1. Separate ghost, flare and veiling glare
Ghosts are structured artifacts commonly produced by reflections between optical surfaces or between the sensor stack and lens. Scattered light from edges, barrel surfaces, contamination or micro-roughness can create veiling glare that lowers contrast over a wider region.
Use shared definitions and example images. Different artifacts require different optical, coating, mechanical and cleanliness countermeasures.
- Focused or defocused ghost images
- Veiling glare and local contrast loss
- Aperture or barrel-edge artifacts
- Scatter from particles and surfaces
2. Build a source-position test matrix
Automotive scenes include low sun, oncoming headlamps, streetlights, tunnel exits, reflective signs and wet roads. Artifacts change as the source moves inside, near and outside the FOV.
Define angular paths rather than one showcase position. Include source spectrum, apparent size, distance, intensity ratio and camera orientation.
- In-field and out-of-field source sweep
- Sun, LED and headlamp spectra
- Source size and intensity ratio
- Horizontal, vertical and diagonal paths
3. Define metrics that reflect perception risk
A visible spot count is not enough. Measure local and global contrast loss, ghost luminance relative to the source, saturated area, artifact position and whether important targets become unusable.
Freeze exposure, gain, HDR mode, tone mapping and black level. Otherwise the same optics can appear to pass or fail because the camera pipeline changed.
- Contrast loss or veiling-glare index
- Ghost intensity and occupied area
- Artifact position versus target region
- Camera exposure and HDR configuration
4. Control every reflecting and scattering surface
Optical prescription, anti-reflection coatings, element edges, aperture, barrel ribs, adhesives, cover windows, filters and the sensor surface can all create unwanted paths. Solving only the front element is rarely sufficient.
Use non-sequential stray-light analysis to rank paths, then confirm coating lots, blackening, surface finish and cleanliness in real hardware.
- Optical-surface reflection paths
- Sensor and filter return paths
- Barrel, aperture and edge scatter
- Coating, blackening and cleanliness controls
5. Validate variation and difficult environments
Ghost behavior can shift with focus, spacing, coating variation, contamination, cover-window condition and camera assembly. Test multiple production-representative units, not only the best prototype.
Repeat critical scenes after temperature, humidity or mechanical loads when those stresses can move elements, change surfaces or introduce condensation. Record raw and processed data for root-cause work.
- Multiple units and coating lots
- Nominal and tolerance conditions
- Before/after environmental stress
- Raw-image and ISP-output evidence