`
`PCT PUB. NO. WO 93/11631, PUBLISHED JUNE 10, 1993
`
`("DENYER")
`
`TRW Automotive U.S. LLC: EXHIBIT 1309
`PETITION FOR INTER PARTES REVIEW
`OF U.S. PATENT NUMBER 8,599,001
`
`
`
`PCI‘
`
`International Bureau
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`
`
`
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(51) International Patent Classification 5 =
`
`(11) International Publication Number:
`
`WO 93/11631
`
`H04N 5/335, 9,097: 5/225
`
`(43) International Publication Date:
`
`10 June 1993 (10.06.93)
`
`(21) International Application Number:
`
`PCT/GB92/02260
`
`(22) International Filing Date:
`
`4 December 1992 (04.12.92)
`
`(81) Designated States: GB, JP, US, European patent (AT, BE,
`CH, DE, DK, ES, FR, GB, GR, IE, IT, LU, MC, NL,
`PT, SE).
`
`Published
`With international search report.
`Before the expiration of the time limit for amending the
`claims and to be republished in the event of the receipt of
`amendments.
`
`(30) Priority data:
`91259549
`
`6 December 1991 (06.12.91) GB
`
`(71) Applicant (for all designated States except US): VLSI VI-
`SION LIMITED [GB/GB]; Technology Transfer Cen-
`tre, King’s Buildings, Mayfield Road, Edinburgh EH9
`3JL (GB).
`
`(72) Inventor; and
`(75) Inventor/Applicant (for US only) : DENYER, Peter, Brian
`[GB/GB]; 91 Colinton Road, Edinburgh EH10 SDF
`(GB).
`
`(74) Agents: McCALLUM, William, Potter et al.; Cruikshank
`and Fairweather, 19 Royal Exchange Square, Glasgow
`G1 3AE (GB).
`'
`
`
`
`
`
`(54) Title: SOLID STATE SENSOR ARRANGEMENT FOR VIDEO CAMERA
`
`(57) Abstract
`
`The present invention relates to an image capture system suitable for use in an electronic camera system C and comprising
`a solid state image capture device (1) comprising an integrated circuit (5) having at least two sensor arrays (4), each said array
`having an image sensing surface (3) and a respective lens system (8) associated therewith.
`
`1309-001
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`1309-001
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`(l
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`{V
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`FOR THE PURPOSES OF INFORMATION ONLY
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`Codes used to identify States party to the PCT on the front pages of pamphlets publishing international
`applications under the PCT.
`
`Viet Nam
`
`France
`Gabon
`United Kingdom
`Guinea
`Greece
`Hungary
`Ireland
`Italy
`Japan
`Democratic People‘a Republic
`of Korea
`Republic of Korea
`szikhslan
`Liechtenstein
`Sri lanka
`Luxembourg
`Monaco
`Madagascar
`Mali
`Mongolia
`
`AT
`AU
`BB
`BE
`BF
`BC
`8.]
`BR
`CA
`CF
`CG
`CH
`CI
`CM
`C5
`CZ
`DE
`DK
`PS
`Fl
`
`Amtria
`Australia
`Barbados
`Belgium
`Burkina Faso
`Bulgaria
`Benin
`Brazil
`Canada
`Central African Republic
`Congo
`Swit'lcrland
`('51:: d‘lvoire
`'ameroon
`(In-choslovakia
`Cluck Republic
`Germany
`Denmark
`Spain
`Finland
`
`Mauritania
`Malawi
`Netherlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
`Russian Federation
`Sudan
`Sweden
`Slovak Republic
`Senegal
`Soviet Union
`Chad
`Togo
`Ukraine
`United States of America
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`1309-002
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`1309-002
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`WO93/ll63l
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`_ 1
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`_
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`PCT/GB92/02260
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`VSOLID STATE SENSOR ARRANGEMENT FOR VIDEO CAMERA
`
`The present invention relates to electronic cameras
`
`including electronic colour cameras.
`
`It is well known that colour sensors can be produced by
`
`discriminating three images of the primary colours
`
`(blue, green, red) of the scene. All colours can be
`
`analysed and synthesised via these primaries (or other
`
`complementary triples like cyan, magenta, yellow).
