TVI (Dot Gain)

#48: Make Proofs That Match Your Press

by JimRaffel on February 16, 2007

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.

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Continue Reading 1 comment }color, color bars, delta E, GRACoL, L*a*b*, L*C*h*, measurement, process capability, proofing, TVI (Dot Gain)

#44: Why process control works

by JimRaffel on November 17, 2006

Earlier this month I was visiting a customer who utilizes multiple ColorMetrix licenses to monitor and control; plate making; proofing; and pressroom. Several years ago this customer used ColorMetrix in his plate making operation to uncover a processor replenishment problem that not even the plate vendor was able to unravel. During this visit, he told me about a recent experience involving a pressman who came to him asking for a new plate so that he could achieve a match on press. For some reason he could not get the cyan to fall in appropriately. My customer consulted his ColorMetrix plate database and confirmed that the plate was properly made. He then measured a press sheet provided by the pressman and compared it to his historical data for that press and paper combination. The cyan dot gain (TVI) was about 10 points away from the expected values.

He agreed to make a new plate with an adjusted curve in the interest of getting the job off press with acceptable color, but also suggested the pressman take a long hard look at the cyan printing unit. Before the plate was even processed the pressman returned and said to never mind he had uncovered a roller problem in the cyan unit.

Yes, all the data collection our client does takes time and effort, but what is an hour of your press time worth? He pointed out that this is not an isolated occurrence. Just having a densitometer and measuring density and dot gain would have done no good in this situation. My customer and his pressman needed to know what the expected density and dot gain would be on the press and paper combination being run.

By simply measuring the OK sheet from most jobs, within 30 days you will have a very substantial database to fall back on when problems like the one illustrated above occur. So, process control is not free, but instead an investment with a fairly easy to calculate return. There are more examples of how process control has saved our clients money at here at JimRaffel.com, so feel free to read the archives.

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Continue Reading 0 comments }blogging, density, process capability, TVI (Dot Gain)

#32: Tales from the Press Trial (Part 2)

April 28, 2006

This week I will be providing more information about the MacDermid Printing Solutions Stabil-X press trial April 17th and 18th . This week I will review the variation data from two of the trial conditions: STX opt – Stabil-X blanket run at optimum packing level Press std – The set-up of the press when we [...]

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#31 Tales from the Press Trial

April 21, 2006

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. We ran five different conditions during the course of the trial. All [...]

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I still love the smell of ink in the morning

April 19, 2006

Over the coming weeks I will be writing a great deal about my last two days in Chicago. Kevin Kocher of MacDermid Printing Solutions (offset blanket manufacturer) invited me to a press trial of their new Stabil-X blanket. So, right about now if I was one of my readers I would be thinking how exciting [...]

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#27: Measuring TVI on Inkjet proofs is Meaningless

March 9, 2006

Part 5: I should start by saying I have covered the topic of using graphic arts densitometry to evaluate inkjet proofs once before. Back in July ’05 GN#5 addressed this same issue so you may wish to refer back to it. I considered changing this topic, because the title is a bit inflammatory. Understand that [...]

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#26: Density is king

February 28, 2006

Part 4: TVI is not measured it is calculated from density which is king. All the other values our modern densitometers display are simply calculated values from the densities the instrument measures. In short, all a densitometer does is transmit a predetermined amount of light and then measure how much comes back to the instrument. [...]

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#25 TVI Notebook (part 3 of 5) TVI is not a bad thing

February 21, 2006

Part 3: TVI in and of itself is not a bad thing: Back when TVI was called Dot Gain, I remember going into print shops and having pressman tell me “No, we don’t have any dot gain.” This was not ignorance (they knew they did), but instead a misconceived notion that TVI was a bad [...]

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TVI Notebook (part 2 of 5) GRACoL & TVI

February 14, 2006

Part 2: GRACoL 7 appears to be taking our pressrooms in a direction where TVI will be significantly less importance in monitoring production run stability. Instead GRACoL 7 is based on maintaining gray balance utilizing density and L*a*b* values. Over all, I feel this is the right direction to go and from what I have [...]

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#23: TVI is a better term than Dot Gain

February 7, 2006

This is Part 1 of a 5 part series from Jim Raffel’s TVI notebook. Part 1: Tone Value Increase (TVI) really is a better term than Dot Gain: My short answer for this is that a densitometer (or spectrophotometer acting as a densitometer) does not actually measure dots, so how can we really call it [...]

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