Stochastic screening

[prasadhh]

Stochastic - (stō kas΄tik) 1. of, pertaining to, or arising from chance; involving probability; random. 2. Math. Designating a process having an infinite progression of jointly distributed random variables.

AM screening – Amplitude Modulated screening – modulates the screen area by changing the size of halftone dots that are in an ordered pattern in a given area. This has been the typical method for creating halftones and process screens for the last 100 years or more.

FM screening – Frequency Modulated screening – modulates the screen area by changing the number of “randomly distributed” dots of the same size that appear in a given area. This is the method used in the various stochastically driven methods for creating screens and “halftones”.

Nice information for u all.

 

[rich apollo]

Thanks, prasadhh. Nice article.

 

[gordo]

Thanks, prasadhh. Nice article.

Actually they simply paraphrased the text and reprinted the images (without permission) of the marketing materials I produced at Creo (CreoScitex in this case)

There's more info here: Quality In Print: FM Screening Dot Shapes/Patterns
and here: Quality In Print: Second Order FM Screen

BTW "Stochastic" used to describe the patterns of FM screening actually comes from the lexicon of statistics "having a random probability distribution or pattern that may be analyzed statistically but may not be predicted precisely" It is the opposite of "metronomic" (a term which could be applied to AM screening)

best, gordon p

my print blog here: Quality In Print

 

[SpeedKing]

i am a big fan of staccato the detail is always good.

 

[amomtaz93]

Stochastic screen also solves many problems due to low resolution images and dot gain but you should care about plate making in case you do not hv a CTP

 

[Sfdp2300]

Im new to this Stacato style screening and just wondering if this is a new direction the industry is moving as a standard?

Also thanks to those that have posted articles on this style of screening. I am a pressman by trade and would hate to be slammed on press with this one day and not know anything about it...

Some of the articles are talking about printing by the numbers.

When we do new jobs our color proofs come from a variety of different places when they are customer supplied, so we do alot of color adjustments on press. Would going to a stacato screening be an issue? Would we have to get customer supplied proofs with the same format as stacato? , And is it easier to image scan, record data onto disk for ink-preset on press. we currently have no ink-preset, but with the demand for quicker M/R this might be an expendature we might be able to request.

 

[gordo]

Im new to this Stacato style screening and just wondering if this is a new direction the industry is moving as a standard?
Also thanks to those that have posted articles on this style of screening. I am a pressman by trade and would hate to be slammed on press with this one day and not know anything about it...
Some of the articles are talking about printing by the numbers.
When we do new jobs our color proofs come from a variety of different places when they are customer supplied, so we do alot of color adjustments on press. Would going to a stacato screening be an issue? Would we have to get customer supplied proofs with the same format as stacato? , And is it easier to image scan, record data onto disk for ink-preset on press. we currently have no ink-preset, but with the demand for quicker M/R this might be an expendature we might be able to request.

Staccato is Creo/Kodak's brand of stochastic/FM screening. It is arguably the most used - however all the prepress vendors offer this type of screening as an option. I doubt that it will become an industry standard because not all CtP devices can consistently image the small dots that make up this type of screen. About 80% of Yellow page directories in N America are printed with this type of screening. So many of the entries to the Premier Print Awards/Bennies are printed with FM that they decided to drop FM screening as a separate category.
FM screening, like heavy GCR separations, is a perfect complement to by the numbers printing because it makes colors and tones more stable when SIDs vary. Color can be moved - but it does not react as fast nor in quite the same way as AM screening. It is also more forgiving of slight misregistration. It also reduces ink consumption by about 15%. FM will be the same as AM screening as far as ink key presets is concerned.

While I understand your problem in dealing with color proofs that come from a variety of different places or are customer supplied - it is very expensive and inefficient to use a press as a color correction device. That problem is an issue that might best be resolved in other ways especially if you are being asked to reduce makeready times.

best, gordon p

my print blog here: Quality In Print

 

[Deleted member 16349]

I would expect that the presets would be slightly different since with FM, the higher dot gain and less ink used on the dots means that overall less ink will be required to obtain the same or similar visual look. Less ink required will affect the presetting of ink keys. Ink consumption is not directly related to image area.

