Overview - ISO/TS 18621-21:2023 (Graphic technology)
ISO/TS 18621-21:2023 defines a standardized, instrumented method to quantify 1D distortions in the macroscopic uniformity of printed areas (e.g., banding and streakiness) using scanning spectrophotometers. The method produces a single Macro‑Uniformity‑Score (0–100) based on averaged CIELAB measurements and adjacent CIEDE2000 colour differences along horizontal and vertical directions. The procedure is tailored for large, uniformly tinted areas and intentionally excludes non‑adjacent, diagonal or high‑frequency defects (for example, missing nozzles).
Key topics and technical requirements
- Test form and layout
- Uniformly tinted area on an A4 test page with a minimum dimension of 156 mm.
- Typical 2D sampling matrix assuming 6 mm pitch: ~31 × 26 patches (about 806 spots); perimeter patches may be omitted for processing.
- Measurement grid and device
- Use a scanning spectrophotometer or a handheld device mounted on an XY table to capture a well‑defined 2D sampling grid.
- Aperture diameter should be between 3 mm and 6 mm.
- Maximum sampling pitch: 6 mm in both directions.
- Measurement conditions
- Conform to ISO 13655; white backing per ISO 13655 Annex A.
- Prefer M1 measurement condition and store results in ISO 28178‑compliant format when applicable.
- Computation and scoring
- Average CIELAB values along rows and columns, compute adjacent CIEDE2000 differences, normalize and combine horizontal and vertical components.
- Macro‑Uniformity‑Score is computed using a formula (includes fitted factors 40 and 15) and rounded to zero decimals; higher is better (100 = perfect uniformity).
- Reporting
- Record test page dimensions, colour encoding, measurement condition/backing, any omitted perimeter patches, and final score.
Practical applications
- Objective evaluation of banding, streaks and large‑scale color non‑uniformity in digital, toner and inkjet printing systems.
- Quality control and acceptance testing in print production, OEM process validation, color laboratory benchmarking, and R&D for print engine development.
- Useful in process control when comparing printers, substrates or ink sets under defined test conditions.
Who should use this standard
- Print service providers, OEMs of printers and presses, color quality labs, prepress engineers, and researchers working on image quality metrics and print defect characterization.
Related standards
- ISO 13655 - Spectral measurement and colorimetric computation (measurement conformance).
- ISO/CIE 11664‑6 - CIEDE2000 colour‑difference definition.
- ISO 28178 - Data format for storing colorimetric measurements.
- ISO 12647‑7 - Reference point for proofing sampling (9‑point method comparison).
Keywords: ISO/TS 18621-21:2023, Macro-Uniformity-Score, macroscopic uniformity, scanning spectrophotometers, image quality evaluation, banding, streakiness, CIEDE2000, ISO 13655.