U.S. patent application number 10/909409 was filed with the patent office on 2005-02-10 for image capturing device.
Invention is credited to Chikugawa, Hiroshi, Kametani, Eiji, Yamamoto, Yoshihiko.
Application Number | 20050030416 10/909409 |
Document ID | / |
Family ID | 34117945 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050030416 |
Kind Code |
A1 |
Kametani, Eiji ; et
al. |
February 10, 2005 |
Image capturing device
Abstract
An image capturing device employing as illumination source(s)
(flash apparatus(es)) a plurality of light emitting diodes emitting
light of different colors; wherein such light emitting diodes are
respectively made to emit light in pulsed fashion in turn by
emitted color during exposure time(s). Furthermore, during exposure
time(s), such light emitting diodes may be made to sequentially
emit light in pulsed fashion in turn by emitted color, and/or such
light emitting diodes may be made to sequentially emit light in
pulsed fashion in turn by emitted color over multiple
iterations.
Inventors: |
Kametani, Eiji;
(Yamatotakada-shi, JP) ; Yamamoto, Yoshihiko;
(Yamatokoriyama-shi, JP) ; Chikugawa, Hiroshi;
(Kashihara-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
34117945 |
Appl. No.: |
10/909409 |
Filed: |
August 3, 2004 |
Current U.S.
Class: |
348/370 ;
348/372 |
Current CPC
Class: |
H04N 5/2256 20130101;
G03B 2215/0503 20130101; H04N 2101/00 20130101; H04N 5/2354
20130101; H01L 2224/48247 20130101; H01L 2224/48465 20130101; H01L
2924/00 20130101; H01L 2224/48091 20130101; H01L 2224/48247
20130101; G03B 15/05 20130101; H01L 2224/48091 20130101; H01L
2924/00 20130101; H01L 2224/48091 20130101; G03B 2215/0567
20130101; H01L 2924/00014 20130101; H01L 2224/48465 20130101; H01L
2224/48465 20130101 |
Class at
Publication: |
348/370 ;
348/372 |
International
Class: |
H04N 005/225; H04N
005/222 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 4, 2003 |
JP |
2003-286030 |
Jun 11, 2004 |
JP |
2004-174230 |
Claims
1. An image capturing device comprising a plurality of light
emitting diodes used as one or more illumination sources and
respectively emitting light of different colors; wherein the
plurality of light emitting diodes are respectively made to emit
light in pulsed fashion in turn by emitted color during one or more
exposure times.
2. An image capturing device according to claim 1 wherein: the
plurality of light emitting diodes are made to sequentially emit
light in pulsed fashion in turn by emitted color during at least
one of the exposure time or times.
3. An image capturing device according to claim 2 wherein: the
plurality of light emitting diodes are made to sequentially emit
light in pulsed fashion in turn by emitted color over multiple
iterations during at least one of the exposure time or times.
4. An image capturing device according to any of claims 1 through 3
wherein: one or more image capturing elements in the image
capturing device is or are electronic; in correspondence to at
least one timing with which the plurality of light emitting diodes
are made to emit light in turn by emitted color, one or more
monochromatic images corresponding to at least one of the emitted
color or colors is or are respectively acquired by at least a
portion of the image capturing element or elements; and one or more
color images is or are formed by combining at least a portion of
the respective acquired monochromatic image or images.
5. An image capturing device according to any of claims 1 through 3
wherein: at least one luminous intensity and at least one total
illumination time for each of the plurality of light emitting
diodes during at least one of the exposure time or times are
respectively made variable.
6. An image capturing device according to claim 5 wherein: at least
one luminous intensity and at least one total illumination time for
each of the plurality of light emitting diodes during at least one
of the exposure time or times are varied, altering at least one
ratio between or among luminous intensity time integrals of at
least a portion of the respective colors.
7. An image capturing device according to claim 5 wherein: at least
one luminous intensity and at least one total illumination time for
each of the plurality of light emitting diodes during at least one
of the exposure time or times are varied by at least one
substantially identical ratio.
8. An image capturing device according to any of claims 1 through 3
further comprising: one or more luminous energy detection means for
detecting light incident thereon after passing through one or more
photographic lenses of the image capturing device; wherein at least
one of the illumination source or sources is made to emit light
prior to at least one of the exposure or exposures; and one or more
exposure conditions is or are set based on at least one result of
detection carried out by at least one of the luminous energy
detection means at at least one time when at least one of the
illumination source or sources is made to emit light prior to at
least one of the exposure or exposures.
9. An image capturing device according to claim 8 wherein: the
exposure condition or conditions set based on at least one result
of detection carried out by at least one of the luminous energy
detection means include at least one shutter speed.
10. An image capturing device according to any of claims 1 through
3 wherein: at least one illuminative locus of at least one of the
illumination source or sources is varied in correspondence to at
least one photographic field angle of the image capturing
device.
11. An illumination source for an image capturing device, the
illumination source comprising: a first light emitting diode for
emitting a first color of light; and a second light emitting diode
for emitting a second color of light; wherein the first and second
light emitting diodes are driven to emit light in pulsed fashion
during an exposure time of the image capturing device.
12. The illumination source of claim 11 further including a third
light emitting diode for emitting a third color of light, wherein
said third light emitting diode is driven to emit light in pulsed
fashion during the exposure time of the image capturing device.
13. The illumination source of claim 12 wherein the first, second
and third light emitting diodes are driven to emit light
sequentially in pulsed fashion during an exposure time of the image
capturing device.
14. The illumination source of claim 13 wherein the first, second
and third light emitting diodes are driven to emit light
sequentially in pulsed fashion a plurality of times during an
exposure time of the image capturing device.
15. A method of providing illumination for an image capturing
device comprising the steps of: providing a first light emitting
diode for emitting a first color of light; providing a second light
emitting diode for emitting a second color of light; and driving
the first and second light emitting diodes to emit light in pulsed
fashion during an exposure time of the image capturing device.
