Normal vs. Fine Screen mode

[Prepper]

We currently use Normal mode for 175 lpi plates with 2400dpi on our 6600E and are going to try FM screening using Harlequin's HDS Medium which is about 20 micron at 2400dpi according to their info.

My question is, will our platesetter have to be recalibrated in any way for this switch and also wondered what is the difference between Normal and Fine Screen mode? Plates and processing will be the same as we're using now for 175lpi AM screening.

Terry

 

[gordo]

We currently use Normal mode for 175 lpi plates with 2400dpi on our 6600E and are going to try FM screening using Harlequin's HDS Medium which is about 20 micron at 2400dpi according to their info.

This is how the HDS screens were defined when I worked with them:

HDS-Fine 10 micron 2nd order equals about 650 lpi
HDS-Medium: 18 micron 2nd order equals about 550 lpi
HDS-Coarse 20 micron 2nd order equals about 500 lpi

You'll need to make sure that your CtP and plates are able to resolve the size of dot you're trying to image. You'll also need to build and apply a dot gain compensation curve when you image the plate.

best, gordon p

 

[Prepper]

Hds

Hds

Thanks Gordo, I went back and looked at the info again and noticed in the paragraph above the chart on page 9 of the white paper that is states "theoretical spot sizes in microns for the different HDS models and different output resolutions for 20% HDS screen".

I didn't notice the 20% part before. The chart says HDS Medium 2x2 pixels, at 2400 resolution is about 21 microns, so does that mean a 20% is about 20 microns and say a 5% would be much smaller?

So if my platesetter is certified for 20-21 microns, plates for 10 microns which HDS version would you recommend if we've been printing 175 AM successfully?

Terry

 

[gordo]

Thanks Gordo, I went back and looked at the info again and noticed in the paragraph above the chart on page 9 of the white paper that is states "theoretical spot sizes in microns for the different HDS models and different output resolutions for 20% HDS screen".

I didn't notice the 20% part before. The chart says HDS Medium 2x2 pixels, at 2400 resolution is about 21 microns, so does that mean a 20% is about 20 microns and say a 5% would be much smaller?

So if my platesetter is certified for 20-21 microns, plates for 10 microns which HDS version would you recommend if we've been printing 175 AM successfully?

Terry

I don't find the explanation in the HDS white paper very clear. :-(
And, unfortunately, I dealt with HDS naming mostly by halftone pattern name (a, b, c, d, etc.) rather than by the commercial screen name (which changes according to the marketing dept.)

That being said, what I think they mean moderated by my experience....

HDS Medium at 2400 dpi
At 1% tone value the majority of dots will be 21 microns (square dots that are 2 pixels x 2 pixels in size (4 10.6 micron pixels per dot.) There will also be a few single, 10.6 pixels, pixels in the tone as well as a few 3 pixel features).
As tones get darker, more of these 2 pixels x 2 pixels dots will be added to darken the tone.
At a certain tone value there will be no dots made up of fewer than a 2x2 cluster of pixels. That tone value might be the 20% value they refer to in their white paper.
The below image might help you understand.
The tones from left to right are 1%, 2%, 3%, 4%, 5% 10%, 20%

If you look closely you can see that among the 2x2 pixel dots in the 1% tone that there are a few single, two, and three pixel dots - but the vast majority are 4 pixel dots. You'll see that same mix of dot sizes as you go from the 1% to the 5% tone in the above illustration.
As tones get darker pixels are no longer added between dots but are instead added in order to create the "worm" features.

So, from a plate imaging point of view you are probably OK to use HDS medium.

hope that helps a bit, gordon p

 

[Prepper]

HDS Screening

HDS Screening

Yes Gordo, that does help, I see what you're saying, but my head is getting in the spin cycle on this now.

My plates say certified for 10 micron. 1-99% 200lpi conventional, 300lpi FM or hybrid. How does this translate into spot size? What is 300lpi FM?

I imaged a plate at 175 with a scale on it and I can barely see a dot at 1%, 99% is ok. I changed to 385lpi, regular HPS screening, and output a plate and can barely see anything below 4-5% but 99% does have an open dot. These are positive plates so leads me to think may be overexposing for this fine screen?

So when someone says they're printing 20 micron FM, what size dot are they having to print? Can presses print a 1-99% at 200lpi like the plates are capable of?

Are people doing this successfully in commercial sheetfed type work? Everyone I talk to about it seems to be of the opinion that you may not be able to do it based on platesetter and plates and press and when you tell them that all that seems to be okay then they ask well why do you want to?

