Densitometry as a means of SPC

http://www.flexoglobal.com/flexomag/08-November/flexomag-toc.htm

Density & Dot Gain

Please, submit any comments on the article in this post.

http://www.gravurexchange.com/gravurezine/0804-ezine/ploumidis.htm
http://www.flexoglobal.com/flexomag/08-July/flexomag-ploumidis.htm

Quality Control & The Role of Color Management

Hello all,
I throught to provide this area in case you would like to comment on my articles published on GravurEzine and FlexoGlogal.
http://www.gravurexchange.com/gravurezine/0803-ezine/ploumidis.htm and/or
http://www.flexoglobal.com/pdfs/01-May%202008.pdf

I chose the topic of Quality Control as a means to emphasize the importance on color management and to provide an outline of the topics i'll be discussing.

Regards,
-D

Inkjet Proofing

Hello again,

The most interesting area I've been involved during these months of absence from the blogging community was inkjet proofing. There are plenty of variables involved in this process.

The simplest and most reliable way to inkjet proofing is continuous tone proofs. I am not very interested in discussing continuous tone proofs, as there are plenty of software packages that are able to provide a reliable proof with certain pre-engineered color management algorithms. They certainly need their mastery and a critical visual evaluation, but the calculations, after approximately three iterations of optimization, can provide results that are really close to a visual target. In that, either EFI's rip or ORIS Color Tuner, provide very good results (i'm not all inclusive here... this is just what i tried). Then, certain adjustments for visual match give a very good proof.

Where do the complications of inkjet proofing start?

1. The white point of the target paper and absolute colorimetric intent.
2. Banding.
3. Halftone proofs
4. Hexachrome proofing
5. The color of black

To begin with:
1. WHITE POINT
Mapping the white point of the target paper through absolute colorimetric intent is not always perfect. Introducing the LAB value of the target paper into the proofing media alters the color of the proof. This is obvious especially in the highlight regions where the yellowness or blueness is introduced in the light areas. This problem is dealt with certain software packages where the user is able to affect only a small region of the color gamut. Relative intent works much better, but at cases where the target white points differs significantly from the proofing medium, there is a discrepancy that might be confusing to the press/customer. It is nevertheless astonishing that the profiling software is not able to map the white point with relative ease. I could make a wild guess and say that this is being caused due to chromatic adaptation, but it would be wild and uneducated.

2. BANDING
I've seen certain banding problems that can only be associated with the color algorithms of certain packages or with the ICC profile itself. I would guess again that the more you tweak a profile the more likely it is banding to occur. Then again, the way the software packages work, by trying to minimize the color difference from the profiling target to the media profile, some clustering of the target LAB values is not unlikely.

3. HALFTONE PROOFS
This is where the party starts. The rest is manageable. There isn't a software that is able to effectively color manage halftone proofs. EFI's rip offers a color management option with halftoning, but my experience is that the moire you get is unsaleable! Then again, you can separate the digital file to 1-bit TIFFs and try to work them around. How is color management applied to four channels that are a. already separated into 1010101 dots and b. translated into 7 or 8 eight channels based on the proofer? Only solution that we came up with was through editing the source profile. Results were decent, but unless my vision is all messed up it takes about 40 iterations, and then again... at some point... you just cannot get any closer to the target, since the above-mentioned clustering that would bring all the colors closer to the target LAB values is impossible through the naked eye. This might be a thesis topic for my valuable friend Arvind (http://cias.rit.edu/printmedia/03_programs/grads/karthikeyan.html) who's been helping me with proofing.

4. HEXACHROME
Ha! Forget about it, especially if you want halftones or spot colors as 7th or 8th channels. Then again, even halftone offset printing is kind of weird...

5. BLACK INKS
This is a colorant issue. Again, depending on the software, the color of the black might be unmanageable. I don't think that EFI has a good solution, as I was getting the cast of the inkjet proofers inks, and that was different from that of the ink supplier. I haven't seen such an issue yet with ORIS software.

In conclusion, inkjet proofing can have very good results in continuous tone proofs. My belied is that inkjet is the way of the future though, and that film based proofs with significantly lose their value, even if they provide higher stability and larger gamut (plus halftoning!!!) at this point of time. It is up to smart color scientists and engineers though to come up wth the algorithms that would eliminate all or some of the factors I discussed above, and -my belief again- that this is only a matter of time.

