German government comes to Heidelberg's aid

[Lukas Engqvist]

I'm sure that's not what you meant. TVI and dot gain are the same thing. TVI is just the new term for dot gain. The term (TVI - Tone Value Increase) describes more clearly what is being measured. Densitometers/spectrophotomers don't see dots but tones instead. Also, tone patches aren't always made up of dots. Measuring solid ink density, not TVI, gives an indirect measurement of ink film thickness. Measuring TYI is one way of seeing halftone dot distortion in the process.

I don't think it is just a new name, as you say there is a reason behind the name change. That reason is key.
Talking only of film thickness distorts the picture since "film thickness" at solid is not a full value of a printed page. Very little of a printed page is full film thickness, and so discussing how to acheive consistent results and simplifying to talk about just full tone film thickness I do not think will give us any answers. I guess you could say a 20% tone has and average film thickness, but that too is a simplification, it may work in primary colours, but again how much of a page is made up of primary colours? I do realise that changing TVI curves cannot bridge the differences between printing techniques, but are much more than just seeing distortion.

 

[Deleted member 16349]

As I say I have a practical approach, and there is much I can agree with. At the same time the "link" you refer to between the press and the image does include several stepps. As I understand the that is the function of the curves. The curves do cover the press and the plate making.

Lukas,

At this time and for practical reasons, yes you need curves but that is because the existing methods require that. It is the existing methods that makes things complicated and requires many steps that are not always predictable.

The kind of "link" I am thinking of requires no curves for plate making or anything. The colour output result is also the colour target input. This in principle would work for any inks, screens, paper, press combination. The physics of how the colour is printed are not considered, only the result. It gets around the complications of the physical process as long as the physical process on a particular press is consistent. If the physical process is not consistent then no method would work.

I am sure that there are a lot of issues to be considered in the development of such a method but the aim of that would be a system that is predictable, consistent and very easy for a printer to use. (No G7 required.) It is a method that can be tested today, in simple ways, to prove the concept.

But until there is an effort to change things, you are stuck with using curves.

 

[Deleted member 16349]

I don't think it is just a new name, as you say there is a reason behind the name change. T

TVI and got gain (from apparent dot area) are mathematically the same but philosophically different. That is true.

Most people do not understand how the values is derived. Most people do not understand some of the physical factors that affect the result.

Most people do not understand that what is measured and the resulting calculation of TVI is something that one can not see. As an example, if you are measuring to obtain the TVI for a magenta screen, the densitometer is using the green filter for looking at green reflected light. Can you see green in magenta? No. This is also true for SIDs. You do not see what you are measuring. It is good as a process control method to see changes in values. That is what it is good for.

In the past, the measuring of dot gain was done with black print and it does have a direct link to visual tone changes of gray. Measuring CMY is a bit different. With CMY you are measuring at only specific regions in the reflected spectral curves of these inks and it is a part of the curve that you do not see directly.

The technique is used as an indirect indication of changes in tone. Also this indirect technique does not tell you that the hue is changing as the screen values are changing. Good for process control but not for colour reproduction.

 

[meddington]

Lukas,

At this time and for practical reasons, yes you need curves but that is because the existing methods require that. It is the existing methods that makes things complicated and requires many steps that are not always predictable.

The kind of "link" I am thinking of requires no curves for plate making or anything. The colour output result is also the colour target input. This in principle would work for any inks, screens, paper, press combination. The physics of how the colour is printed are not considered, only the result. It gets around the complications of the physical process as long as the physical process on a particular press is consistent. If the physical process is not consistent then no method would work.

I am sure that there are a lot of issues to be considered in the development of such a method but the aim of that would be a system that is predictable, consistent and very easy for a printer to use. (No G7 required.) It is a method that can be tested today, in simple ways, to prove the concept.

But until there is an effort to change things, you are stuck with using curves.

Erik,

How is what your describing different from color management via device link (which can be implemented without the need for curves?

 

[Deleted member 16349]

Erik,

How is what your describing different from color management via device link (which can be implemented without the need for curves?

Probably not much different. I don't know the details of the device link method. The fact that such a method does not use curves tends to confirm that curves are not needed in a general solution.

But it is similar to the idea of using G7 but then using colour management to make things work better. If the intermediate steps are not sufficient, why use them when one might be able to get to the final result directly.

Rearranging existing technology might be all that is required to get to the goal. I suspect that it will not be as hard as most imagine. My primary interest is in getting the press problem corrected but after that I am curious to find out how easy one can make the prepress process more predictable and easy to use. That is just my personal priority view.

The industry has to decide that it wants to do something different and take some kind of action, instead the experts and gurus are just talking about the need for improvement. When they have been given opportunities, they never followed up.

