머신 비전에서의 산란광: 베일링 플레어, 고스팅, 글레어 및 BBAR 코팅 해결 방안
Veiling flare, ghosting, and target-side glare are different problems with different fixes. BBAR coatings, lens design, and filters address each one.
Stray light is non-image-forming light that reaches the sensor after reflecting or scattering inside the lens, not a bright object in the scene. It raises the dark-region floor, compressing contrast until low-luminance detail is unresolvable. Veiling flare spreads it as haze. Ghosting forms a localized secondary image. Target glare is a separate, scene-side problem. Fixing stray light means addressing the optics: lens design, coatings, window count, and shielding.
머신 비전에서 ‘미광’이란 무엇인가
Stray light is any light reaching the sensor that did not follow the lens's intended image-forming path: light reflecting off the inner barrel wall, scattering off a polished element edge, bouncing between two surfaces, or scattering from dust near the aperture stop.
The result is a background signal on top of the real image, which lifts the shadow floor and compresses usable dynamic range. It shows up as:
- 초점이 정확히 맞춰져 있어도 MTF 값과 겉보기 선명도가 저하됨
- 장면의 휘도가 높아질수록 악화되는 명암도 저하
ISO 9358 quantifies this floor as the veiling glare index (VGI): the fraction of scene luminance reaching the sensor as non-image-forming light, against a defined target and black reference. A 1% VGI caps surviving contrast near 100:1, the 40 dB figure under a 20 log convention. A different target or convention moves that number.
다중 요소 렌즈에서 왜 잔광이 발생하는가
Every air-glass interface reflects a fraction of incident light. An uncoated surface reflects about 4-5%. A well-coated surface reduces that to 0.1-0.5%, but not to zero.
Ten surfaces give 45 surface pairs that can fold light back toward the image plane, plus higher-order paths and the sensor cover glass. One reflection alone mostly costs transmission; the second is what sends light forward again, and which pairs make a visible ghost depends on the stop, focus, and surface geometry. The design task is keeping those reflections off the sensor area, absorbing them in baffles (internal blackened rings that trap stray rays), or scrambling them into the noise floor rather than a coherent artifact.
산란광 대 눈부심, 플레어, 고스트 현상
These terms get used interchangeably, but the fix depends on which problem is present. The table maps each failure mode to its usual cause and fix.
| 문제 유형 | 시각적 증상 | 일반적인 원인 | 가능성 높은 해결 방법 |
|---|---|---|---|
| 산란광 (일반) | 프레임 내 어느 곳에서든 명암 대비가 약해지거나, 그림자 하한이 상승하거나, 헤이즈 현상 또는 아티팩트가 나타나는 경우 | 센서에 도달하는 광학 경로 내부의 비이미지 형성 광 | 렌즈 설계(배플, AR/BBAR 코팅), 창 수 감소, 차폐 |
| 베일링 플레어 | 화면 전체에 균일한 흐림 현상이 나타나며, 어두운 부분이 검은색이 아닌 회색으로 보입니다. | 여러 내부 표면에서 발생하는 확산 산란이 넓은 배경 신호로 누적됨 | AR/BBAR 코팅이 적용된 저산란 렌즈; 보호 유리 수 감소; 렌즈 후드 |
| 고스팅 플레어 | 밝은 광원으로부터 어긋나 있는 구조화된 2차 이미지(고리, 원반, 줄무늬) | 두 표면 사이에서 일어나는 반사로, 센서 평면 상 또는 그 근처에 2차 이미지(대개 초점이 맞지 않은)를 형성함 | 고스트 현상이 적은 광학 설계; 밝은 광원을 고스트가 발생하기 쉬운 시야각에서 멀리 떨어뜨립니다. |
| 표적 눈부심 | 장면 오브젝트의 채도가 높은 스페큘러 하이라이트, 반사 지점에서의 디테일 손실 | 장면 대상에서 렌즈로 직접 들어오는 거울 반사 | 교차 편광, 조명 기하학, 조광각 변화 |
A camera losing contrast outdoors could have any of these, and each needs a different fix: a polarizer will not reduce ghosting from internal reflections, and a lens hood will not remove a specular highlight from a shiny part.
