Q100255: How to use the color picker's 'Enable Display Transform' option to apply an OCIO display transform

Iulia

Updated : November 07, 2023 16:00

Created : December 21, 2016 17:27

SUMMARY

This article explains how the Katana color picker option, 'Enable Display Transform', works.

MORE INFORMATION

In OCIO you can enable a color picker display transform for gamma corrections of the color picker thumbnail, similar to the Monitor when converting from linear to your Monitor's colorspace. Katana uses the OCIO color picker display transform when the 'Enable Display Transform' option is checked.

The color transformation should be specified under the OCIO configuration file roles section, and you can find more information regarding this on the Config syntax page of the OpenColorIO documentation. the following is an example roles section:

  roles:
    color_picking: cpf
    color_timing: lg10
    compositing_log: lgf
    data: ncf
    default: ncf
    matte_paint: vd8
    reference: lnf
    scene_linear: lnf
    texture_paint: dt16

color_picking - Colors in a color-selection UI can be displayed in this space, while selecting colors in a different working space (e.g scene_linear or texture_paint)

Depending on whether you are using Katana's default OCIO configuration or a custom one, when looking into the configuration file you should see the specific color transform applied to your color picker. 

For example, Katana's default OCIO configuration is nuke-default and the color picker display transform is set as sRGB. This information can be found in Katana's installation directory under: $KATANA_ROOT/etc/ocio/nuke-def ault/config.ocio

Color transformation logic

Within Katana, with display transform (filmlook) enabled, the raw screen color values provided by the color picker are passed through the processor and returned by the following Python statement:

OCIO.GetCurrentConfig().getProcessor(OCIO.Constants.ROLE_COLOR_PICKING,
OCIO.Constants.ROLE_SCENE_LINEAR)

NOTE: The color picker works under the assumption that you want to adopt the values that produce the picked screen color when piped through the display transform (if enabled): i.e. that the color preview matches the screen color whether or not the display transform is enabled.