ISO 3664:2025

Overview

ISO 3664:2025 - Graphic technology and photography - Viewing conditions - provides internationally agreed specifications for how images on reflective and transmissive media (photographic and photomechanical prints, transparencies, backlit signs) should be viewed for consistent, repeatable visual assessment and comparison. The fourth edition (2025) updates tolerances for modern lighting, adds D50 conditions with UV excluded (P3/P4), introduces a colour fidelity index for LED sources, and removes monitor/soft‑proofing conditions.

Key topics and technical requirements

• Scope: Applies to critical comparison, tone reproduction appraisal, routine inspection of prints and transparencies, and projected transparency comparison. Not applicable to soft‑proofing displays or paper manufacture.
• Reference illuminant: Uses CIE standard illuminant D50 as the basis for spectral requirements; new options exclude UV to reflect typical indoor LED lighting.
• Viewing condition classes:
  • P1 / P3 / T1 - conditions for critical comparison (prints and transparencies)
  • P2 / P4 - practical appraisal and routine inspection of prints
  • T2 - conditions for viewing small transparencies by projection
• Measured parameters:
  • Spectral power distribution and chromaticity of the illuminant
  • Illuminance (for reflection viewing) and luminance (for transmissive viewing)
  • Surround and backing, diffusion/uniformity, veiling flare, resolution and distortion for projection
• Conformance and test methods: Includes spectral measurements, illuminance/luminance testing, resolution assessment and a normative conformance test for UV content (Annex D).
• Maintenance and tolerances: Updated tolerances reflecting advances in LED technology and guidance for maintaining consistent viewing apparatus.
• Informative guidance: Annexes provide summaries of conditions, validity considerations, exhibition/judging guidelines, and best practices for multi‑site comparisons.

Applications and who uses it

ISO 3664:2025 is essential for professionals who require accurate visual evaluation and color matching, including:

• Photographers and photographic labs
• Print and prepress professionals, colour proofing houses
• Packaging and label manufacturers
• Sign and display producers (backlit/transmissive media)
• Museums, galleries, and curators evaluating prints and transparencies
• Quality control teams ensuring consistent tone and colour reproduction

Use cases include critical proof approvals, routine inspection of production prints, comparison between transparencies and prints, and setting up standardized viewing booths or lightboxes.

Related standards

• ISO 13655 (measurement conditions M1/M2) - referenced for correspondence between visual viewing conditions (P1/P2 vs P3/P4) and instrument measurement conditions.
• Developed by ISO/TC 42 (Photography) in collaboration with ISO/TC 130 (Graphic technology).

Keywords: ISO 3664:2025, viewing conditions, graphic technology, photography, D50, illuminance, luminance, LED lighting, UV excluded, color fidelity index, proofs, color matching.