16. The method of claim 15 including the additional steps of:
providing a third light emitting diode for emitting a third color
of light; and driving the third light emitting diode to emit light
in pulsed fashion during the exposure time of the image capturing
device.
17. The method of claim 16 wherein said step of driving the first,
second and third light emitting diodes comprises the step of
driving the first, second and third light emitting diodes so that
the first, second and third light emitting diodes emit light
sequentially in pulsed fashion during an exposure time of the image
capturing device.
18. The method of claim 16 wherein said step of driving the first,
second and third light emitting diodes comprises the step of
driving the first, second and third light emitting diodes so that
the first, second and third light emitting diodes emit light
sequentially in pulsed fashion a plurality of times during an
exposure time of the image capturing device.
19. The method of claim 15 including the additional steps of:
acquiring a first monochromatic image during a time when the first
light emitting diode is emitting light; acquiring a second
monochromatic image during a time when the second light emitting
diode is emitting light; and forming a color image by combining at
least a portion of the first monochromatic image and the second
monochromatic image.
20. The method of claim 15 including the additional step of varying
a luminous intensity of the first light emitting diode
independently of the luminous intensity of the second light
emitting diode.
21. The method of claim 15 including the additional steps of:
emitting light from at least one of the first, second and third
light emitting diodes prior to the exposure time; detecting light
at a luminous energy detector; and setting an exposure condition of
the image capturing device based on the light detected by the
luminous energy detector.
22. The method of claim 15 including the additional step of varying
an illuminative locus of the illumination source in based on a
photographic field angle of the image capturing device.
Description
BACKGROUND OF INVENTION
[0001] This application claims priority under 35 USC 119(a) to
Patent Application No. 2004-174230 filed in Japan on 11 Jun. 2004,
the content of which is incorporated herein by reference in its
entirety.
[0002] The present invention relates to such image capturing
devices as movie-type equipment, CCD cameras, CMOS imagers, and
silver halide cameras employing LED device(s) as illumination
source(s); and in particular, relates to image capturing devices
permitting increased effective luminance of illumination source(s)
employing LED device(s).
[0003] Use of R, G, and B light emitting diodes (LEDs) as
illumination light source (flash apparatus) for cameras has been
proposed conventionally (see, e.g., Japanese Patent Application
Publication Kokai No. 2002-116481). As compared with xenon
discharge tubes and the like, use of R, G, and B LEDs is
advantageous because adjustment of light source color temperature
is facilitated, less time is required for power supply charging and
discharging, and so forth.
[0004] Furthermore, known in connection with cinematic light
sources or stroboscopic light sources for cameras for capturing
images of moving subjects is a usage wherein light source(s) is/are
sequentially lit (see, e.g., Japanese Patent Application
Publication Kokai No. H5-328210 (1993) or Japanese Patent
Application Publication Kokai No. S63-274934 (1988)). Here, light
of identical color is sequentially emitted synchronously with
respect to shutter timing.
[0005] However, when attempting to use LED(s) as flash
apparatus(es) as in the aforementioned conventional art, there has
been the problem that luminance has been insufficient. This fact
will be described with reference to FIG. 8.
[0006] FIG. 8 is a graph (Id-Po characteristics) showing the
relationship between LED drive current Id and luminance (optical
output Po) in the conventional art.
[0007] As shown in FIG. 8, LED luminance (optical output Po) is
roughly proportional to electric current (drive current Id) when
the amount of current flowing through the LED is small. Here, the
constant of proportionality is referred to as the luminous
efficiency .eta.(=.DELTA.Po/.DELTA.Id). When drive current Id is
large, .eta. decreases due to generation of heat by the LED
element, and optical output Po saturates at maximum value Po1 as
indicated by the curve shown in FIG. 8. That is, no matter how
large LED drive current is made, LED luminance does not exceed some
fixed limit; and it is consequently impossible to obtain luminance
as necessary for flash use.
[0008] Specific numerical values for generation of heat by
chip-type LED elements follow. Results of measuring respective R,
G, and B LED elements indicated, for example, that whereas junction
temperature Tj for respective LED elements was between 34.degree.
and 44.degree. C. and power consumption Pd was between 40 mW and 78
mW when Id=20 mA, junction temperature Tj was between 49.degree.
and 71.degree. C. and power consumption Pd was between 110 mW and
230 mW when Id=50 mA. Because there is almost no change in the
voltage applied at the respective LEDs, power consumption Pd should
be roughly proportional to drive current Id absent any effect due
to generation of heat. That is, if drive current Id increases by a
factor of 2.5 in going from 20 mA to 50 mA, then power consumption
Pd should also increase by a factor of 2.5, going from between 40
mW and 78 mW to between 100 mW and 195 mW. And yet, power
consumption Pd actually increases by more than a factor of 2.5.
[0009] When used as a camera flash, because drive current Id will
reach far greater value(s), at on the order of 200 mA for each LED
element of each respective color, the effect of the heat generated
thereby will be even more serious. Moreover, there has also been
the problem that over the course of usage the resin that
encapsulates the LED element(s) can crack due to heat (cracking)
and/or separation thereof from package(s) may occur.
[0010] The present invention was conceived in light of such
problems in the conventional art, it being an object thereof, where
LED(s) is/are used as flash apparatus(es), to provide an image
capturing device permitting increased effective luminance of camera
flash(es) employing LED(s). It is moreover an object to provide an
image capturing device that will simultaneously permit increased
flash effective luminance as well as increased life of LED(s)
employed and so forth.
SUMMARY OF INVENTION
[0011] In order to achieve the foregoing object(s) and/or other
objects, an image capturing device in accordance with one or more
embodiments of the present invention may comprise a plurality of
light emitting diodes used as one or more illumination sources and
respectively emitting light of different colors; wherein the
plurality of light emitting diodes are respectively made to emit
light in pulsed fashion in turn by emitted color during one or more
exposure times.
