Screening for printing smooth skintones

[amccolor]

Hi all,

What do people recommend for printing the smoothest fleshtones. We are going to do a very demanding bridal catalog and the client said that smooth skin is a big deal for them.

We are running a Lotem 800 with a Quantum head. Currently, we use 20-micron staccato screen but find that skin prints kind of grainy. We used to use print 175 line with a round dot but definitely did not like seeing the rossettes.

Any recommendations?

Thanks in advance.

Anton Cheng
AMC Colorgrafix

 

[gordo]

Hi all,
What do people recommend for printing the smoothest fleshtones. We are going to do a very demanding bridal catalog and the client said that smooth skin is a big deal for them.
We are running a Lotem 800 with a Quantum head. Currently, we use 20-micron staccato screen but find that skin prints kind of grainy. We used to use print 175 line with a round dot but definitely did not like seeing the rossettes.
Any recommendations?

Interestingly many bridal magazines are printed with Staccato for its smoothness (and detail rendering). You may want to find out why yours appears grainy (it may be some other reason than the screening itself).

Failing that, you could up your AM round dot to 240 lpi. There'll still be rosettes but by being much smaller they won't be as visible.

best, gordo

 

[SteveAgfa]

Anton:

First of all, is the grainy objection from a naked eye, or from a loupe?
Regardless, if the customer is complaining, then I'd agree with Gordon.

However, at 240 you might start to run the risk of losing highlight detail,
with the process not necessarily being able to hold a 1 pixel dot. This would
tend to look posterized, or perhaps red blotches on the cheeks. (dropping cyan)

I believe Kodak still offers MaxTone (from the Scitex portfolio) which is their
implementation of an XM or Hybrid screening. Agfa's Sublima XM screening
delivers the smoother appearance that Gordon is referencing from higher-
line AM screening, but prevents the loss of highlight dots by employing
a dot no smaller than what you are using now with your Staccato 20.

I hope this helps,

Regards,

 

[meddington]

We've been using 20 micron HDS (Harlequin Dispersed Screening - not stacatto, but stacatto-like) and do not have issues with graininess in flesh tones. Black gradations tend to show a slight graininess, but flesh tones and most all other hues are very smooth. As Gordo pointed out, a LOT of magazines are using Stacatto or other stochastic screening. Looking at the scantily clad models on the mags at the supermarket check out, graininess doesn't appear to be a huge issue ("Its ok, I'm evaluating the print screening", I tell my wife).

What type of paper are you printing on, ad could that have an effect of the perceived graininess?

 

[gordo]

Anton:
[SNIP]
I believe Kodak still offers MaxTone (from the Scitex portfolio) which is their implementation of an XM or Hybrid screening.[SNIP}

A clarification - Maxtone wasn't from the Scitex portfolio.

best, gordon p

 

[amccolor]

Thanks for the feeback. We have run Staccatto 20-micron for about 2 years now and really like the smoothness and the ability to hold detail in most cases. Only issue we have run into has been single-color tints (such as 50% black only screens). We don't run a tremendous amount of flesh tones, but the some of the flesh tones that we do run seem kind of grainy to me.

The darker skintones seem to reproduce great, but very light colored skin (particularly in smoother areas such as the cheeks) seem to show some grain. Haven't heard any complaints from existing clients though. It's just that we are approaching a new client and they are making a huge deal about smooth skin tones. That is why I am staring at previous work we have printed and noticed this grain.

Now I am thinking that maybe the graininess is coming from the digital images themselves. It could be that they were not very good captures to begin with....

 

[gordo]

[SNIP]Now I am thinking that maybe the graininess is coming from the digital images themselves. It could be that they were not very good captures to begin with....

That is quite possible. Since the FM screening has a higher resolution than the AM/XM screening it may show issues in the original art that the AM/XM may not. 20 micron second order FM (like Staccato) is equivalent to around a 400 lpi AM/XM screen.

Graininess may also be a symptom of poor ink transfer. You'd need to look at the dots under at least 25x to confirm if that's an issue.