`
`Conventional electronic cameras classically use one of
`
`two approaches for forming the separate colour images.
`
`3-tube cameras use a single lens followed by a prism
`
`which forms three separate r.g.b images. Three sensors
`
`are used simultaneously to detect these three images.
`
`If the sensors are accurately aligned the resulting
`picture is of very high quality. However the sensors
`
`are separated in space and orientation and their
`
`assembly and alignment with the prism and lens is
`
`difficult for a volume manufacturing process. This
`
`technique is therefore used exclusively for expensive
`
`broadcast-quality equipment. Colour-Mosaic Cameras use
`
`a single lens and sensor, but the sensor surface is
`
`covered with a high-resolution mosaic or grid of colour
`
`filters, with the pattern dimension equal to the
`
`pixel-pitch for a semiconductor CCD or MOS sensor
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`array. Pixels of different colours are demultiplexed at
`the sensor output and interpolated to form synchronous
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`parallel colour signals. This is well-suited to volume
`
`production as the surface colour mosaic can be
`
`fabricated as an extension of the semiconductor wafer
`
`fabrication process.
`
`The techniques for mosaic
`
`3O
`
`fabrication are restricted to relatively few companies
`
`worldwide who supply the colour sensor market and thus
`
`they are not commonly available. Furthermore,
`
`associated with this technique there are technical
`
`problems concerned with resolution and aliasing. Much
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`1309-003
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`W0 93/1 1631
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`- 2
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`PCT/(2892/02260
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`work has been done to correct these effects, but usually
`
`at some cost in image-processing hardware.
`
`It is an object of the present invention to avoid or
`minimise one or more of the above disadvantages.
`
`5
`
`the present invention
`In one of its broadest aspects,
`provides an image capture system comprising a solid,
`state image capture device which device comprises an
`
`integrated circuit having at least two sensor arrays,
`each said array having an image sensing surface and a
`respective lens system associated therewith.
`
`10
`
`Thus in effect the present invention provides two or
`more cameras on one chip each with its own lens system
`
`and sensor array. With such an arrangement the problem
`of alignment is greatly reduced by the fabrication of
`the various sensors required one one chip. This ensures
`
`that the sensors all lie in the same plane and have the
`
`same rotational orientation, and this is an important
`advantage. Assuming lenses can be accurately assembled
`in a parallel plane (see below),
`the only alignment
`errors which are likely to occur are simple orthogonal
`translations in the form of vertical and horizontal
`errors in the centres of the optical axes.
`It is
`
`relatively easy though to calibrate these cameras after
`assembly and electronically to correct for these
`translations. Whilst the inevitable lateral off-set
`between the cameras at even the closest dispositions of
`the cameras on the chip, will of course give rise to a
`
`degree of parallax error, it has now been found that
`with a preferred system of the present invention with
`generally adjacent sensor arrays, the degree of error in
`producing a single composite image (i.e. a single image
`produced by the more or less accurately aligned super
`imposition of two or more corresponding images e.g. at
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`1309-004
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`- 3
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`PCT/GB92/02260
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`different wavelengths, of the same scene) can be
`
`acceptably small for small camera geometries for low to
`
`medium resolution applications.
`
`Thus in said one
`
`preferred aspect the present invention provides a
`
`composite image camera of particularly simple and
`
`economic construction.
`
`The present invention also provides in another aspect a
`
`stereoscopic image capture system where larger sensor
`
`spacings are used to provide a greater parallax
`
`differential for producing different images with a more
`
`or less accurately defined parallax differential for use
`
`in producing stereoscopic image pairs. Again the use of
`
`two or more cameras mounted on a single chip helps
`
`substantially to minimise alignment problems in
`
`producing an accurate stereoscopic view.
`
`Advantageously the lens systems are mounted
`
`substantially directly on the image sensing surfaces.
`
`Preferably there is used a lens system in accordance
`
`with our earlier British Patent Application No.
