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Help! How to proceed with the line spacing!

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riquet06 Posted messages 56 Status Member -  
riquet06 Posted messages 56 Status Member -
Hello everyone,

I'm a beginner in graphic design, I'm doing a (crappy, we can say...) training program, and I've been given an exercise to do.

Anyway, I have to create and print in color a small leaflet that will feature photos taken in RAW format with my hybrid camera.

The constraint is to print with a line screen of 75 lpi.

From my research, I've seen that I need to respect a quality factor of 2 times the line screen and sometimes 16. I understood that this depends on the input image and the output image regarding the 256 levels of gray.

This is where my questions are. I'm not sure I fully grasp what is meant by input resolution, output resolution, and especially when to apply the line screen x16...

Let me explain:
For my leaflet, I export my RAW files from Bridge to Photoshop, where I save my images in .psd format at a resolution of 150 ppi (my incoming resolution as I see it) to match 2 times my line screen of 75 lpi (by the way, should I adjust this somewhere?).

I then import these files into InDesign for layout. Once finished, I export the print PDF. Is it at this point that I need to set the final resolution to 16 times the line screen?

Basically, I'm a bit lost about how to proceed.

If anyone who knows their stuff could explain to me if my approach is correct up to this point and when I should set to 1200 ppi or dpi, depending on whether it's only at the time of printing?..

Thanks a lot!

(Oh, and for those who will complain about the crappy training... I’m disappointed to see how some schools make money off our backs. But sometimes to evolve quickly, we don’t have many options, we go with what we have...).

4 answers

  1.
    contrariness Posted messages 17903 Registration date   Status Member Last intervention   6 243
     
    The line screen (at the time of printing) only concerns images (or areas that are not at 100% color) that are screened. This setting (in InDesign, for example) is only available if you print in color separation so that you can also adjust the screen angles.
    If you print in composite, the setting is not available (greyed out).

    You can very well exceed a resolution of 150 ppi; it does not pose a problem. The higher the resolution in your image, the more precise its definition is (the details of the image will be present), but if you print with a line screen that is too low, all the details of the image will be degraded.

    There is also an interest in knowing the line screen for printing, for example for posters. When you make a poster of 6 x 4 meters, we do not use images at 300 dpi (which would be cumbersome to work with) but at a resolution 1/2 or 1/3 smaller, knowing that you do not look at a poster of this size up close!

    Regarding the 16 times the line screen rule, it relates to Photoshop's bitmap mode. When you convert a grayscale image to a bitmap image (1 bit), the rule is that to have correct definition, you should set the output resolution to 16 times the line screen. But personally, I've long pushed well beyond that..!
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  2. contrariness Posted messages 17903 Registration date   Status Member Last intervention   6 243
     
    So here it is... odd!
    When it comes to printing, resolution is one thing and line screen is another...

    The standard is to have images at 300 dpi for offset printing because we used to have a line screen of 150 lpi... but that was before...
    The standard is now 175 lpi (and even more) and that doesn’t mean we have increased the resolution of the images... the eye cannot see the difference in magazines..
    Only fine art prints benefit from special treatment.

    Printing line screen is the domain of printing... the only information that might interest you is how the document will be printed..

    For example, in screen printing, the line screen will be 35 to 45 lpi if we are printing on a coarse mesh fabric but 150 lpi if we are printing on very smooth paper.
    That doesn’t mean we will downsample images at 300 dpi just because the line screen is 45 lpi..! .. it's pointless, the RIP or the driver will handle the conversion at the time of printing.
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  3. riquet06 Posted messages 56 Status Member 3
     
    Thank you for your response, Contrariness. I deduce that the 75 lpi screen ruling is part of the topic assigned to me and that I need to create a document considering this parameter (which will be set by the printer). So it is not my responsibility to adjust the screen ruling, is that correct?

    Regarding the famous quality factor of 2 times the screen ruling... in my case, with a screen ruling of 75 lpi, the resolution of my images cannot exceed 150 ppi, right? I understood that if the resolution is too high, there would be a loss of information during the final conversion.

    And the famous 16 times the screen ruling, when does this setting come into play? During the plate-making process before printing?

    As a beginner, despite scouring the internet in every direction, I lack practical experience!
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  4. riquet06 Posted messages 56 Status Member 3
     
    Alalaa, it’s starting to clear up in my head! :-) Thank you very much!
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