Don hutcheson's equations and npdc graphs, and color management

[disbellj]

Hello all,

My name is Don Isbell, Jr.

I have not been in prepress or printing for about a year now (I am now a Forex trader, Don Isbell, Jr. | LinkedIn), but was looking at an Excel document that I made years ago, and converted to Apple Numbers.

Background:

I've kept up with GRACoL since its beta stage, and although this is old stuff, it is and will be relevant in the future as time passes. I figure for many the Excel doc and understanding the graphs may be new, and helpful, so I am posting it here.

Understanding the graph:

INDEPENDENT OF PAPER DENSITY, there are CURVES (named Neutral Print Density Curve, or NPDC, that Don Hutcheson, www.hutchcolor.com, who also chaired GRACoL, and introduced NPDC to the community).

After seeing that SWOP separations could be printed without color managing CMYK, on coated (GRACoL2006_Coated1v2) or uncoated (Beta Uncoated 2009), and appearance between SWOP and GRACoL separations when printed on GRACoL, plus U.S. and Europe appearance was so close (within a couple percent), I was satisfied with my research.

Also, through experience I honored embedded RGB profiles, and used sRGB IEC61966-2.1 profile for RGB images received that has no ICC profile embedded, and had no color problems

Bottom line, I was able to easily implement GRACoL by first getting within LAB tolerances for solid C-M-Y-K-CM-CY-MY using an Eye-One with no filtration, then easily using the graph/the DENSITIES WITHOUT PAPER to GET my TARGETS, and getting TO those ON PRESS with a densitometer SET to give readings SUBTRACTING paper.

Consequently, this math is SO precise that it shows how the official ICC profiles FOR EACH PAPER TYPE could be tweaked to better conform to the NPDC for that particular paper type and density range that the paper has (in fact, most color "problems" come down to coated papers can hold higher densities and result in brighter colors than is possible on uncoated paper). COMMON PROBLEM: MISUNDERSTANDING BY PRINTER AND/OR CUSTOMER OF WHAT IS ACHIEVABLE ON UNCOATED PAPERS AND THEY MAY NEED TO USE COATED PAPER AND NOT UNCOATED TO GET TO THEIR COLOR.

This graph and the target densities at 25, 50, and 75%, with VISUAL way that these ICC profiles interact with graph of GRAY DENSITY is basically one tool that can be used to not only understand color and printing, but can be used to correct printing too.

You can get the original Excel document (in Excel format) at:
COMPARE NPDCs - DON HUTCHESON FORMULA.xls - 4shared.com - online file sharing and storage - download
COMPARE NPDCs 2009.xls - 4shared.com - online file sharing and storage - download
TVI 2009-ADOBE GRACOL TO GRACOL.xls - 4shared.com - online file sharing and storage - download
TVI 2009R-ADOBEGRACOL TO GRACOL.xls - 4shared.com - online file sharing and storage - download

There are others I made, but I can't find them, and they are superfluous.

Thanks goes to Don Hutcheson for making this available freely to the community, so that we can get to ISO standards in a more precise way, even more precise than ISO defines Thanks to Don for doing what he could to get us on the same page. I am just a lover of color, and tested and verified for myself and the community what Don was putting forth. I like it a lot. I could be a color consultant, but would rather trade. I hope these documents help you, like Don did, and like I have always tried to do on here when I participated - given freely - and I just love math, so checked his math and see the great benefit of G7 process/graphs.

You'll also see that I use TVI (tone value increase aka dot gain) to compare Adobe and GRACoL ICC profiles using math from color scientist Bruce Lindbloom, www.brucelindbloom.com. These are ONLY VALID for comparison of TVI from two papers with these characteristics:
Printed solids and paper color with very close LAB values between the two papers.

I just like TVI (I'm old school), but see it also is not necessary with the NPDC graphs. So it's here FOR TEACHING/COMPARISON PURPOSES ONLY.

Kind regards,

Don

[J]

Have a consultant create a print methodology and what you get is a methodology that only a consultant can implement. :-P

J

[disbellj]

Are you saying can't implement this? OK. I found it quite easy myself. Do you have questions?