[0012] Here, as the plurality of light emitting diodes emitting
light of different colors, combination(s) of light emitting diodes
emitting red, green, and blue (the colors referred to as "the three
primary colors") may, for example, be cited. Use of the three
primary colors will make it possible to faithfully reproduce the
color balance of the photographic subject. Where the image
capturing device is equipped with mechanical and/or electrical
shutter(s), exposure time(s) may correspond to time(s) during which
such shutter(s) is/are open (as determined by shutter speed(s)).
While the timing with which light emitting diode(s) is/are made to
emit light may be such that timing(s) of each emitted color is/are
completely different from that or those of the other(s), the timing
with which any two colors, for example, are emitted may partially
or completely overlap.
[0013] In image capturing device(s) in accordance with
embodiment(s) of the present invention, because plurality of light
emitting diodes used as illumination source(s) are not driven
continuously throughout entire exposure time(s) but are driven in
pulsed fashion in turn by emitted color, it is possible to suppress
generation of heat by light emitting diode element(s) and reduce
adverse effect(s) on luminous efficiency, making it possible to
achieve higher light emitting diode drive current value(s) at which
optical output saturates than would be the case had light emitting
diode(s) been driven continuously. As a result, increased luminance
of light-emitting-diode illumination source(s) is permitted; this
being suited, for example, to use in applications such as where
compensation of backlighting is carried out at bright locations. As
a result of suppression of generation of heat by light emitting
diode element(s), it is also possible to achieve increased light
emitting diode element life, improved reliability, and so
forth.
[0014] Furthermore, in image capturing device(s) in accordance with
embodiment(s) of the present invention, the plurality of light
emitting diodes may be made to sequentially emit light in pulsed
fashion in turn by emitted color during at least one of the
exposure time or times. Moreover, the plurality of light emitting
diodes may be made to sequentially emit light in pulsed fashion in
turn by emitted color over multiple iterations during at least one
of the exposure time or times.
[0015] Furthermore, in image capturing device(s) in accordance with
such embodiment(s) of the present invention, plurality of light
emitting diodes used as illumination source(s) may be sequentially
driven in pulsed fashion in turn by emitted color. It is possible
to suppress generation of heat by light emitting diode element(s)
itself or themselves and to suppress effect(s) of generation of
heat exerted between or among light emitting diode elements of
different emitted colors, making it possible to achieve higher
light emitting diode drive current value(s) at which optical output
saturates than would be the case had light emitting diode(s) been
driven continuously. As a result, increased luminance of
light-emitting-diode illumination source(s) is permitted; this
being favorable, for example, for compensation of backlighting at
bright locations. Furthermore, because light emitting diode(s) of
each color may be driven with different timing(s), it is possible
to avoid placing excessive load(s) on image capturing device power
supply or supplies. Moreover, in the event that sequential lighting
of the plurality of light emitting diodes in turn by emitted color
is made to occur over multiple iterations, width(s) of drive
pulse(s) for each luminous emission of each iteration may be made
shorter. This makes it possible to further suppress generation of
heat by light emitting diode element(s), permitting further
increase in luminance of light-emitting-diode illumination
source(s).
[0016] Furthermore, in image capturing device(s) in accordance with
embodiment(s) of the present invention, one or more image capturing
elements in the image capturing device may be electronic; in
correspondence to at least one timing with which the plurality of
light emitting diodes are made to emit light in turn by emitted
color, one or more monochromatic images corresponding to at least
one of the emitted color or colors may be respectively acquired by
at least a portion of the image capturing element or elements; and
one or more color images may be formed by combining at least a
portion of the respective acquired monochromatic image or
images.
[0017] Here, whereas with conventional electronic image capturing
element(s) a full-color signal might be obtained by applying red
filter(s), green filter(s), and/or the like at individual
element(s), where image capturing device(s) in accordance with
embodiment(s) of the present invention is/are employed it may be
possible to do without filter(s) at individual element(s).
Monochromatic images respectively corresponding to colors emitted
by LED elements may be acquired through a method in which, for
example, only red signal(s) is/are integrated while R LED
element(s) is/are emitting light, and only green signal(s) is/are
integrated while G LED element(s) is/are emitting light.
[0018] Furthermore, with image capturing device(s) in accordance
with such embodiment(s) of the present invention, because it is
possible to do without filter(s) at individual element(s), all
image capturing elements may be utilized in acquiring monochromatic
image(s). This being the case, where the same image capturing
element(s) is/are used it will be possible to obtain color image(s)
having three times the resolution, or if color image(s) of the same
resolution is/are to be obtained it will be sufficient to use
one-third the number of image capturing elements.
[0019] Furthermore, in image capturing device(s) in accordance with
embodiment(s) of the present invention, at least one luminous
intensity and at least one total illumination time for each of the
plurality of light emitting diodes during at least one of the
exposure time or times may respectively be made variable. Moreover,
at least one luminous intensity and at least one total illumination
time for each of the plurality of light emitting diodes during at
least one of the exposure time or times may be varied, altering at
least one ratio between or among luminous intensity time integrals
of at least a portion of the respective colors. Alternatively, at
least one luminous intensity and at least one total illumination
time for each of the plurality of light emitting diodes during at
least one of the exposure time or times may be varied by at least
one substantially identical ratio.
[0020] With image capturing device(s) in accordance with such
embodiment(s) of the present invention, where it is possible to
vary luminous intensity or intensities and total illumination
time(s) for plurality of light emitting diodes used as illumination
source(s), altering ratio(s) between or among luminous intensity
time integrals of respective colors, it will be possible to adjust
illumination source color balance(s). Furthermore, by varying
luminous intensity or intensities and total illumination time(s)
for respective color(s) by substantially identical ratio(s), it
will be possible to adjust total exposure dose(s) produced by
illumination source(s) while maintaining illumination source color
balance(s).