 

[gordo]

A quote from Albert Einstein seems apt:

"We can't solve problems by using the same kind of thinking we used when we created them."

best, gordon p

 

[Alois Senefelder]

Clarification

Clarification

Hello Mr Erik Nikkanen, I am referring to Dahlgren's "Ink Metering System" for commercial presses [ US Patent 4,287, 828 ] --- your ITB and Dahlgen's IMS share similar INK TRANSFER MECHANICS.
The gist of your patent is that using a doctor blade metering the ink outflow, so that a
"Bead of Ink" forms and bridges the gap between rollers 12 and 35 ?????
The next difficulty is the "Plate Cylinder Gap", which can be 30% of the cylinder circumference. This gap presents an additional obstacle to providing an Even Ink Feed Rate,

30% gap = 108 degrees cyl. rotation 20% gap = 72 degrees 15% gap = 54 degrees

causing disturbances in Ink Film thickness propagate throughout the roller train by the intermittent rotation of Plate Cylinder Gap.

Regards, Alois
I enclose some PDFs

 

[Alois Senefelder]

Quote

Quote

A quote from Johann Wolfgang von Goethe

" All intelligent thoughts have already been thought: what is necessary is only to try to think them again"


Regards, Alois

 

[dimitri]

I do not think that this discussion is about color management, rather press engineering. Color management is very useful in a lot of forms, and will always envolve (so I could have a job). What needs to be looked at is the mechanical/chemical part of the press design so that color management can be more successful. What I mean:

What is the natural/inherent variation of density on a press sheet, on the circumferential direction of the press...0.08 points? How does that affect grey balance at the midtones... or the highlights... or both? How much density variation could you afford from left to right on a 50 inch sheet? 0.05 points? less? How much density variation can you afford from the beginning to the end of the run, and what does the craftsman have to doto minimize it?

At least in my world, in order to succesfully apply fancy color managed workflows, we need to shut down the press 2 hours per week to clean the rollers and reset the stripes, and then once per month we got to open each unit (14-16 rollers or something per unit) and reset the internal stripes...and i'm only mentioning the work on the roller train.

I do not have a lot of experience and I kind of live in my own world (with the exception of reading what is going on in such forums to expose myself to new ideas)... so I haven't seen what other printers are doing. But does anyone think that the press is a stable device? I mean, I am curious to know if I am mis-addressing the root cause of the process variation and this is the reason I have to spend so much time working on the roller train...

We need ideas to fundamentally decrease the variation of the printing press. We work with fluids, and this is kind of a curse. I was initially skeptical to Eric's arguments, but now I see that the engineering of the presses is poor, and we just accept it.... unless 0.08 density point across the cylinder (as an example) is only something that happens in my own world!

-D

 

[Deleted member 16349]

Hello Mr Erik Nikkanen, I am referring to Dahlgren's "Ink Metering System" for commercial presses [ US Patent 4,287, 828 ] --- your ITB and Dahlgen's IMS share similar INK TRANSFER MECHANICS.
The gist of your patent is that using a doctor blade metering the ink outflow, so that a
"Bead of Ink" forms and bridges the gap between rollers 12 and 35 ?????
The next difficulty is the "Plate Cylinder Gap", which can be 30% of the cylinder circumference. This gap presents an additional obstacle to providing an Even Ink Feed Rate,

30% gap = 108 degrees cyl. rotation 20% gap = 72 degrees 15% gap = 54 degrees

causing disturbances in Ink Film thickness propagate throughout the roller train by the intermittent rotation of Plate Cylinder Gap.

Regards, Alois
I enclose some PDFs

Alois, that is good that you have provided images and patent numbers. It is much easier to address your questions now.

There is no similarity between my ITB inventions and Dahlgren's invention. I had not seen this invention by Dahlgren before. I had seen a related invention of his where instead of a blade to meter the ink on the form roller, he was using another roller that turned in the same direction as the form roller (eg. both clockwise) and sheared a thin ink film on the form roller which applied ink to the plate.

Actually Dahlgren's concept is more related to Heidelberg's Anicolor concept than it is to mine.

Both Anicolor and Dahlgren's concept are an attempt to apply a uniform ink film to the form roller. So they are trying to be "constant ink film" concepts. My ITB does not try to control ink films at all. The ITB is a concept that transforms an existing ink fountain design into a constant displacement ink feed. Basically to feed constant volume of ink into the system. The ink films on the rollers are not necessarilly constant but on average the ink film printed on the paper will be due to constant volume ink feed. Constant volume ink feed does not mean that the ink feed is equal across the width of the press but that what ever volume rate is set, that stays constant.

