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

Adjust tone values and apply gradation curve to select 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 file, called curvefile.

Syntax of a curve file

The curve file needs to be a tab delimited text file with the suffix ".crv" structured as following:

DisplayName 1 Example 
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_".

Using curve files

  1.  Create a Fixup with type "Adjust dot gain".
  2. The setting for the tone value can be changed to a customised setting using an own curve file (explained later) or the predefined settings.
  3. Here you have to specify a filter that determines which objects have to be 'fixed' or- adjusted for dot gain.

Set up a curve file as described above and copy it into the respective directory (depending on currently used Library), which can be opened using the entry "Open folder with configuration files" in the pop-up menu "Dot gain curve setting" as shown below:

Copy your curvefile into the folder.
After closing and reopening the Fixup, the new dot gain curve setting is visible in the dropdown and can be selected.

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 customised 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 customised Check.

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 customised Check in the 'Adjust dot gain' Fixup

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

Open the dot gain curve setting folder

  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).

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 botton the original dashed line with the lighter tone of 35%. In both PDF files the remaining lines are unchanged.