as Black Magic and Star Proof. Expect to spend about $15,000 for the RIP software, not including the computer to run it on or the hardware to connect it to the Epson.

Actually, after reading your posting, it sounds like you have to get a proof from the actual printing press to be sure the colors come out right. Is that true?

No. You’ll get an off-press proof, such as a MatchPrint or a 3M Waterproof. These contract proofs use the same film that would be used to make a printing plate, but they’re not run on a press. The proof is then given to the press operator, who adjusts the ink flow on press to match the proof.


Art, literature, shareware, polyamory, kink, and more:
http://www.xeromag.com/franklin.html

MacBook Pro 16” Mockups 🔥

– in 4 materials (clay versions included)

– 12 scenes

– 48 MacBook Pro 16″ mockups

– 6000 x 4500 px

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