[0021] Furthermore, image capturing device(s) in accordance with
embodiment(s) of the present invention may further comprise one or
more luminous energy detection means for detecting light incident
thereon after passing through one or more photographic lenses of
the image capturing device; at least one of the illumination source
or sources may be made to emit light prior to at least one of the
exposure or exposures; and one or more exposure conditions may be
set based on at least one result of detection carried out by at
least one of the luminous energy detection means at at least one
time when at least one of the illumination source or sources is
made to emit light prior to at least one of the exposure or
exposures. Moreover, the exposure condition or conditions set based
on at least one result of detection carried out by at least one of
the luminous energy detection means may include at least one
shutter speed.
[0022] With image capturing device(s) in accordance with such
embodiment(s) of the present invention, effect(s) of illumination
by illumination source(s) may be accurately detected prior to
exposure(s), and exposure condition(s) (e.g., exposure time(s) as
determined by shutter speed(s) and/or the like) may be
appropriately set based on result(s) of such detection. This being
the case, it will be possible for exposure time during flash
photography, determined conventionally based on flash intensity or
the like, to be accurately determined by means of exposure control
apparatus(es) internal to image capturing device(s) in similar
manner as was the case with ordinary photography.
[0023] Furthermore, in image capturing device(s) in accordance with
embodiment(s) of the present invention, at least one illuminative
locus of at least one of the illumination source or sources may be
varied in correspondence to at least one photographic field angle
of the image capturing device. Moreover, at least one of the
illumination source or sources may have a plurality of light
emitting diodes respectively irradiating light in different
directions.
[0024] Here, as method for varying illuminative locus or loci of
illumination source(s), a method in which variable-magnification
optical system(s) is/are arranged in front of illumination
source(s), magnification-varying operation(s) of such
variable-magnification optical system(s) being linked to change(s)
in photographic field angle(s) of image capturing device(s), may
for example be cited. Alternatively, plurality of light emitting
diodes may be arranged such that directions in which light is
irradiated thereby are different, such light emitting diodes being
selectively made to emit light in linked fashion with change(s) in
photographic field angle(s) such that only light emitting diode(s)
corresponding to location(s) within photographic field angle(s)
is/are made to emit light.
[0025] Image capturing device(s) in accordance with such
embodiment(s) of the present invention make it possible to achieve
appropriate illumination in correspondence to change(s) in
photographic field angle(s) of image capturing device(s). Causing
plurality of light emitting diodes to be selectively made to emit
light in linked fashion with change(s) in photographic field
angle(s) such that only light emitting diode(s) corresponding to
location(s) within photographic field angle(s) is/are made to emit
light makes it possible to eliminate waste and so forth associated
with illumination of location(s) outside photographic field
angle(s) by light emitting diode(s).
BRIEF DESCRIPTION OF DRAWINGS
[0026] FIG. 1 is a drawing showing the external appearance of a
camera associated with a first embodiment of the image capturing
device of the present invention.
[0027] FIG. 2(a) is a top view showing constitution of LED devices
for flash use in a camera associated with a first embodiment of the
image capturing device of the present invention; and FIG. 2(b) is a
view of section II-II indicated in FIG. 2(a).
[0028] FIG. 3 is a graph (Id-Po characteristics) showing the manner
in which the relationship between LED drive current Id and optical
output Po might change with changing LED drive pulsewidth and so
forth.
[0029] FIG. 4 is a graph showing change in optical output Po over
time when LED element drive current is held constant.
[0030] FIG. 5(a) indicates when a shutter might be open and when it
might be closed in an example of a drive signal timing chart for
LEDs for flash use in a camera associated with a first embodiment
of the image capturing device of the present invention; and FIG.
5(b) shows the corresponding LED drive signals.
[0031] FIG. 6(a) indicates when a shutter might be open and when it
might be closed in another example of a drive signal timing chart
for LEDs for flash use in a camera associated with a first
embodiment of the image capturing device of the present invention;
and FIG. 6 (b) shows the corresponding LED drive signals.
[0032] FIG. 7(a) indicates when a shutter might be open and when it
might be closed in an example of a drive signal timing chart for
LEDs for flash use in a camera associated with a second embodiment
of the image capturing device of the present invention; and FIG.
7(b) shows the corresponding LED drive signals.
[0033] FIG. 8 is a graph (Id-Po characteristics) showing the
relationship between LED drive current Id and luminance (optical
output Po) in the conventional art.
[0034] FIG. 9 is a graph showing spectral sensitivity
characteristics of conventional CCDs.
[0035] FIG. 10 is a graph showing spectral sensitivity
characteristics of a conventional CMOS.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0036] Below, embodiments of the present invention are described
with reference to the drawings.
[0037] First Embodiment
[0038] FIG. 1 is a drawing showing the external appearance of a
camera associated with a first embodiment of the image capturing
device of the present invention. Note that this camera is assumed
to use silver halide film.
[0039] As shown in FIG. 1, photographic lens 130 equipped with
multibarrel lens barrel is arranged toward the bottom in roughly
the central region of the front of body 101 of squat box-shaped
camera 100. This photographic lens 130 can be extended and/or
retracted as a result of actuation by actuating member(s), not
shown; extension and/or retraction of photographic lens 130
permitting change in photographic magnification. Three LED devices
120 for flash use are arranged at protruding region 102 formed in
the upper right region at the front of camera body 101. These LED
devices 120 for flash use are arranged so as to permit light to
respectively be irradiated centrally within the field angle of
photographic lens 130 as well as to the left and right thereof.
Arranged near the left edge of the top of camera body 101 is
shutter button 110, actuation of this shutter button 110 causing
photograph(s) to be taken by camera 100.