Kind regards,

Don

BTW, I'm no consultant, just said with my knowledge of color all around, I could be one. 15 years was enough for me in prepress and color. Don't want to be in the industry myself, but still have friends I made in the industry and an understanding of print process from beginning to end. Have a more fulfilling career for me now IMHO. Just wanted to share stuff I consider valuable from my previos career. Maybe it's only valuable to me. BTW, on a press, you get to solid densities you need to reach LAB target (yes, it's possible, I did it), you move just the 50% on plate per NPDC chart, and rest falls into place on press. On an inkjet printer, just use GRACoL as source for CMYK sent to printer, sRGB for source on RGB sent to printer, and convert to printer profile as destination, and you're done. Using the Adobe North American General Purpose defaults is efficient. Sorry if I made this sound difficult.

Happy New Year.

Have a consultant create a print methodology and what you get is a methodology that only a consultant can implement. :-P

J

[gordo]

Are you saying can't implement this? OK. I found it quite easy myself. Do you have questions?

I have some questions.
But first an observation.
Dot gain is not a print production target. Tone reproduction is. i.e. it does not matter what dot gain occurs as long as final presswork tone reproduction aligns with the industry standard.

1) Is there an ISO specification for tone reproduction? ISO 12647 is very unclear on this point. Can you provide insight?

2) How does the NPDC tone curve compare with a tone reproduction curve compared with ISO 12647. I.e. when a press is set up according to G7 what does the tone reproduction curve look like?

3) Do you achieve grey balance if you simply follow ISO 12647 vs G7? AFAIK this has not been tested.

4) Since G7 only deals with gray balance, not color, has its premise that grey balance/NPDC, results in a common appearance across different print methods ever been formally tested? AFAIK the answer is no.

best, gordo

BTW several vendors including Heidelberg, 3M, and Creo, and others, all had/have grey balancing software.

[Erik Nikkanen]

1) Is there an ISO specification for tone reproduction? ISO 12647 is very unclear on this point. Can you provide insight?

.

Gordon,

This paper might be related. As I understand it, conformance to ISO is not so good. Maybe I am not reading the paper properly but that is what it implies to me.

http://cias.rit.edu/~gravure/bob/pdf/picrm201108.pdf

There is also another paper, not published yet on Robert Chung's RIT site that seems to specifically refer to the G7 data. That might be of interest when it finally is provided there.

See: Bob Chung

It is a nice idea to have standards or specifications or methods but in the end if a large group of printers can not meet them, there is something wrong.

As you know, I think it is due to capability issues which are not being addressed.

[disbellj]

gordo,

How's it going my friend? Long time.

This is my understanding, perception and implementation of freely available math in G7 beta original documentation, as well as updates up to end of 2010, and freely available math on the internet at a few different sources that helped me implement it, in essence building my own software that is like IDEAlink Curve. We have targets, we have tolerances, so if we have Excel, willing to put in some time, then we can build what we need. Thing is, it took me some time to get all that together and implement, so for others I ended up saying that the IDEAlink Curve software was worth buying, and that I didn't want to cause conflict by making my own version available publicly basically. Using the graphs will get you there without my automation as far as NPDC. But the first part is important and must not be overlooked.

In a way, I see what you're saying about dot gain. But that is only part of the picture. Allow me to try and simplify by an example.

Let's say we have a tent to put up. We have the tent, four stakes, and a pole for the center that makes the whole thing stand up straight. We must have all parts for it to work, right? Right.

Tent = Laid out flat = same dot response on plate as in file, or in other words 50 in file comes out to 50 on plate.
Four stakes = Four primary solid COLOR (LAB). Get C, M, Y, & K . This is the first part that must not be overlooked.
Center pole = Gray tone scale response curve. What gray is wanted on press for K or CMY. What makes the whole thing "stand up". It's definitive. Not arbitrary in any sense.

ISO 12647-2 lacks, where ICC color management does not. With an ICC profile, you have an EXACT target.

When Europe came out with ICC profile ISO Coated, the primaries were not right, blue was purple on conversion from RGB to CMYK due to the software made to make the profile.

Europe updated to ISO Coated v2. GRACoL uses exact same four primary CMYK solid LAB targets as ISO Coated v2 (and same secondary CM,MY,CY overprints). So U.S. and Europe are same on solids. So we all have the stakes in the ground at the right place.

