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  • 1bit_Tiff
    replied
    Hi,
    We use 175lpi for our commercial jobs for both coated and uncoated stock, for magazine jobs we use 350lpi. Both lpi have process calibration curve.

    Leave a comment:


  • digiservice_it
    replied
    Hi,
    we use Sublima by Agfa from 240lpi to 340lpi with Fuji PJE Plates.
    I love this screening......Very high quality.
    In Italy we use minimum of 200lpi ABS for better quality not for production.

    Leave a comment:


  • disbellj
    replied
    Re: Standard Line Screen

    Gar,

    Thanks man.

    Note: I have to set Preps template orientation to 1 and Nexus orientation in Make Separation module to 270, for the job to get put on plate in orientation I need it.

    Dotspy preferences, under Units > Angles, set to 0.. 180 degree (setting to -90.. +90 degrees doesn't change anything that I see)
    Dotspy preferences, under Display Rotated, set to None (and page is displayed head left)
    Angles read: C 14.8, M 45, Y 0, K 75.2 (wrong, and not what Nexus says it's doing)
    Dotspy preferences, under Display > Rotated, set to CounterClockwise (which changes Display > Mirrored to Vertical automatically)
    Angles still read wrong.
    Dotspy preferences, under Display > Mirrored, set to None again (this makes the display head down Wrong Reading aka backwards). The values for the angles read right now, but only when reading from the back and upside down essentially. Still not fixed.

    So I tested again. This time I set rotation in Nexus to 0 (which gives me a head up file, not correct orientation for platesetter).
    Opened seps in Dotspy and set dotspy prefs to Display > Rotated and Display > Mirrored both to 0.
    Still reads the same. Wrong angles.

    Maybe there's something else that you meant, and that I can try?

    I'm not going to worry too much about it just because there have been no problems, but it would be nice to know what's going on. Will I pay for support for it though? No. We've paid too much already for the little support/help we've actually received.

    Don

    Leave a comment:


  • Chaos
    replied
    Re: Standard Line Screen

    Don,
    This happened to me thru Nexus. I thought my Cyan and Mag had flopped only to notice I had the orientation flopped. Quite embarassing after I had thrown the red flag up to supervisors and such.

    Gar

    Leave a comment:


  • disbellj
    replied
    Re: Standard Line Screen

    G_Town,

    I just recently found this. We haven't had any complaints from customers or pressmen.

    I know that Nexus 7.5 and the program that creates cal files for the 7.5 version (FastCalibrator 7.0) has listed screen angles such as 165 (Cyan), 45 (Magenta), 90 (Yellow), and 104.8 (Black). But although that is what they say in Nexus 7.5 and FastCalibrator 7.0, when reading the screened file with DotSpy 2.5 Rev. 3, DotSpy 3.0 Rev. 1, or DotSpy 3.0 Rev. 2 (the latest version I have, because I don't know what version was used with 7.5), I get 14.8 (Cyan), 45 (Magenta), 0 (Yellow), 75.2 (Black). The thing I can't understand is that although the wrong angle is used (such as 15 for Cyan and 75 for Black), the correct bump curve is used for both Cyan and Black. Weird.

    Yes, it is unsettling when you think (are told by software) that one thing is going on and another really is. BTW I wouldn't be surprised if the angles were flopped (any good reason given?). I've upgraded and then had to downgrade so I can't remember which version it was when it was right (I just remember that at one time the angles that Nexus said it was using was verified by myself in DotSpy as being what they were said to be in Nexus).

    Don

    Leave a comment:


  • G_Town
    replied
    Re: Standard Line Screen

    Did the angle thing just happen recently or did you just find it recently?

    The reason I ask is because I was told that going from 7.5 to 8 for some reason they basically "flopped" the angles ie..75 becomes 15 and 15 becomes 75.

    We check angles on every job anyway as a QA thing but that would suck if we have something like this start to happen.

    Leave a comment:


  • prexpresso
    replied
    Re: Standard Line Screen

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    Jeg vil bede dig kontakte Scanprints reception, på telefon 8733 6699 for yderligere betjening.