[0040] During telephoto photography as takes place when
photographic lens 130 is in its extended state, only the one flash
LED device that is centrally disposed among the three flash LED
devices 120 is made to irradiate light. The reason for this is that
because photographic field angle is narrow during telephoto
photography, locations within the photographic field angle can be
adequately irradiated when only the one flash LED device that is
centrally disposed among the three flash LED devices 120 is made to
irradiate light. Conversely, during wide-angle photography as takes
place when photographic lens 130 is in its retracted state, because
photographic field angle is wide, all of the three flash LED
devices 120 are made to irradiate light. Note that the present
invention is not limited to the number, arrangement, and so forth
of flash LED devices 120 presented here.
[0041] Whereas flash LED devices 120 are for clarity depicted as
protruding from camera body 101 at FIG. 1, these may be internal to
camera body 101, protruding region 102, and/or the like.
Furthermore, variable-magnification optical system(s) may be
arranged in front of flash LED device(s) 120, and
magnification-varying operation(s) of such variable-magnification
optical system(s) may be linked to change(s) in photographic field
angle(s) accompanying extension and/or retraction of photographic
lens 130 so as to alter illuminative locus or loci of flash LED
device(s) 120. Moreover, to cause illuminative locus or loci to be
more uniformly illuminated, constitutions such as that in which
diffuser plate(s) is/are provided in front of flash LED device(s)
120 may be adopted.
[0042] FIG. 2(a) is a top view showing constitution of LED devices
for flash use in a camera associated with a first embodiment of the
image capturing device of the present invention; and FIG. 2(b) is a
view of section II-II indicated in FIG. 2(a).
[0043] As shown at FIG. 2(a), at flash LED device 120, red LED
element 8, blue LED element 9, and green LED element 10 are housed
within a single package 20 which is box-like in shape and has
cross-section in the shape of a square with rounded corners.
[0044] Lead frames 1, 2, 3 and lead frames 4, 5, 6 are arranged in
mutual opposition at the lower portion of package 20. These lead
frames 1 through 6 are made to form an integral structure as a
result of conventional insert molding with Amodel or other such
white resin 11 making up the upper portion of package 20. Recess
20a, in the shape of a round, shallow bowl of diameter slightly
smaller than package 20, is formed at the top of package 20 so as
to expose respective portions of lead frames 1 through 6, and
serves as location for receiving resin as well as for wire bonding.
Note that sidewall 20b of recess 20a also serves as reflecting
surface. Furthermore, notch 20c is formed at a top corner of
package 20 above lead frame 4, making it possible to determine the
orientation of package 20 from the external appearance of package
20.
[0045] Rectangular-chip-type red LED element 8, blue LED element 9,
and green LED element 10 are respectively mounted on lead frames 3,
5, and 1 at respective locations thereof exposed within recess 20a.
Red LED element 8 which is mounted on lead frame 3 is electrically
connected by wire bonding by way of metal wire 7a to lead frame 6
which is arranged opposite lead frame 3 and serves as the other
electrode paired therewith. Blue LED element 9 which is mounted on
lead frame 5 is electrically connected by wire bonding by way of
metal wire 7b to lead frame 2 which is arranged opposite lead frame
5 and serves as the other electrode paired therewith. Moreover,
green LED element 10 which is mounted on lead frame 1 is
electrically connected by wire bonding by way of metal wire 7c to
lead frame 4 which is arranged opposite lead frame 1 and serves as
the other electrode paired therewith. In addition, after the
respective LED elements have been mounted thereon and wire bonding
has been carried out, recess 20a of package 20 is encapsulated with
epoxy-type transparent resin 12, preventing deterioration of the
respective LED elements.
[0046] Here, red LED element 8, blue LED element 9, and green LED
element 10 are arranged so as to be as close to each other as
possible in order to facilitate mixing of colors (improve color
mixture characteristics) of the respective LED elements. That is,
consideration may be made for causing distances between and/or
among lead frames to be as small as possible, for arranging
respective LED elements at the vertices of a roughly equilateral
triangle, and/or the like. On the other hand, to improve heat
dissipation, for a given area at the floor of recess 20a, lead
frame area at the side on which the chip is mounted may be made as
large as possible, while lead frame area at the side to which the
wire is directly bonded may be made small. To further improve color
mixture characteristics, transparent resin 12 may be made to
contain filler(s) and/or void(s).
[0047] Furthermore, as shown at FIG. 2(b), thickness of lead frame
5, on which blue LED element 9 is mounted, is different at the
region 5a thereof at which blue LED element 9 is mounted than it is
for other locations thereof. More specifically, whereas thickness
T2 of mounting region 5a is on the order of 0.5 mm to 0.6 mm,
thickness Ti at other locations is on the order of 0.3 mm; the
reason for which is as follows.
[0048] Where an LED element is made to emit light as a result of
being driven in CW (Continuous Wave) fashion (i.e., where it is
being driven continuously), because heat is being constantly
supplied from the LED element, the amount of heat that can be made
to flow therefrom will be determined by that location in the entire
region delimited by the LED element on the one hand and the
external circuitry on the other that has the poorest heat
dissipation characteristics. Accordingly, there would be little
point in making the entire lead frame anything other than the same
thickness. On the other hand, where an LED element is made to emit
light as a result of being driven in pulsed fashion, LED element
heat dissipation can be improved if the lead frame is made thicker
at the LED element mounting region. This is because, unlike the
situation in which the LED element is being driven in CW fashion,
supply of heat from the LED element is intermittent; making it
possible for heat produced when the LED element is emitting light
to be quickly dissipated into the frame which has good thermal
conduction, preventing a rise in temperature, and for heat to be
released to the exterior by way of the lead when the LED element is
not emitting light.
[0049] Furthermore, if the lead frame is made thick, then a great
deal of force will be required during cutting thereof, making
formation of a gap at the region of the cut unavoidable. Where this
is the case, it will only be possible during working thereof to
achieve a distance between lead frames that is on the same order as
the thickness thereof or possibly on the order of three-fourths of
the thickness thereof. Accordingly, where distance between lead
frames is to be made small in order to improve color mixture
characteristics, it will not be possible to employ lead frames that
are very thick. And it will also be necessary to keep the lead
frame thin at locations thereof at which the LED element is not
mounted so as to avoid difficulty when the lead frame is bent into
shape.
