how do i figure out what kind of dot shape to use where?

[ashwini singh]

what is the basic way to start planning jobs by just a glance that what kind of dot and screen ruling should be used. ofcourse the paper would be known to us.

 

[gordo]

what is the basic way to start planning jobs by just a glance that what kind of dot and screen ruling should be used. ofcourse the paper would be known to us.

Generally the lpi is determined by the standard that the printer has targeted - either industry standard (e.g. 175 lpi/60 lcm) or an internal shop standard (e.g. 240 lpi). It is not usually changed on a per job basis. Some printers will go to a slightly lower lpi (e.g. 150 lpi) for uncoated papers - but this a carry over from film days as a way to lower lpi. It is better to use plate curves to optimize for the press.

For dot shape, if you are using CtP, then round dot is the best.

With round dot the dots are round through the tone range.
Benefits: Dot shape is the same for all screen angles and frequencies, optical bump is hidden in the shadows at the 75% tone, dot is non-directional so it is less affected by press problems. Reduces single channel moiré issues. Dot is non directional, i.e. all screen angle dots react the same to directional press issues such as slur and doubling.

BTW, Round dot was used for the GRACOL 7 characterization press runs.

A more complete discussion with images can be found here:

Quality In Print: AM Screening Dot Shapes

Again, dot shape is not typically changed on a per job basis. The shop has its standard dot shape and that is applied for all jobs unless there is a specific print buyer requirement for a different dot shape.

best, gordon p

 

[mazengh]

question.... is FM/XM screening better for uncoated paper? 20 micron for example...

 

[gordo]

question.... is FM/XM screening better for uncoated paper? 20 micron for example...

XM is AM screening - put them side by side and, viewed under a loupe, very few people could tell them apart.

FM screening can certainly be used for uncoated paper.

In N America FM screening is even used for telephone directory printing and newspaper inserts - and that's about as uncoated as you can get.

best, gordon p

 

[mazengh]

we use spekta2 from screen it's supposed to be XM but it's very different under the loop and when soft proofed.... in addition dot gain is much higher than a regular round dot....

is FM better suited for uncoated? or is it just a matter of calibrating an FM screen on uncoated paper?

 

[gordo]

we use spekta2 from screen it's supposed to be XM but it's very different under the loop and when soft proofed.... in addition dot gain is much higher than a regular round dot....

is FM better suited for uncoated? or is it just a matter of calibrating an FM screen on uncoated paper?

It's all very confusing....

Spekta2 is technically a "2nd order" FM screen. Its halftone pattern is similar to other 2nd order FM screens like Staccato, Taffeta, Satin, Organic, etc. Like those other screens, it does not have screen angles and does not form a rosette structure.

XM screening is a term coined by Agfa to describe their :Sublima screening and has been picked up by other vendors as a generic term. Kodak's Maxtone is another example of this class of screening. An XM screen is an AM screen and has screen angles and forms a rosette structure. Where an XM screen differs from an AM screen is in the extreme highlight and shadow dots. Typically in the range between 3% and 1%, 97% and 99%, the size of the does is constrained to a fixed size, e.g. a 3% dot. To make lighter tones, the 3% dots are systematically removed. Changing the number of dots of a fixed size to change tones is a characteristic of first order FM screens. Hence the 1%-3% and 97% to 99% tones of an XM screen are actually FM but the range from about 4% to 96% is a conventional AM screen.

When FM is run on uncoated paper, the result (depending on the dot size used) can look like continuous tone lithography - even when viewed under a loupe. Basically, yes, it is a matter of building a plate calibration curve to bring the tone reproduction in line with your coated presswork.

best, gordon p

 

[mazengh]

thanks gordo, it's all clear now...

 

[maas]

what are the benefits of FM screening in coldset/newspaper print environment?, compared to the conventional am screening

 

[VladCanada]

Environmentaly - less ink usage, but press calibration curve needs for FM plus another ink/"water" balance on dumping section of the press.
Mr. gordo explained a lot at his webpage,
thanks Gordon!

 

[mazengh]

how is the ink/water balance usually affected by FM screening?