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  • Concentric Screening ?

    Possible switch to concentric screening coming. Sheetfed. Should the press room be concerned ?

  • #2
    Re: Concentric Screening ?

    Both press room and prepress will need to be concerned.
    Concentric screening is really an AM screen ruling multiplier and will have similar behaviour to any very fine AM or FM screen and carry many of the same benefits.
    Patterning within each color channel can be an issue because it destroys visible uniformity. This patterning is partly influenced by imaging, plates and presswork and requires users to experiment till they find something suitable. Essentially, the screening math is hampered by geometric constraints (angle, resolution, lpi, dot shape + ring width).
    Visible structure is kept to a minimum by specifying very narrow rings, BUT this pushes the frequency so high that process stability and imaging are compromised. Even when screens are free from visible artifacts, they are often so fine that it is difficult to support their use on plate let alone find a way to implement them in the press room. The problem is that some concentric screen settings drive rulings way over what plate imaging can support - on the order of 1-2 pixel widths for the rings, which is understandably problematic. For example, a 200 lpi screen with 2 pixel ringwidths = 600 lpi which is finer than, for example, Kodak Staccato 10.
    Coarser ring widths are easier to implement but at that point it is probably more effective to use an AM screen of equivalent lpi. Since it is still an AM screen there is still the opportunity for screening and subject moiré - although the finer the screen the less likely that will be a problem.
    From a print buyer point of view there will likely be no visible difference between a 2-300 lpi conventional AM screen and concentric screening - even under a loupe.

    best gordo

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    • #3
      Re: Concentric Screening ?

      >Patterning within each color channel can be an issue because it destroys visible uniformity.

      Hi Gordon,

      I had not heard of this technology until I saw the first post in this thread. So I did a Google search and found some interesting links. This one below, page 6, seems to contradict your point directly. I realize it is by the vendor, but the disagreement seems to be one of fact.

      http://print05.gasc.org/PDF/mse_individual.pdf

      Al

      Edited by: Al Ferrari on Feb 25, 2008 2:22 PM

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      • #4
        Re: Concentric Screening ?

        I don't think there's a contradiction. We are speaking about two different issues. They are referring to the "graininess" sometimes associated with FM/stochastic screens (a separate discussion). I was referring to "patterning". Here's what the screen looks like:



        I'll try to explain. In a conventional AM screen, the vertical and horizontal distance between successive dot centers is constant and is a function of the screen frequency. Unfortunately, the combination of screen frequency and angle results in halftone dot cells that, other than at 45 and 90 degrees, do not intersect the recorder grid in any consistent way. As a result, the halftone cells in a single color channel are not identically shaped and do not contain the same number of pixels. If the difference in dot shapes in a single color channel repeats itself , i.e. has a frequency, the result is a type of patterning within one screen called single channel moir�. (Unless the screening developer has taken steps to avoid it)
        Dividing the AM dot into thin concentric rings adds complexity to the design of the screen while still being limited to the geometry of the AM screen. You can see this problem clearly in the illustration. This can result in the "patterning" that I referred to in my original post.

        best, gordo
        Last edited by gordo; 07-23-2009, 12:12 PM.

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        • #5
          Re: Concentric Screening ?

          Thanks for the illustrated response. I accept your explanation.

          Learned several things today.

          Al

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          • #6
            Re: Concentric Screening ?

            The idea for this type of screening came from hollow dot printing. With improper chemistry solid dots will tend to print hollow in the middle.
            To compensate for this ink water issue the screening was developed.

            Pat Berger

            Mercer Color

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            • #7
              Re: Concentric Screening ?

              Hi Pat,

              Can you please say more about this "hollow dot printing", or post a link where we could follow up on it? I tried Googling for it, but didn't get too far.

              Thanks,

              Al

              Comment


              • #8
                Re: Concentric Screening ?

                Re: Pat wrote:
                "The idea for this type of screening came from hollow dot printing. With improper chemistry solid dots will tend to print hollow in the middle. To compensate for this ink water issue the screening was developed."