[0050] Note at FIG. 2(a) and (b) that the dimensions and
arrangement of the lead frames and the arrangement of the
respective LED elements are examples for purposes of illustration,
and the present invention is not limited thereto.
[0051] Next, the effect of heat dissipation on maximum LED optical
output is described in detail with reference to the drawings.
[0052] FIG. 3 is a graph (Id-Po characteristics) showing the manner
in which the relationship between LED drive current Id and optical
output Po might change with changing LED drive pulsewidth and so
forth.
[0053] As shown in FIG. 3, curve G31, indicating Id-Po
characteristics of one LED among three LEDs (these being R, G, and
B) when these are driven simultaneously in CW fashion to produce
emission of white light, has maximum optical output Po1. Curves G32
and G33, respectively indicating Id-Po characteristics of any one
among the R, G, and B LEDs when driven with drive pulsewidth 2 msec
and 0.2 msec, respectively have maximum optical outputs Po2 and
Po3. At curve G34, LED drive conditions per se are identical to
those at curve G33, but the Id-Po characteristics indicated are for
when the thickness in the region of the lead frame at which the LED
chip is mounted is 0.6 mm, this being greater than at other
locations.
[0054] Curves G31 through G34 all indicate that optical output Po
is roughly proportional to drive current Id when LED drive current
Id is small, but that optical output Po begins to saturate as drive
current Id grows larger. When an LED is driven in CW fashion to
cause it to emit light, as indicated by curve G31, output saturates
at roughly the same optical output Po1 regardless of the thickness
at the frame region at which the LED chip is mounted.
[0055] On the other hand, when LED drive pulsewidth is 2 msec
({fraction (1/500)} of a second), as indicated by curve G32,
maximum optical output Po2 reaches twice the value of Po1 or more.
When drive pulsewidth is shortened to 0.2 msec ({fraction (1/5000)}
of a second), maximum optical output Po3 reaches almost four times
the value of Po1. Moreover, when the thickness of the frame in the
region at which the LED chip is mounted is made 0.6 mm, this being
greater than at other locations thereof, maximum optical output Po4
reaches almost six times the value of Po1. That is, when one color
of light is emitted at a time with LED drive pulsewidth set to 0.2
msec and the thickness of the frame in the region at which the LED
chip is mounted is 0.6 mm, saturation does not occur until optical
output Po reaches almost six times the value of the maximum optical
output Po1 applicable to the situation in which the three colors of
LEDs are simultaneously made to emit light in continuous
fashion.
[0056] FIG. 4 is a graph showing change in optical output Po over
time when LED element drive current is held constant. Curve G41
indicates driving in pulsed fashion, and curve G42 indicates
driving in CW fashion, total amount of luminous energy being the
same in either case.
[0057] The reason that as shown in FIG. 4 optical output falls off
more rapidly for CW drive than for pulsed drive is thought to be
due to the fact that separation of encapsulant resin occurring as
result of the effect of heating accompanying emission of light by
LED element(s) causes occurrence of optical losses at the interface
between resin and air, and due to the fact that exposure of LED
element(s) to air as a result of separation of encapsulant resin
promotes deterioration of LED element(s).
[0058] FIG. 5(a) indicates when a shutter might be open and when it
might be closed in an example of a drive signal timing chart for
LEDs for flash use in a camera associated with a first embodiment
of the image capturing device of the present invention; and FIG.
5(b) shows the corresponding LED drive signals. Note as mentioned
above that this camera is assumed to use silver halide film.
[0059] As shown at FIG. 5(a), it will be assumed for purposes of
discussion that during flash photography the time during which the
camera shutter is open might conventionally be on the order of
{fraction (1/100)} of a second. As shown at FIG. 5(b), when LED
elements of respective colors R, G, and B are sequentially made to
emit light with different timings but such that each is made to
emit light for 2 msec, it is possible to make each LED element in
its turn emit light in pulsed fashion over one iteration during the
time when the shutter is open.
[0060] At the silver halide film or other such image capturing
element(s), because light is in effect being integrated over the
time during which exposure is taking place while the shutter is
open, regardless of whether light of respective colors R, G, and B
is irradiated with different timings it will be as if exposure had
been caused by light of color corresponding to the relative
intensities thereof. For example, sepia-colored exposure might be
carried out by lowering B intensity. This fact is not limited to
situations in which the image capturing element is silver halide
film, but is similarly true for CCD(s) and other such electronic
device(s) provided integration occurs in electrical fashion.
[0061] Here, the total exposure dose imparted when R, G, and B LED
elements are made to emit light as a result of being driven
simultaneously in CW fashion throughout the entire exposure time
during which the shutter is open (10 msec) is taken to be 1. But
when the LED elements of the respective colors are each in its turn
separately made to emit light for a drive pulsewidth of 2 msec over
one iteration, where maximum optical output Po is held to the same
value the total exposure dose obtained as determined by the
fraction of time that each LED is emitting light (2 msec/10 msec)
will be only 1/5.
[0062] However, as has been described with reference to FIG. 3,
where each LED element is made to emit light for a drive pulsewidth
of 2 msec (curve G32 in FIG. 3), it is possible to achieve a
maximum optical output Po that is two or more times the value that
would be obtained were driving to have been carried out in CW
fashion to produce emission of light. Accordingly, a total exposure
dose of up to on the order of 2/5 can be attained. Because the
value of the time integral of electric current which is required
need only be on the order of 2/5 that which would be required had
driving been carried out in CW fashion, this is suited, for
example, to use in applications such as where compensation of
backlighting is carried out at bright locations.