`
`9103846.3 dated 23rd February 1991 (published in
`
`International Publication No. WO92/15036) which lens
`
`comprises a lens and a spacer in substantially direct
`
`contact with each other, said spacer preferably having a
`
`refractive index not less than that of said lens, said
`
`lens and spacer having refractive indices and being
`
`dimensioned so as to form an image in a plane at or in
`
`direct proximity to a rear face of said spacer element
`
`remote from said lens element,
`
`from an object, whereby
`
`in use of the lens system with said lens system mounted
`
`substantially directly on the image sensing surface of
`
`the image capture device an optical image may be
`
`captured thereby.
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`1309-005
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`WO 93/11631
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`- 4
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`"
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`PCT/GB92/02260
`
`These lens systems have the advantage of physical
`dimensions which can be made similar to those of the
`sensor array itself, so that sensors and lenses may be
`immediately adjacent to each other. Camera separations
`
`The flat surfaces of the
`minimise the parallax error.
`cylindrical lens spacer also help to maintain accurate
`planarity for groups of lenses attached to the same chip
`substrate.
`
`It is also possible though to use more conventional,
`albeit similarly small,
`lens systems which are mounted
`on a suitable support so as to be spaced from the sensor
`surface with an air gap therebetween. One advantage of
`such systems is that they allow the use of more
`conventional and cheaper lens materials without the need
`for special materials having particular refractive
`indices.
`
`In general at least one of the individual cameras
`constituted by respective lens system and sensor arrays,
`is provided with a filter means for passing a desired
`wavelength (or wavelength range) of the electromagnetic
`radiation spectrum, whereby there may be captured a
`composite image comprised of two or more (depending on
`the number of individual cameras used)
`images of the
`same object differing substantially only in the
`
`wavelength thereof.
`
`In one preferred form of the invention the integrated
`circuit has three sensor arrays provided with respective
`lens systems and filters for three different wavelengths
`e.g. red, green, and blue, or cyan, magenta, and yellow
`for providing a desired composite image e.g. a
`
`full-colour image.
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`1309-006
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`1309-006
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`\V()93/11631
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`'
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`— 5
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`—
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`PC17(}B92/02260
`
`Where three or more individual cameras are used, it will
`
`be appreciated that various different layouts of the
`
`sensor arrays relative to each other may be employed
`
`including e.g.
`
`linear arrangements or generally
`
`"circular" or other close-packed arrangements.
`
`In cameras using the 3 primary colours, green is
`
`dominant in providing image acuity since it generally
`
`dominates the derived luminance.
`
`In all cases
`
`therefore,
`
`the green camera is desirably made as central
`
`10
`
`as possible, and the red and blue cameras are referenced
`
`to it.
`
`The parallax errors will therefore show up on
`
`red and blue only.
`
`With reference to lens systems of our earlier
`
`application No. 9103846.3,
`
`the expression "substantially
`
`15
`
`direct contact" is used to mean that there should not be
`
`any significant interspace containing low refractive
`
`index material such as air i.e. no interspace having a
`
`thickness resulting in a significant optical effect.
`
`In
`
`the case of an air gap this should normally be not more
`
`20
`
`than 500 um, preferably not more than 100 um,
`
`thick,
`
`In
`
`the case where resin or like material is used between
`
`the components adhesively to secure them together and
`
`has a refractive index comparable to that of the lens or
`
`spacer, it may be considered as an extension of the lens
`
`25
`
`or spacer and thus need not be so restricted in
`
`thickness though preferably the thickness thereof should
`
`not be excessive and should be more or less similarly
`
`restricted.
`
`Advantageously there is used a plane-convex (or possibly
`
`30
`
`plano-concave - see below)
`
`lens with a substantially
`
`plane spacer for manufacturing convenience and economy
`
`but other combinations e.g. a bi-convex lens and a
`
`plane-concave spacer, may also be used°
`
`1309-007
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`1309-007
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`
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`“093/1163:
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`_ 6' _
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`PCT/GB92/02260
`
`Preferably the lens system is secured to said image
`sensing surface by an optical grade adhesive i.e. a
`substantially transparent optically uniform adhesive.
