ISO 20462-3:2012

Overview

ISO 20462-3:2012 - Photography - Psychophysical experimental methods for estimating image quality - Part 3: Quality ruler method describes a standardized psychophysical procedure for measuring image quality using a quality ruler. The standard defines the nature of quality rulers, both hardcopy and softcopy implementations, how to generate or obtain ruler stimuli, and the Standard Quality Scale (SQS) - a fixed numerical scale calibrated in units of just noticeable differences (JNDs).

Key takeaways:

• The SQS is anchored to physical references, with one SQS unit ≈ one JND and a zero point corresponding to minimal image information.
• Digital Reference Stimuli (DRS) and Standard Reference Stimuli (SRS) are provided or referenced for absolute and relative calibration when viewed under controlled conditions.

Key technical topics and requirements

• Nature and construction of quality rulers: specification of ordered univariate reference stimuli that differ by known JND increments for quality or individual attributes.
• Hardcopy and softcopy implementations: physical apparatus, reference prints (SRS), display hardware requirements, and controlling software for softcopy experiments.
• Reference stimuli and generation: guidance on producing quality ruler images, including calibration workflows and available DRS/SRS resources.
• Standard Quality Scale (SQS): properties, procedures for primary and secondary SQS determinations, and how observer ratings map to JNDs in real time.
• Measurement and calibration methods: scene-dependent ruler calibration, Modulation Transfer Functions (MTFs) considerations, and required experimental conditions and reporting.
• Psychophysical context: relation to paired-comparison and magnitude-estimation approaches; use of observer instructions, experiment design, and data reduction to express differences in JND units.
• Supporting material: informative annexes with sample instructions, example datasets, calibration notes, and even sample code for softcopy experiments.

Note: the document references viewing conditions (ISO 3664) and includes a notice about potential patent claims related to the quality ruler method.

Practical applications

• Imaging system testing: objective comparison of cameras, scanners, printers, and displays using a calibrated perceptual scale.
• Algorithm evaluation: quantifying visible improvements or degradations from image processing (sharpening, denoising, compression).
• Quality assurance and R&D: rapid, JND-calibrated assessments during product development or manufacturing.
• Research and standardization: experiments requiring absolute or relative image-quality scales that are comparable across labs and studies.

Who should use this standard

• Camera, display and print manufacturers
• Image processing and codec developers
• Conformance and test laboratories
• Academic and industrial researchers in imaging science
• Standards bodies and quality assurance teams

Related standards

• ISO 20462-1: Overview of psychophysical elements
• ISO 20462-2: Triplet comparison method
• ISO 3664: Viewing conditions for image assessment

Keywords: ISO 20462-3:2012, quality ruler method, image quality, Standard Quality Scale (SQS), JND, digital reference stimuli (DRS), standard reference stimuli (SRS), psychophysical methods, MTF, image calibration.