Overview
ISO/TS 20498-4:2020 specifies performance criteria for peripheral visual instruments used in a Computerized Tongue Image Analysis System (CTIS) for Traditional Chinese Medicine (TCM). The Technical Specification defines measurable requirements for accurate colour reproduction, display resolution, geometric distortion, and the viewing environment to ensure reliable tongue image capture, display and interpretation.
Key SEO terms: ISO/TS 20498-4:2020, CTIS, computerized tongue image analysis system, peripheral visual instruments, colour reproduction, sRGB, CIELAB ΔE.
Key Topics and Requirements
- Colour reproduction
- Devices must accurately reproduce the CTIS colour chart.
- Maximum CIE Lab* colour difference (ΔE*ab) per patch: ≤ 5.
- Conformity is verified by displaying the image of the colour chart and measuring with a colour spectrophotometer against ISO/TS 20498-3 values.
- Recommendation: use primary (CMY/RGB) and grey-scale patches for monitor calibration.
- Display resolution
- Minimum resolution: 1024 × 768 pixels at 4:3 aspect ratio.
- Distortion
- Maximum allowable distortion: ≤ 1% in both horizontal and vertical directions.
- Test method uses a concentric test card (small circle d = 20 mm ±0.1 mm; large circle D = 100 mm ±0.1 mm) and measurements at eight directions to calculate distortion percentage.
- Viewing environment (sRGB)
- Specified viewing parameters include:
- Display luminance: 80 cd/m²
- Adaptive white point: x = 0.3127, y = 0.3291 (D65)
- Encoding ambient illuminance: 64 lux; typical ambient: 200 lux
- Encoding/typical white point: D50 coordinates
- Image surround reflectance: 20%; viewing flare specified (1% encoding, 5% typical)
- Colour chart data
- Annex A provides sRGB coordinates for color and tongue-specific patches used in CTIS calibration and testing.
Applications and Users
- Intended for manufacturers and integrators of CTIS hardware and display subsystems.
- Useful to:
- Medical device developers (TCM diagnostic devices)
- Clinical imaging departments implementing tongue imaging workflows
- Quality assurance and calibration labs validating display performance
- Regulatory and procurement teams specifying acceptance criteria for CTIS displays
- Ensures consistent tongue colour rendering for clinical assessment, automated analysis, and telemedicine consultations.
Related Standards
- ISO/TS 20498-3 - Computerized tongue image analysis system - Part 3: Colour chart (normative reference)
- IEC 61966-2-1 - sRGB colour space (referenced for colour management)
- Additional medical imaging display QA guidance referenced in the document bibliography (e.g., IEC guidance).
This specification helps ensure that peripheral displays in CTIS deliver reproducible, diagnostically meaningful tongue images by setting clear, testable performance limits for colour, resolution and distortion.