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WO2000057638A1 - Capteur de lumiere ambiante a domaine dynamique destine a des cameras a imagerie electronique - Google Patents

Capteur de lumiere ambiante a domaine dynamique destine a des cameras a imagerie electronique Download PDF

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Publication number
WO2000057638A1
WO2000057638A1 PCT/US2000/007550 US0007550W WO0057638A1 WO 2000057638 A1 WO2000057638 A1 WO 2000057638A1 US 0007550 W US0007550 W US 0007550W WO 0057638 A1 WO0057638 A1 WO 0057638A1
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WO
WIPO (PCT)
Prior art keywords
light
ambient
cast
shadow
reading apparatus
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US2000/007550
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English (en)
Inventor
James F. Alves
Zazuo Nomura
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Individual
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Priority to AU43260/00A priority Critical patent/AU4326000A/en
Publication of WO2000057638A1 publication Critical patent/WO2000057638A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/70—Circuitry for compensating brightness variation in the scene
    • H04N23/71—Circuitry for evaluating the brightness variation

Definitions

  • This invention relates to light sensing devices, and more specifically it relates to apparatus and methods of improving the dynamic-range control of 24-hour electronic- imaging surveillance cameras, particularly such apparatus operating under outdoor ambient-light and artificial-light environmental conditions.
  • U.S.Pat.#5,455,685 (f ⁇ led: 8/1992 via FUJI Photo Co of Japan) is shown a "video-camera exposure-control apparatus for controlling iris-diaphragm and automatic-gain control operating-speed", wherein operating-speed control-circuit simultaneously increases or decreases the respective operating-speed of the iris-diaphragm control and the automatic- gam control, based upon the state of the photographing scene as is regulated by a
  • the purpose of the invention is to provide an improved method of adapting the
  • This invention allows a camera to create high-contrast images of desired objects moving through the camera's field-of-view regardless of the specific background light-levels within the camera's field-of-view.
  • the invention's reliability is good in that it is involves no moving parts, nor does it require ultra-high speed AGC/ALC-circuitry to successfully adapt to objects moving rapidly through the camera's field-of-view; and, is suitable for video-cameras operating in a snap-shot (asychronous reset) mode, since the camera is not required to be continuously generating images to perform AGC and ALC.
  • a traffic-surveillance camera mounted to view a single-lane of traffic from an approximate 30-degree downwardly pitched camera-lens axis; -such as may be provided from a mounting point perched upon an overhead-gantry structure for example.
  • Our invention monitors the dynamic-range of the ambient-lighting condition, and dynamically adapts camera-gains and pedestal functions as to produce high-contrast
  • the common AGC response approach will generally generate low-levels of gam, resulting in low-contrast images of the passing license-plates; a problem made especially difficult when trying to image highspeed vehicle license-plates dwelling very briefly in the wmdow-of-opportunity (depth-of- O field) of the camera.
  • the AGC has very little time to respond to the instantaneous changes in scene illumination conditions, and it can be difficult to discern which changes should be used to decide on AGC and ALC level settings.
  • Various weather conditions or road-surface materials can also affect the light-reflecting properties of the road, and produce poor gam-settings to be chosen by the camera.
  • the essential purpose of video-camera gain-control is to adjust the amount of light being gathered, and/or the degree of sensitivity of the light-to-elect ⁇ city producing elements, so that the electrical-signals generated by the camera viewing targets of interest, are widely spread across the available output dynamic-range and limited in their degree of saturation or clipping
  • the changes in gam are required so that as light-levels
  • the overall ambient- ght level is directly monitored by few of the camera's internal sensing elements, regardless of what objects the camera is viewing A separate light-sensor and associated electronics to sense the ambient-light condition, is avoided by this instant invention, since a small portion of the camera's existing imaging sensor is utilized as the ambient-light sensor.
  • the problems and cost associated with trying to match the response of a separate 5 ambient-light sensor to the response of the camera's own internal light-sensing elements over the extremely wide-range of outdoor light-levels and over temperature varations, is also avoided, -since the same element standard-of-reference is adapted for both imaging and ambient-light sensing.
