.png)
Manual zebra angle evaluation depends heavily on what an operator can visually distinguish in the reflected zebra pattern.In practical float glass inspection, subtle optical distortion may produce only very small changes in stripe displacement, making consistent visual interpretation difficult under real production conditions.
Request InformationView FZT-2 →
At a viewing distance of approximately 9 metres, the theoretical angular resolution of average human vision corresponds to roughly 2.6 mm of detectable detail.
When using a standard 25 mm zebra stripe pattern, visible deformation may need to exceed approximately 10% of the stripe width before it becomes reliably distinguishable to an operator.As a result, fine optical streaks, wave-like distortion and localized deformation zones may produce zebra pattern changes that are close to or below practical visual detection thresholds.
An important practical consideration is that human visual resolution is not identical from person to person.
Although approximately 2.6 mm is often considered an average theoretical visual resolution threshold at a 9 metre viewing distance, actual visual acuity can vary significantly between operators.
Some individuals may distinguish much smaller deformation patterns, while others may lose visibility at larger displacement levels. In certain cases, visual sensitivity differences may approach a factor of two between operators.
This means that when zebra angle evaluation relies on determining the point at which distortion is “no longer visible,” the final result can depend strongly on the individual observer.
As a result, the same glass sample may be interpreted differently depending on:
Certain optical distortion defects create only minimal or localized zebra pattern displacement.
Examples include:
- fine optical streaks
- surface waviness
- localised deformation near optical defect points
- small-area roller distortion
In these situations, the visible zebra change may remain close to the practical visual resolution limit of the observer, making consistent judgement increasingly difficult.
Automated optical measurement systems help reduce dependency on subjective visual interpretation by using structured image analysis and consistent evaluation logic.
Instead of relying solely on what an individual operator can visually distinguish, image-based optical measurement provides:
Explore how structured optical measurement can improve repeatability and reduce operator dependency in your production environment.
LUARI Insights explores practical challenges in optical distortion evaluation, measurement repeatability and industrial optical quality control systems for glass manufacturing.
.svg){kind=small}