Does anyone have idea how to process these images so I could print them in offset without moire? Already tried stochastic method, but it didn't help, it's still easy to see moire.
This artwork you show is now already line copy. After it is separated it is plate-ready. As it is already screened, there should be no moiré problems out of the ordinary rosettes formed by screens overlap. There is nothing more for you to do. Send the a/w to the printer.
Coincidently, Your illustration shows the correct screen angles for CMYK printing. This image is already (coarsely) screened (or magnified).
Conventional (AM) screen angles for reference are: C=105°, M=75°, Y=90°, K=45°
Screening is used to convert continuous tone into line art. Avoid re-screening the a/w when it is already line art. Re-screening will result in moiré pattern(s) most of the time. Moiré is most evident in darker coverage areas such as cyan.
Stochastic (FM) screening will not affect the image insofar as printing this is concerned.
You can start working on the billing. : )
Your illustration shows that the image is like printed in flexo using the angles of Y=7.5, M=52.5, C=22.5, K=82.5 and now you print it in Offset (e.g. Newspaper,Magazine, Print Media)
Let the Pre-press deside to avoid Moire.
But just to calm your mind try pre-setting it. Try these angles this is good for offset printers according to a big printing company which i will not mention because of copyrights reasons (I read it in their manual) :-) Yellow = 0 Magenta = 75 Cyan = 15 K (blacK) =45 Note: If you use Spotcolors it use the angle that is not used in the pallete/swatches (e.g. you have a plain yellow which is 0 and then you have Pantone1205C which is like Yellow also but this time you will use the angle of Magenta or Cyan or even blacK to be different with each other)
The fact that they are in different angles, moire issue will be illiminated. try to research also the "Dotshapes" you should only use 1 dotshape for all angles so that they are blended perfectly .
If these are what you claim they are then you have several problems.
- Your printers resolution plays a important part.
- The underlying offset on printer plays a part.
It would be better to let the RIP engine do the halftone. There are several reasons for this but mainly because with vectors your decoupled with the printers grid.
Even if you get the angles right, you still have a offset problem thus your results will fluctuate by 2 dot rows. This makes for a printing artifact that you will not easily be able to fix. Indeed this may be the moire your seeing. Now you have no real way of aligning this inside your vector app, its mostly a hit and miss thing. The printer RIP knows this so it has no bigger problems.
Talk to your printer.