ISo 3664:2025 Introduction (4th Edition)
ISO 3664 defines standardized viewing conditions for the visual assessment of color in graphic technology and photography. While instrumental measurements such as colorimetry and densitometry are essential, the final evaluation of complex images still depends on the human observer under controlled lighting conditions.
The standard addresses the fact that differences in illumination and viewing environments can significantly affect the perceived color appearance of prints, proofs, transparencies, and substrates. To reduce misunderstandings and improve consistency across the production chain, ISO 3664 provides specifications for reference viewing conditions based primarily on CIE Standard Illuminant D50.
A major update in the 2025 revision reflects the transition from fluorescent lamps to modern LED technology, driven by both improved LED quality and global efforts to eliminate mercury-containing lighting. The 4th edition introduces new viewing conditions P3 and P4, representing D50 illumination excluding UV, to better match typical indoor viewing environments where optical brightening agents fluoresce less strongly. These conditions align with the M2 measurement condition of ISO 13655, while the traditional P1/P2 conditions remain consistent with M1.
The standard retains established requirements for chromaticity and spectral conformity, but adds stricter recommendations enabled by advanced LED systems. It also introduces the CIE 224 color fidelity index as an additional metric, expected to become more important in future revisions.
ISO 3664 further specifies surround, ambient, and illumination levels to ensure proper visual adaptation. Two illumination levels are defined: a high level for critical comparison and a lower level for routine appraisal under more typical viewing conditions. Special guidance is also included for transparency viewing and photographic exhibition.
Finally, the standard no longer covers requirements for digital image display evaluation, as this topic is now addressed in separate ISO/IEC standards.
Viewing Conditions according to ISO 3664:2025
1. Viewing conditions for Print (P)
| Condition | Application | Illuminance E (lx) | UV content | According to ISO 13655 |
|---|---|---|---|---|
| P1 | Critical comparison of prints | required: 2000 ± 500, prefered: 2000 ± 200 | Incl. UV | M1 |
| P2 | Practical appraisal of prints | required: 500 ± 125 | Incl. UV | M1 |
| P3 | Critical comparison of prints without UV | required: 2000 ± 500, prefered: 2000 ± 200 | no UV | M2 |
| P4 | Practical appraisal of prints without UV | required: 500 ± 125 | no UV | M2 |
Note: all conditions based on CIE Illuminant D50
2. Viewing conditions for Transparency (T)
| Condition | Application | Luminance L (cd/m²) |
|---|---|---|
| T1 | For Tansparency Illuminator | required: 1270 ± 320, prefered: 1270 ± 160 |
| T2 | Transparency viewing by projection | required: 1270 ± 250 |
3. Other requirements
| Parameter | Normative requirement |
|---|---|
| Chromaticity tolerance | 0,005 (0,003) (CIE 1976 UCS) |
| Color Rendering Index CIE 13.3 | CRI (Ra) > 90 |
| CIE 224 Color Fidelity Index (optional) | Rf ≥ 95 |
| Metamerism index ISO/CIE23603 | Mivis ≤ 1,0 (≤0,5) / Miuv ≤ 1,5 (≤1,0) |
| Uniformity of Illumination ≤ 1m² | ≥ 0,75 (≥ 0,85) |
| Uniformity of Illumination ≥ 1m² | ≥ 0,6 (≥ 0,75) |
| Surrounding | Matte, neutralgrey, L* > 38 und < 82; Chroma value C*ab ≤ 2,0 |