머신 비전에서 눈부심을 줄이려면 어떻게 해야 하나요?
Diagnose the failure mode first. Specular highlights on non-metallic surfaces call for cross-polarization; ambient contamination for a bandpass filter matched to the illumination wavelength; sensor clipping for less exposure or an ND filter.
비금속 표면의 교차 편광
Cross-polarization uses two linear polarizers 90 degrees apart: one over the source, one (the analyzer) over the lens. Specular reflection off a smooth non-metallic surface keeps its polarization and is blocked. Diffuse light depolarizes and partly passes, so surface detail survives. It works best on glossy dielectrics: plastics, glass, ceramics, solder mask. It can still reduce specular glare from bare metals, but less predictably, because metallic reflection alters the polarization state and the result depends on the metal, its surface roughness, and the incidence angle.
Each polarizer transmits about 50% of unpolarized light, so cross-polarization costs roughly two stops of signal. Set the F# from the depth of field the inspection needs, then add illumination to cover the loss, since lighting in most machine vision cells is programmatically controlled. Opening the iris on a Commonlands C-mount lens recovers that light only while the shallower depth of field stays acceptable.
대역통과 필터 및 ND 필터
A bandpass filter passes a narrow band matched to the illumination source and blocks out-of-band ambient light, stabilizing contrast between day and night. It does not suppress specular reflection at the target wavelength. Neutral-density filters cut transmission uniformly but recover nothing lost to specular geometry. See the bandpass filter guide for selection by wavelength.
HDR과 야외 장면에서 왜 문제가 드러나는가
Indoors, with controlled lighting and a matte target, stray-light contributions from any single path are small, and a 0.1% floor is invisible. Outdoors, direct sunlight runs about 100,000 lux and deep shadow near 10 lux. Illuminance is not the ratio the sensor sees, since reflectance, BRDF, view angle, and atmospheric scatter intervene, but a scene lit across that range still hands the lens a luminance ratio in the thousands. Bright sources like sun, sky, and headlamps can appear anywhere, including just outside the field of view.
Take a luminance range of 10,000:1 and normalize the peak to 1.0, so shadow detail sits at 0.0001. A 1% veiling-glare floor adds 0.0100 everywhere, so that shadow signal now rides on a floor 100 times larger than itself, leaving about 1% local modulation, below what the pipeline and shot noise preserve.
시야 범위를 벗어난 축외 광원
A lens keeps admitting light past its specified field of view. Sources well outside it still enter the barrel and reach the sensor by reflection. Which angles hurt follows the barrel, its baffles, and element geometry, so take the danger band from an angular stray-light scan of the lens rather than a generic number.
A stray-light-optimized lens absorbs these in baffles. One that is not produces haze or ghosts that seem to come from nowhere. This matters most for fixed automotive and outdoor cameras that cannot avoid bright sources.
HDR 센서가 그 성능 범위를 제대로 발휘하려면 잔광이 적은 렌즈가 필요합니다.
HDR sensors reach 120 dB or more of dynamic range, but the lens sets the ceiling: a stray-light floor holding surviving contrast near 60 dB on the same convention throws most of that away. Commonlands treats a stray-light-optimized lens as close to a prerequisite for an HDR sensor outdoors.
BBAR 코팅이란 무엇이며, 어떻게 미광을 줄여주는 것일까요?
BBAR stands for broadband anti-reflective coating: a multilayer thin-film coating that reduces Fresnel reflection across a wavelength band rather than at a single design wavelength. A BBAR-coated surface typically reflects under 0.5% across the band, against roughly 4-5% for uncoated glass. Lower surface reflection means more light reaches the sensor and less bounces between elements.
A single quarter-wave AR layer gives a broad but shallow minimum (roughly 1.2-1.4% for MgF2 on crown glass). A V-coat drives reflection near zero at one wavelength, good for a single NIR line but poor elsewhere. BBAR instead holds low reflectance across a band, commonly 400-700nm for visible or 400-900nm for combined visible and NIR use.
BBAR is applied to individual elements during manufacturing, so a datasheet note like "BBAR on Lens 1 Surface 1" means exactly one surface in the stack carries it. The other surfaces may use standard AR, MgF2, or nothing.
