Standard ink densities?

[Deleted member 16349]

.

In any event, I look forward to the day when we finally start using the tools available to us and eliminate color bars and SID target patches altogether. While it had value in the old days, measuring a proxy target like a color bar when the actual live color target is right beside it seems quite foolish today given gthe technology we now have.

best, gordon p

my print blog here: Quality In Print current topic: naming image files

Nice examples. Gordon, do you use those perfumes? It may also be that my experience tended to be with packaging and not commercial printing. The packaging that I was involved with tended to print with stronger colours. More mid range and higher screen percents and higher densities.

If you are refering to measuring the image and controlling the press from that, there is the problem of what to adjust. It is not a simple problem of determining which CMY ink channel to adjust from a measurement of the image directly. There are systems that claim to do that but it is not trivial or cheap and may not be totally effective.

Gordon, have you changed your views? You used to agree that measuring SID was for process control. Are you saying now that one should use images for process control which can have all kinds of factors affecting the viewed result.

 

[meddington]

I suspect thyat the +/- .05 tolerance simply was the result of the opinions of a group of "greybeards"

What color is your beard Gordo? Looks like it might measure a zero a* & b* or thereabouts.

In any event, I look forward to the day when we finally start using the tools available to us and eliminate color bars and SID target patches altogether. While it had value in the old days, measuring a proxy target like a color bar when the actual live color target is right beside it seems quite foolish today given gthe technology we now have.

Like a Prinect Image Control system?

 

[gordo]

Nice examples. Gordon, do you use those perfumes?

I just stuff some seaweed under each arm pit and I'm good to go!

It may also be that my experience tended to be with packaging and not commercial printing. The packaging that I was involved with tended to print with stronger colours. More mid range and higher screen percents and higher densities.

If I'm not mistaken, the higher the density the less impact an incremental amount like .05 would have.

If you are refering to measuring the image and controlling the press from that, there is the problem of what to adjust. It is not a simple problem of determining which CMY ink channel to adjust from a measurement of the image directly. There are systems that claim to do that but it is not trivial or cheap and may not be totally effective.
Gordon, have you changed your views? You used to agree that measuring SID was for process control. Are you saying now that one should use images for process control which can have all kinds of factors affecting the viewed result.

What I'm suggesting is that it would be interesting to see print manufacturing controls/metrics etc. being rethought in the light of the tools we now have rather than simply continue to digitally entrench 19th century methodology.

Yes I would like to see the live image area being used as both the target as well as the possible source for measurement. You are right that it may not be possible to totally eliminate some kind of live image independent targets. I don't know. But I do think there should/can be a better way than what is now being done.

best, gordon p

 

[Deleted member 16349]

I just stuff some seaweed under each arm pit and I'm good to go!



If I'm not mistaken, the higher the density the less impact an incremental amount like .05 would have.



What I'm suggesting is that it would be interesting to see print manufacturing controls/metrics etc. being rethought in the light of the tools we now have rather than simply continue to digitally entrench 19th century methodology.

Yes I would like to see the live image area being used as both the target as well as the possible source for measurement. You are right that it may not be possible to totally eliminate some kind of live image independent targets. I don't know. But I do think there should/can be a better way than what is now being done.

best, gordon p

Gordon,

BC seaweed is the best that money can buy.

The higher the density has more impact on the increase on mechanical dot gain IMO. All along the Density/Ink curve an increase in density, say 0.05 pts requires a greater and greater amount of increase in ink film. This means that at higher densities, the absolute amount of ink increases more for the same density increase.

Look at the Density/Ink curve and you see that it arches over and ultimately has a maximum density value. It can be seen from the curve how more and more ink is required to increase the density. It is easier to squeeze out ink from a thick ink film on the dot than from a thin ink film. Anyway, that is how I see it.

I agree that there should be better ways. I just don't believe that it is the measure and adjust method. If one thinks of printing metallics or opaque inks, the measuring of solid prints to control the press, would be a problem.

Why measure at all? If one feeds the ink at the right rate, then there is no need to measure. In principle, there would be no need for any control bars.

Measuring the image is not a bad idea. It would be good for verification that nothing was going wrong but I don't think it is a good idea for control. Closed loop colour controls basically adjust the ink keys, etc. to adjust for variations in the rate of ink feed into the roller train. Make the ink feed positive and then you don't need closed loop. Goss's positive ink feed system does not require closed loop. One of their marketing slogans has been "Set and forget". So in a way, it is already being done in the industry. It is just not done well enough for technical reasons that I have written about before.