If we want to go to a finer screen than 175 would you recommend going to 200 AM or going to FM? From what I've read 200 AM is tougher in some respects than FM but I'm getting a lot of negative feedback about trying FM also.

Terry

 

[gordo]

Back up the truck a bit

Vendors can be a bit....shall we say, fuzzy....when it comes to specifications.

A starting point to keep in mind - on a 2400 dpi CtP device, at 240 lpi, a 1% dot is one pixel. On a 2400 dpi device one pixel is 10.6 microns in size. (For a 2540 dpi CtP it's a 10 micron pixel). Also, a CtP device can only image complete pixels. I.e. the smallest mark a 2400 dpi device can make is a pixel that's 10.6 microns. In order to make halftone dots, the device will group (cluster) pixels of 10.6 microns.

Using your example, mathematically, a 1% dot at 200 lpi requires a halftone dot of about 14.5 microns.*
However, your CtP device cannot image a dot of 14.5 microns since it only has a 10.6 micron pixel to work with. So, to create a 1% dot, the screening engine will alternate between single 10.6 pixel dots and groups of 2 pixel dots i.e.10.6 x 21.2 sized dots so that the average of dot sizes for that tone area works out to 14.5 microns.

If you increase the lpi e.g. to 385 lpi in your example, the smallest dot will still be a 10.6 micron dot - which is too large for a 1% tone. You'd need a pixel that's about 6 microns. So, since it can't make smaller pixels the screening engine simply removes a percentage of 10.6 micron pixels from the tone area. Removing pixels from an area makes it lighter, and thus allows the representation of a 1% tone even though the pixels are too large.

So, if the vendor says that the plates say certified for 10 micron (one pixel at 2540 dpi or one 10.6 sized pixel at 2400 dpi) that's not quite the same as saying 1%-99% 200lpi conventional AM since the 1% tone at 200 lpi will be a mix of single and grouped pixels. In my experience, when a vendor says 1%-99% at 200lpi conventional AM they actually mean that it cannot image single pixels, only groups of pixels. I.e. it means they cannot reliably image a dot smaller than 21 microns (a group of four 10.6 pixels). If they could reliably image single pixels they'd say: "1%-99% 240 lpi conventional AM".

Yes, because you are using positive plates you may be overexposing and losing the highlight dots, or your CtP is just not capable, or your plates don't actually have the resolution, or your plate processing is causing the loss.

When someone says they're printing 20 micron FM, they are printing dot sizes that range from 20 microns (1% dot at 120 lpi made up of 4 pixels) to a dot that's about 30 microns in the midtones.

Presses are not the limitation to printing fine screens. Presses can and do print screens like 10 micron FM. For example Canadian Stamps and those of over 30 European, African, Asian and Caribbean countries have been print 10 micron FM for at least the past 10 years:

Also, most of the Yellow Pages Directories and newspaper inserts in North America are printed FM.

So, yes, absolutely people doing this successfully in commercial sheetfed type work? (Over 70% of the print entries for the Benny Awards use FM screening).
Yes, it's correct that you may not be able to do it based on platesetter and plates and press - but if you can reliably print 175 lpi then you should be able to print 20 micron FM.
Why do you want to? Here are a few reasons:

1 - No screen angle moiré
2 - No subject moiré
3 - No rosettes
4 - Photographic/contone look
5 - Greater tone and color stability as SIDs naturally vary during press run
6 - Larger color gamut
7 - Faster drying
8 - Reduced ink usage
9 - Tonal and color stability when misregistration occurs
10 - Halftone dot structure stability when misregistration occurs
11 - Competitive differentiator

(More info here: Quality In Print: FM/Stochastic Screening - Part 1 of 5 - The benefits )

If you want to go to a finer screen than 175 lpi then I would "bite the bullet" and go straight to FM. Just like making any other change in the print process - how you go about making the change will determine how successful you are. Most of the problems I've encountered are people-related not technical. But that's a whole other thread

best, gordon p


*The formula for calculating dot size in microns is here: Quality In Print: How to calculate halftone dot sizes in microns

 

[marktonk]

Prepper,

Good info from Gordo. Another consideration is the laser system and what it is rated for. I looked but it does not seem to be published. Check with the manufacture, the plate is rated for 10 micron but is the CtP. Laser spot size and the optics need to be able to image what size you are looking to image (be careful, laser spot size is not the same as addressability but sometimes they seem to interchange them). I seen a laser system where the spot size was 21 microns but addressability was 10. Not too good for imaging small or fine details, slur target center looked like a football on the plate. Knowing what your CtP is rated for will save you many tests, press runs and time.

