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Description

This article describes the process of making a dot (halftone) proof with Pack Proof.

The principle of making a dot proof with Pack Proof is that a compensation curve is applied (because the dot gain on the press and proof are different) when ripping the production job and these compensated bitmap files are then proofed with a proofing color strategy to color the inside of the dots.

Software and hardware requirements

Limitations

  • A color accurate output is not guaranteed when making a dot proof with Pack Proof!
  • An LPI value higher than 150 is not supported (to avoid moire).
    • Offset using AM screening - dot shapes (C, R, E, S) up to 133lpi/50 lpcm.

    • Flexography using AM screening – dot shapes (C, R, E, F) up to 133lpi/150 lpcm.

    • Proofing of special screens (e.g. hybrid) subject to limitations.

Procedure

A dot proof requires a printer operating in optimal printing conditions! Therefore one must start with creating a custom paper type!

Firmware update

Verify the printers' firmware before starting with this procedure and update when required!

Creating a custom paper type

For an optimal and stable print result, it is important to load the correct paper type when loading the media. In case of making a dot proof with Pack Proof, it is however mandatory to use generic Esko EPL files for any type of paper. So no matter what paper type is used, "Epson Proofing Paper White Semimatte" should be used because that is the paper type the generic Esko EPL files are based on. To compensate for the possible different used paper type a custom paper type should be used:


Print direction

When using generic Esko EPL files one should go for a Uni-D Print Head Alignment!

Proof Server configuration

  • Open the proof client and create a new output device.
  • Assign a generic Esko EPL file to the output device.
    • Download the generic Esko EPL file here:


      Don't forget to scroll down for the evaluation procedure of the EPL files!

      Print resolution versus LPI

      Select an EPL with a print resolution suitable for the LPI used by the production jobs you want to make a dot proof from. Consult below table to find the optimal resolution:

      Print resolutionMaximum LPI
      600 dpi90 LPI
      720dpi100 LPI
      1200 dpi133 LPI
      1440 dpi150 LPI
      Pack Proof uses the lowest resolution when using an EPL with an asymmetric resolution (e.g. 720x1440). More info can be found in this KB article:

  • Create a new workflow based on the High Resolution Esko Proofing (screened) template.



  • Go to the Workflow tab and make sure the Print bi-directional option is disabled.

Profile and color strategy creation

To color accurately, fill the dots of the bitmap files a color strategy is required!

  • Create a proofer profile
    • Color Engine Pilot 14.1.x > use the Standardized Proofing layout.
    • Color Pilot 16.1.1 and newer > no choice, use the default Proof Overprint chart.
  • Import or create the target press profile.

  • Create a proofing color strategy

    • Color Engine Pilot 14.1.x

      • Recommended device link settings:

        • Rendering Intent: Absolute Colorimetric.

        • Gamut Mapping: Closest Color (Classic).

        • Output Channels:
          • If the source profile fits inside the destination profile: Generate only CMYK. Check the below "Info" window about "Gamut comparison" how you can find whether the source profile fits inside the destination profile or not.

          • If the source profile doesn't fit inside the destination profile: Generate all channels.
        • Black Generation:

          • Depends on the output channels choice.

            • Generate only CMYK: No Black Mapping.

            • Generate all channels: No choice (Not available).

        • Illuminant: CIE Illuminant D50.
        • Refinement: <None>

    • Color Pilot 16.1.1 and newer

      • Select as Rendering Intent ("Match Colors" tab) "Absolute Colorimetric".

Gamut comparison

Especially for dot proofing it is important to have a proofer gamut covering completely the press profile!
One can verify this as follows:

Color Engine Pilot 14.1.x:

  • Tools > Gamut Check.
  • Select the Color Strategy and in the Check Inkbook option select Source Process Inks.

A green check icon for all inks in the second last column is a confirmation that the press profile fits inside the proofer gamut!

Color Pilot 16.1 and newer:

  • Add the solid process colors to a designer ink book.
    • Open the Compare Inks tool (Ink Books library view).
    • Click the cogwheel icon > Add Color from profile.



  • Select the proofing color strategy and click the Check Gamut button in the bottom tool bar.
  • Add the process colors to the Check Gamut tool.

Consider another type or brand of paper when one of the source inks is not in gamut. Glossy papers have a bigger gamut then matte papers...

Calculation of the dot gain compensation curve

The dot gain on the press and the proofer are different which makes we can't use the bitmap files going to the imaging device to make a dot proof. A new set of bitmap files which compensate for the dot gain difference is required. PressSync (included in Pack Proof) is an ideal tool to create such a compensation curve. By measuring a P2P25 chart with a spectro it is possible to create in an easy way such a curve!

We first need to find out what the dot gain is on the proofer for the specific screening parameters used during production.

  • Copy the P2P25 chart to the Automation Engine container and normalize it.
    One can find the P2P25 chart here: "x:\Esko\bg_prog_intellicurve_v161\dat\doc\P2P25vR1.pdf"

RIP the P2P25vR1.pdf with the same screening parameters (angle, LPI and dotshape) you use when ripping production jobs. Do NOT apply any curve (plate and press) in the RIP ticket!

RIP resolution

RIP the P2P25vR1.pdf with the same resolution you use when ripping production jobs.

Simulation of Advanced Screening Effects

Advanced screening effects modify specific parts of your screen, to improve how the plate interacts with the ink and paper, and achieve a better printed result in those areas. Typically they are applied in the highlights (highlight effects), or the shadows (surface screening effects). Some examples: PerfectHighlights, Groovy, Microcell, Concentric (Consult the Imaging Engine manual for more info).

