Loading ...
Sorry, an error occurred while loading the content.

Re: Wildly varying Dmax

Expand Messages
  • Joost Horsten
    First of all, a happy 2007 to you all! I hope in this year the world will not be as black and white as our pictures ;-) ... The same thought occurred to me. I
    Message 1 of 9 , Jan 1, 2007
    • 0 Attachment
      First of all, a happy 2007 to you all! I hope in this year the world
      will not be as black and white as our pictures ;-)


      --- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Greg"
      <dfaprinting@...> wrote:

      > Do you
      > have something that is fairly stable like a Macbeth chart that you can
      > measure? That way you can check for consistency between sessions.

      The same thought occurred to me. I did checks with both the GMcB
      Digital Color Checker SG (a semi-matte plastic camera target) and the
      GMcB Eye-one Scan Target 1.4 (a glossy paper target).

      There seems to be nothing electronically wrong with my Eye-one. With
      the glossy scan target the measurements were immediately very
      reproducible (noise of L* = 0.1/0.3). With the semi-matte camera target
      I did have some performance issues on the start. Especially the blacks
      showed a similar problem (L* varying between 7.4 and 11). Upon closer
      inspection however it turned out to be the result of a very slight
      (frankly invisible) contamination. After cleaning the results were very
      reproducible, also the L* values dropped. Perhaps cleaning is not even
      the right word. I rubbed the targets with my finger after which they
      looked a tiny bit "smoother". The midtones and higlights were much less
      susceptible to this effect.

      So this probably points to the source of my problems with the EEM/Eboni
      targets. I have noticed before that the eboni prints are quite
      sensitive (note my remark on the printer rollers in the original post).
      I have done nothing special with the targets, neither handled them
      roughly, but also did not protect them in a special way. The have just
      been laying around for a day or two. But that's maybe not the way to
      deal with them.

      Going back to the semi-matte camera target, another, slightly related
      explanation could be that I did not actually clean the target, but put
      some tiny bit of grease on them with my finger, thereby "polishing" it.
      In that way, it might be on optical effect, perhaps similar to the
      difference between matte and glossy papers. Then again, it would be an
      inherent effect of the matte print.

      Does this make sense to anyone?

      Joost
    • Ernst Dinkla
      ... A happy 2007 for all. ... It could be different on the Eye One but my SpectroCam is quite sensitive to the distance to the target and the angle. The
      Message 2 of 9 , Jan 1, 2007
      • 0 Attachment
        Joost Horsten wrote:
        > First of all, a happy 2007 to you all! I hope in this year the world
        > will not be as black and white as our pictures ;-)

        A happy 2007 for all.


        > So this probably points to the source of my problems with the EEM/Eboni
        > targets. I have noticed before that the eboni prints are quite
        > sensitive (note my remark on the printer rollers in the original post).
        > I have done nothing special with the targets, neither handled them
        > roughly, but also did not protect them in a special way. The have just
        > been laying around for a day or two. But that's maybe not the way to
        > deal with them.
        >
        > Going back to the semi-matte camera target, another, slightly related
        > explanation could be that I did not actually clean the target, but put
        > some tiny bit of grease on them with my finger, thereby "polishing" it.
        > In that way, it might be on optical effect, perhaps similar to the
        > difference between matte and glossy papers. Then again, it would be an
        > inherent effect of the matte print.
        >
        > Does this make sense to anyone?

        It could be different on the Eye One but my SpectroCam is
        quite sensitive to the distance to the target and the angle.
        The automatic measuring setup with an old HP plotter had the
        spectrometer slightly higher at first and the results were
        darker readings. A slightly different angle of the head on the
        patch showed similar changes. I had already made another strip
        guide that allows longer strips to be measured manually and
        that works good. The head doesn't touch the strip but is at
        the right height and a thin PET foil protects the rest of the
        target when the spectrometer is running over it.

        I'm an advocate for multiple targets and multiple measurements
        + averaging. The SpectroCam does that already on its way over
        the patches, between 7-15 readings per patch. But I use more
        targets where possible, the targets printed in another
        direction etc.

        An interesting fact about the HP Z3100 and Z2100 is that the
        integrated calibration and profiling measures per patch and
        the dark patches get a longer time for the measurement.
        Something that is difficult to achieve with strip reading or
        one should increase the size of the dark patches.

        Any change in the surface of matte black should give different
        readings.