Good luck.

Regards,

Mark

 

[gordo]

Prepper,
Another consideration is the laser system and what it is rated for. I looked but it does not seem to be published. [SNIP] (be careful, laser spot size is not the same as addressability but sometimes they seem to interchange them)[SNIP]

Mark is correct. The information from most CtP vendors about their device's screening capabilities seems to have been disappeared from their specifications (Heide's included ;-). What this forum needs is a good dust up from the vendors on this topic.

Make sure you get your system's capability/specification in writing.

For more info on the difference between addressability and resolution go here: Quality In Print: Hybrid AM Screening/XM Screening - Addendum, part 1


best, Gordon p

 

[Prepper]

FM

FM

Gordo, the 1-99% at 200 was the certification on the plates, Screen rep says the setter "is certified for 20-21 micron FM screening".

I am interested in giving it the best shot we can and see what happens, I think we would need to get the exposure on the plates fine tuned first though. The pressman is on board and wants to try it also. We have been printing 175 AM for 2-3 years now very successfully on our 1989 model Heidelberg 72SM.

Our plate rep says none of his other customers are using FM screening, so that's a red flag to our manager here. But he also says we'd have a better chance if we use his inks cause they have a finer grind . So like you said biggest obstacle may be resistance\culture. We use a Harlequin rip so HDS is what's available for us to use. You said you worked with them at one time and Medium may be too fine and equals a 500 AM screen and that the white paper isn't very clear. Now you're an expert and I am not, just researching, so where does that leave me in trying to figure this all out?

Other people tell me also that Medium probably won't work and we may have to use coarse. If that's the case why don't they update their white paper to fit the real world, as it is 4 years old now and surely they have experience to back it up now if lots of people are using it? Cause they're telling me that even coarse may still plug in the shadows.

Ok, just looked at your link on Halftone dot sizes and what that shows, if I'm looking at it correct, a 175lpi AM screen a 2% dot is 21 microns? If so, then that is why you say if you can print 175 successful, you should be able to print 20 micron FM, right? If that's the case, then I am imaging 21 micron dots now with our 175 AM screening whenever it has a 2% tint, right? If the plates, setter and processing is set up right. So my plates are rated for a 1% dot at 200lpi AM which according to the chart is 13 microns.

So my main question and I guess you'll say test it and see, is Medium or Coarse? You were saying that Coarse is 20 micron or 500lpi so in your chart the 250lpi would be the smallest I could image a 1% dot with 2400dpi? Its says a 1% 250lpi dot is 10 microns and 10.6 is the smallest 2400 can image. How would you ever be able to image a 1% or 2% dot of 500lpi equivalent? What am I missing here?

So in my test of imaging a 385lpi screen with 2400dpi and looking at your chart I wouldn't expect to be able to see a dot below 4-5% right? It would require a hybrid screening that would scatter the dots below what the setter is capable of to image anything there wouldn't it? Or what does regular AM screening do when highlight dots go smaller than what the resolution (2400 in my case) is capable of, does it start scattering them or just not image them at all?

Sorry about the rambling but maybe you can make enough sense of it to try and help me a little further,
Thanks,
Terry

 

[gordo]

Our plate rep says none of his other customers are using FM screening, so that's a red flag to our manager here.

Maybe two ways to look at that:
1) Forget the red flag - that means you have an opportunity to differentiate against your competition. Go for it.
2) Red flag means that your suppliers don't have experience and may not be able to provide technical support if needed. In my experience most printers do it themselves anyway.

But he also says we'd have a better chance if we use his inks cause they have a finer grind .

With ink formulation "finer grind" actually means that the ink particles are more evenly dispersed which is a good thing when you use finer screens.

Other people tell me also that Medium probably won't work and we may have to use coarse. If that's the case why don't they update their white paper to fit the real world, as it is 4 years old now and surely they have experience to back it up now if lots of people are using it? Cause they're telling me that even coarse may still plug in the shadows.

Vendors and engineers are not always the best communicators. It's very hard to look at products from the customer's perspective and write for that audience in a clear, concise, and effective fashion. This issue is one of the reasons that prompted me to start my print blog.

