Proper color workflow with CMYK inkjet printer

Thanks again to all for your suggestions and help. You have no idea how helpful this is to me.

(BTW, Aandi, we are a Mac-centric group.)

My plan is as follows:

1) First I'll verify that this is indeed a CMYK RIP. (I"m virtually certain it is, but can easily run the test that Marco suggests.)

2) If it is CMYK, I will profile it with i1 using the ECI2002 target (which comes with my i1 software). I've already calibrated my monitor, BTW.

3) When setting up CS3, we will choose the North American Prepress 2 settings (which is Adobe RGB for RGB and SWOP v2 for CMYK).

4) We will work in RGB mode in Photoshop, Illustrator and InDesign, but view our art while soft-proofing as per Rick's instructions, using the HP800ps profile.

5) Then we print using that same profile.

Makes sense?

Thx.

"I work in an academic science group that has a networked HP DesignJet 800ps printer (postscript RIP)"

From his first sentence...

I don't think that Carl mentioned using any RIP. As far as I can tell, he is just using the printer's driver.

So, all he should be making sure to confirm is that his printer driver is either CMYK or RGB.

To this end, Carl, please do the following:

1) In Photoshop, create a new CMYK file (make it a 6"x6" square; the color space is irrelevant, so just pick any -- SWOP v2 will be fine);
2) Fill the whole canvas with C100, M100, Y100, K100;
3) With your marquee tool, drag a square area in the center of the image area (say, 2.5"x2.5" or so -- it needn't be precise);
4) Change your foreground color to C0, M0, Y0, K100, and fill the newly selected area with it. Once you do that, the selected area will look lighter than the surrounding. That is OK.
5) Print this file to your printing device using the same print settings that you would use for your color-managed Workflow ("No Color Management" in Photoshop's Print window, plus "No Color Adjustment" in the driver's color management settings).

Examine the printed page: if there is *no* perceptible difference between the two areas of black, then your printer driver is RGB. If there *is* a clearly-perceivable difference, then the printer driver is CMYK.

Good luck.

> profile them as RGB devices" (to quote the book). The printers that I've profiled in the past with i1 worked this way.

As Peter points out in his post, it is most likely that your RIP is a CMYK RIP (most RIP's are.) If that is the case, you'll be profiling a CMYK device, not an RGB device (as you have in the past.) It is a totally different exercise to profile a CMYK device - ink limits and Kgen are variables that must be dealt with.

> Yes, details would be very helpful. Thanks.

Color management is all about moving from one device/color space to another device/color space while maintaining color appearance as closely as possible.

1) Based on the description of your workflow, step one is to create your original art in a well-behaved RGB color space (like Adobe98) while viewing it on a well-calibrated monitor.

2) If your final output is to be on the HP 800ps, step two would be to preview that art on your monitor as it would look on the HP. This is called soft-proofing - a process by which the art is viewed through the HP profile on-screeen so you can see what happens to all those beautiful, rich RGB colors when they're squeezed into the smaller gamut of the HP profile.

To do this, you go to View > Proof Set-Up > Custom, and choose the HP 800ps profile from the pop-up of all the profiles on your system. You can also choose from among 4 rendering intents - Relative Colorimetric, Perceptual, Absolute Colorimetric, and Saturation. Choosing the correct rendering intent is key - this willl determine how Photoshop deals with the out-of-gamut colors. Without getting into an explanation of what each RI does, the important thing is to choose the one that LOOKS the best on screen. There's no magic to it. In general, for photographic images, you'll be choosing from Relative or Perceptual. For vector graphics (which it sounds like you're doing), throw Saturation into the mix as well. Just try them and see which looks best.
Additionally, be sure to check "Black Point Compensation."

This will give you a good idea of what the final printed version will look like. While you're in soft-proof mode, you can edit the RGB file to alter the way out-of-gamut colors appear. In fact, there's no reason why you couldn't create your art from the beginning while in soft-proof mode. Using a well-built profile and a good calibrated monitor, you should be able to get an extremely close match between monitor and print.

3) When you print, be sure to choose the same profile/rendering intent that you used in Proof Setup.