`Desirably there is used between the lens and spacer an
`adhesive having the same refractive index as the lens
`(or if preferred, as the spacer) and between the spacer
`and the sensing surface, an adhesive having the same
`
`refractive index as the spacer.
`
`10
`
`Preferably the spacer has a higher, most preferably a
`substantially higher, refractive index than the lens.
`Where the same refractive index is acceptable for both
`
`then it will be appreciated that the spacer could be
`
`formed integrally with the lens.
`
`15
`
`It will be appreciated that the radius (or radii) of
`curvature of the lens element and its refractive index
`may be varied through a wide range of values depending
`on the required performance in terms of depth of field,
`image size,
`freedom from aberrations etc.
`In general
`there will desirably be used solid state image capture
`
`20
`
`devices in the form of photoelectric sensor arrays
`
`(wherein photons are used to generate electric current
`and/or voltage or change electrical properties such as
`resistance etc.) which have relatively small size image
`
`in the range from 0.1 to 5 cms
`sensing surfaces e.g.
`across. Thus the lens system should in such cases
`desirably be formed and arranged to provide a similarly
`small-sized image. Where a wide angle field of view is
`also required (e.g.
`in surveillance applications),
`then
`a lens of relatively short focal length should be used
`
`e.g. for a field of View angle of 80 degrees the
`(maximum) focal length will not normally exceed 1.19
`times the image height and for 60 degrees will not
`normally exceed 1.73 times the (maximum)
`image height,
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`25
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`3O
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`J‘a
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`q!
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`1309-008
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`1309-008
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`'wo 93/11631
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`_ 7
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`_
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`PCT/GB92/02260
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`the (maximum)
`
`image height corresponding to half the
`
`sensing surface diameter.
`
`The use of a high refractive
`
`index spacer and the exclusion of any low refractive
`
`index material from the optical path significantly
`
`decreases aberration due to Petzval Curvature (otherwise
`
`known a curvature of field aberration) and limits
`
`spherical aberration.
`
`The lens system is therefore
`
`particularly advantageous in wide field and/or large
`
`aperture applications required for low light
`
`conditions.
`
`In general there is desirably used, for
`
`such wide angle applications, a lens element having a
`
`refractive index and in the range from 1.45 to 1.65, and
`
`a spacer element with a higher, refractive index and in
`
`the range from 1.45 to 1.85.
`
`Various optical grade materials having suitable
`
`refractive indices are widely available. Low—dispersion
`
`glass such as type BK7 (available from various sources
`
`e.g. Schott Glaswerke)
`
`is particularly suitable for the
`
`lens element.
`
`The spacer element may be made of LaKlO
`
`glass also readily available.
`
`other materials that may
`
`be used for the lens and/or spacer elements comprise
`
`plastics materials, although these are generally less
`
`preferred in view of their lower resistance to
`
`scratching and other damage and the lower refractive
`
`indices available. Nevertheless they may be acceptable
`
`for certain applications requiring low cost such as
`
`consumer door-entry and security cameras.
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`Suitable adhesive materials for use between the spacer
`
`and lens elements and between the spacer element and the
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`30
`
`solid state image capture device include optical grade
`
`epoxy resins.
`
`In a preferred image capture system of the present
`
`invention the solid state image capture device comprises
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`1309-009
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`1309-009
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`PCTIGB92/02260
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`an integrated circuit image array sensor such as that
`disclosed in our earlier International patent
`application No. PCT/GB90/01452 (publication No.
`W09l/O4633 the contents of which are hereby incorporated
`wherein by reference thereto) which has on-board signal
`processing means formed and arranged for directly
`providing a video signal output. Naturally though other
`image capture devices such as CCD, MOS and CCD sensors
`may also be used. Also the image capture device may
`comprise simply a sensor chip on which are only provided
`the sensor arrays with all the electronic circuitry
`required to detect the response of individual sensor
`cells to incident radiation and further processing of
`
`the detected response provided externally of the sensor
`chip, and of course other arrangements with a greater or
`lesser part of this electronic circuitry provided on the
`chip bearing the sensor arrays, are also possible.