-D

PS> I would like to mention and thank my friend Rob Seckendorf of Color Correct Solutions, who has been providing his support and expertise with inkjet proofing (www.colorcorrectsolutions.com)

It is what it is

When I visited TAGA I saw lots of concern about the G7 method of calibration. I only saw some results, and one paper saying that ISO actually outperformed G7.
Still, I was frustated by the general feeling of discontent about the G7 process. Sometimes it sounded like unreasonable, and sometimes I was hearing people that I overall trust to say that it doesn't work; yet I saw no valid research.

There, I made up my mind: I would try it out for myself and see if it would work or not. And I did.

I setup my roller stripes, drained my fountain solution and cleaned up the 64" beastie and there we were: ready to run with our hybrid ink set... shooting for grey.

To make a long sorry short, the results were disappointing. As with everything in litho, there can be numerous reasons.
1) idealliance software on shadows
2) measuring devices & idealliance software
3) natural press variation
4) ink set

I'm going to proceed from bottom to top:
4) We used the hybrid process ink set and the hybrid hexachrome ink set. On the color analysis tab we were getting the LAB values for paper grade #1 stock and the respective solid CMY. However, is the hybrid ink set supposed to be matching the NPDC curve, and whatever calculation thereafter? My speculation would be that the curves and calculation thereafter were done based on press runs with conventional ink sets. I might be lacking in theoretical understanding of the G7 calibration, but how can we use one set of curves for all the processes when there is a significant difference in dot gain between hybrid process, hybrid hexachrome (just the CMYK out of it), and conventional process inks? Should I be expecting to get my gray balance? I didn't... and this might be one reason. Even still, wet trapping our inks would allow us to be close to conventional TVI, and thus the software should work.
3) You know ;-)
2) I was getting significant differences in the suggested plate curves when measuring the targets with different measuring devices. Does the idealliance software work only with DTP70 and Eye-One? What prohibits it from working with x-rite 530 or spectroscan. Why in this earth do i get a difference of 20% on the yellow midtones between different devices? Praise the Lord! I guess the problem is that x-rite bought Gretag or WHAT HAVE YOU (i admit... i'm frustrated).
1) OFF.

SO... after such knowledge what forgiveness...

There are consultants who vouche that it works. I believe them.
There are other people who vouche that it doesn't work. I believe them too.

Thing is, at about 11:00 pm yesterday (and after missing a girl's birthday due to working late), I decided to get rid off all the software, match my densities, and calculate the curves on my own. I got my gray balance nice and neat! Am I G7 certified? I am 'Dimitri' certified. Why? I didn't use the software. Is grey balance tied up to G7? We were using the Brunner system before G7 and we were grey balanced already.

There is a long way to standardization... a long damn way and billions of variables to take into account. There is no magic; there is no beauty! Even if someone comes up with the perfect solution, nothing assures that we have the variables of the process under control. We are drifting and misjudging the effect as the cause... basic human fallacious reasoning... the dream within the dream... (i used to read Nietzsche instead of doing my homework at highschool).

What is the main problem? Calibrating something for certain conditions, or fixing these conditions? And I mean ink-water balance...

Here's my frustated plan of action:
1) trust noone
2) set up ISO densities and possibly TVI
3) get grey balance
4) train our operators
5) get device link software or other software with smart color management options.
6a) and MOST IMPORTANTLY: prioritize press maintenance
6b) and optimize support systems and supplies.

-D

PS1> Good luck to all... let me know if I am easily getting frustated...
PS2> Some people don't like feta cheese even though they have never tried it.

The Devil and the Virus

We've got an old saying in Greece -maybe people have it in other countries as well- that says that there is a devil in every printshop, meaning that there are countless things that can go wrong.

Funny or not, I'm feeling that in order to be a printer you've got to have religious feelings: they are forced into us, and there is a certain amount of give-and-take with a higher deity when we are setting up a job. Are my prayers going to be answered, I ask myself time and again? is it going to work? is there a God above? What NOW? Is there a secret cord that David played to please the Lord?

Am I being sarcastic? Kind of!

Has anyone heard of having a malicious virus hitting the press? It CAN happen if your windows 2000 server is connected to a network. I guess, I could pose this question in reverse order, asking what is the least likely cause of press downtime. A damn virus! Presses connected to a network need Spyware and Virus protection I guess.

