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Calibration Curves

Depending on the target selected, the measurement file (whether measured or imported) will be assessed and calibration curves will be created to fit the target.

1. Select target

The measurements will be compared to the target selected in this section in order to create the curves.

You can sort all the default targets in the Select Parameters section depending on the standard (ISO or G7®), the substrate (Coated or Uncoated) and the type of use by the press (Production or Proof). You can also use Show all targets to access to the full list of targets. If some targets don't match any of the sorting options, a checkbox Show other targets will appear to get the list of all the targets with no match.

In Target list, you can find all the sorted targets using a self-describing title to help you do the correct comparison; they all use the same format:

CRPC | FOGRA (Coated | Uncoated) - G7 | ISO (Production | Offset | Digital) - SCCA - Scoring

The first information is the Color Aims: - CPRC or - FOGRA CRPC corresponds to Universal datasets for G7® (CRPC3 is uncoated and CRPC6 is coated). FOGRA corresponds to the following standard profiles:

  • FOGRA 39, also known as ISO Coated v2
  • FOGRA 47, also known as PSO Uncoated
  • FOGRA 51, also known as PSO Coated v3
  • FOGRA 52, also known as PSO Uncoated v3

Next comes the calibration : - G7® or - ISO. G7® calibration follows the NPDC (Neutral Print Density Curves) method.

The information in parenthesis corresponds to the G7® Production Verification standard or the Press the ISO standard is made for. G7® (Production Verification) control is based on measurement of at least 3 to 46 gray patches, CMY overprint. This assessment conforms to G7® Pass/Fail criteria except for the number of required gray patches.

SCCA stands for Substrate Color Correction Aims. This option adapts Process Color when measured paper is different from the reference, depending on the ΔE2000 difference: If Paper ΔE2000 ≤ 2: No SCCA applied If 2 ≤ Paper ΔE2000 ≤ 5: SCCA applied If Paper ΔE2000 ≥ 5: SCCA applied with caution

Finally, the scoring part gives a score to the assessment depending on how many criteria are conform.

2. Measurement

There are 3 ways to use measurement files:

  • Upload files button: opens the window to select the measurement file to import
  • Measure it button: opens the Measurement Module window (see below for the Measurement Module; not available on Safari)
  • Drag and drop the measurement file directly in the field outlined

Only dataset with spectral data are accepted. Adding measurements files to the list allows to select or deselect the measurements to use. All the measurement selected will be averaged.

3. Report

3.1 Conformity

Each parameter defined in the target is displayed, comparing the aim values to the measurement file. Some parameters can have the result "Not enough Data" when the patches in the file don't correspond to the assessment parameters selected in the target. If the "Scoring" is part of the target selected, the score will be shown with the conformity logo on the left of the window and the % of each criteria will be displayed at the right of the window. The Conformity tips link opens a new page explaining the cause of the non-conformity and suggestions on how to address them.

3.2 Curves

This section displays the Tone Value Increase (TVI) depending on the Tone Value (%) for each ink defined in the measurement file. The colored curves correspond to the measurement while the gray curves correspond to the target. The dashed lines represent the range of curves that passes the assessment.

3.3 G7® Gray Balance

If the measurements contain G7 patches it will show this section. The G7® Gray Balance curves correspond to the weighted Delta Chroma of the CMY combination of the Gray Balance patches, the a* and the b*. To check if the measurement is close to neutral in the gray, check if the curves are close to 0 for each percent of ink.

4. TRCA

The Tone Reproduction Curve Adjustment (TRCA) generated are shown here. For G7 curves (and correct set of G7 patches), it is possible to change the feather-off. The values selected shows where it starts to be applied (up to 100%). The name of the curves file and the format of export can be selected.

Measurement Module

This tool contains all the information needed to measure correctly your charts.

0. Interfacing with the computer

The first time trying to use the Measurement Module displays instructions to install the Alwan Endpoint allowing to interface the instrument connected to your computer with the Measurement Module on the website. After downloading the software, you have to install it on the computer and allow the website to call it.

  • On macOS: for some user the application is recognized as "from an unidentified developer". If it happens, you need to go in System Preferences -> Security & Privacy, click on the lock to make changes and then on "Open anyway". Finally, the first window will show again with the option to "Open".

Once installed, the browser asks to allow this site to open the alwan+endpoint link with Alwan Endpoint. Check "Always allow https://colorcloud.alwancolor.com to open alwan+endpoint links" to have a working connection.

1. Connection

If you don't see the list of all the instrument, please check "Interfacing with the computer" first. All the instrument that we support are available in the carrousel which rotates using the arrow on the left and right of the instruments displayed. The instrument needs to be on and linked to the computer. Bluetooth is not supported, the connexion needs to be via cable.

Techkon instruments are only supported on Windows.

2. Configuration

Mode

The Measurement Mode, as defined by ISO 13655, can be selected depending on the instrument used:

  • M0: illuminant A - UV not controlled
  • M1: Simulate illuminant D50 - with UV conform to standard
  • M2: Simulate any illuminant - without UV
  • M3: Simulate any illuminant - with polarization filter

M0 is the most frequent mode used in today production. M1 is selected by default.

Illuminant

Standard illuminant can be computed depending on the parameter selected.

Observer

The instrument observer can be 2° (by default) or 10°. The 2° Observer refers to CIE 1931 standard colorimetric observer model. It will be used for colorimetric computation of CIELab tristimulus values.

Density Status

Density will be computed according to the Density Status thanks to the spectral values in the measurement file. Status E is commonly used in Europe while Status T is commonly used in America.

White Base

White Base can be Paper (by default) or Absolute. If Paper is selected, Density will only take into account the ink density (zero density is paper). If Absolute is selected, Density will take into account paper and ink density.

Backing

It depends on the backing of the measurement used. By default the White backing is selected. Some instrument also supports the Black backing.

3. Chart selection

In this step you can select one of the Alwan charts or import your own chart. Depending on your needs, you can download the following packages to print the chart to use:

When importing charts, please respect the CGATS formats for the order of the patches to be correct and measurable. Multiple page charts can't be used.

4. Measurement

Settings

This tab concentrates all the settings to manage your device: the patch length, the patch weight (depending on the instrument) and the mode of measurement (patch mode or scan mode). The Disconnect button will put you back to the selection of the instrument. The Calibration button is mandatory for most instrument when starting to measure. It can also be asked to click it after multiple measurements or a long time without any measurement done.

Chart

This field contain the information about the chart to measure and the results of such measurement once it is done. Also, the chart at the top of the window will show the top part of each patch as the reference color and the bottom part as the color measured. Below it, the Graph tab will show the curves of the measurement done and the Table tab will show the numeric values.

Info

This tab shows all the steps to take in order to measure correctly. Any error of manipulation or device will also appear in this zone. The three available buttons are:

  • Revert: for manual instruments it helps to go back one patch or one line (depending on the mode) to measure it again. For automatic instruments, it will help to re-triangulate before doing the measurement.
  • Stop: to stop the device in the middle of a measurement. Some automatic instruments may have to finish the line they are measuring before being able to stop.
  • Measure: to start the measurement.

Measurement list

This field contains all of the measurement done. Clicking on one of them will select it and show a representation of the patches, the graph curves of what was measured and the table of the numeric values. It is possible to remove it with the Clear button.