        Met vriendelijke groeten, Ernst


        | Dinkla Grafische Techniek |
        | www.pigment-print.com |
        | ( unvollendet ) |
      • Joost Horsten
        Hi Ernst, Thanks for your suggestions. ... I checked this and it does not seem to explain what happens. The eye- one is well constructed to keep the angle
        Message 3 of 9 , Jan 1, 2007
        • 0 Attachment
          Hi Ernst,

          Thanks for your suggestions.

          > It could be different on the Eye One but my SpectroCam is
          > quite sensitive to the distance to the target and the angle.
          > The automatic measuring setup with an old HP plotter had the
          > spectrometer slightly higher at first and the results were
          > darker readings. A slightly different angle of the head on the
          > patch showed similar changes. I had already made another strip
          > guide that allows longer strips to be measured manually and
          > that works good. The head doesn't touch the strip but is at
          > the right height and a thin PET foil protects the rest of the
          > target when the spectrometer is running over it.

          I checked this and it does not seem to explain what happens. The eye-
          one is well constructed to keep the angle fixed. Also distance seems
          to be wel controlled, both with and without guide. Furhtermore, if I
          artificially increase the distance a bit, the meaused l* LOWERS (i.e.
          less light light reflected, which is logical to me) instead of
          increasing (what is what I find if the measurement seems not to be
          OK).

          > I'm an advocate for multiple targets and multiple measurements
          > + averaging. The SpectroCam does that already on its way over
          > the patches, between 7-15 readings per patch. But I use more
          > targets where possible, the targets printed in another
          > direction etc.

          Given my recent experience, I'll will make this common practice as
          well. However, my current results seem to be obscured by systematic
          artifacts. No stochastic process will eliminate this.
          >
          > An interesting fact about the HP Z3100 and Z2100 is that the
          > integrated calibration and profiling measures per patch and
          > the dark patches get a longer time for the measurement.
          > Something that is difficult to achieve with strip reading or
          > one should increase the size of the dark patches.

          That's interesting indeed, confirming that black readings are more
          prone to errors.

          > Any change in the surface of matte black should give different
          > readings.

          I come to that conclusion as well. It's not illogical. My explanation
          is that any contamination or damage increases the scattering at the
          surface and, by that, increases the reflectivity of the surface. Is
          that what you mean as well? But I'm surprised by the size of the
          effect.

          Joost
        • Ernst Dinkla
          ... Given the up to 0.6 D differences between matte and gloss prints (with PK) it can be expected. A superb gloss top coat applied on a textureless matte print
          Message 4 of 9 , Jan 1, 2007
          • 0 Attachment
            Joost Horsten wrote:

            >> Any change in the surface of matte black should give different
            >> readings.
            >
            > I come to that conclusion as well. It's not illogical. My explanation
            > is that any contamination or damage increases the scattering at the
            > surface and, by that, increases the reflectivity of the surface. Is
            > that what you mean as well? But I'm surprised by the size of the
            > effect.

            Given the up to 0.6 D differences between matte and gloss
            prints (with PK) it can be expected. A superb gloss top coat
            applied on a textureless matte print (with MK) will show
            similar differences. It is the well known effect you get with
            spot varnishing on a matte or semi-gloss black offset print.
            Different visual density and a more selected view angle for
            the deeper black of the varnished area. So the grease
            (varnish) or marks (texture is reduced like in paper
            satination) reduce the scattering and the spectrometers
            light/sensor geometry results in less light reflectance to the
            sensor itself as it isn't in the the direct angle of reflection.

            Once we had a discussion here on the differences between dye
            ink matte Dmax and pigment ink matte Dmax. That's a harder nut
            to crack.

            Met vriendelijke groeten, Ernst


            | Dinkla Grafische Techniek |
            | www.pigment-print.com |
            | ( unvollendet ) |
          • CDTobie@aol.com
            ... Yes, reading darkness with a light sensor is less effective than reading light with a light sensor, this is true of all such devices. C. David Tobie
            Message 5 of 9 , Jan 2, 2007
            • 0 Attachment
              In a message dated 1/1/07 1:50:37 PM, j.h.j.h@... writes:


              > That's interesting indeed, confirming that black readings are more
              > prone to errors.
              >

              Yes, reading darkness with a light sensor is less effective than reading
              light with a light sensor, this is true of all such devices.

              C. David Tobie
              Product Technology Manager
              ColorVision Business Unit
              Datacolor Inc.
              CDTobie@...
              www.colorvision.com


              [Non-text portions of this message have been removed]
            Your message has been successfully submitted and would be delivered to recipients shortly.