`Accordingly references to "cameras" herein includes
`references to apparatus in which substantially the whole
`of the electronic circuitry required to produce a video
`output signal is provided on the same chip as the sensor
`arrays, as well as apparatus in which a greater or
`lesser part is provided separately. Thus references to
`camera alignment relate only to alignment of the lenses
`and sensor arrays (and not to any other components that
`may be required to produce a video signal output.
`
`Thus using miniature, chip-mounted lenses, it is
`possible to fabricate multiple independent cameras on
`single VLSI chips. These cameras accurately lie in the
`same plane and are rotationally in substantially perfect
`alignment.. Any remaining alignment errors are primarily
`translational and can be easily corrected by retiming
`
`the readout control sequences.
`
`Us):
`
`‘1
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`PCT/GB92/0226U
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`Further preferred features and advantages of the present
`
`invention will appear from the following detailed
`
`description by way of example of a preferred embodiment
`
`illustrated with reference to the accompanying drawings
`
`in which:
`
`Fig.
`
`1 is a schematic perspective view of a composite
`
`image colour video camera of the invention with three
`
`individual camera units;
`
`Figs 2(a)
`
`to (d) are schematic views showing 4 different
`
`2-D arrangements of the three camera elements relative
`
`to each other;
`
`Fig.
`
`3 is a schematic illustration of the optical
`
`performance of a camera of the invention;
`
`, Fig. 4 is a block circuit diagram of one possible
`
`electronic architecture for a camera of the invention;
`
`Fig. 5 is a sectional elevation of another camera of the
`
`invention; and
`
`'
`
`Fig.
`
`6 is a schematic perspective View of a spacer
`
`support element suitable for use in the camera of Fig. 5.
`
`Fig.1 shows a miniature colour video camera system 9
`
`having three cameras 1 each comprising a lens system 2
`
`mounted directly onto the image sensing surface 3 of a
`
`respective solid state image capture device in the form
`
`of an integrated circuit image array sensor 4.
`
`The
`
`sensors 4 are formed as separate sections of a single
`
`monolithic VLSI microchip 5 mounted in a suitable
`
`housing SE containing a power supply 6 and provided with
`
`a video signal output interface 7.
`
`In more detail the lens system 2 comprises a generally
`
`hemispherical lens 8 having a radius of curvature of the
`
`order of 0.85 mm, and a cylindrical spacer element 9 of
`
`substantially larger diameter
`
`(ca. 1.7mm) and a length
`
`of 1.59 mm, with an aperture stop 10 therebetween.
`
`The
`
`aperture stop 10 is of metal e.g. steel alloy with a
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`wo 93/11631
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`— 10 —
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`PCT/GB92/02260
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`thickness of 0.15 mm and an iris diameter of 0.8 mm
`
`The
`providing an effective lens aperture of f2.0.
`aperture opening is filled with clear epoxy resin 11
`which has a refractive index substantially similar to
`
`that of the lens 8 and secures the lens 8 and spacer 9
`
`to each other and to the aperture stop 10.
`
`Alternatively an aperture stop of metal or other
`
`material could simply be printed onto the spacer or lens
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`10
`
`The R, G, B
`e.g. using a photolithographic technique.
`(red, green and blue) filters 12 for the three
`respective lenses 8 can also be disposed between the
`
`lenses 8 and spacers 9.
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`0
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`The lens 8 is of low dispersion glass (Bk?) having a
`
`refractive index nd of 1.568 and the spacer is of LaKlO
`
`15
`
`glass which has a higher refractive index nd of 1.7200.
`This combination produces low image blur and large image
`
`size (ca. 1.4mm image height from central axis). The
`
`spacer 9 has a length of around 1.59mm. This lens
`
`system has an effective depth of field of from 2cms
`to
`CX> with a field of View angle of 90° and has an
`
`20
`
`rms blur of around 5um which is within the unit sensor
`
`pixel dimensions thereby providing a reasonably good
`video signal image output from the video signal output
`
`connection 7.'
`
`25
`
`It will be appreciated that various modifications may be
`
`made to the above described embodiment without departing
`from.the scope of the present invention. Thus for
`example the spacer element could be a composite element
`
`made up of a plurality of plane components.