BBAR is also distinct from a hydrophobic coating. BBAR reduces Fresnel reflection, while a hydrophobic coating is a fluoropolymer layer on the front element that repels water and oil. It still sits on top of the optical stack, so ask for measured reflectance over wavelength and angle with the overcoat applied instead of assuming it is negligible. A lens can specify both as separate features.
| 코팅 유형 | 무엇을 줄여주는가 | 해결하지 못하는 점 |
|---|---|---|
| BBAR | 코팅된 표면에서 파장 대역 전반에 걸친 프레넬 반사 | 코팅되지 않은 표면, 배럴 내벽 또는 배플 틈새에서 발생하는 산란광; 왜곡; 수차 |
| 협대역 AR | 특정 표적 파장(예: 850nm)에서의 반사 | 다른 파장에서의 반사; 가시광선/근적외선(NIR) 병용 |
| 소수성 코팅 | 전면 표면의 물, 기름 및 지문 부착 | Ghosting, flare, and throughput set by the rest of the stack; it is not an AR design |
Verify coating claims against the current datasheet: the design band, which surfaces carry the coating, and average reflectance (Ravg) across the band all vary by product. With BBAR on only one or two surfaces, ghosting and flare still depend on element count, baffling, and barrel design.
One failure to watch: if a coating covers only 400-700nm but the system runs active NIR, the uncoated NIR reflections create ghosts that are invisible at the bench but clear in sensor output. Match the coating band to every illumination source.
엔지니어들이 실제로 어떻게 잔광을 줄이는가
There is no single universal fix. The approach depends on which part of the optical system generates the stray light.
The first tool is anti-reflection coating on every surface, since every uncoated interface reflects several percent. A stray-light-optimized design adds black-coated barrel baffles, matte aperture stops, and attention to which surfaces can form second-order reflections toward the sensor.
Every extra surface, including a flat protective window, adds to the budget. For environmental protection, an IP-rated lens that seals internally usually costs less stray light than a separate window. A sealed M12 lens such as the Commonlands CIL034 in its M12A variant, rated IP67, provides outdoor protection with no additional air-glass interfaces. The M12B build of the same optics carries no ingress rating, so check the variant suffix before assuming a lens is sealed.
A window still earns its surfaces where impact, abrasion, chemical exposure, field replacement, or sealing a whole enclosure is the requirement.
A lens hood or housing extension blocks off-axis sources before they reach the front element, one of the lowest-cost fixes for fixed-mount cameras. Where packaging limits hood size, as in automotive, the lens design has to do more. With programmable lighting, arranging sources out of the direct lens view lowers stray-light loading.
Image processing is a fallback, not a substitute. Flat-field correction addresses fixed multiplicative shading and pixel-gain non-uniformity, not the additive, scene-dependent background that veiling flare adds, so it does not generally remove flare; only a background that stays fixed can be subtracted by a separate calibration, and neither approach removes ghosts that move with the source.
미광을 최소화하도록 최적화된 M12 렌즈 및 눈부심 방지 액세서리
Commonlands stocks optical filters for ambient rejection below. A sealed IP-rated M12 lens can replace a separate protective window in outdoor builds.
이광 및 눈부심 문제 해결 체크리스트
Work through these when an outdoor, HDR, or reflective-scene camera shows unexpected contrast loss, haze, or ghost artifacts.
- Identify the artifact. Uniform haze (veiling flare), a structured spot displaced from a bright source (ghosting), or a saturated highlight on one surface (target glare). Each maps to a different fix.
- Capture a frame with the illuminator off. Usable signal from ambient alone points to a bandpass filter matched to the illumination wavelength.
- Move the light or camera 10-20 degrees. A highlight that tracks the source is specular geometry, not internal stray light.
- Count optical surfaces in the path. An uncoated window adds two 4-5% reflection surfaces. Where the window is only keeping water out, an IP-rated lens that seals internally does the same job without adding any.
- Test cross-polarization on non-metallic parts, and expect to add illumination or open the aperture to compensate. Reduced exposure that recovers gradient means the highlight was clipping, not a geometry issue.