                Pat, actually I believe this screening was born in the land of flexo, where Artworks was looking to texture the surfaces of the dots without using FM screening techniques which patents prevent them (and others) from doing. So, it's not to solve an ink/water issue at all.

                best, gordo

                Comment


                • #9
                  Re: Concentric Screening ?

                  Yes, both prepress and pressroom need to be aware of what's going on.

                  From my testing, the key component to the ability to do concentric screening is your plate. While EAWS claims maintaining a 2x2 grid to plate may work, maintaining a 1x1 grid to plate (without patterning) works much better. I'm lucky in that our Javelin with Fuji LH-PJ plates were properly configured from the start and holding the 1x1 grid to plate happened by default. EAWS won't say it specifically but Fuji thermal plates are good, Kodak and Agfa not so much.

                  The pressman will also need a heads up. The thinner the ring widths, the less ability they'll have to move the color on press.

                  Are you using Paragon Screening? Concentric Screening is a unique dot shape for the Paragon Screens. Paragon Screens give the anti-moire with better rossettes. Pushing it to the Concentric dot will give you some ink savings and better consistency on press (ring width dependent) as well as slightly brighter/cleaner color.

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                  • #10
                    Re: Concentric Screening ?

                    GinSu gave you a pretty thorough explanation.

                    I'll just add some notes. Some of the pro's are:
                    - Reduced ink layer thickness - giving you far more chromaticity on your halftones (in comparison, regular AM screened will look as if there were some 10% dirtying colours with the main colour.)
                    - More stable in print due to inherent limit of ink layer thickness variation. Faster set-up time.
                    - High details as in FM, while avoiding the graininess of FM in flat tints.

                    Some of the con's:
                    - Demanding on plates and exposure. See GinSu's notes on Fuji thermal plates. When plates are in good shape, the printing should be no problem in modern press.
                    (Uh... Didn't come up with anything else...)

                    Gordon is wrong in what he says about the origin of Concentric Screening. Former AWS did not develop this for flexo. This is definitely for Offset. Maybe he is confusing this with PlateCell Patterning for adding pattern to solid areas to help ink transfer in flexo. Totally different thing.

                    Edited by: Jukka Lindgren on Mar 6, 2008 3:56 PM

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                    • #11
                      Re: Concentric Screening ?

                      I must say, from the looks of the image / example posted... that looks terrible!
                      Still to this day, I've never seen a prettier screen than Heidelberg's IS Classic 2540/200lpi
                      Super clean and never one single moire.

                      Comment


                      • #12
                        Re: Concentric Screening ?

                        Jukka,

                        I may possibly be wrong about the origin of concentric screening - however it is the history as I understand it. Perhaps EAWS can clarify.

                        You wrote:
                        "Reduced ink layer thickness - giving you far more chromaticity on your halftones (in comparison, regular AM screened will look as if there were some 10% dirtying colours with the main colour.)"

                        I have to disagree, reduced ink layer/film thickness is not the cause of increased chroma. Chroma in halftones derives primarily from the ratio of light being filtered by ink vs light reflected off the paper that hasn't been filtered by the ink. Light that is unfiltered by the ink effectively contaminates the color you see. There are other contributors to increased chroma, one of which is the more even film of ink across the surface of small dots, or in the case of concentric, ring width.

                        And "High details as in FM, while avoiding the graininess of FM in flat tints."

                        I agree that some FM screens are grainy in flat tints particularly first order FM screens - however it is not correct to say that it is true of all FM screen implementations.


                        best, gordo

                        Comment


                        • #13
                          Re: Concentric Screening ?

                          Gordo, you wrote:

                          >" I have to disagree, reduced ink layer/film thickness is not the cause of increased chroma...
                          >There are other contributors to increased chroma, one of which is the more even film of ink across the surface of small dots, or in the case of concentric, ring width."

                          After the first few reads it appeared to me that you were contradicting yourself. However, I've summized that this is what you are saying:

                          You contend that the primary contributor to the increased chroma from concentric dots is the increased amount of paper that is unfiltered by ink, the spaces between the rings of the individual dots. The reduced ink film thickness of the concentric rings also results in more even ink film, which can also contribute to increased chroma, and in your opinion is a secondary consideration.