On a sidebar, you could ask your Kodak rep to send you some samples of bridal presswork done with Staccato so that you could see for yourself whether it provides the smoothness you're looking for.

best, gordon p

 

[marktonk]

If you do go to AM, use an elliptical dot shape, this typically will provide smoother flesh tones then other dot shapes. This will also provide smoother tints but if you do go to higher screenings, Hybrid will maintain the highlights and shadows that you will lose with conventional AM. Good luck.

Bet regards,

Mark

 

[Bart Lammertyn]

Concentric Screening

Concentric Screening

I know that my "old" colleagues of EskoArtwork have Concentric Screening in their portfolio.

A full AM Screening Technology, so regular rosette, sharper, better in colour and it should save you some ink. Obviously, you would need an EskoArtwork RIP.

More info can be found on : http://www.esko.com/concentric

 

[gordo]

If you do go to AM, use an elliptical dot shape, this typically will provide smoother flesh tones then other dot shapes. This will also provide smoother tints but if you do go to higher screenings, Hybrid will maintain the highlights and shadows that you will lose with conventional AM. Good luck.
Bet regards,
Mark

I would have to disagree.
Elliptical dots can be smoother than Euclidean because they split the optical bump that can occur a the 50% tone into two less visible bumps at 40% and 60%. Unfortunately those tones are still very prominent in flesh tones. Also elliptical dots are directional which can result in lines forming where the dots join if slight slur or doubling occurs.

Round dot screening puts the optical bump in the shadows typically around the 75% tone - very much in the shadows so it's not visible.

Both you and Steve mentioned Hybrid AM a.k.a. XM screening as a way to recover highlight and shadow tones that might otherwise be lost when going to higher lpi screening. While that is true, one has to be careful with that type of screening in applications where there are large areas of pastel and very light colors as in the bridal work that the OP is needing to do. The problem with hybrid AM/XM screening for that kind of application is that the dots forming those light tones are 4 or more times the size of the dot that would have been created by a conventional AM screen. That larger dot size, in turn, may result in a grainy appearance in those pastel tones.

More info is available here: Quality In Print: AM Screening Dot Shapes

best, gordon p

 

[PACH]

What plates are you running? It is also woth looking at the final lens? Staccato is prone to a dirty lens. Are you using any Tone Rep Curves?

 

[marktonk]

Hi Gordon,

You are correct with the dot gain being with connecting in two areas instead of one but with controlled curves this is not as much of an issue as it use to be. My experience is mainly with Irrational Screening which has a smoother transition then traditional postscript screening such as HQS or other such AM. No crosshatch effects either.

We have run several jobs that showed that our Hybrid screening has reduced the grainy look that stochastic has a tendency to produce in flat tint areas and pastels. This was compared in a demo with a 2nd order stochastic screening that you are very familiar with. By the way, our highlight are typically 20 micron with our Hybrid, same size as most commonly printed stochastic jobs.

Best regards,

Mark

I would have to disagree.
Elliptical dots can be smoother than Euclidean because they split the optical bump that can occur a the 50% tone into two less visible bumps at 40% and 60%. Unfortunately those tones are still very prominent in flesh tones. Also elliptical dots are directional which can result in lines forming where the dots join if slight slur or doubling occurs.

Round dot screening puts the optical bump in the shadows typically around the 75% tone - very much in the shadows so it's not visible.

Both you and Steve mentioned Hybrid AM a.k.a. XM screening as a way to recover highlight and shadow tones that might otherwise be lost when going to higher lpi screening. While that is true, one has to be careful with that type of screening in applications where there are large areas of pastel and very light colors as in the bridal work that the OP is needing to do. The problem with hybrid AM/XM screening for that kind of application is that the dots forming those light tones are 4 or more times the size of the dot that would have been created by a conventional AM screen. That larger dot size, in turn, may result in a grainy appearance in those pastel tones.

