Step by step - Learn how to use callas productscallas pdfToolbox Color conversionAdjust tone values and apply gradation curve to selected objects

Adjust tone values and apply gradation curve to selected objects

Adjusting tone values

Besides the ICC based color conversion, it is possible to adjust the tone values in a PDF file. This can be performed with a different configuration settings, called curves or curvefiles.

Applying dot gain adjustment

  1. Create a Fixup with type "Adjust dot gain".
  2. A predefined tone value could be used OR the setting for the tone value can be changed to a customized setting by duplicating an existing curve file (explained later).
  3. Here you have to specify a filter that determines which objects have to be 'fixed' or- adjusted for dot gain.

Apply gradation curve to select objects

The tutorial below demonstrates:

  • Setting up the appropriate filter
  • Configuring a level for special requirements
  • Performing levels
  • And finally checking the result

The purpose of this tutorial is to make a narrow black line with a tone value of 35% a little bit darker. The line that has to be correct uses a particular type of color coding, know as "Separation Black". Other lines in the PDF file are thinner or thicker and has a different tone value.

Inspect the demo file

Upon inspecting (View>Object Inspector) the middle dashed line in the attached PDF, you will find that the dashed line appears too light in the print. The tone has to be changed from 35% to 55%.

Create a Fixup

  1. Create a Fixup with type "Adjust dot gain".
  2. The setting for the tone value has to be changed to a customized setting (explained later).
  3. Here you have to specify a filter that determines which objects have to be 'fixed' (explained next).
  4. Click on the "plus" button to open a new customized Check.

Adjust the dot gain setting

The following steps are showing the current way of editing or creating a dot gain curve setting.
Before pdfToolbox 13, this had to be done via modifying an external configuration file. This procedure is described here.

  1. Best is to duplicate an existing setting. Duplication will open the window as shown below.
  1. Change the name to "Change to 55 percent".
  2. In this case the target value should be 55% (written as 0.55).
  3. Press OK to save this setting.
Open the dot gain curve setting folder (until pdfToolbox 13)
  1. Open the "Dot gain curve setting list".
  2. In the list select "Open folder with configuration files".
Modify existing dot gain curve setting file
  1. Select and make a copy of the dot gain curve setting file "010_25perc.crv".
  1. Change the name to "Change to 55 percent".
Review existing dot gain curve setting data

Open the dot gain curve setting file "010_25perc.crv" in a text editor to review the data. Most text editors are free. For example on Mac you have "TextEdit" and "TextWrangler"; on Windows "Notepad" and "Notepad ++".

Modify the new 'Change to 55 percent.crv'

Open the dot gain curve setting file "Change to 55 percent.crv" in a text editor to modify.

NOTE: When you edit or change the curve setting file, you have to make absolute sure to maintain the existing gaps between the values as tabs, and not to replace them with single spaces.

  1. If you want to specify a different name, this value must be set from 1 to 0.
  2. The name must be set to an appropriate value that is used. Here "FEATURE_AdjustDotGainMinus25Perc_long" should be "Change to 55 percent".
  3. The desired target values for levels must be registered in the rows affected by tabs. In this case the target value should be 55% (written as 0.55).

Please make sure the text file uses the suffix ".crv".

Syntax of a dot gain curve

The curve file needs to have a tab delimited structured as following:

DisplayName 1 Example 

When using the build-in editor in pdfToolbox 13 or later, syntax issues will be highlighted automatically.

INPUT
DEFAULT
Cyan Magenta Yellow Black REGEX::.*Spot.*
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.1
0.1
0.1
0.12
0.1
0.1
0.11
0.2
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.4
0.4
0.4
0.44
0.4
0.42
0.4
0.5
0.5
0.52
0.5
0.45
0.5
0.5
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.7
0.7
0.7
0.7
0.66
0.68
0.7
0.79
0.8
0.8
0.8
0.76
0.78
0.8
0.85
0.85
0.86
0.85
0.8
0.82
0.9
0.9
0.9
0.9
0.92
0.9
0.91
1.0
1.0
1.0
1.0
1.0
1.0
1.0

Not all values have to be listed in this file. For intermediate values not present a spline based interpolation is used.

Besides adjusting the tone values for each CMYK separation, you could also use the column title "All" to adjust all separations to the same value or "RGB::Red", "RGB::Green" and "RGB::Blue" for RGB as well as "LAB::L" for Lab color spaces. Every other column title will be considered as a spot color name. In order to be able to address a group of spot color channels regular expressions are supported as follows: "REGEX::_some_regular_expression_".

Add and configure the Checks for the 'Apply to' filter

  • Check property: "Object uses Black"
  • Check property: "Is Separation color space"
  • Check property: "Is line"
  • Check property: "Color value 1 for stroke"
    • Number: 0,35
      Plus/minus: 0,01
  • Check property: "Line width"
    • Number: 1
      Plus/minus: 0,01

Finally, name the Check 'Separation black line, 35%, 1pt'

Apply a customized Check in the 'Adjust dot gain' Fixup

  1. In the 'Apply to' filter, select "Separation black line, 35%, 1pt".

Apply dot gain curve setting

NOTE: After saving the new dot gain curve setting file, the setting is not in the tone configuration list. You have to close the dialog and open again to see the new setting in the list.

  1. In the list click "Change to 55 percent".

Rename the Fixup: "Set 35% line to 55%"

Apply Fixup on PDF file, save the Resultant PDF and review the report

The 35% line tone is changed to 55%.

Inspect the processed PDF file "Left_Demo file_Processed"

  1. Select the dashed line.

The tone of the dashed line is changed from 35% to 55%.

At the top is the processed PDF file where the tone of the dashed line is changed to 55%. At the bottom, the original dashed line with the lighter tone of 35%. In both PDF files the remaining lines are unchanged.