    Med venlig hilsen | Best regards

    Ole Hansen
    IT Administrator

    Scanprint
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    Phone +45 8733 6699
    Fax +45 8733 6698

    Direct +45 8733 6645
    Mobile +45 6155 8081

    Leave a comment:


  • stargate
    replied
    Re: Standard Line Screen

    175 for printing in house jobs

    Leave a comment:


  • disbellj
    replied
    Re: Standard Line Screen

    John W,

    Yes, at midtone, the cyan dot on plate is 5 (%, points, dots, however it's correct to say it) higher than the black dot on plate, and this would show a color difference. However, I don't have a problem with this because although Nexus switched screen angles for black and cyan (on all impo and autotrap workflows), the correct bump curve is being used for each. So angles got swapped, but not bump curves. So black looks correct on press sheet and cyan looks correct on press sheet. The angles being switched has not caused a problem that I know of. This does go to show however how I can set it and forget it (and it change somehow after it is set up correctly). The workflows have the correct angles set up, and the override doesn't work on the angles (it says it's screening one angle and then screens another angle. Maybe if I have a Cyan sep I can choose the Black angle it may give me a Cyan angle). So either Nexus or DotSpy (both from AWS) is lying to me as for as what angle it is. Just another example of me feeling like I'm dealing with some sort of beta software when stuff is set up correctly and then something changes without me telling it to, not working as advertised, etc. I digress.

    Don

    Leave a comment:


  • John W
    replied
    Re: Standard Line Screen

    Don,
    That's 5% dot not 5% effect. At the 50% area, any change has the largest effect because the dots have the maximum surface area and perimeter to gain. The 49 vs 50 is probably no big deal but the 50 to 54 is huge IMO and may translate into much more than a 5% visual effect depending on what the subject matter is, n'est-ce-pas?
    I get upset if I am outside a plus or minus 1% dot at the 50 and for stamp work that tolerance is more like plus or minus half a percent.
    I hope you can resolve the variance your set up seems to make. Do you have a swap c for k angles at the last minute as a quick workaround?
    Cheers,
    John W

    Leave a comment:


  • disbellj
    replied
    Re: Standard Line Screen

    Gordo,

    Unfortunately if I call our vendor, since we are no longer under support contract with them, they will want to charge us thousands of dollars to renew the contract before answering the simplest of questions. So I will not be talking to them if I can help it. We already paid too much for them causing and not fixing issues for me to want to give them another dime at this point. Although I like their software that I use, we were sold what I consider additional (beta) software and I haven't put that stuff into production.

    Heck, just in the last couple days I checked my screens and although it's set in Nexus to be CQS Quality Screening (CQSNominal), and screen angles being C 165 (aka 75), M 45, Y 90 (aka 0), K 105 (aka 15), when I checked my screen angles on the screened file in DotSpy, the angles were C 15, M 45, Y 0, K 75. I know it was correct at one time, but Nexus has gotten corrupted or something and now I'm getting switched angles for cyan and black! I was fixing to start worrying, but I checked the dot percentages and the bump curve is getting applied correctly, so that's why no one has noticed it (otherwise it would be hard to match proofs because the bump on cyan is 50 in = 54 out and black is 50 in = 49 out, so switched would see a 5% difference in color than expected). Oh well, just another example to me of stuff changing that shouldn't be, but glad I didn't "get bit" by it since it's at least using the correct bump curves still.

    Don

    Leave a comment:


  • gordo
    replied
    Re: Standard Line Screen

    Don,

    RE:
    "So I used the formula, and 2400/150 = 16, and 16 squared is 256, so for my uncoated (where I use 150 l.s.) has 256 levels of gray according to the formula provided.
    But when I use the same formula for my coated (which uses 175 l.s.), I get 2400/175 = 13.714285, and that squared is 188.08161, so for my coated I have 188 levels of gray according to the formula provided. This means I can expect banding because I don't have 256 levels of gray. I'm asking is this correct? I use round dot screens, Nexus' CQS Nominal screening 165,45,90,105 (aka 75,45,0,15). Does the formula still apply, and should expect banding? And if so, what could I do to fix it?"

