# Krita implements CSS-4 chroma reduction for HDR gamut mapping

> **Key takeaway:** Krita introduces advanced gamut mapping using CSS-4 chroma reduction to prevent hue and luminosity shifts when converting high-dynamic-range colors to standard sRGB.

**Published:** 2026-11-10T10:56:40+00:00 
**Source:** Planet KDE (Desktop Engineers) 
**Category:** distro-planet 
**Canonical URL:** https://fosswire.org/news/krita-implements-css-4-chroma-reduction-for-hdr-gamut-mappin.html 

## Summary
Krita has implemented a new tone and gamut mapping filter as part of its ongoing High Dynamic Range (HDR) development project. This update addresses a long-standing issue where unbounded floating-point color values, such as those in linear Rec.2020, would suffer from hue and saturation shifts when clipped to the standard sRGB color space.

By utilizing chroma reduction algorithms, the software can now shift out-of-bounds colors into the target gamut while preserving their original luminosity and hue. This technical improvement ensures that highly saturated colors, such as those found in sunset photography, do not erroneously shift toward yellow or cyan during the conversion process.

## Technical implementation of gamut mapping in Krita
- **Algorithm Standard:** The implementation utilizes the CSS-4 chroma reduction method to manage color transitions between different color spaces.
- **Opponent Color Spaces:** Krita supports three distinct opponent color spaces for mapping: LAB, ICtCp, and OkLAB, with the latter two providing superior handling of blue hues compared to the traditional LAB space.
- **Mapping Logic:** The software employs a binary search to locate the gamut edge, iteratively adjusting chroma until the difference between the desaturated color and the clipped version falls below a specific minimum delta E threshold.
- **Cusp Method Implementation:** A lookup table of 'cusps' per hue is used to approximate the gamut boundary, allowing for more accurate color preservation across RGB and CMYK spaces.
- **Color Space Support:** The system is designed to work with unbounded floating-point editing and LCMS-based color management to handle wide-gamut data.

## Why it matters
This update significantly enhances Krita's capabilities for professional digital artists and photographers working with HDR content on Linux. It provides a more mathematically accurate way to prepare wide-gamut digital art for web-standard sRGB displays, reducing the need for manual color correction.