There will be better ways, hopefully for commercial and packaging printers. The ITB is just one way to go down that road.

 

[Deleted member 16349]

Like a Prinect Image Control system?

I hope I am not confusing technologies here.

If I remember correctly, the PIC system looks at the image and makes adjustments to the CMY ink values in line with the image to get the image colour correct. It is not looking at the whole image but only a smaller section of the image. Some area of most concern.

In getting the target area to the correct colour, it is potentially also moving other areas off colour.

This seems like a good technology but one can argue that it is an expensive way to get around the problem of the prepress image not being good and the problem of the press not printing consistently at all points on the image. The second issue can be due to problems in the even inking of the plate.

I suggest that a better solution is to solve the prepress errors and the problem in the press with uneven inking.

I would be very surprised if this technology was offered to anyone who had the Anicolor press, where the plate is basically inked evenly and therefore the profiles for that press should also be more predictable.

Get the core technology right and then one does not need the expensive band aid technologies.

 

[gordo]

What color is your beard Gordo? Looks like it might measure a zero a* & b* or thereabouts.
Like a Prinect Image Control system?

Dang! Where's my Grecian Formula? LOL !

Yes, something like the PIC system - but more sophisticated.
I don't know enough about it to speak intelligently about the PIC system in depth though, as I've only had a brief experience with it - at GATF, where it was used to try and balance a press sheet that had a mix of screening (AM/XM and FM). Unfortunately, it failed. It was thought that the reason it failed was because the FM side of the sheet did not react in the same way that the AM/XM side did to SID moves that the PIC system calculated would be needed - so it gradually made more adjustments that just made the FM color side go further and further away. There's also very little info on HD's web site.

Basically, the notion could be to scan the proof (since that is the target for the press) possibly at the press during make-ready, then scan the sheets as the press is coming up to color and compare the scanned sheet to the scanned proof. Software might then compare the data of those two with the bitmap data that's on the plate to determine what would happen to color if SIDs (effect on solid ink areas and effect through the tone scale for single and overprinted colors) would be changed. So, as the system is used, it would learn and hence its predictive ability would become better.
The system could then identify and report on color area differences between proof and press sheet. Conceivable a print buyer could have previously indicated to the printer which image areas were color critical and which were not - perhaps even indicating the acceptable deviation. That info could also be used by the system to determine whether a SID move that brought a color into spec would result in a color deviation elsewhere to be out of spec.
Since the system "knows" what the bitmaps on the plates are, while doing the color check, the system could also check for and report defects such as hickeys.
All this information could be made available on-line to stakeholders, which in turn would allow for remote press color approval. I would also mean that the person doing a color approval wouldn't need a color calibrated screen. The could do it using an iPod.
Finally, the system might generate a report that certified the presswork to proof match.

I agree when Erik says to get the core technology right so that one does not need the expensive band aid technologies, however there is still a need to achieve sellable presswork with the least amount of wastage as well as to certify/validate that presswork meets expectations.

best, gordo zero a* & b* beard

 

[dimitri]

There are some closed loop color control systems for web presses that take an RGB image of the actual job, on chosen areas, and make adjustments thereafter.

KBA's press consoles for sheetfed, Densitronic, also allows to select areas of the print areas of the job to take spectral or density maesurements. It is a more lengthy process, since the scan takes longer, but it allows control of selected regions. It is really useful for controlling spot colors that you actually do sell to the customer.

 

[vaithi47]

the density values depend on the stock and the ink .the density which gives the standard Lab values within adelta e of 5,which gives the maximum contrast when measured with the densitometer is the correct density to run.further the density combinations should give the correct grey balance over 5% to 95%, as this depends on the press conditions ie the dotgain values.

 

[meddington]

.the density which gives the standard Lab values within adelta e of 5,which gives the maximum contrast when measured with the densitometer is the correct density to run.

Let's not forget the often omitted delta h of 2.5 for solid primaries. A delta E76 of 5 for solids in an of itself is a barn door and can result in a density spread approaching 0.40 in some cases between upper and lower limits. Lowest delta e is also not always the best goal, but rather concentrating on lowering the particular a*, b* metrics appropriate for each ink, while also aiming the secondary overprints toward their "targets".

further the density combinations should give the correct grey balance over 5% to 95%, as this depends on the press conditions ie the dotgain values.