`
`The lens
`
`30
`
`element could also be composite though this would
`
`normally be less preferred due to the significantly
`
`increased complexity.
`
`The various surfaces of the lens
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`system could moreover be provided with diverse coatings.
`for e.g. reducing undesirable reflectidns and selective
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`PCT/GB92/02260
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`filtration of the incident light rays in generally known
`
`manner. Also the R, G, B filters could be mounted on a
`
`suitable support in front of the lenses 8 as further
`
`described hereinbelow.
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`
`Fig. 2 shows some possible alternative layouts for the
`
`individual cameras on the single chip.
`
`In layout
`
`(a)
`
`the absolute red-green and blue-green distances are
`
`minimised. All of the parallax error is vertical. This
`
`may not be optimum for TV applications, as in this case
`
`the colour signal is greatly averaged horizontally, but
`
`not at all vertically. Layout
`
`(b) forces all of the
`
`parallax error into the horizontal dimension to take
`
`advantage of this. Layout
`
`(c) has slightly worse
`
`red-green and blue-green parallax than (a), but the
`
`red-blue distance is greatly less.
`
`Intuitively, this
`
`configuration minimises the total parallax error.
`
`Layout
`
`(3)
`
`is as for (c), but pushes most of the r-g,
`
`b-g errors into the horizontal axis.
`
`Apart from its substantial simplicity,
`
`the colour camera
`
`system of the present invention provides two further
`
`potential technical advantages over the alternative
`
`known approaches. Axial colour aberration causes the
`
`focal plane for blue to be slightly closer to the lens,
`
`and for red slightly further from the lens,
`
`than green.
`
`This aberration may actually be an advantage if we
`
`design the lens for green light and the blue and red
`images become slightly defocussed,
`thereby also blurring
`
`the effect of parallax errors.
`
`For ordinary glasses,
`
`the blue and green images are blurred by around 1 pixel
`
`at the geometries used above.
`
`If we wish,
`
`the 3—lens
`
`approach could be adapted to accommodate this aberration
`
`by fine-tuning the focal length of each lens. This is
`
`impossible with either of the existing single-lens
`
`approaches. Transversal colour aberration is a change
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`in magnification factors at different wavelengths.
`Again it may be possible to correct for this by
`modifying slightly the red and blue lens geometries.
`
`3 shows how the parallax errors between closely
`Fig.
`adjacent identical cameras can be maintained at or below
`one pixel for cameras with useful resolutions of several
`hundred pixels.
`If the cameras are calibrated to
`then an
`provide image alignment for objects at infinity,
`object at distance 0 (on the optical axis of one camera
`for simplicity) is imaged at an offset of e pixels in
`the second camera.
`It is obvious that the parallax
`
`error is greatest for objects which are closest to the
`
`cameras.
`To help in generalising the result, suppose we
`wish to image objects at minimum range 0mm with a field
`of View of 2c degrees and sensor resolution of P
`pixels.
`Then by trigonometry,
`the parallax error e,
`
`in
`
`10
`
`15
`
`pixels, is:-
`
`e = P.s / 0.2 tan (o) pixels
`
`(1)
`
`where s is the camera separation. This important result
`
`20
`
`is independent of the focal length of the lens and shows
`that the error is reduced by lowering s,
`lengthening O
`
`or increasing o.
`
`25
`
`is the parallax error for a
`Actually, e in equation (1)
`close object with reference to objects at infinity.
`Advantageously we might calibrate the cameras to provide
`alignment for objects at some mid range and achieve a
`balance of errors between close and far objects.
`It is
`
`easy to show that if we calibrate on objects at range
`2x0 then the worst case parallax error for near and far
`
`It
`
`30
`
`objects is:-
`
`e’ % P.s / 0.4 tan (o) pixels
`
`(2)
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`Thus in the case of a colour camera for computer vision
`
`using a typical standard resolution of e.g. 240 x 320
`
`pixels,
`
`then if we require a lens with 52° angle~of-view
`
`(o = 26°), horizontal resolution, P, of 320 pixels,
`
`minimum range 0, of 50cm and We achieve a separation, s,
`of 3mm, e' will be slightly less than one pixel.