So be warned my fellow printers: don't put your pin in your press, and don't pay your bills online through the press console, and first and foremost, don't visit adult content sites between the scans.

-D

And one more thing...

... now that I think of it directed to TAGA administration peoples.

Please, publish the TAGA Proceedings online!!! Please!

This wealth of information is going to waste in this digital age and it is a shame not to utilize the technologies available to help researchers further their work and professionals get answers. I became a member hoping to be able to access these issues and I cannot (unless I am doing something wrong). Not even the abstracts!!!

I'm not strong with economics and market prices, but you could sell each article for like $12-15 to non members, and $8-10 to members... or something similar. IS&T has a model website for it, where we can review the abstract and go on and purchase the article.

I would love to have the TAGA proceedings online. Please do something about it. I volunteer to help.

-D

Summing up TAGA 2007

Well... I had a nice time myself. The hotel bar was pretty good and I hit Pittsburgh on Saint Patrick's day!

Seriously now:
I would love to see more attendants next year in SF. We were about 170 people. We can be more. There are lots to learn. Technical people can have a serious benefit in attending this meeting: Networking! Not so much in terms of making friends, but in terms of meeting the people that can provide an answer to their questions when the need arises. As Mr. B. Blom put it, throughout his years at TAGA that was the main benefit: the people! Well, you got to be a printing nerd too to enjoy it.

The students were an enthusiastic crowd as well (getting lost in conversations about density at the bar is absolutely awesome). Compliments on Cal Poly on winning the brochure award - of which I am particularly proud since my company happened to design and produce their packages; which I only became aware at the conference, mainly because I am knee deep in our litho department at work.

Top topics of what I have retained:
#1 There is a lot of research going on on RFID. I hope it works out.
#2 There is another definite tendency to move to colorimetry for process calibration, and why not control. It shall need a huge effort on technical and managerial level, but it can work and provide solutions were density fails short (workflow solutions and color portability, as well as spot colors I would say on top of my head).
#3 I retain the research on the low VOCs. It is important to be prepared for it... if possible!
#4 The discussions and presentations on colorimetry issues and ICC profiling (including mine) however -I have to say- are falling short of the research that is going on in imaging and color conferences. We cannot expect the printing industry to lead in this field, but we can definitely expect to publish some research on the applied elements of ICC profiling and colorimetry for the printing processes.
#4a. we need to work on color difference equations
#4b. we need to establish a linear relationship between IFT, density, dot gain and CIELAB.
#5 Paper companies were criticised -and forgiven nonetheless since it is realized that they are bound to price demands- for UV brighteners, standardization of white point, and to a lesser extend paper properties that affect printability for various processes.
#6 G7... well... read previous post!
#7 Process variation issues discussed and researched and found awful. Well: welcome to litho... and as professor Chung would say: variation is the 'nature of the beast'. Pretty much: 0.10 density units is something very common as natural variation, and it results in about 5.0 DEab... reminding me of William Burroughs novels, where drunk and angry press-boys wonder on saliva and the loose limbs of grey crocodiles and pink elephants (huh?!?)

Farewell,
-D

G7 on TAGA

There was lots of discussion regarding G7 on this years TAGA conference. There was a session devoted on it. Everyone could chip in a comment. Most of the comments were against it. Why? There was only one published paper on it. Apart from this, there was no published research to substantiate the unfavorable comments. The research community should be the first to know that we need to back up our claims with research.

Being on the field right now, I NEED to be able to read published results regarding any new technology that can help me be more productive, and I need it from this community. Going into endless discussions about how and why it doesn't work is totally worthless, if not damaging.

The main argument against G7 is that it doesn't take into account the color of the inks. Profiling does. Even more, device link profiling is able to calibrate the presses and in the same time take into account the colorants. I buy that. I have tested device link profiles and I know that they are able to do an amazing job. Within the next month, I will test out G7 as well and see for myself if it works.

I have to comment on Dave McDowell's efforts (who was awarded for his immense contribution to the industry) to close the gap between the group that is for and the group that is against G7. Dave, and the particular ISO committee are trying to put G7, ISO 12647 and device link profiles into agreement taking the strenghts of each method into account. I would love to see the ISO document and I hope that it comes out soon enough.