Erik

 

[gordo]

I would expect that the presets would be slightly different since with FM, the higher dot gain and less ink used on the dots means that overall less ink will be required to obtain the same or similar visual look. Less ink required will affect the presetting of ink keys. Ink consumption is not directly related to image area.Erik

Just a clarification - what I meant was that there is no difference in ink key preset implementation. Settings will of course be different.

best, gordon p

 

[amomtaz93]

Dear sfdp 2003

I think your problem about color varying and having jobs from many custumers and trying to adjust every job can be more easy in one step...YOU SHOULD HAVE a COLOR MANAGMENT SYSTEM AND YOU SHOULD SUPPORT ICC PROFILE TO WORK WITH YOUR COMPUTERS, PROOFS ,CTF-CTP AND IN YOUR PRESS ROOM trying to make the press machine as color processing unite is very danger and expensive and useless just like gordo said try this and you will be completely satisfied good luck

 

[gordo]

[snip]YOU SHOULD HAVE a COLOR MANAGMENT SYSTEM AND YOU SHOULD SUPPORT ICC PROFILE TO WORK WITH YOUR COMPUTERS, PROOFS ,CTF-CTP AND IN YOUR PRESS ROOM

I'm not sure that I would agree that strategy would solve the problem of expecting to match customer supplied proofs.
At the very least, a printshop should have a standard that they run to. In a case where files are coming from different sources - the standard should be an industry one (e.g. GRACoL) rather than a shop specific one. They should also run to their proof based on that standard. They should make their customers aware of this and encourage their customers to adhere to those same standards as it benefits the customer as well as the print service provider.
Print manufacturers need to take some ownership of the quality and suitability of the raw materials that they work with or face the probability of going out of business.

best, gordon p
my print blog here: Quality In Print

 

[Deleted member 16349]

Just a clarification - what I meant was that there is no difference in ink key preset implementation. Settings will of course be different.

best, gordon p

Yes I can agree that the implementation is basically the same.

I would add that modern ink key algorithms still are not accurate in calculating ink key values and therefore ink key presetting for AM or for FM is not precise. Errors can be as high as 40% in the simplest versions of ink key presetting packages and probably in the more expensive ones too.

The problem of presetting ink keys is also of the kind that self learning software does not work well. The idea of a self learning method is that one has a particular problem with serveral variables and that over a number of iterations one can approach the mathematical solution.

This is like having a set of simultaneos equations and by changing the values via iterations, one can approach the values of the variables, say x, y z, etc. This requires that the variable values of x, y, z, etc. are not changing.

The mathematical problem with the ink key presetting problem is that for each press set up ( each printed image) the values of x, y, z, etc. are changing. It's a new set of simultaneous equations for each set up. Iteration can not solve that kind of problem. It is a non linear problem and a multi factored problem. Complicated but not difficult. The solution has to be approached from a different direction.

Anyhow, even poor presetting is much much better than no presetting.

Erik

 

[amomtaz93]

I'm not sure that I would agree that strategy would solve the problem of expecting to match customer supplied proofs.
At the very least, a printshop should have a standard that they run to. In a case where files are coming from different sources - the standard should be an industry one (e.g. GRACoL) rather than a shop specific one. They should also run to their proof based on that standard. They should make their customers aware of this and encourage their customers to adhere to those same standards as it benefits the customer as well as the print service provider.
Print manufacturers need to take some ownership of the quality and suitability of the raw materials that they work with or face the probability of going out of business.

best, gordon p
my print blog here: Quality In Print

OK i am sure gordo in case the customer provided his ICC to the print shop it will work maybe i was not clear but many clients now load their own profiles to print shops to have the same results me my self i did it many times of corse some variations will accure because of ink and substrate but in the acepted limites...

 

[Heidelberg]

What you will notice is that a job printed with FM screening will use approx 15 - 20% less ink than the same job ran with AM screening. Ink presetting curves should be adopted acordingly.

 

[Sfdp2300]

Once again this group has performed to the highest standards. I thank you all.

 

[assman]

Stochastic screening or FM screening is a halftone process based on pseudo-random distribution of halftone dots, using frequency modulation (FM) to change the density of dots according to the gray level desired. Traditional amplitude modulation halftone screening is based on a geometric and fixed spacing of dots, which vary in size depending on the tone color represented (for example, from 10 to 200 micrometres). The stochastic screening or FM screening instead uses a fixed size of dots (for example, about 25 micrometres) and a distribution density that varies depending on the color’s tone.

The technique of stochastic screening, which has existed since the seventies,[citation needed] has had a revival in recent times thanks to increased use of computer-to-plate (CTP) techniques. In previous techniques, computer to film, during the exposure there could be a drastic variation in the quality of the plate. It was a very delicate and difficult procedure that was not much used. Today, with CTP during the creation of the plate you just need to check a few parameters on the density and tonal correction curve. When you make a plate with stochastic screening you must use a tone correction curve, this curve allows one to align the tone reproduction of an FM screen to that of an industry standard. Given the same final presswork tone value, an FM screen utilizes more halftone dots than an AM/XM screen. The result is that more light is filtered by the ink and less light simply reflects off the surface of the substrate. The result is that FM screens exhibit a greater color gamut than conventional AM/XM halftone screen frequencies. The creation of a plate with stochastic screening is done the same way as is done with an AM/XM screen. A tone reproduction compensation curve is typically applied to align the stochastic screening to conventional AM/FM tone reproductions targets