- Confirm the lens is validated as low-ghost or stray-light-optimized for HDR or outdoor use, then verify with a hood on and off before locking the build.
자주 묻는 질문
Commonlands lenses use anti-reflection coatings to cut internal reflections. These answers explain what coatings can and cannot fix.
머신 비전 시스템에서 ‘미광’이란 무엇인가요?
이방광이란 렌즈를 통해 의도된 촬영 경로를 따르지 않고 센서에 도달하는 모든 빛을 말합니다. 이는 내부 배럴 표면에서 산란되거나, 렌즈 요소의 가장자리에서 반사되거나, 표면 사이를 오가며 반사되는 빛에서 비롯되며, 단순히 장면에 있는 밝은 피사체가 아닙니다. 이는 이미 광학 경로 내에 존재하는 원치 않는 빛으로, 그 영향으로 인해 배경 신호가 발생하여 명암비를 떨어뜨리고, 저휘도 조건에서는 피사체의 세부 특징을 식별하기 어렵게 만들 수 있습니다.
글레어, 플레어, 고스팅, 그리고 산란광의 차이점은 무엇인가요?
미광(Stray light)은 광학 시스템 내부에서 센서에 도달하는, 이미지를 형성하지 않는 빛을 포괄적으로 지칭하는 용어입니다. 베일링 플레어(Veiling flare)는 이러한 빛을 균일한 안개처럼 넓게 퍼뜨려, 뚜렷한 구조 없이 명암비를 떨어뜨립니다. 고스팅(Ghosting)은 국소적인 인공 현상으로, 특정 표면 간 반사로 인해 발생하는 구조화된 2차 이미지입니다. 글레어(Glare)는 이와 달리, 피사체 자체에서 발생하는 포화 상태의 정반사이며, 이는 피사체 측의 문제입니다. 편광 필터나 기하학적 구조를 통해 피사체의 글레어를 해결한다고 해서 내부 미광이 해결되는 것은 아니며, 그 반대의 경우도 마찬가지입니다.
머신 비전에서 눈부심을 줄이려면 어떻게 해야 하나요?
먼저 고장 원인을 진단하십시오. 비금속 표면의 정반사 하이라이트의 경우, 교차 편광 방식을 사용하십시오. 즉, 조명 장치에 선형 편광판을 장착하고 렌즈에 교차 편광 분석기를 장착하는 것입니다. 주변광 오염의 경우, 조명 파장에 맞는 대역통과 필터를 사용하십시오. 센서 클리핑의 경우, 노출을 줄이거나 ND 필터를 추가하십시오. 조명 기하학적 구조를 변경하여 정반사 각도를 축에서 벗어나게 하는 것이 대개 가장 빠른 초기 테스트 방법입니다.
렌즈의 BBAR 코팅이란 무엇인가요?
BBAR는 광대역 반사 방지 코팅(Broadband Anti-Reflective Coating)의 약자로, 단일 설계 파장이 아닌 특정 파장 대역 전반에 걸쳐 프레넬 반사를 줄여주는 다층 박막 코팅입니다. 코팅이 되지 않은 유리는 표면당 입사광의 약 4~5%를 반사하지만, BBAR 코팅이 적용된 표면은 일반적으로 설계 파장 대역 전반에 걸쳐 0.5% 미만의 반사율을 보이며, 이를 통해 투과율을 높이고 플레어 및 고스트 현상을 유발하는 내부 반사를 줄여줍니다.
보호용 창은 어떤 경우에 잔광을 더 악화시키나요?
A protective window adds at least two new air-glass interfaces. Uncoated, each reflects roughly 4-5% of incident light; even AR-coated, a few tenths of a percent remain. Those accumulate, so a standard flat window in front of a well-designed lens can increase veiling flare in high-dynamic-range scenes. An IP-rated lens that seals at the front element keeps those interfaces out of the budget, though a window still wins where impact, chemical exposure, or field replacement is the requirement.
사용 목적에 맞는 저산란광 렌즈를 선택하는 데 도움이 필요하신가요?
Commonlands engineering can help identify whether stray light, ghosting, or target glare is the root cause in your build, then match the lens, coating, or filter to your sensor format and environment.