While screening effects improve print quality, bitmap files with those effects do not look like your printed sheets. Imaging Engine offers a solution for this problem: when you are making your screened files for production, you can create print simulation
files at the same time. These print simulation files look like your production files, but with the advanced screening effects removed!

This way you can make a dot proof simulating the printed job even when using Advanced Screening Effects.

How to create print simulation files?

  1. Open the Image to Screened Separations ticket.
  2. Go to the output settings and select the Save print simulations option.

Print simulation files have a view file extension and are generated next to the output files!

  • Proof the bitmap OR .view files WITH a proofing color strategy (the one created in the "Profile and color strategy creation" step).
    • Use a workflow using the Create Wrapper File and Proof for Contract Approval ticket.
      Example workflow: Bitmap_to_DotProof.zip



      Create Wrapper File settings

      Proof for Contract Approval only accepts PDF files, not bitmap files. That is the reason why the Create Wrapper File ticket is needed. This task will put all bitmap files into a single PDF, but only when the Combine multiple input files (separations) to a single composite wrapper file option is enabled.

      Anti-aliasing

      Anti-aliasing (recommended value is 3) must be applied in order to avoid moire.

  • Do a first evaluation.


  • Start PressSync and create a new curve set based on the cmyk_ISO_PT1&2 template.
  • Click the Setup... button.
  • Select the press profile you want to use as desired printing condition (target) in the General tab (click the Change... button to change the default).
  • Go to the Process Colors tab and select %dE-SP as the Measure unit.
  • In the same tab, check the Extract Curves from desired printing condition option.
  • Click the OK button to close the Setup window.
  • Now it is a good time to save the curve set.
  • Go to the Measure menu and select Measure Automatic (make sure the Spectro is connected - only the i1 and i1iO are supported).
  • Select the P2P25.it8 layout in the Layout drop down list.


  • Click the Start button to start the measuring process.
  • Click the OK button to return to the measure window.
  • Click the Go To Results button to evaluate the results.
  • Click the Process Colors tab and select Tone Measurements only in the Select curves based on drop-down list.


  • Switch to the Process Colors > Selected Curves to see the compensation curves.
    In above sample the compensation curves are C53 for cyan, C51 for magenta, C52 for yellow and D53 for black.

  • Click the Save... button to save the curve set.
  • Choose Save curves in the Save window.



  • Click the Select Curve Names... button.
  • Define a letter and number for Other Inks. This will be the compensation curve for spot colors. Typically the black compensation values are taken.

Creating compensated bitmap files

Now that you have a compensation curve available, you can start ripping production files of which you want to make a dot proof of.

  • Select the production job in the Automation Engine Pilot.
  • Open the RIP ticket (Image to Screened Separations).
    • Make sure you select a ticket with the exact same screening parameters you used when ripping the P2P25 file!
  • Select the compensation curve (PressSync curve set) in the Separations tab of the RIP ticket.
    • Default Press Curve > Curve Strategy.

Making a compensated dot proof

  • Select the compensated bitmap files.
  • Proof these files with a dot proof workflow (Create Wrapper File + Proof for Contract Approval).
    • Check the Calculation of the dot gain compensation curve section for specific settings which must be used!

Refinement

A dot proof can be refined if your are not satisfied with the match.

Dot gain refinement:

  1. Rip the P2P25 chart according to the steps as explained in the Creating compensated bitmap files section.
  2. Open the PressSync curve set.
  3. Measure the P2P25 chart.

    The compensation curves will be shown as Used Curves in the Measure windows (Used Curves tab).
  4. Click the Go To Results button to evaluate the results.
  5. Click the Save... button when it's worth updating the curves. It's worth updating the compensation curves when there is a considerable difference between the Used Curves and New Curves (see below the Select curves based on option).

Highlight refinement:

The accuracy of the highlight simulation on proof depends on the used reference, it can be either a press profile, a DGC curve or characterization data. Press profiles and characterization data might not describe in detail the highlight behavior because of the fact that the overprint charts they are based on might not contain a lot of highlight values. For example, the ECI2002 chart jumps directly to 10%! As such, an interpolation (guess) will be done for any value between 0% and 10%.

Improving the highlight simulation can be done by using a correction curve (Apply Correction Curve = Between Press & Plate Curve) in the Separations\Corrections settings of the Image to Screened Separations ticket.

Spot color refinement:

Spot colors can be refined on the level of the color and/ or the dot gain.

Color refinement:
Use the default spot color refinement tools in Color Pilot to refine the color simulation.

Refinement of the dot gain:
Easy method: the dot gain compensation curve for ALL spot colors is defined in the PressSync curve set as Other Inks (see section Calculation of the dot gain compensation curve). An easy way to refine the dot gain is by changing the Curve definition for Other inks in the PressSync curve set.

Extended method: you can also refine a specific spot color by following this procedure:


Verification of a dot proof

The Esko dot proof solution doesn't guarantee a color accurate output, as such the verification is not covered in this KB article.

Proof for Contract Approval verification function

Verification can't be done with the verification function of the Proof for Contract Approval ticket. This method of verification uses unscreened strips and therefore doesn't match with how tints are perceived in case of a dot proof!

Article information
Applies to

Pack Proof all versions

Created
14-Mar-18
Last revised 
AuthorSDOB
Case Number 
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