                          Right? I'm not wanting to argue, just trying to understand your statement.

                          Comment


                          • #14
                            Re: Concentric Screening ?

                            No worries.

                            RE: "You contend that the primary contributor to the increased chroma from concentric dots is the increased amount of paper that is unfiltered by ink, the spaces between the rings of the individual dots. "

                            No. You see color because light is filtered by the ink. Assuming that you are operating at an appropriate SID/ink film thickness breaking the dot into rings and increasing the lpi effectively increases the ratio of inked area to non inked area. Hence more light is filtered by ink and you get an increase in chroma. The same thing happens with an FM screen (lots of little dots per area) and high lpi AM screens (typically over 300 lpi) - remember that originally wrote that Concentric screening is really an AM screen ruling multiplier and will have similar behaviour to any very fine AM or FM screen and carry many of the same benefits.
                            Also, when dots become smaller - whether because they're rings, squiggles, FM or high frequency AM screens - the ink film density across the surface of the dot is more homogenous (even). A TAGA paper written I think in the late 90s studied this contributor to increased gamut.
                            Here's a 3D rendering of ink film thickness - on the left 175 lpi. On the right an FM screen. (Sorry I don't have a like image for Concentric). Both areas would measure the same tone value.

                            !http://www.bytephoto.com/photopost/data/500/10692InkThickness.jpg!

                            Their findings showed that the variations in ink film thickness across the surface of the AM dot created areas where light is not filtered as efficiently and hence contributed to lowering the gamut of the gamut.
                            So, while ink film thickness will impact chroma, the primary cause of increased gamut with any halftone screen is the size of the individual halftone dot and its frequency and the area of ink coverage relative to non inked area. Another way to put it is that halftone screens do not increase gamut - it's the light hitting paper between dots reduces gamut.
                            That's why you will see a similar midtone gamut increase with any high lpi AM screen or FM screen that you see with Concentric screens.

                            best gordo

                            Comment


                            • #15
                              Re: Concentric Screening ?

                              With small dots and thinner ink film, one also has the phenomena of having more light go into the paper and diffuse under the dot and come up through the dot. This light is then filtered by the ink on one pass. Thinner ink films in general can but not always shift the hue. It depends on the shape of the spectral curve. A single pass through the ink film would act like it was filtered by a very thin ink film.

                              So with FM dots, one has both the affect from a thinner ink film in the dot in general and a greater percentage of light coming up through the dot via diffusion, because the distance from the edges of the dot is so short. This can result in hue shifts and light than expected print.

                              There is also a more subtle affect. Possibly too low to be significant but it is still there. It has to do with the difference between reflected light and transmitted light through an ink film.

                              Density is just a calculation from reflectance. We all know that density of a solid ink increases with ink film thickness but does not go up to infinity. Density of a solid goes up and then reaches a maximum value. This is basically because all the light that shines on the solid does not reach the paper. Some of it is reflected by the pigments in the ink film and at the surface.

                              Transmitted light is a little different. Again, density is a calculation of transmitted light. If you shine light through an ink film and measure it on the other side, the density increases as the ink film increases. The density does not level out but theoretically goes to infinity as the ink film does.

                              The point here is that reflected light on and ink film and transmitted light are filtered a little differently.

                              We can all understand the light path of reflected light relative to the ink film. The light goes into the ink film. Most of it gets to the paper and is reflected back out. Some is reflected back out from the pigments.

                              But with very small dots and edges of solids there is also transmitted light. Some light goes into the ink and into the paper and is diffused about and comes out in the non printed regions just outside the dot. Also light goes directily into the paper, is diffused and is filtered as it comes up through the ink of the dot.

                              So there are lots of interesting and complicated phenomena happening with dots that affect colour.

                              That is why I tend to say that CMYK inks are not colours but are filters. There is no CMYK colour space. Dealing with CMYK as a colour space is an oversimplification that leads to less predictable results.

                              Comment

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