NOW, SINCE THIS IS TRUE, WE CAN USE NPDC OR TVI/DOT GAIN IMHO for next step. Europe uses TVI/DOT GAIN. GRACoL/U.S. uses NPDC (gray tone scale in DENSITY, for all paper types, using one graph which I've attached. In the Excel documents, you will see input printed LAB values for grayscale. The readings can come from PhotoShop using official ICC profile and Absolute Colorimetric Intent in color settings and reading Lab values in palette. The readings can also come from a GRACoL 7 proof. The readings can also come from a printed GARCoL 7 piece on press.

After the readings are obtained in LAB, the L* is converted to density using math. Then paper is subtracted, and finally the value is plotted on NPDC graph. Because of the "steps" in Excel, you also have the opportunity to bypass LAB, and input density values with paper and let program subtract paper and plot the result on graph, -OR- bypass LAB and density with paper input, obtain readings with densitometer set to subtracting paper.

Now with the NPDC graph, we have definitive targets. Funny thing is, difference between TVI Europe and NPDC U.S. is a "big" as a couple precent. Almost indistinguishable.

I would highly recommend deleting values from column named "PLOT ON NPDC GRAPH" for those printing conditions you don't want to see, and compare e.g. ISO coated v2 and GRACoL2006_Coated1v2, to see the difference in NPDC, and how close U.S. and Europe is. You can not save the Eccel document, and open again and compare another paper type, etc.

Like I said, I do have my own version of IDEAlink Curve that I built from G7 How-To documentation and freely given math in that document, on Don's website, but because of all the hours that went into me building it, I fully understand the price charged for the software, so recommend it to others for easy implementation of G7 for press. I myself, to automate the NPDC graph, had to find math for bezier curves and implement that, after finding and implementing math from most recent update to G7 that gives custom target values for solids and overprints - with new aim values dependent on paper.

Also, as far as others having gray-balancing software, unless you have a paper where the SWOP separations that prepress receives from customers has too high Total Ink Limit (too much ink for paper type), there is no reason to even touch the CMYK in the file. Everyone used old SWOP as their target when making these new printing conditions. It's all basically the same sep on different papers, with TIL in software only for papers who can't take the 300 TIL in the default SWOP profile.

Kind regards,

Don

I have some questions.
But first an observation.
Dot gain is not a print production target. Tone reproduction is. i.e. it does not matter what dot gain occurs as long as final presswork tone reproduction aligns with the industry standard.

1) Is there an ISO specification for tone reproduction? ISO 12647 is very unclear on this point. Can you provide insight?

2) How does the NPDC tone curve compare with a tone reproduction curve compared with ISO 12647. I.e. when a press is set up according to G7 what does the tone reproduction curve look like?

3) Do you achieve grey balance if you simply follow ISO 12647 vs G7? AFAIK this has not been tested.

4) Since G7 only deals with gray balance, not color, has its premise that grey balance/NPDC, results in a common appearance across different print methods ever been formally tested? AFAIK the answer is no.

best, gordo

BTW several vendors including Heidelberg, 3M, and Creo, and others, all had/have grey balancing software.

[gordo]

Thanks Don for the additional information, however, you did not answer my questions.
Unfortunately Don's math - e.g. NPDC ND = IF(SiCoY > 0, LOG10(100/SiCoY), 1000) - is beyond me.

best, gordo

[gordo]

[snop]
It is a nice idea to have standards or specifications or methods but in the end if a large group of printers can not meet them, there is something wrong.

Before you can try and meet them you have to understand them. IMHO, they are so poorly written that I don't think the average printer is able to understand them. Also, some methods, and core underlying principles are not based on any actual scientific testing. It is very often a faith-based manufacturing process.

best, gordo

[Erik Nikkanen]

It is very often a faith-based manufacturing process.

best, gordo

Amen and hallelujah!
Pass the CTP (collection to plate) and your printing sins will be forgiven and have faith that the customer will pay.

[disbellj]

Well, I use a microwave, drive a car, and use all kinds of things that I don't know how they work. So to USE this, it's OK if you don't understand the underlying math.

To know how color works though, you must educate yourself on properties of light - where color comes from, work that was done many years ago dealing with Lab, standard observer, etc., etc..- OR- you can have a mathematician make it easy for you.

When you use a spectrophotometer, you don't have to know math. You know that getting gray you need to deal with L* channel and not a* and b* channels, which should both be as close to 0 to get gray.

When you have IDEAlink Curve you don't have to know math. You want to BUILD what I've built? You must get some understanding of what it is you are doing (what IS the process you are implementing? I had to do that and wanted to do that to make sure it wasn't far from what we were printing, and actually was an improvement. The answer was yes on both accounts, so made sense to move to GRACoL 7 via my software I had built for verification and education purposes.

