Overview - ISO/TR 20791-1:2020 (Photography, Photographic reflection prints - Evaluation methods of image quality)
ISO/TR 20791-1:2020 provides guidance and examples of measurement methods for evaluating the image quality of digital photographic reflection prints. It covers prints produced by inkjet, thermal dye transfer, electrophotography and silver‑halide (chromogenic) technologies and is aimed primarily at small prints with picture areas from 35 mm × 45 mm to 360 mm × 450 mm. The report defines terms (e.g., reflectance factor, mura, MTF, CTF, LSF), describes the principal image‑quality properties and explains measurement approaches applicable to modern digital printing processes. The document also clarifies the definition of “digital print” (prints made directly from digital data, with no persistent intermediate image carrier).
Key topics and technical requirements
- Five major image‑quality properties: density, colour, uniformity, tone and detail reproduction - plus glossiness as an important perceptual factor.
- Density and colour:
- Measurement of optical density (R, G, B, V values) and chromaticity.
- Consideration of additional colorants (e.g., black, orange, violet) and colour‑gamut metrics.
- Uniformity:
- Three scales: micro uniformity (granularity, graininess), semi‑micro (mottle) and macro (mura, banding, shading).
- Effects of dot structures, dot gain, dot placement, registration and rosette/moiré artefacts.
- Tone:
- Tone reproduction curves and capacity for tone reproduction (number of tonal steps).
- Detail reproduction:
- Spatial‑frequency metrics such as MTF/CTF, contrast response, resolution measured with fine‑line patterns and contrast‑resolution targets.
- Glossiness and reflected‑light sharpness:
- Specular gloss measurement and distinctness of image (DOI) or image clarity of reflections.
- Terminology and measurement apparatus: introduces VTF, LSF, addressability, spots per inch (spi), cycles per millimetre (cy/mm), and related test methods.
Practical applications and who uses it
- Quality control and R&D in photographic print manufacturing (inkjet, dye, electrophotographic, silver‑halide).
- Test laboratories and third‑party certification bodies establishing reproducible image‑quality metrics.
- Imaging scientists and product designers developing printers, papers and profiles.
- Photographic service providers, archivists and technical evaluators who need standardized measurement approaches for small‑format photographic prints.
Related standards
- The report references related work by ISO/TC 42 (Photography) and notes applicability of standards from ISO/IEC JTC 1/SC 28 and ISO/TC 130 where common imaging measurement methods exist. ISO/TC 42 also plans additional test targets and related parts in the ISO 20791 series.
Keywords: ISO TR 20791-1, photographic reflection prints, image quality measurement, digital photographic prints, density, colour, uniformity, tone reproduction, MTF, glossiness.