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Thread: I want to learn trapping for litho, where do I start?

  1. #1
    Member todesign is on a distinguished road
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    Arrow I want to learn trapping for litho, where do I start?

    I've been wanting to learn trapping for ages just don't know where to start.
    I know different processes require different amounts e.g litho, flexo etc..

    I only want to learn trapping for litho at the moment.
    can people list me some good practises for them.

    I know about chokes and spreads and you always spread or choke the lighter colour into the darker colour.

    what about values? like how much trap do you apply. I know how to actually do it in illustrator but have no clue what value to put in the box.

    I've found a good article here http://www.trapping.org/tips.html do I need to know anything else. again no valules listed. I gather this changes from press to press?

    would love any information been searching for what seems like months.

  2. #2
    PRC Member spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all
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    Quote Originally Posted by todesign View Post
    I've been wanting to learn trapping for ages just don't know where to start.
    I know different processes require different amounts e.g litho, flexo etc..

    I only want to learn trapping for litho at the moment.
    can people list me some good practises for them.

    I know about chokes and spreads and you always spread or choke the lighter colour into the darker colour.

    what about values? like how much trap do you apply. I know how to actually do it in illustrator but have no clue what value to put in the box.

    I've found a good article here http://www.trapping.org/tips.html do I need to know anything else. again no valules listed. I gather this changes from press to press?

    would love any information been searching for what seems like months.
    dont waste your time! manual trapping was required fifteen years ago. this was very time consuming and not 100% perfect. nowadays every modern prepress workflow has built in automatic trapping without any user interaction required. this is perfect for cmyk offset printing. some special packaging jobs with lots of spot colours may require some manual tweeking for the trap parameter settings, thats all!

    today the trapping has to be done by the printing factory according to their individual printing characteristics. you cant use the same trapped job file for different output situations.

    and if you prefer to do your trapping interactively there a lots of software solutions which make the job a lot easier and faster.

    but dont forget: your printing factory doesnt like already trapped files. so please dont complicate the job preparation for both sides!

  3. #3
    PRC Member SimonCharlie will become famous soon enough SimonCharlie will become famous soon enough
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    Quote Originally Posted by todesign View Post
    I've been wanting to learn trapping for ages just don't know where to start.
    I know different processes require different amounts e.g litho, flexo etc..

    I only want to learn trapping for litho at the moment.
    can people list me some good practises for them.

    I know about chokes and spreads and you always spread or choke the lighter colour into the darker colour.

    what about values? like how much trap do you apply. I know how to actually do it in illustrator but have no clue what value to put in the box.

    I've found a good article here http://www.trapping.org/tips.html do I need to know anything else. again no valules listed. I gather this changes from press to press?

    would love any information been searching for what seems like months.
    Spider is right, most all of trapping is now automated at RIP stage, and 90% of the time it is fine, especially in litho printing. Flexo on the other hand may require a bit more trap manipulation with grip back of certain colours and not others, but this can be all pre set with various "trap tickets"...

    If you are after typical trap distance values, I normally use 0.1mm - 0.25mm depending on the material being printed on, some stocks stretch more than others, and for flexo, anything from 0.2mm for label printing up to 1mm if printing on plastic substrate for instance.

    Sc

  4. #4
    PRC Member spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all
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    Quote Originally Posted by SimonCharlie View Post
    Spider is right, most all of trapping is now automated at RIP stage, and 90% of the time it is fine, especially in litho printing. Flexo on the other hand may require a bit more trap manipulation with grip back of certain colours and not others, but this can be all pre set with various "trap tickets"...

    If you are after typical trap distance values, I normally use 0.1mm - 0.25mm depending on the material being printed on, some stocks stretch more than others, and for flexo, anything from 0.2mm for label printing up to 1mm if printing on plastic substrate for instance.

    Sc
    you cant give a "general" trapping distance for standard cases.

    the distance depends on the kind of printing material, size of the printing "sheet", number of press runs and the age / manufacturer of the printing machine.

    another aspect is the neutral density of the colour. most workflows have extra settings for dark colors like black to establish stronger trapping. on the other hand
    opaque and metallic colours need some other special treatment regarding trapping distance and trapping direction.
    and trapping direction is not only affected by colour density. the printing colour sequence is also important for choosing the right trapping direction and trapping width.

    so please forget your thinking about "general rules"!
    Last edited by spider; 06-04-2014 at 08:29 AM.

  5. #5
    Member todesign is on a distinguished road
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    Quote Originally Posted by spider View Post
    . some special packaging jobs with lots of spot colours may require some manual tweeking for the trap parameter settings
    You hit the nail on the head there that's exactly what I want to learn. I'm in the packaging industry and want to move into artworking. More trapping with spot colours and metallics I guess.

    I know most of the CMYK general printing trapping will all be taken care of. What about opaque colours? Do they cause any problems.

    I did think that would be the reply I would get spider no general rules.

    What's grip back? I know loads of packaging pre press companies that still do all there trapping on illustrator.

    Thanks for the info I'm going to compile some notes lol.

  6. #6
    PRC Member SimonCharlie will become famous soon enough SimonCharlie will become famous soon enough
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    Quote Originally Posted by spider View Post
    you cant give a "general" trapping distance for standard cases.

    the distance depends on the kind of printing material, size of the printing "sheet" and the age / manufacturer of the printing machine.

    another aspect is the neutral density of the colour. most workflows have extra settings for dark colors like black to establish stronger trapping. on the other hand
    opaque and metallic colours need some other special treatment regarding trapping distance and trapping direction.

    so please forget your thinking about "general rules"!
    I was merely trying to say that what might work on one substrate will not work on another, not to generalise, in fact just the opposite, as well as metallics there are also line and tone separations to consider as well as opaque white(s) when printing on clear transparent material or holographic substrate.
    So I agree there are no "general" or "global" trap settings, certainly in the packaging sector, each job must be assessed on an individual basis for the print process and printer that is going to be used...

    Sc

  7. #7
    PRC Member spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all spider is a name known to all
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    Quote Originally Posted by todesign View Post
    You hit the nail on the head there that's exactly what I want to learn. I'm in the packaging industry and want to move into artworking. More trapping with spot colours and metallics I guess.

    I know most of the CMYK general printing trapping will all be taken care of. What about opaque colours? Do they cause any problems.

    I did think that would be the reply I would get spider no general rules.

    What's grip back? I know loads of packaging pre press companies that still do all there trapping on illustrator.

    Thanks for the info I'm going to compile some notes lol.
    once again: the trapping parameters depend on your print supplier and the condition of his machine.

    you have to ask him for technical details. and serious trapping is NOT done manually anymore!
    this would be like mechanical typesetting with lead letters in the 21st century!

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