This revision is an essence of this branch: https://phabricator.kde.org/source/krita/history/kazakov%252Fhdr-support/
It enables HDR painting workflow in Krita:
- Window surface format can be selected in Preferences->Display
- Rec 2020 PQ color space is added to LCMS engine
- Small Color Selector support selection of HDR color. You image should be in a floating point format to enable "Brightness" slider.
- Allows saving HDR PNG images according to the standard