More info is available here: Quality In Print: AM Screening Dot Shapes

best, gordon p

 

[gordo]

Hi Gordon,
You are correct with the dot gain being with connecting in two areas instead of one but with controlled curves this is not as much of an issue as it use to be. My experience is mainly with Irrational Screening which has a smoother transition then traditional postscript screening such as HQS or other such AM. No crosshatch effects either.
We have run several jobs that showed that our Hybrid screening has reduced the grainy look that stochastic has a tendency to produce in flat tint areas and pastels. This was compared in a demo with a 2nd order stochastic screening that you are very familiar with. By the way, our highlight are typically 20 micron with our Hybrid, same size as most commonly printed stochastic jobs.
Best regards,
Mark

Sorry Mark, but I've had quite a bit of practical experience with HD's Irrational Screening, as well as stochastic screening (from several vendors including HD) (I've personally owned both HD and Agfa RIPs and output devices) and I have disagree with your conclusion regarding graininess. The fact that highlight dots with a hybrid AM screen are typically 20 micron does not determine or suggest what would happen with a stochastic screen since the organization of the dots as well as their size range is quite different - and that's not considering the fact that different vendors may have different stochastic screening patterns.
I do not believe that it is fair to make gross generalizations like "stochastic as a tendency to produce in flat tint areas and pastels." Some stochastic screens imaged on some CtP devices will appear grainy. However some stochastic screens on some CtP devices will appear smooth.

I cannot argue against your personal testimony so the issues that I raised have to stand on their own technical merits. You say that "Irrational Screening has a smoother transition then traditional postscript screening such as HQS or other such AM" OK, then show us the bitmaps and explain why this would be true.
In any case, I cannot argue the point much further without promoting certain vendors - which I have no intention of doing. So I'm at a bit of a disadvantage.

So can we leave it at that?

thanks, gordo

 

[Barry Brown]

Screening for printing smooth skintones

Having read all the responses in this thread I'd add the following.
The human eye can resolve at best 28 line pairs/mm (ref. Schlapfer & Widmer, UGRA); that's why 150 lpi (60l/cm) screen was the original choice for monochrome printing, because its 30 line pairs/mm falls just outside visula perception. In colour printing the rosette pattern of 150 lpi screen falls within what the eye can see, so a finer screen ruling is needed (on good paper).

Any changes in screening method will change dot-gain and ink transfer; only 0% /white paper) and 100% (solid covereage) are not affected by changes in screening method. Solid ink density MAY however be affected by screening, if the press minder has to reduce inkfilm thickness to compensate for dot-gain that has not been precompensated for in the plate-making process. If you want to print the maximum colour space you have to ensure that your screening method is fully accounted for with the dot-gain compensation and colour management.

Finer screening (finer screen ruling) means smaller dots for a given percentage coverage. Stochastic screening also means smaller dots for a given percentage coverage. Smaller dots translate to thinner inkfilm transfer (compared to the solid area, and compared to the bigger dots of a coarser screen ruling), and this in turn translates to different colour management ( a wider colour gammut).

The graininess sometimes associated with stochastic screening happens because in a certain tone (let's say a tone that should be a flat tone) some of the dots touch, and some of them don't. A tone-jump, caused by the ink transfer characteristic from plate to blanket and blanket to paper, accentuates the differences between dots that touch and dots that don't touch.

In AM screening all of the dots are identical in a flat tone. The tone-jump caused by press dot gain applies equally to all dots. Of course when the dots to touch in AM screening you'll have a dot-gain tone jump; with square dotes is at 50%, with elliptical dots at say 40% and 60% (half the jump at each, because only two of the corners are touching at one time), and with round dot at about 70%. The star-shaped hole caused when the traditional round dot joins accentuates dot-gain (ink gathers in the corners), so the euclidean screen was invented; it migrates from round highlights through square midtone back to round shadows.

There is another important difference between stochastic and AM screening, and that is the dot size/plate life situation. Tiny dots will wear-out faster. With AM screening is your 1 or 2% dots dissappear, your 5% dot will still be there, just a little smaller than at the beginning of the run. With stochastic screening all of your light tones are made-up of 1-2% dots, so when they go eveything goes.

Your choices of screening are limited to that which your thermal CTP system, limited to 2400 dpi exposing resolution, can accurately expose.

If you want smooth fleshtones I would say use AM screening, at a ruling fine enough that the rosette is not visible. The smaller dots of fine-screen AM give the same ink transfer benefit (thinner ink film) that you get with stochastic screening, but without the dot-gain inferred graininess.