`In the
`
`case of a low resolution colour camera for video
`
`telephones using the QCIF standard (144 X 178 pixels),
`
`this device must work at close range, say down to 25cm.
`
`Say we use the same angle of view, 52°, and achieve a
`
`lens separation of 1.5mm (allowing for the smaller
`
`array),
`
`then the error in this case will be
`
`approximately 0.5 pixels.
`
`In both cases,
`
`the parallax
`
`error is less than one pixel and therefore of the same
`
`order as aliasing and interpolation errors in
`
`single-chip colour mosaic cameras and accordingly
`
`reasonably acceptable.
`
`Conversely it will be appreciated that where it is
`
`desired to capture stereo images the parallax error and
`
`should be greater than 1.
`
`It may be seen from the above
`
`equations that parallax error increases for small object
`
`ranges or distances 0 and for larger camera separations
`
`5. With a sensor size P of 240 pixels, camera pitch
`separation s of 3.1.mm, and field of View of 45°
`(2o),
`
`rstereo image capture is feasible at ranges up to 1.8
`
`metres. This range can be increased simply by
`
`corresponding increases in the camera separation s.
`
`The electronic architecture of the camera is
`
`substantially independent of the optical and sensor
`
`arrangement described above. Nevertheless,
`
`the
`
`availability of synchronous, continuous RGB colour
`
`signals minimises the required image processing. This
`
`results in a simpler and lower-cost electronic
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`10
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`15
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`20
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`25
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`implementation than for colour—mosaic cameras.
`
`the electronic requirements may be
`Furthermore,
`implemented feasibly on the same chip as the sensors
`where CMOS sensor technology such as that described in
`
`our earlier Patent Publication No. W091/04498,
`
`is used.
`
`Figure 4 gives an overview of one possible electronic
`architecture. Three colour arrays are driven in similar
`
`style to a monochrome array, except that the timing of
`
`vertical and horizontal control on the red and blue
`
`10
`
`arrays is altered by offset values loaded into the
`
`controller from an off-chip PROM (Programmable Read Only
`
`Memory) Chip which has been programmed with the offset
`
`calibration data.
`
`is provided as for
`(ABC)
`Automatic Exposure Control
`monochrome arrays.
`The same exposure value is used for
`
`15
`
`all three arrays. Exposure is monitored via the green
`
`output alone, or possibly by deriving luminance from a
`
`combination of RGB signals.
`
`Automatic Gain Control
`
`(AGC)
`
`is also provided as for
`
`20
`
`monochrome arrays, but in this case,
`
`independent gains
`
`can be set for each colour.
`
`AGC provides three
`
`functions:—
`
`(i)
`
`automatic peak level calibration using a saturated
`
`reference line in the Green array.
`
`In normal exposure
`
`25
`
`circumstances,
`
`the gain of the green channel is fixed at
`
`this value and this forms a nominal gain for the red and
`
`blue channels also.
`
`‘11
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`K9
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`PCTVGB9ZNH2MD
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`(ii)
`
`dynamic colour balancing to correct for variations
`
`in the colour of ambient light by adjusting the blue and
`
`red gains according to colour analysis of the three
`channels.
`
`(iii)
`
`automatic gain of weak images in low light
`
`conditions when ABC has reached maximum exposure. At
`
`first dynamic colour balancing can continue, but at the
`
`lowest light levels (maximum gain), flexibility may be
`
`lost. This is characteristic of many colour cameras.
`
`10
`
`15
`
`The resulting balanced colour signals are passed through
`
`a colour correction matrix, which performs weighted
`
`mixing of the three colours (see e.g. D'Luna and
`
`Parulski,
`
`IEEE JSSC Vol. 26, No. 5, pp. 727-737)
`
`followed by gamma correction on each colour. Both these
`
`functions are standard requirements for colour cameras
`
`intended for TV displays as they correct for known
`
`colour and amplitude nonlinearities in the display tubes.