If you can run both screens (medium and coarse) on the same plate, then you'll be able to create a direct comparison between the two.

You'll be building tone reproduction curves for your plates that will align your FM to your 175 lpi. There shouldn't be any more, or less, plugging.

Ok, just looked at your link on Halftone dot sizes and what that shows, if I'm looking at it correct, a 175lpi AM screen a 2% dot is 21 microns? If so, then that is why you say if you can print 175 successful, you should be able to print 20 micron FM, right?

It's not just the dot size - it's the print production process controls. In my experience printers who have a reliable print production process - i.e. they don't do color corrections on press - have the basic process controls in place that allows them to be successful with FM.

If that's the case, then I am imaging 21 micron dots now with our 175 AM screening whenever it has a 2% tint, right? If the plates, setter and processing is set up right. So my plates are rated for a 1% dot at 200lpi AM which according to the chart is 13 microns.

Yes.

So my main question and I guess you'll say test it and see, is Medium or Coarse?

Yes. Especially since Harlequin's info is not clear. It's best if you can try both sizes on the same plate.

You were saying that Coarse is 20 micron or 500lpi so in your chart the 250lpi would be the smallest I could image a 1% dot with 2400dpi? Its says a 1% 250lpi dot is 10 microns and 10.6 is the smallest 2400 can image. How would you ever be able to image a 1% or 2% dot of 500lpi equivalent? What am I missing here?

AM to FM equivalencies - i.e. 20 micron to 500 lpi are only approximations. There are two forms. One is equivalency of detail rendering - that's usually measured by drawing a line through the FM screen and counting how many dots are crossed in a one inch length. The other is lithographic equivalency i.e. how they perform on press lithographically. That's usually measured by counting the length of edges (transitions) in a square inch.
It sounds like you'll be fine.

So in my test of imaging a 385lpi screen with 2400dpi and looking at your chart I wouldn't expect to be able to see a dot below 4-5% right? It would require a hybrid screening that would scatter the dots below what the setter is capable of to image anything there wouldn't it? Or what does regular AM screening do when highlight dots go smaller than what the resolution (2400 in my case) is capable of, does it start scattering them or just not image them at all?

On a 2400 dpi device, when the lpi exceeds 240 lpi, yes, it typically acts like a hybrid AM/XM screen and uses a "scattering" of 10.6 micron dots (the smallest size it has available) to create a 1% tone. So, at 385 lpi, you should probably still see dots below 4-5% - but it does depend on your RIP's screening engine design - so you might not see any dots.

Sorry about the rambling but maybe you can make enough sense of it to try and help me a little further.

No worries. I get as much out of trying to answer these kinds of questions as I hope you get out of reading the answers.

best, gordon p

 

[Prepper]

FM Screening

FM Screening

Gordo, you said...

"When someone says they're printing 20 micron FM, they are printing dot sizes that range from 20 microns (1% dot at 120 lpi made up of 4 pixels) to a dot that's about 30 microns in the midtones."

So if I tell you I'm imaging 175lpi and getting a 1-99% dot on plate and a 1% dot at 175lpi, 2400 dpi is about 15 microns, a 2% is about 21 microns and I'm getting a good 2% on that 175lpi, that I should be fine then to image a 20 micron FM because that's going from a 1%, being 20 microns, up to about 30 microns at the largest?

Terry

 

[gordo]

We currently use Normal mode for 175 lpi plates with 2400dpi on our 6600E and are going to try FM screening using Harlequin's HDS Medium which is about 20 micron at 2400dpi according to their info.

My question is, will our platesetter have to be recalibrated in any way for this switch and also wondered what is the difference between Normal and Fine Screen mode? Plates and processing will be the same as we're using now for 175lpi AM screening.

Terry

If it's operating within normal parameters I doubt that your platesetter will have to be recalibrated, but that's really a question for your system vendor to determine.

I don't know what difference there is between Harlequin Normal and Fine Screen mode. There tech support should be able to tell you - and if they do, please post the info here.

best, gordon p

 

[Prepper]

Normal and Fine Mode

Normal and Fine Mode

Is on the platesetter, not the screening, they tell me its just a way to allow 2 different sets of exposure parameters to be tied to one plate, for normal and FM use, not actually a fine and normal mode as the name might seem to imply.

They also said as you have, if I'm imaging a 1-99% dot now at 175lpi, no further adjustment or fine tuning of exposure needed probably so no need to setup a Fine Mode exposure set.

Terry