Archive for the 'color bars' Category

#58: I Still Love the Smell of Ink in the Morning

Published
by
Jim Raffel
on June 28, 2007
in calibration, color, color bars, density, measurement, press run and process capability
. 0 Comments

I have been so immersed in virtual proofing over the last several posts, that I had almost forgotten how much I still love the smell of ink in the morning. Last week I had the privilege of spending two days assisting a customer in the set-up of our software primarily for use as a pressroom monitoring tool.

The experience reminded me of #55: Just Measure It! The customer is a web offset shop and has the same problem that most of our digital printing customers have (Oh, I love the smell of toner in the morning too!). The problem is that their press product is finished product and has no trim. Color bars are not an option on production work, and changing the design to incorporate color swatches would also be impractical at this time.

The solution turned out to be the same solution we employee with our digital printing customers. A test form is put on press twice a day and the results of those measurements are used to verify conformance to density standards across the web. A second control strip can be scanned to gather other print metrics like TVI, Print Contrast, etc.

The results in a sister shop have been improved consistency from day to day and the ability to monitor changes in density and TVI from morning (cold press) to afternoon (warm press). In a perfect world I would love to see color bars on every job, but we thought outside the box and found them a solution that allowed us to measure. Once they started measuring quality and consistency improved. Profitability and productivity are never far behind quality and consistency improvements.

I raise the challenge again…today start measuring something in your color workflow that you are not measuring today. Within seven days those measurements will point the direction you need to go to improve the quality and consistency of that process.

#48: Make Proofs That Match Your Press

Published
by
Jim Raffel
on February 16, 2007
in GRACoL, L*C*h*, L*a*b*, TVI (Dot Gain), color, color bars, delta E, measurement, process capability and proofing
. 0 Comments

Since #45 in December we have been discussing resolutions to improve the quality of your proofs. In order to gain the full benefit of this installment one should have read and implemented the suggestions in #46 & #47.

Proceeding forward it does not matter if you are utilizing a methodology like GRACoL G7, or a more traditional color management approach. In either case you will include a target on each print job with the same color bar swatches that you output on the proof (#46). This will allow you to measure the press ok sheets and compare them to the proofs, thus building even a larger statistical database to call upon.

When utilizing software like our ColorMetrix and ProofPass.com products for process control and print certification purposes it does not matter if you are using a methodology like G7 or traditional color management. While there are some new formulas out there to run the collected data through the tried and true colorimetric data (L*a*b* and derivatives along with some version of Delta E), do a great job comparing two similar or dissimilar imaging systems.

Unlike density and dot gain values which must be used with pigment sets designed for 4/color process printing, L*a*b* values allow the comparison of an inkjet proof and an offset press sheet. This is possible because we are looking at the actual colors, not values derived from a formula which assumes a certain pigment set.

Not only will you be comparing the measurements of the proof to the press sheet, but you will be building a history of what is a “normal” print condition of each press and paper combination. Some refer to this as finding the “sweet spot” of the printing press.

Overall, as your volume of collected data grows you will be able to refine the system in small steps by reviewing the proofing and press information both independently and together. Using numeric results, charts, and graphs you will be able to see small differences in color that can be adjusted for over time. No system is stable over time, so continuous monitoring is a must in order to maintain stable color.

#35: Excellent reader responses to GN#34

Published
by
Jim Raffel
on June 13, 2006
in color bars
. 0 Comments

It has been quite a while since I dedicated an entire Golden Nugget to responses I received to a previous Golden Nugget. Two of the responses to ‚Äú#34: On needing color bars to print well“, however, are far too good to not be shared with the rest of my readers.

Comment #1:

While I agree with the end result of your GN, there is 1 VERY, if not MOST important reason for instituting the use of color bars to control and maintain the printing process that was left out.

Even with typical production run lengths becoming shorter and shorter, the fact remains that many jobs carry over from 1 shift to the next. No 2 sets of eyes view color the same way; and I’ve witnessed countless occasions in my career where the “next” pressman makes arbitrary and unnecessary changes to ink viscosity and impression settings only because the color “didn’t look right ” to him. The use of color bars creates an OBJECTIVE set of numerical reference criteria that is agreed upon and maintained by all operators; not having them is an open invitation to SUBJECTIVE and oft times incorrect decision making that adds unwanted variability and cost to the process.

Comment #2:

While I like your map analogy, I think that color bars are more critical than that. I would compare it to an experienced driver making that same route without a gas gauge, speedometer, or mirrors, and with a splintered windshield. Yeah, you could do it, but who would want to?!?

Name withheld

PS-I am a prepress manager :-)

#34: On needing color bars to print well

Published
by
Jim Raffel
on June 6, 2006
in color bars
. 1 Comment

No, one does not need color bars to print well. You also do not need a map to get from Los Angeles to New York City. I believe we would all agree that with a map, however, the trip from Los Angeles to NYC would be by a more direct route. A more direct route would be faster (more productive) and cost less (use less gas, stay in fewer hotels, etc…).

Yes, I view color bars as the map in the above analogy. I view a pressman with 20 years experience as the truck driver who has made the long haul from LA to NYC several hundred times. Even that truck driver, however, benefits from a map when problems arise (construction, bad weather conditions, etc…).