  • the primary object of this invention is to ensure that the camera gams will be 0 set properly to produce high-contrast images of vehicle license-plates in particular, by adapting the camera-gams based upon instantaneous measurements of both the brightest and darkest light-levels of interest, -and not on unreliable road-reflectance property indexes.
  • the object of this invention is to provide a reliably durable if relatively inexpensive, as well as much more accurate method and apparatus by which to sense around-the-clock dynamic (that is, subject to ongoing sometimes intense variations in light amplitude) ambient-light conditions. Conceived primarily for critical outdoor lighting conditions which can for
  • this invention disclosure sets forth the novel notion of a control apparatus 5 employing a microcosm like quasi-mockup device capable of virtually simulating the environmental lighting conditions posed by a typical license-plate (which in terms of chroma, or grey-value, may bare alphanumereic-indicia which are dark on a light- background, or light indicia upon a dark-background), that can be affected by all sorts of ambient lighting changes 24-hours a day.
  • the camera may encounter a car which rear license-plate lights (required by law) are not working, and the plate is located inset beneath the bumper splashed with mud, -as one extreme.
  • the nature of this invention is to set forth an improved ambient-light sensor device, which works well under all weather conditions and road-surface reflectance-index properties; so as to operate in conjunction with existing and future automatic license-plate reading surveillance apparatus employed by civil departments of transportation, -which can include monitoring of traffic-light intersections, and transportation monitoring systems used on tool-roads for example.
  • the novel ILS( intelligent light-sensor) hereof is to employ a microcosm device comprising elements which are capable of essentially simulating the worst-case scenario for a license-plate as described above (an elongate planar surface canted about 20-degrees toward a horizontal road-plane surface representation, beneath an eyebrow like overhang) by employing a special dual-opposed first and second surface-plane cast-shadow simulation.
  • unique microcosm device shall further be oriented in azimuth, as to place the second/cast-shadow simulator surface-plane 180-degrees out of phase relative to a first/cast-shadow surface-plane; - and just as significantly, the aggregate two surface-planes (each thus respectively depicting difficult to read front and rear vehicle license-plates) being oriented in azimuth parallel with the surface-plane of the object(s) being simulated (a vehicle license-plate generally).
  • a non-intrusive light-level reading device be included to read the instant light condition prevailing upon the simulated cast-shadow surface-planes housed within the ambient-light sensor apparatus.
  • the preferred reading device is a tiny periscope-like vertical fiberoptic unit, having a light-collecting nose facing slightly downward toward the miniature canted license-plate simulated surface-plane, and thereby piping the collected light into a light-occluded chamber where it is projected upon a photovoltaic-cell, for a light-amplitude reading; which voltage signal-level generated is thus sent on to an ECU(electronic control unit)-comparator, for ultimate real-time regulation of a remote electronic-imaging camera aperture-setting.
  • ECU electronic control unit
  • the ILS( intelligent light-sensor) implement AGC and ALC algorithms for digital video-cameras that need to capture images of license-plates from rapidly moving vehicles in ambient outdoor lighting environments; via: a.) a fully auto-ranging light- measurement device capable of rapidly determining the minimum and maximum light— amplitudes that the camera's dynamic-range must span under any given ambient outdoor- lighting condition; and- b.) a programmable micro-processor to translate the light- sensor's measurements into camera gain and pedestal controls, which are inputed directly to the camera and/or auto-iris lens; and- c.) a discrete control signal to turn on/off nighttime illuminators at predetermined light levels.
  • the ILS utilizes two preferably fiber-optic (or approximately 1/8th-inch diameter plexiglas-rod optical-piping) to collect ambient-light reflected off of the two azimuthally opposed-facing macrocosm target surface planes. These targets are surfaced in a planar bright-white non-retroreflective material.
  • Each of the two opposed inverted J-shaped rod fiberoptic light collector elements is arranged(directed) as to read the instant light-level upon the target cast-shadow simulator surface planes, the pick-up nose of which is aimed at substantially the same slightly downward looking pitch and azimuth orientation as the actual remote picture taking camera-lens.