`
`The matrix may be implemented in analogue CMOS, either
`
`by using switched capacitors or switched
`
`20
`
`current-sources. Either of these can accommodate
`
`alterable coefficients in digital form, or they could be
`
`fixed in layout.
`
`In the former case the coefficients
`
`,may be stored in the PROM already provided for offset
`
`25
`
`calibration and this may afford a useful degree of
`flexibility.
`
`The gamma corrected RGB signals are then passed to an
`
`appropriate encoder for whatever standard is required.
`
`Suitable encoders for e.g. NTS/PAL are readily available.
`
`In Figs.
`
`5 and 6 like parts corresponding to those in
`
`30
`
`Fig.
`
`1 are indicated by like reference numerals.
`
`The
`
`Figs.
`
`5 and 6 illustrate an alternative embodiment
`
`in
`
`which is used a lens system 20 supported at its edges 21
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`on spacer elements 22 with a substantial free air space
`23 between the three lenses 8 of the lens system and the
`respective sensors 4.
`In more detail,
`the lens system
`20 is a one-piece moulding from a suitable optical grade
`plastics material and incorporating an array of three
`lens portions 8 joined edge-to—edge.
`It will be
`appreciated that this affords a particularly economic
`and convenient form of production whilst at the same
`time simplyfying assembly of the camera insofar as the
`three lenses for the R, G, B components of the image,
`are automatically aligned with each other. Nevertheless
`
`it will be understood that, if desired,
`
`the lenses 8
`
`could be manufactured from other materials e.g. glass or
`any other suitable optical material and/or as discrete
`individual components. Moreover each lens could
`comprise more than one element e.g. a doublet. The
`lenses 8 may conveniently be aspheric or spherical or
`
`planar at either surface thereof.
`
`As in the first embodiment,
`the sensors 4 are formed as
`separate sections of a single monolithic VLSI microchip
`5, mounted in a housing pg (only part shown).
`An
`optical support sub-housing 24 has various shoulder
`portions 25-28, for respectively securing the monolithic
`chip 5 to the housing gfl, supporting the lens system 20
`on the spacer elements 22 above the chip 5, supporting
`R, G and B filters 29-31 above the lenses 8, and
`supporting a protective outer Infra Red filter 32
`(conveniently of doped glass e.g. Schott KG3 or BG39).
`Additional support to the lens system 21 and the filters
`
`10
`
`15
`
`20
`
`25
`
`30
`
`29-31 is conveniently provided by spacer walls 33, 34
`
`which have the further advantage of acting as light
`
`C)
`
`baffles between the three, R, G, B, cameras 1 to prevent
`
`cross-imaging between each lens 8 and the other sensors
`
`4. As shown in Fig.
`
`6 the lower spacer walls 33 may
`
`35
`
`conveniently be formed integrally with the support
`
`sub-housing 24.
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`It will be understood that various modifications may
`
`readily be made to the above described embodiment.
`
`Thus, for example,
`
`the order of the filters 29-31 and 32
`
`may be changed.
`
`(I
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`
`CLAIMS
`
`PCT/GB92/02260
`
`1. An image capture system comprising a solid state
`
`image capture device which device comprises an
`
`integrated circuit having at least two sensor arrays,
`
`each said array having an image sensing surface and a
`
`respective lens system associated therewith.
`
`'0
`
`2.
`
`A system according to claim 1 in which system at
`
`least one of the lens systems is mounted spaced apart
`
`from the sensor means with a fluid medium between the
`
`lens and the sensor.
`
`10
`
`A system according to claim 1 in which system at
`3.
`least one of the lens systems, comprises a lens in
`
`substantially direct contact with a transparent spacer
`
`in substantially direct contact with.the sensor and
`
`extending between said lens and sensor, said lens and
`
`15
`
`spacer having refractive indices and being dimensioned
`
`so as to form an image in a plane at or in direct
`
`proximity to a rear face of said spacer element remote
`from said lens element,
`from an object, whereby in use
`
`of the lens system with said lens system.mounted
`
`20
`
`substantially directly on the image sensing surface of
`
`the image capture device an optical image may be
`
`captured thereby.
`
`4.
`
`A system according to claim 3 Wherein sai