Parametric Gamma

Working with Parametric Gamma.

Any colour space held within LightSpace CMS can have Parametric Gamma Controls added to it, enabling non-power law variable gamma profiles to be defined by the user.


Parametric Gamma

Parametric Gamma

To add Parametric Gamma controls first save the basic colour space to be modified with a custom name, and then export via the Manage Colour Space library. Open the colour .bcs file in any text editor and add the required Parametric Gamma variables required by the user.


Parametric Gamma Controls

Any colour space can have Parametric Gamma Controls added to it, enabling non-power law variable gamma profiles to be defined.

To add Parametric Gamma controls first save the basic colour space to be modified with a custom name, and then export via the Manage Colour Space library. Open the colour .bcs file in any text editor and add the required Parametric Gamma variables using the following standard.

  <?xml version="1.0" encoding="UTF-8" ?>
  <builder_color_space name="test_Rec709_Mtx" version="2">
    <head>
      <x red="0.64" green="0.3" blue="0.15" white="0.3127" />
      <y red="0.33" green="0.6" blue="0.06" white="0.329" />
      <L red="1" green="1" blue="1" white="1" />
      <gamma>2.2000</gamma>
    <para points="3">
    <point idx="0">
      <ig>0.0000</ig>
      <og>0.0000</og>
    </point>
    <point idx="1">
      <ig>0.5000</ig>
      <og>0.8000</og>
    </point>
    <point idx="2">
      <ig>1.0000</ig>
      <og>1.0000</og>
    </point>
    </para>
    </head>
  </builder_color_space>

The section (para) is optional, and is used to define the Parametric Gamma points. If used it MUST contain a minimum of 2 points, and the first and last points MUST be 0.0 and 1.0. The in-between values are normalized between the first and last values of 0.0 and 1.0.

There can be as many points as needed in the list, and they should be monotonically increasing (in input value). The recommendation is to not exceed 101 pairs.

In the Manage Colour Space GUI a text message is displayed defining the Parametric Points if you have an active parametric gamma. In the Manage Colour Spaces library any matrix transform with parametric gamma is indicated with a star (*).

To download an example Rec709 colour space parametric gamma curve with Roll-Off, please select from the Downloads options.

The download can be loaded into LightSpace CMS for direct use, or opened via Windows Notepad, or similar, so the data entries can reviewed.


Using Parametric Gamma Controls

As it is possible define Parametric Gamma with up to 100 adjustment points it can be a great help with displays and projectors that struggle with constant gamma output, or that clip data in the blacks when a standard power law gamma is used.

As an example, a user can create a custom colour space using the Rec709 standard, using a standard power law gamma of 2.2, 2.4, etc, as a starting point, and then make parametric gamma adjustments along the gamma curve to compensate for the display's gamma inconsistencies.

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