  • Both of the fiberoptic light-gathering rods pipe the target-light onto a preferably photo-diode type sensor device capable of making accurate 1/10th-second(or less) light-amplitude measurements over light-levels ranging from direct sunlight to twilight; and, the combined spectral-response of the preferably fiberoptic (or acrylic-rod piping) stem conduit and their photo-diodes, is closely matched to the overall response of the digital-camera and its associated optical-components.
  • the mini/max. light-level the camera must image without saturation is determined as the minimum of: a. ) the opposite cooperating target's light-reading multiplied by "p"(rho is approx 1/3rd, that is- the ratio of the reflectivity of the darkest license-plate symbol material area of interest, to the reflectivity of the white plate-material used as the target sample specimen), or, b.) the maximum light-level multiplied by "p", and then l ⁇ divided by a factor (preferably approximately 3) that estimates the light-reduction caused by cast-shadows.
  • the microprocessor can then be programmed to translate these readings into auto-iris, shutter-speed, video-signal amplifier-gain, and pedestal (dc level ) adjustments for the iS given camera/lens combination to be controlled by the ILS.
  • the predefined light-levels used to switch on/off nighttime auxiliary-lighting are separately adjustable to account for the maximum usable camera gam setting, the quantity of light provided by the external- lighting source, and to provide hysteresis during the transition from the "on to the off" state, and vice-versa.
  • F ⁇ gure-1 is a pictorial perspective-view of the overall invention apparatus
  • F ⁇ gure-2 is an upper plan-view thereof
  • F ⁇ gure-3 is a semi-diagrammatic cross-sectional side-elevation view thereof, including partial cutaway portions therein,
  • F ⁇ gure-4 is an environmental depiction of an exemplified roadway installation, showing the positioning of the ILS relative to the camera optical-axis and the sun-rays,
  • F ⁇ gure-5 is a reference-chart tracing a ten-hour plotting of ambient-light brightness deviations owing to sun-overcastmgs, measured relative to the opposed front- target and rear-target surfaces
  • a second preferably identical surface-plane element 16" likewise having non-functional (structural only) backside 17", plus, a respective first fiberoptic (or equivalent piping- rod) light-collector stalk 19' (inverted J-shape), and a respectively identical, albeit arranged in 180-degree opposition, second identical fiberoptic light collector stalk 19"
  • the surface-plane elements 16' and 16" are here shown as dual opposed members
  • Fig's. -1 ,2, 3 demonstrate how how the exemplified sunrays 26 projecting from above (ref. Fig. -4) will desirably cast a major shadow 21 (dependent upon lighting conditions, -such as time of day, generally casting two shadows at around noon), as well as minor shadows 21 ' and 5 21 ", from their respective stalks 19' and 19", upon the primary preferably matte-white (or possibly a grey-value approximately simulating the environmental road-surface 27 in Fig.- 4) finished areas 15' and 15" of the staging platform 15, which 1 st-reflectance 20' (action ref.
  • the DCC can thus change image gain and level command parameters accordingly, thereby critically preventing saturation of the instantaneous dynamic-range measured at the ILS 10 (as is being delineated in our Fig. -5 reference-chart).
  • PCC input-power conditioning circuit
  • the exemplified underslung block 27 is representative of a preferred thermostatically controled electric I resistive-heater device, which below a threshold of approximately 67f-degrees(Fahrenhe ⁇ t) for example is automatically activated to radiate heat via thermal-conductivity, as to maintain the baseplate 12 and associated electronic-componentry at a moderate temperture, while also acting to reduce presence of excessive humidity.
  • S 12 thus warmed is capable of radiating sufficient BTU's to also intended keep the dome 14 from fogging-up do to normal effects of internal dome-surface moisture condensation as well.
  • FIG. -4 shows an exemplified street enviornment where a motor-vehicle is depicted moving briskly through a red-light 30, clearly visible to its incautious driver.
  • the ILS-unit 10 is shown generally situated proximal the roadway 28', in this example an intersection (comprising roadways 28' and 28") having exemplified conventional stoplight-signal fixtures 30' and 30".
  • ILS-unit reading realistic preference is to situate the ILS-unit as near to the vehicle position portrayed here as possible, so that the ILS-unit is capturing the same exact manner of environmental reflections, shadows, and artificial night-lighting influences affecting the actual license-plate 32 as possible.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Studio Devices (AREA)