So, while an excellent pressman can probably produce most jobs quite nicely without ever seeing a color bar; even the seasoned professional benefits from having a color bar when things do not go smoothly. With the color bar we can check density, TVI (Dot Gain), Grey Balance, L*a*b* or inks and spot colors, etc… Armed with that kind of information even a junior pressman can make better decision about how to improve the quality of every job.

More importantly, the color bar is not just for the pressman. The information gathered from the color bar should be fed back to the pre-press department on a regular basis. Pre-press needs to know that the press in continuing to run the same (similar densities, similar TVI, correct L*a*b* of solid ink colors, etc…). With this information pre-press will know that ICC profiles, and plate cut-back curves are still correct. Without it they will just be guessing.

In summary, while complete color quality control systems cost money to put in place the payback is typically much less than one year. Proper use of color measurement instruments and software will result in higher productivity and lower costs. Want to know more? Please feel free to contact me anytime for more information.

#31 Tales from the Press Trial

Published
by
Jim Raffel
on April 21, 2006
in TVI (Dot Gain), color, color bars, curves, densitometers, density, measurement, press run and process capability
. 1 Comment

On April 17th and 18th I had the pleasure of participating in a press trial with MacDermid Printing Solutions to evaluate the effectiveness of their new Stabil-X offset printing blanket. I am writing today about the TVI curve of the various trial conditions.

Stabil-X TVI

We ran five different conditions during the course of the trial. All the trials shown in the graph involved only one printing unit running magenta ink. The curves also represent the averaging of 10 press sheets. The five trial names and descriptions are:

  • STX opt - Stabil-X blanket run at optimum packing level
  • Press std - The set-up of the press when we arrived
  • STX -.003 - Stabil-X purposely under packed by 3 thousandths
  • STX +.002 - Stabil-X run at 2 thousandths over
  • STX +.004 Stabil-X run at 4 thousandths over

As one might expect the STX -.003 has not only the lowest TVI, but also a very poorly formed curve. A pretty good example of why you do not want to run your press under packed.

The Press std curve shows how this shop runs the press on a regular basis. Notice the hump in the TVI curve from 25 to 50%. Not an uncommon condition on many presses.

The STX opt curve is much smoother than the Press std curve, missing the hump from 25 to 50%. Also, run at virtually the same densities the dot gain (50%) and overall TVI is lower at all points than the normal press set-up.

Even the two STX over pack conditions produced smoother overall TVI curves than the press standard set-up. While the TVI is higher in most cases this is to be expected when adding that much squeeze to a blanket that really does not need it.

I will continue to write about this press trial for a least 2-3 more weeks. There is a great deal of data and information to still go over. I even have some sheets here I will be doing additional readings on.

If you would like more information about the MacDermid Stabil-X blanket, please contact me and I will put you in touch with the right people at MacDermid.

#17: What should my color bar look like?

Published
by
Jim Raffel
on November 3, 2005
in color bars
. 0 Comments

This week as part of a larger conversation a potential client asked, “What should my color bar look like?” My first thought was that it would be easier to answer the following question…”What is the meaning of life?” The answer to the color bar question can be both simple and complex, at the same time. We should begin with why this potential client was asking the question. The company involved is a very large consumer products concern. As such they are the ultimate consumer of the print (i.e. - they pay for it). Others in the supply chain are pushing for a fairly large color bar to be included on each package. While in principle I agree with measuring as much as you can, I have also assisted customers with almost not space for a color bar and found a way to measure enough to be meaningful.

The interesting trend I see in consumer product printing (i.e. - packaging) is towards more informative color bars. While in the past getting designers to allow even solid blocks of the process and spot colors was like pulling teeth, now you see targets approaching the size of the ECI target (sarcasm). I believe the reason for this is simple. Managing libraries of dozens, hundred, or even thousands of spot colors can be almost impossible. If, however, one moves towards some form of 6 or 7 color process printing some pretty amazing economies of scale begin to occur.

The trick is that if you are producing a critical spot color with some build of process inks those inks and all associated print attributes need to be “spot on.” The only way I know to control critical press factors like density, dot gain, print contract, etc… is to measure as many color bar patches as possible. See how simple the answer to these complex questions can be?

So, ranked in order of importance (Jim Raffel’s order) here are the patches I would want to see on a press color bar. (We can talk about proof control bars in another Golden Nugget)

  1. Unprinted substrate patch (to zero out substrate when necessary)
  2. Solid patch for each process (and spot) color (needed for solid ink density (SID))
  3. 3/Color Grey patches at multiple tone values (if you are not sure why please re-read all your Golden Nuggets before proceeding)
  4. Mid-tone patch for each process color (only way I know to gather dot gain (TVI) values)
  5. Process color over prints (needed to measure trapping efficiency of inks, this gets a bit tricky in 6 and 7 color printing)
  6. Additional highlight and shadow tone patches of each process color (i.e. - we need a 75% patch to calculate print contrast)
  7. GATF Star targets or microline targets (used to visually evaluate for press slur and doubling issues)

All of the 7 items listed above are important and truly necessary but if space is an issue start with number 7 and work backwards removing items until the bar fits. Also, items 3 and 4 could be easily reversed; having one without the other makes diagnosis of grey balance issues difficult at best. Now, for my radical comment of the week….if you do not have room for items 1-3 and quality print is important to you…redesign the piece.