Often there can be a compromise between targeting solids/secondaries and gray balance (not to mention between target dotgain and target gray balance).this is where a decision could be made to adjust curves for gray balance as well as tonality.

 

[Tarun Chopra]

There are some closed loop color control systems for web presses that take an RGB image of the actual job, on chosen areas, and make adjustments thereafter.

KBA's press consoles for sheetfed, Densitronic, also allows to select areas of the print areas of the job to take spectral or density maesurements. It is a more lengthy process, since the scan takes longer, but it allows control of selected regions. It is really useful for controlling spot colors that you actually do sell to the customer.

Its kind of interesting to know about these technologies, but how does one control density (ink film thickness) in a specific inkzone from gripper to tail end of the sheet in a multi-up design to control color variation using these technologies and how effective are they?

To the best of my understanding the density (ink film thickness) variation between gripper to tail end of the sheet is an inherent flaw of the present inking unit design of printing press which is usually exaggerated by other variables like temperature, emulsification etc, that's why there exists a tolerance of 0.05 (not sure on this) density units on all modern presses.

Does this technology deliver what we are made to understand? Real world observations will be of great help.

Thanks

 

[dimitri]

I completely agree with you. It is actually very frustrating...
These are measuring technologies, not related with the ink unit design, and as such they cannot correct its inherent flaws, just measure it.

I guess we have to simplify our designs and say to our customers we cannot do multiple ups

 

[Tarun Chopra]

Why invest in expensive measurement tools to read across the sheet without any press control is the big question. My question was directed mainly with packaging printers in mind who have invested in such technology... how are they justifying such investments.

Thanks

 

[dimitri]

It has been useful with monitoring spot colors at different locations throughout the sheet. Being able to have a DE reading on the monitors have helped the operators catch non-conformities. Just an extra set of eyes to make sure we do not ship non-conforming color. I do not know about investing on it though. A choice to get such systems hasn't been made with this perspective in mind, at least in my case.

As for the RGB camera, I think that this applies mostly on closed-loop web printing, newspapers, magazines. I guess it is a selling point directed towards accurate reproduction of ad colors... and you could compromise the reading from the tail edge of the sheet to get the density you want on the location of choice.

 

[Deleted member 16349]

I

To the best of my understanding the density (ink film thickness) variation between gripper to tail end of the sheet is an inherent flaw of the present inking unit design of printing press

Tarun,

If you are having this problem on your press, maybe I can suggest something to help or at least some interesting test for you to do.

Can you send me a sketch of your roller train? There might be some things that can be done. I can't promise success but it could be worth a try.

[email protected]

Erik

 

[Tarun Chopra]

Erik,

Density variation across the sheet height is some thing I have seen with almost every machine that I have tested. The density difference is 0.04~0.06 between three points of the sheet ie gripper end (hi density), center (low density) and tail end (hi density) of the sheet (in a straight line) is usually seen with new presses. The engineers change the behavior based on oscillating roller adjustment changing it to low density at gripper end, hi density at center and low density at tail end.

Your pointer is forcing me to think if this is standard behavior of presses, have you not observed this in day to day working?

I cant do the test on a Heidelberg MOV 19x25 press, I will have to try and get the ink roller train sketch for the same but I will need sometime for it. If you have the idea on this press then I can try it out for sure

Thanks

 

[Alois Senefelder]

Heidelberg Roller Train

Heidelberg Roller Train

Hello everyone,

I'm posting a PDF of M series Heidelberg Press, roller train, hopefully be of some use.



Regards, Alois

 

[vaithi47]

the density variation between the gripper and tailend can be adjusted by setting the oscillation roller starting and ending timings. in heidelberg this can be done very easily by following the operators manual.a variation in the region of +/- 0.05 can be ignored

 

[Deleted member 16349]

the density variation between the gripper and tailend can be adjusted by setting the oscillation roller starting and ending timings. in heidelberg this can be done very easily by following the operators manual.a variation in the region of +/- 0.05 can be ignored

Can you clear up some confusion.

Are you talking about the oscillation of vibrator rollers that move laterally or the timing of the ductor that moves from the ink fountain roller to the roller train?

Sometimes printers use terms that mean different things in different parts of the world.

Thanks.

 

[vaithi47]

is there a relationship between the ink film thickness and density? is it true that by using a high pigmented inks you will be able to print with a thinner ink film and this helps in printing with less water therby avoiding all problems associated with ink water balance.can anybody throw some light pl

 

[vaithi47]

i am talking about the vibrator which moves laterally ofcourse