[0063] Moreover, because LED elements of respective colors are
driven with different timings, it is possible to avoid situations
such as occur when respective LEDs are driven simultaneously and
drive currents Id overlap, with excessive load being placed on
image capturing device power supply or supplies. Or it will be
possible by driving LED elements with different timings to obtain
higher drive current(s) Id without placing excessive load on image
capturing device power supply or supplies than would be the case
were the LED elements driven simultaneously.
[0064] Moreover, settings affecting LED drive currents Id,
illumination timings, and illumination times for respective colors
R, G, and B are made variable.
[0065] In order to adjust flash color balance, LED drive currents
Id for respective colors R, G, and B may be varied over range(s)
within which optical output(s) Po do not saturate so as to alter
ratio(s) between or among luminescent intensities of respective
colors, and/or ratio(s) between or among total illumination times
for respective colors may be varied while LED drive currents Id for
respective colors are left unchanged. Or alteration of ratio(s)
between or among total illumination times for respective colors may
be combined with alteration of LED drive currents Id for respective
colors. In this way, it is possible to alter ratio(s) between or
among exposure doses (time integrals of luminescent intensity) for
respective colors, flash color balance being determined by ratio(s)
between or among exposure doses for respective colors as modified
by such alteration.
[0066] Furthermore, adjustment of total exposure dose(s) produced
by flash(es) may be accomplished by causing LED drive currents Id
for respective colors to be altered by the same ratio, by causing
total illumination times for respective colors to be altered by the
same ratio, or by combination of these types of alteration. In this
way, it is possible to alter total exposure dose(s) produced by
flash(es) while preserving flash color balance.
[0067] FIG. 6(a) indicates when a shutter might be open and when it
might be closed in another example of a drive signal timing chart
for LEDs for flash use in a camera associated with a first
embodiment of the image capturing device of the present invention;
and FIG. 6 (b) shows the corresponding LED drive signals.
[0068] As shown at FIG. 6(a), it will be assumed for purposes of
discussion that during flash photography the time during which the
camera shutter is open is the same as at FIG. 5(a), this being on
the order of {fraction (1/100)} of a second. As shown at FIG. 6(b),
when respective LED elements are made to emit light with different
timings, sequentially emitting light for 0.2 msec over multiple
iterations, it is possible to make LED elements of respective
colors R, G, and B each in its turn emit light in pulsed fashion
over 16 iterations during the time when the shutter is open.
[0069] Here, the total exposure dose imparted when R, G, and B LED
elements are made to emit light as a result of being driven
simultaneously in CW fashion throughout the entire exposure time
during which the shutter is open (10 msec) is taken to be 1. But
when the LED elements of the respective colors are each in its turn
separately made to emit light with drive pulsewidth equal to 0.2
msec over 16 iterations, where maximum optical output Po is held to
the same value the total exposure dose obtained as determined by
the fraction of time that each LED is emitting light (16.times.0.2
msec/10 msec) will be only 0.32.
[0070] However, as has been described with reference to FIG. 3,
where each LED element is made to emit light for a drive pulsewidth
of 0.2 msec (curve G33 in FIG. 3), it is possible to achieve a
maximum optical output Po that is four or more times the value that
would be obtained were driving to have been carried out in CW
fashion to produce emission of light. Accordingly, a total exposure
dose of up to on the order of 1.3 (=4.times.0.32) can be attained.
Moreover, when the thickness of the frame in the region at which
the LED chip is mounted is made 0.6 mm (curve G34 in FIG. 3), this
being greater than at other locations thereof, it is possible to
achieve a maximum optical output Po that is six or more times the
value that would be obtained were driving to have been carried out
in CW fashion to produce emission of light. As a result, total
exposure dose can be increased to on the order of 2
(=6.times.0.32), permitting use as a flash of higher effective
luminance.
[0071] Moreover, with regard to the order in which respective LED
elements are made to emit light at such time, by causing R (red LED
element 8 at FIG. 2(a)) and G (green LED element 10 at FIG. 2(a)),
which are disposed to either side within package 20 (see FIG.
2(a)), to emit light in sequence first and by causing B (blue LED
element 9 at FIG. 2(a)) to emit light last, it will be possible to
further reduce the effect of heating, since heat produced by R is
not readily conveyed to G, which emits light immediately after
emission of light by R. In addition, by mounting the G LED element,
which generates a large amount of heat, at one side rather than in
the center of package 20, it is possible to avoid the effects that
generation of heat by G would otherwise have on the other LED
elements.
[0072] To further increase total exposure dose, the timing with
which two LED elements are made to emit light may be such as to
cause them to overlap. By so doing, it may be possible to further
increase exposure dose imparted during the time during which
exposure is taking place while the shutter is open. In particular,
where as shown at FIG. 2(a) the locations within the package of the
R LED chip and the G LED chip are separated from each other, this
method will be effective, since causing the G LED chip to turn ON
before the R LED chip has turned OFF will have almost no thermal
effect.
[0073] Furthermore, although no special mention of this has been
made until now, it is also possible to increase exposure dose by
increasing the height (i.e., distance from chip mounting surface to
package top) of reflecting surface 20b (see FIG. 2(b)). This effect
is particularly marked when reflecting surface height is small;
e.g., as compared with a situation where reflecting wall height was
1 mm, increasing reflecting wall height to 2.4 mm caused exposure
dose to increase by a factor of 1.5, and increasing reflecting wall
height to 2.8 mm caused exposure dose to increase by a factor of
1.8. Note, however, that an increase in reflecting wall height will
perforce cause an increase in package width, leading to increase in
the amount of white resin. Since it is often the case that white
resin is expensive and/or that there is a desire not to increase
package width, it may be advantageous to make the package as small
as feasible and to instead attach reflector(s) thereto in the form
of separate component(s). Where reflector(s) is/are instead thus
attached thereto in the form of separate component(s), this will
also have the advantage that it increases degrees of freedom with
respect to selection of reflecting surface material(s), since many
factors will be eliminated from the criteria for selection thereof,
including difference in coefficient of thermal expansion relative
to frame(s), adhesive characteristics relative to resin(s) used to
encapsulate LED element(s), and so forth.
