Overview
ISO/TS 21830:2018, titled Image technology colour management - Black point compensation for n-colour ICC profiles, is a technical specification published by ISO to extend black point compensation (BPC) methods to n-colour ICC profiles, also known as xCLR profiles. These profiles include CMYK plus additional colourants such as red, orange, green, blue, and violet. The standard ensures consistency and accuracy in colour reproduction across digital printing applications utilizing extended colourant sets.
This document builds on the methodology described in ISO 18619:2015 to specifically address profiles with three or more colour channels, excluding 2-colourant systems. It defines key constraints, computational steps, and practical implementation guidance to enable effective black point compensation for advanced ICC profile types used in modern digital printing workflows.
Key Topics
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Scope and Applicability
The standard applies to xCLR ICC profiles where the data colour space contains CMYK plus optional additional colourants from a defined set (red, orange, green, blue, violet), as well as 3CLR profiles with CMY-like chromatic primaries. It explicitly excludes profiles with only two colour channels (2CLR).
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Black Point Compensation Extension
Black point compensation, a process that adjusts dark areas between devices for consistent appearance, is extended to n-colour ICC profiles. The method preserves the behaviour established for CMYK profiles and adapts it to complex extended colour spaces.
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Constraints for xCLR Profiles
To ensure predictable BPC results, the profiles must:
- Contain well-behaved, sufficiently transparent colourants.
- Form a gamut with a large range of neutral colours.
- Avoid using multiple heavy/light versions of the same colourant.
- Not include opaque white colourants.
- Have colourants with orthogonal colour vectors to maintain gamut integrity.
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Computation Procedures
The specification details how to compute the SourceBlackPoint and DestinationBlackPoint using colour transformations in the ICC Profile Connection Space (PCS) Lab* coordinates. It modifies the algorithm in ISO 18619:2015 to accommodate xCLR profiles in calculating LocalBlack and performing colour mapping in BPC.
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Extended Profile Support
Supports both ICC v2 and v4 profiles in compliance with ISO 15076-1, broadening applicability to contemporary printing technologies and devices.
Applications
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Digital Printing Colour Management
Facilitates accurate black point compensation in digital printing workflows that utilize extended gamut printing with more than four colourants, improving print quality and visual consistency.
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Advanced ICC Profile Development
Enables colour scientists and profile developers to create n-colour ICC profiles that support BPC, essential for colour-critical tasks in commercial and industrial printing.
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Colour Workflow Integration
Assists in integrating complex colour profiles in colour management systems, ensuring smooth interoperability between input devices, displays, and output printers with diverse colourants.
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Improved Colour Gamut Handling
Enhances artistic and photographic reproduction by allowing additional colourants beyond CMYK, broadening the achievable colour range while maintaining mid-tone and shadow detail fidelity.
Related Standards
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ISO 18619:2015
Image technology colour management - Black point compensation
Provides the baseline black point compensation algorithm extended by ISO/TS 21830:2018 for n-colour profiles.
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ISO 15076-1
Image technology colour management - Architecture, profile format and data structure - Part 1
Defines architecture and formats for ICC profiles, including xCLR device-dependent colour spaces.
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ICC.1:2001-04
File format standard from the International Color Consortium defining ICC profiles and colour space encodings applicable to this specification.
By adhering to ISO/TS 21830:2018, colour management professionals can ensure precise black point compensation in extended gamut ICC profiles, crucial for maintaining colour fidelity and smooth gradations in modern multi-colour printing environments. This standard is an essential reference for improving image technology colour management in digital print workflows using n-colour ICC profiles.