    Don, that gray level limitation formula is outdated for modern AM/XM screens. I'm not familiar enough with Nexus screening - you will need to check with them directly to find out whether this is an issue for you. Vendors such as Agfa (ABS), Heidelberg (HQS & IS), Kodak (Maxtone) use a technique called dithering to increase the number of tones without the need to increase the resolution and compromising performance. For example, let's say that a combination of resolution and screen frequency (according to the formula) gives us only 100 tones and we want 200. By alternating 70% halftone dots with 71% halftone dots, we can simulate a tone area of 70.5% - an average of the values of the adjacent halftone dots. Doing this for all values from 0% to 100% effectively doubles the number of tones that can be represented. Some screening implementations allow you to set the parameters of how and how many gray levels will be maintained as you increase LPI (to avoid shadestepping/banding). In general, FM screens eliminate shadestepping.
    Just a few more thoughts regarding points raised in this thread.
    1) You do not necessarily need to go to a lower screen ruling when printing on uncoated paper.
    2) Changing screen ruling is not an optimal method of managing dot gain
    3) AM/XM screening dot shape will not impact number of possible gray levels
    4) The actual screen frequency you get at any specific request will depend on the the particular screening algorithm being used (varies by vendor) and device resolution, and sometimes color). for example, on a 2400 dpi device - a request for 175 lpi may actually deliver a 169.706 lpi ruling

    best, gordo

    Leave a comment:


  • disbellj
    replied
    Re: Standard Line Screen

    Gordo,

    I was first talking about resolution and the stair-step effect (pixelization), and said that back in the day we went by 1.2 pixels per printing dot and anything lower would show stair-step effect. So if my l.s. is 175, then the lowest image resolution I need is 175 x 1.2 = 210 dpi. Anything lower and I can expect pixelization.

    Then, umesh gave a formula to calculate if one is getting 256 levels of gray when printing. The formula was:
    levels of gray = platesetter resolution divided by linescreen and the result squared

    So I used the formula, and 2400/150 = 16, and 16 squared is 256, so for my uncoated (where I use 150 l.s.) has 256 levels of gray according to the formula provided.

    But when I use the same formula for my coated (which uses 175 l.s.), I get 2400/175 = 13.714285, and that squared is 188.08161, so for my coated I have 188 levels of gray according to the formula provided. This means I can expect banding because I don't have 256 levels of gray. I'm asking is this correct? I use round dot screens, Nexus' CQS Nominal screening 165,45,90,105 (aka 75,45,0,15). Does the formula still apply, and should expect banding? And if so, what could I do to fix it?

    Don

    Leave a comment:


  • gordo
    replied
    Re: Standard Line Screen

    Hi Umesh,

    RE:
    "Agreed that this is a very basic formula, and now super cell technology is used.But i guess supercells means grouping of number of cells for obtaining accurate screen angles and screen frequency."
    Basically correct.

    RE: "And another thing in offset, variable densities cannot be printed, so number of gray levels per pixel has to be maximum of 2 while imaging the plate, as against the case of digital printers, where number of gray levels per pixel are more than 2,so even low imaging resolution will do.
    I may be wrong sir but if possible please put some light on this part... this may also solve Don's query.."

    I think Don was referring to the resolution of input images.
    Modern supercell screening used for CTP and computer to film eliminate the gray level limitations of old style Rational Tangent screens.
    There is an old resolution formula used for scans that will be used for output. Typically it is expressed as the resolution should be 2x the halftone frequency. I.e. you should have a 300 dpi scan for output at 150 lpi. It's a nice formula that in reality is meaningless. In reality, you can actually go as low as 1 to 1. I .e. you can use a 150 dpi image and output it at 150 lpi without any loss of image intergity - "staircasing". Best thing to do is run the same image, at different resolutions, out to film or plate and run on press and see for yourself if you can see a difference. I.e. use an image at 75, 100, 150, 200, 300, and 400 dpi output at 175 lpi and run on press. See for yourself what the impact of image resolution has, or does not have, on reproduction quality.

    gordo

    Leave a comment:


  • umesh
    replied
    Re: Standard Line Screen

    Hi Mr.Pritchard,

    Agreed that this is a very basic formula, and now super cell technology is used.But i guess supercells means grouping of number of cells for obtaining accurate screen angles and screen frequency.
    And another thing in offset, variable densities cannot be printed, so number of _gray levels per pixel_ has to be maximum of 2 while imaging the plate, as against the case of digital printers, where number of gray levels per pixel are more than 2,so even low imaging resolution will do.
    I may be wrong sir but if possible please put some light on this part... this may also solve Don's query..

    Regards
    Umesh

    Edited by: umesh on Sep 25, 2007 2:31 PM

    Leave a comment:

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