[0074] Furthermore, even where emission of light as a result of
driving of LEDs in CW fashion could produce an amount of light that
is sufficient for flash use, it may still be desirable to cause
LEDs to emit light by driving them in pulsed fashion. This is
because, as has been described with reference to FIG. 4, pulsed
drive better permits suppression of LED element deterioration,
making it possible to achieve lengthened LED element life, improved
reliability, and so forth.
[0075] Whereas the foregoing description was carried out in terms
of an image capturing device that was a camera (still-picture
camera) employing silver halide film to carry out still-picture
photography, the present invention is not limited thereto. For
example, the image capturing device may be movie-type equipment
capable of carrying out motion-picture photography; in which case,
for each motion-picture frame (whether it be film or video), LED(s)
used as flash apparatus(es) might be driven in pulsed fashion so as
to be made to emit light during the time when the shutter is
open.
[0076] Second Embodiment
[0077] FIG. 7(a) indicates when a shutter might be open and when it
might be closed in an example of a drive signal timing chart for
LEDs for flash use in a camera associated with a second embodiment
of the image capturing device of the present invention; and FIG.
7(b) shows the corresponding LED drive signals. Note that because,
except for the features mentioned below, the second embodiment is
identical to the first embodiment which was described with
reference to FIGS. 1 through 6, only those aspects that are
different therefrom will be described here.
[0078] Internal to this camera is/are monitoring light-receiving
element(s) capable of measuring amount(s) of light impinging on
image capturing element(s) after passing through photographic
lens(es). In the event that LED element(s) is/are used as flash
apparatus(es), it is possible, unlike the situation with
conventional xenon discharge tubes, to cause light to be emitted in
repeated fashion. In the present case as shown at FIG. 7(a) and
(b), therefore, before the shutter is actually opened (e.g.,
immediately after the shutter button is pressed), respective R, G,
and B LED elements are made to emit light in preliminary fashion at
the same conditions (same pulsewidth(s), time(s) between pulses,
intensity ratio(s), and so forth) as during flash photography.
Moreover, at monitoring light-receiving element(s) internal to the
camera, optimum exposure time(s) is/are calculated based on signal
output(s) produced as a result of such preillumination, and shutter
speed(s) for flash photography is/are determined.
[0079] By so doing, it is possible for exposure time during flash
photography, determined conventionally based on flash intensity or
the like, to be accurately determined by means of exposure control
apparatus(es) internal to the camera in similar manner as with
conventional photography. Note that in the example shown at FIG.
7(b), shutter speed is set so as to obtain a duration that is 16
times the time required for preillumination.
[0080] Other Embodiments
[0081] Whereas the foregoing first and second embodiments have been
described in terms of cameras employing silver halide film, it goes
without saying that these might just as well have been electronic
still-picture cameras employing CCD(s), CMOS imager(s), and/or the
like as image capturing element(s). Because CCDs, CMOSes, and other
such light-receiving elements exhibit varying sensitivity depending
upon wavelength, adjustment of gain will be necessary. That is, it
is desirable that emission proceed from light of wavelength for
which sensitivity is high. For example, taking the case of CCDs,
with the conventional CCD (curve G91) shown in FIG. 9, because
sensitivity to red is low but sensitivity to blue or green is high,
it is desirable that emission of light be made to proceed from the
blue LED element or the green LED element. Conversely, with the
EXviewHAD CCD (curve G92), because sensitivity is highest with
respect to red, it is desirable that emission of light be made to
proceed from the red LED element. Or in the case of the
conventional CMOS shown in FIG. 10, because sensitivity is highest
with respect to green, it is desirable that emission of light be
made to proceed from the green LED element.
[0082] Whereas even with conventional electronic image capturing
element(s) a full-color signal might be obtained by applying red
filter(s), green filter(s), and/or the like at individual image
capturing element(s), where image capturing device(s) in accordance
with embodiment(s) of the present invention is/are employed it may
be possible to do without filter(s) at individual image capturing
element(s). Monochromatic images respectively corresponding to
colors emitted by LED elements may be acquired through a method in
which, for example, only red signal(s) is/are integrated while R
LED element(s) is/are emitting light, and only green signal(s)
is/are integrated while G LED element(s) is/are emitting light.
Because it may be possible to do without filter(s) at individual
element(s), all image capturing elements may be utilized in
acquiring monochromatic image(s). This being the case, where the
same image capturing element(s) is/are used it will be possible to
obtain color image(s) having three times the resolution, or if
color image(s) of the same resolution is/are to be obtained it will
be sufficient to use one-third the number of image capturing
elements.
[0083] However, where element(s) with filter(s) is/are not
employed, there may be a problem in that it may no longer be
possible to carry out conventional photography, i.e., photography
not accompanied by illumination produced by flash apparatus(es). As
one example of how this problem might be solved, element(s) with
filter(s) could be employed, sensitivity of red-filtered element(s)
with respect to emission of R light, sensitivity of green-filtered
element(s) with respect thereto, and so forth being stored in
advance in memory, and by employing a method in which signals are
integrated in turn by color only during flash photography, it will
be possible to enjoy the advantages of ability to obtain higher
resolution during flash photography while still being able to carry
out conventional photography.
[0084] Moreover, the present invention may be embodied in a wide
variety of forms other than those presented herein without
departing from the spirit or essential characteristics thereof. The
foregoing embodiments, therefore, are in all respects merely
illustrative and are not to be construed in limiting fashion. The
scope of the present invention being as indicated by the claims, it
is not to be constrained in any way whatsoever by the body of the
specification. All modifications and changes within the range of
equivalents of the claims are, moreover, within the scope of the
present invention.
* * * * *