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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

• Pack Proof
• Color Engine Pilot or Color Pilot
• PressSync Pilot
• An HT proof server driver.
  
  • E.g. "EPSON SC-P70x0 HT".
• A supported contract proofing device: https://wiki.esko.com/display/SystemRequirements/Pack+Proof+system+requirements+-+Product+overview+page
• Proofing paper certified for the printing process to be simulated.
  • Recommended proofing paper: EFI CertProof Paper 6225XF Semimatt.
• i1 or i1iO (first or second generation).

Limitations

Procedure

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

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:

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:

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

    Info
    title 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 resolution Maximum LPI 600 dpi 90 LPI 720dpi 100 LPI 1200 dpi 133 LPI 1440 dpi 150 LPI Note 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: Content by Label showLabels false showSpace false cql label = "186581692" and space = currentSpace()

    
    

• 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".
      
      

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!

• 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
    
    
    
    

    Warning
    title 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.

    
    

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

    
    

• Do a first evaluation.
  

  • Evaluate the background simulation. If the simulation is not a good match you can improve it by following this method:  Content by LabelshowLabelsfalseshowSpacefalsecqllabel = "213994806" and space in (currentSpace(),"KBA")
    KB213994806: Pack Proof - How to improve background simulation

  
  
  
• 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.

   Note
   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.