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