Again, it all starts with a good profile. Good luck.

Don Hutcheson has files at: http://www.hutchcolor.com/Images_and_targets.html that can help you determine for certain if you RIP is a true CMYK RIP. If it is, and I'm pretty sure it is, then you can use one of the provided CMYK targets that ships with ProfileMaker. I usually use the ECI2002 target for CMYK profiles. Of course, you'll have to experiment to find the corrrect ink limits and black generation for that printer. Usually substantially different from press conditions.

Aandi and Marco,

I do understand that there is no such thing as an "RGB printer" in terms of the inks used. But my understanding from reading "Real World Color Management" is that non-Postscript inkets are usually referred to as RGB printers "because the vast majority require RGB signals as their input, forcing us to to profile them as RGB devices" (to quote the book). The printers that I've profiled in the past with i1 worked this way.

My confusion stems from the fact that the HP printer we're now using apparently does *not* function this way. Hence my question about whether this is an RGB or CMYK device, and whether this affects: 1) the color workflow we should use; and 2) what reference file I should use when profiling the printer with i1.

I hope this makes sense.

> Do you have a good profile of this printer? (actually, it would be a profile of the RIP/printer combo)

Hi Rick, thanks for replying. I don't have a profile at this point, but I can make one. We do have the i1 Photo package from GretagMacbeth, and I have profiled other printers before with it. So this is feasible. But I am still a little confused about how to implement this. i1 seems to be "leading" me to a CMYK reference file for profiling the printer, rather than the RGB reference file that I used for profiling previous (non-Postscript) printers. That was one of the triggers for my initial query.

> The only hurdle to overcome is the fact that the color gamut of your RGB working space will be larger (in almost all colors) than the gamut of the printer (particularly for this true 4-color printer.) So the question becomes, how do you handle the out-of-gamut colors (like those saturated oranges and blues.) It's very easy to set up a soft proof environment in which you can preview on-screen what will happen to those out-of-gamut RGB colors when they hit the CMYK space. (More details on request.)

Yes, details would be very helpful. Thanks.

Aandi Inston wrote:

>I don't really understand why you are making a point of this being a
"CMYK printer". Except for printers with no colour, and printers with
more than four inks. ALL colour printers are CMYK - there is no such
thing as an RGB printer.

Aandi,

As a general rule, laser printers have an internal CMYK engine in their drivers which ends up assigning the proper toner amounts released from each cartridge.

Inkjet printer drivers, on the other hand, mostly use an internal RGB conversion engine, starting from which they end up determining the exact amounts of ink released from each of the print heads (however many of them there happen to be).

So, although laser printers use toners loosely named C, M, Y, K, and inkjets also have cartridges named C, M, Y, K (plus others, depending on the system), it's the internal driver conversion mechanism that determines whether the device is "CMYK" or "RGB", though (and on that point I agree with you) there is no such thing as an RGB printer, strictly speaking.

Do you have a good profile of this printer? (actually, it would be a profile of the RIP/printer combo) If so, there's no magic to implementing color management with it. Basically, you work in an identified color space (like Adobe98), and then convert to the output space (the HP print space.) Most likely, the RIP will do this on the fly. The fact that this is a local CMYK device and not a commercial offset press is immaterial.

>I would like it if we could stay in RGB at all times - first question: Is this unrealistic given that we have a CMYK printer?

The only hurdle to overcome is the fact that the color gamut of your RGB working space will be larger (in almost all colors) than the gamut of the printer (particularly for this true 4-color printer.) So the question becomes, how do you handle the out-of-gamut colors (like those saturated oranges and blues.) It's very easy to set up a soft proof environment in which you can preview on-screen what will happen to those out-of-gamut RGB colors when they hit the CMYK space. (More details on request.)

Basically, if you know how to implement color management in the RGB world, this won't be appreciably different. THe RIP is the only wrinkle. You have to know what you're doing to create a good profile of a CMYK device - ink limits, GCR and the like. Either HP will have a profile you can use, or you can hire a good profile to be made. If you're not an expert, I'd advise having someone create the profile for you.