The sketch you provided for my invention is only part of the patent drawings and it was just trying to show that the difference in the amount of ink metered by the ink key and the amount of ink metered and return by the ITB, would be the amount of ink that goes to the roller train. In other sketches, the ink that collects at the end of the blade gets pulled into a nip between the ink fountain roller and the pickup roller. That nip is actually a very small gap and the ink that gets pulled into this gap gets sheared down to thinner and manageable ink films that the roller train will continue to work on.

The gap in the plate cylinder is interesting but every press has to deal with a percentage on non printed area of the plate cylinder. If you had an image on the plate that was only 5%, then the total gap is 95%. 30% for the gap where there is no plate and 65% gap where there is no image on the plate. Managing the ink films on the roller train is the responsibility of the roller train design. It is important to design the roller train properly so that it prints evenly from top to bottom. This is still a problem in modern presses.

Wood's design for an inker is what is called an overshot ink fountain. Some newspaper presses in Europe still use this concept. Of course it also has no similarity to my ITB and actully applying an ITB to that concept is problematic. Normally what is on almost all modern offset presses is what is also called an undershot ink fountain. The overshot ink fountain has the keys on top and is not immersed in the ink, while the undershot ink fountain has the keys on the bottom and are immersed in the ink at the bottom of the fountain.

All these different concepts are interesting but one has to look very carefully at them to understand what they do and hopefully why they are good or bad. Both Dahlgren and the Anicolor are NOT positive ink feed systems and therefore will have more density variation than a positive ink feed system. The devil is in the details.

 

[Deleted member 16349]

I do not have a lot of experience and I kind of live in my own world (with the exception of reading what is going on in such forums to expose myself to new ideas)... so I haven't seen what other printers are doing. But does anyone think that the press is a stable device? I mean, I am curious to know if I am mis-addressing the root cause of the process variation and this is the reason I have to spend so much time working on the roller train...

We need ideas to fundamentally decrease the variation of the printing press. We work with fluids, and this is kind of a curse. I was initially skeptical to Eric's arguments, but now I see that the engineering of the presses is poor, and we just accept it.... unless 0.08 density point across the cylinder (as an example) is only something that happens in my own world!

-D

Dimitri,

The press is a stable device. One should not confuse stability with consistency. From a dynamics point of view, stability implies that if one leaves a system alone, it tends to stay where it is. It sits at its equilibrium point. Introduce a disturbance and that can move the equilibrium point to a different point.

With a press, there are so many potential disturbance factors, that the press will move from one equilibrium condition to another. It is then inconsistent. Stable but inconsistent. Working on your roller train, helps to reduce the disturbances and therefore improves stability to some extent but does not ensure consistency. Consistency of average steady state density will come from making the ink feed into a positive volumetric ink feed, which by definition is independent of changes in water, press speed and roller train temperature and even minor differences in roller setting.

The next step is predictability. One can not have predictability without consistency.

It is nice to see how you are developing. You are coming to the point where you doubt what you have been told to some extent. Maybe a few more years of frustration will bring you fully around to moving to a better way.

Keep thinking!

 

[Alois Senefelder]

Roller Trains

Roller Trains

Hello Mr Erik Nikkanen,


So which PDFs of roller trains are the best ????


Regards, Alois

 

[Deleted member 16349]

Hello Mr Erik Nikkanen,


So which PDFs of roller trains are the best ????


Regards, Alois

Both are poor.

Things can be done better.

 

[meddington]

What is the natural/inherent variation of density on a press sheet, on the circumferential direction of the press...0.08 points?

I'm not sure if you're just making a point or truly asking a question here, but I'm not seeing much more than 0.03 - 0.04 max on our end. Average is about 0.025. Though I'm sure other's equipment varies.

 

[meddington]

What is the natural/inherent variation of density on a press sheet, on the circumferential direction of the press...0.08 points?

I'm not sure if you're just making a point or truly asking a question here, but I'm not seeing much more than 0.03 - 0.04 max on our end. Average is about 0.025. Though I'm sure other's equipment varies.

 

[dimitri]

A bit of both.
You do answer that it is possible, so I had to leave the room open for such a reply.

I've seen a 2007 TAGA study (Spatial Uniformity of Offset Printing by Franz Sigg) done on a 74 speedmaster coming up with 0.08 density variation across the sheet as being normal.
I've also seen that with our 64 inch UV KBA presses, the press might well start printing with such variation, and then the operator would need to adjust the timing to correct for it; the controls there are not very accurate either by the way. Then it could go down to 0.03 or possibly less sometimes, but it is not something that is easily manageable. On a 40 inch UV press, this variation could be more easily adjustable, but I still do not think that we are dealing with an ideal process.