I would say if it's beyond your head, think of the solids needing APPEARANCE matched, then grays needing matched, then the rest falls into place, which it does and I know not from only theory but from implementation experience. Then 3/C density does tell you exactly which channel needs moved in C, M, or Y on press to get that channel to be equal gray with the others. I guess it comes down to education. Erik I respect but highly disagree with since he has yet to try and understand what I know, yet a chiller was all we needed other than a well maintained old 628 press to not only reach GRACoL, but hit every job within tolerance every day, day in and day out with little makeready time (50 sheets?). The tolerances are given for each 25, 50, and 75 by the specification.

I didn't invent it. I had questions and found answers through research. I proved to myself it works though. Can't prove to anyone else it works without basically giving away the final G7 calculator I built, which would make IDEAlliance upset I'm pretty sure. I give away for free what they charge money for because I built my own and want to? Hey the math was free, and I built it, so I can give it away. But it would kill IDEAlliance consultancy business. It would actually help people see how easy it is though in implementing once you have the software built. It's simple PASS/FAIL feedback. You are hitting the specification or not. No ambiguity about it. And if you understand Lab as the G7 documentation instructs, then you can either on the computer in Adobe programs set to Absolute Colorimetric and using correct output profile or on press change CMYK until Lab targets are hit or in tolerance for the paper type.

Printers are not meeting specification because they are cheap and don't want to spent a dime on color (what makes the tent stand up aka its their business to know color), yet can spend thousands when a press breaks. It's called bad priorities. My ex-boss after their business closed, called me to get new printer he worked at to GRACoL 7. I said I wouldn't do it for free since I was on unemployment. I never heard back from him. Let's say there is a reason I got out of the industry. Willful ignorance and being treated like what I said was a problem when what I had talked about gave them no color problems. Just like everything else. When the crap hits the fan, you are needed and they see you actually doing something. But when everything is running smooth, it must be by accident and couldn't have possibly been engineered/implemented that way so that you don't have problems <sarc>.

I had to bring the printer I worked for kicking and screaming (no, basically they saw no benefit until they were asked by a customer to do it, and I was ready because of my research, and was able to implement IN SPITE of their WILLFUL IGNORANCE of the subject matter). One bad run by the pressman who didn't use the SIMPLE instructions on a job (the thing didn't even look right, I knew it was going to be rejected, but he ran it anyways, and I wasn't the boss, so what could I say? Well, that one job was my years salary, so they had to let me go, and closed the company a week later. But hey, spending a lot less and obeying the simple instructions were too much. I say you get what you deserve when you don't care and you go out of business due to this. Who paid the price? I did. The one that implemented the specification that would have saved that company were it used on that particular job and the job not be ran by an emotional pressman that didn't care that day.

As far as your questions, I talked about dot gain and:
1. How the standard is not specific enough where the specification ICC profiles made from the standard characterization data (think press fingerprint) IS the proof in the pudding, and is not ambiguous in ANY way.
2. Look at the provided NPDC graphs to see the curve and to match that curve. Use the Excel sheets provided free by me to use Lab or density to do this yourself. You don't have to know math equation to see that what is input (your printing condition if you want) is not matching the specification, and exactly where in the tone scale.
3. Yes it has been tested. The result is called ISO Coated v2 ICC profile, and GRACoL2006_Coated1v2 ICC profile. Kodak has a solution that is most listed on the swop website as getting to #1 (coated aka GRACoL 7), and I used that solution to print proofs that I literally could not get wrong. The whole proofing system locked me in to the right proofs, and gave me no control, which because we were printing to specifications, didn't want prepress to have control in the proofing software (was and is not necessary. Just check match by Lab printed numbers once a week is all prepress has to do for proofer. For plates, it checks 50 dot. In Adobe software it uses the defaults. Since it is SO simple, I figured there would be no need for me. Is there many prepress jobs available? I handled the whole department by myself for 8 years, so it only takes one good person that can handle everything in prepress.

Kind regards,

Don

Thanks Don for the additional information, however, you did not answer my questions.
Unfortunately Don's math - e.g. NPDC ND = IF(SiCoY > 0, LOG10(100/SiCoY), 1000) - is beyond me.

best, gordo