Abstract

La présente invention concerne une unité rentable et fiable de capteur intelligent de lumière (ILS) facilitant une lecture automatique continue jour et nuit de conditions variées de lumière ambiante extérieure via un suivi en temps réel de l'orientation et de l'amplitude solaires et d'autres influences lumineuses d'environnement, permettant ainsi de mettre en oeuvre une régulation de compensation dans un équipement associé de caméra à imagerie électronique conventionnelle. Le logement de l'unité ILS compacte présentée en exemple comporte un dôme (14) hémisphérique protecteur transparent recouvrant une configuration de détecteur double de lumière bidirectionnel, comprenant des surfaces (16, 16') réfléchissantes opposées en forme d'aile de papillon dotées d'éléments (19, 19') jumeaux de fibre optique renvoyant discrètement la lumière recueillie sur une paire de cellules (24', 24'') photoélectriques enveloppées. Les avantages de la simulation macrocosme de la lumière tombant sur une plaque minéralogique de véhicule en mouvement, comprennent la possibilité unique de déterminer des lectures à dynamique supérieure/inférieure extrême (pour cristallin irien, vitesse d'obturateur, amplificateurs électroniques) d'un objet, tel qu'une plaque minéralogique de véhicule, pour l'obtention d'une imagerie finale plus claire au moyen d'une caméra vidéo généralement semi-automatique dont l'axe optique doit seulement être dirigé de manière approximativement parallèle aux capteurs de la scène situés à l'écart de l'axe d'ouverture optique.
PCT/US2000/007550 1999-03-22 2000-03-21 Capteur de lumiere ambiante a domaine dynamique destine a des cameras a imagerie electronique Ceased WO2000057638A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU43260/00A AU4326000A (en) 1999-03-22 2000-03-21 Dynamic-range ambient-light sensor for electronic-imaging cameras

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US12547299A 1999-03-22 1999-03-22
US06/125,472 1999-03-22

Publications (1)

Publication Number Publication Date
WO2000057638A1 true WO2000057638A1 (fr) 2000-09-28

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PCT/US2000/007550 Ceased WO2000057638A1 (fr) 1999-03-22 2000-03-21 Capteur de lumiere ambiante a domaine dynamique destine a des cameras a imagerie electronique

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AU (1) AU4326000A (fr)
WO (1) WO2000057638A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7515822B2 (en) 2006-05-12 2009-04-07 Microsoft Corporation Imaging systems' direct illumination level adjusting method and system involves adjusting operation of image sensor of imaging system based on detected level of ambient illumination
US9884591B2 (en) 2013-09-04 2018-02-06 Gentex Corporation Display system for displaying images acquired by a camera system onto a rearview assembly of a vehicle

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4792675A (en) * 1987-02-06 1988-12-20 Varo, Inc. Diffused surface radiant energy receiver
JPH0885385A (ja) * 1994-09-16 1996-04-02 Nissan Motor Co Ltd 車両用監視装置
US5742340A (en) * 1995-06-06 1998-04-21 Hughes Missile Systems Company Ambient light automatic gain control for electronic imaging cameras and the like

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4792675A (en) * 1987-02-06 1988-12-20 Varo, Inc. Diffused surface radiant energy receiver
JPH0885385A (ja) * 1994-09-16 1996-04-02 Nissan Motor Co Ltd 車両用監視装置
US5742340A (en) * 1995-06-06 1998-04-21 Hughes Missile Systems Company Ambient light automatic gain control for electronic imaging cameras and the like

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7515822B2 (en) 2006-05-12 2009-04-07 Microsoft Corporation Imaging systems' direct illumination level adjusting method and system involves adjusting operation of image sensor of imaging system based on detected level of ambient illumination
US9884591B2 (en) 2013-09-04 2018-02-06 Gentex Corporation Display system for displaying images acquired by a camera system onto a rearview assembly of a vehicle

Also Published As

Publication number Publication date
AU4326000A (en) 2000-10-09

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