Fujifilm's CoRes screening would give you the ability to output 175lpi, 200 lpi, 250 lpi or even 300 lpi screen's at the 2400 dpi your platesetter can manage, but for that you'll have to get a RIP that would support it (speak to Fuji, Rampage or Xitron). You also need to check that your existing RIP can output screened 1-bit TIF coming from another RIP. CoRes reproduces skintones exceptionally well (smooth transitions); probably there are some others that will comment on that.

regards,
Barry

 

[Adriaan]

Smooth Skintones

Smooth Skintones

Hi,
Firstly, if you're going to use Stochastic 20mic, and you still get grainyness, it's well worth to look at the transfer of ink from blankets to paper.

On the other hand, if you want to try using AM screening, use 200lpi euclidean shape dot, BUT try playing around with your yellow and magenta screen angles. I've found that adding another 15 or even 30 degrees difference between the yellow and magenta, the moire disappears completely.

Good Luck

Adriaan

 

[gordo]

To Barry:
RE: "The star-shaped hole caused when the traditional round dot joins accentuates dot-gain (ink gathers in the corners), so the euclidean screen was invented; it migrates from round highlights through square midtone back to round shadows."

Not true. The Euclidean dot results when you use a glass screen with etched grid lines - the type used when halftone screening was first developed.

The star shaped hole that occurs at the 75% tone with a round dot screen may cause a loss of shadow detail - in a film workflow, but in a CtP workflow the tone increase can be compensated for with a plate curve. Incidentally, the 4 original Idealliance GRACoL7 characterization runs that I attended all used round dot for the screening.

RE: "There is another important difference between stochastic and AM screening, and that is the dot size/plate life situation. Tiny dots will wear-out faster. With AM screening is your 1 or 2% dots dissappear, your 5% dot will still be there, just a little smaller than at the beginning of the run. With stochastic screening all of your light tones are made-up of 1-2% dots, so when they go eveything goes."

Maybe, maybe not. Depends on your production environment. I know a printer in Vancouver that prints exclusively 10 micron FM (1% dot at 240 lpi) and does runs to 75K with no plate wear issues.

RE: "Fujifilm's CoRes screening would give you the ability to output 175lpi, 200 lpi, 250 lpi or even 300 lpi screen's at the 2400 dpi your platesetter can manage,"

Any modern RIP can do 175lpi, 200 lpi, 250 lpi or even 300 lpi screen's at 2400 dpi. CoRes screening is supercell screening they're just a little late to implement it.


To Adriaan,

RE: "Firstly, if you're going to use Stochastic 20mic, and you still get grainyness"

That depends on whose screening, CtP, and plates you're using as well as your press condition.

 

[amccolor]

What plates are you running? It is also woth looking at the final lens? Staccato is prone to a dirty lens. Are you using any Tone Rep Curves?

We are running Fuji LHPJ's on a Lotem 800V2 with staccato 20-micron (Kodak). Yes, we have tone rep curves in place.

We will check out the lens. Calibration is still ok though. Could it be grainy due to a dirty lens without messing up the calibration?

 

[marktonk]

Gordo,

Let's agree to disagree....over the years I have had many clients that were running HQS switch to IS and state it was smoother, no more checkerboard moires, etc. I have also have many clients that were running DI's go switch rip from one that was a postscript AM to Meta with IS and also state a quality improvement. I also have been involved with printing supplied plates with a well known Stochastic screening and ran out the same images with Hybrid and the Hybrid did not have the graininess in flat tints. Now our Hybrid is generated with IS Screening, perhaps that makes a difference? You are right that there are allot of variables, how good are the screening algorithms, how good are the optics, laser spots size, paper characteristics, etc. But on the rest, let agree to disagree

Regards,

Mark

 

[PACH]

We are running Fuji LHPJ's on a Lotem 800V2 with staccato 20-micron (Kodak). Yes, we have tone rep curves in place.

We will check out the lens. Calibration is still ok though. Could it be grainy due to a dirty lens without messing up the calibration?

It will be worth checking the lens as the Fuji plate is VERY ablative. If you are using Brisque try and use Composed dot instead of Staccato for this particular job. As I said before, you can get away with a dirty lens using AM, but Staccato is diferent. Also a good TRC is very important. The more points you have the more the steps are.

 

[gordo]

[SNIP] But on the rest, let agree to disagree
Regards,
Mark

Seems I have a talent for being disagreeable.

best, gordo