U.S. patent application number 14/089394 was filed with the patent office on 2014-03-27 for camera flash with reconfigurable emission spectrum.
This patent application is currently assigned to Core Wireless Licensing S.a.r.l.. The applicant listed for this patent is Core Wireless Licensing S.a.r.l.. Invention is credited to JOHAN BERGQUIST.
Application Number | 20140085534 14/089394 |
Document ID | / |
Family ID | 41113008 |
Filed Date | 2014-03-27 |
United States Patent
Application |
20140085534 |
Kind Code |
A1 |
BERGQUIST; JOHAN |
March 27, 2014 |
CAMERA FLASH WITH RECONFIGURABLE EMISSION SPECTRUM
Abstract
A method and an apparatus for spectrum synthesis for use in a
flash unit, wherein the spectrum synthesis includes combining a
plurality of emissive light sources in order to provide a combine
output beam and producing the output spectrum for the combined
output beam at least based on a reference spectrum. The reference
spectrum can be obtained by sensing the spectrum of ambient light
or selected from a plurality of stored spectra. The flash unit has
at least two emissive light sources and each of the light sources
can be adjusted relative to each other so that the outputs from the
light sources can mimic a selected illumination scenario. It is
possible to use a mixture of quantum dots to tailor each light
source so that the combined spectra from different light sources
can reasonably mimic a number of frequently used illumination
scenario.
Inventors: |
BERGQUIST; JOHAN; (TOKYO,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Core Wireless Licensing S.a.r.l. |
Luxembourg |
|
LU |
|
|
Assignee: |
Core Wireless Licensing
S.a.r.l.
Luxembourg
LU
|
Family ID: |
41113008 |
Appl. No.: |
14/089394 |
Filed: |
November 25, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12322709 |
Feb 4, 2009 |
8598798 |
|
|
14089394 |
|
|
|
|
61072151 |
Mar 28, 2008 |
|
|
|
Current U.S.
Class: |
348/371 ; 362/3;
362/4 |
Current CPC
Class: |
G03B 2215/0567 20130101;
H04N 5/2256 20130101; G03B 2215/0571 20130101; G03B 15/05 20130101;
G03B 15/02 20130101; H05B 47/10 20200101 |
Class at
Publication: |
348/371 ; 362/3;
362/4 |
International
Class: |
G03B 15/05 20060101
G03B015/05; G03B 15/02 20060101 G03B015/02; H04N 5/225 20060101
H04N005/225 |
Claims
1. A method for producing an output spectrum of a flash unit,
comprising: displaying one or more illumination scenarios, the
illumination scenarios each having a particular illuminant spectral
distribution; receiving a selection of an illumination scenario;
and adjusting base spectra of a plurality of light sources to
create a combined output beam having an output spectrum that
corresponds to the selected illumination scenario's spectral
distribution.
2. The method of claim 1, further comprising: determining the
spectral distribution of ambient light surrounding the flash unit;
comparing the spectral distribution of the ambient light to the
selected illumination scenario's spectral distribution; and
adjusting the base spectra at least partially based on the
comparison.
3. The method of claim 2, further comprising sensing the spectral
distribution of ambient light to providing a reference
spectrums.
4. The method of claim 1, wherein the illumination scenarios
include at least one of sunlight, cloudy sky, tungsten lamp,
fluorescent light, and candle light.
5. The method of claim 1, further comprising: sensing a spectrum of
ambient light for providing a sensed spectrum; and selecting a
reference spectrum at least partly based on the sensed
spectrum.
6. An apparatus for producing an output spectrum of a flash unit,
the apparatus comprising: a user interface for displaying one or
more illumination scenarios, the illumination scenarios each having
a particular illuminant spectral distribution; a unit that receives
a selection of an illumination scenario; and a control module in
communication with the user interface and the unit, the control
module adjusts spectra of a plurality of light sources to create a
combined output beam having an output spectrum that corresponds to
the selected illumination scenario's spectral distribution.
7. The apparatus of claim 6, wherein the unit determines the
spectral distribution of ambient light surrounding the flash
unit.
8. The apparatus of claim 7, wherein the unit compares the spectral
distribution of the ambient light to the selected illumination
scenario's spectral distribution.
9. The apparatus of claim 8, wherein the unit adjusts the base
spectra at least partially based on the comparison the spectral
distribution of the ambient light to the selected illumination
scenario's spectral distribution.
10. The apparatus of claim 6 further comprising: a connector for
receiving the flash unit; and a processor in communication with the
control module, the processor is configured, at least, to adjust
electric current to the light source.
11. The apparatus of claim 6 further comprising a camera.
12. The apparatus of claim 6 further comprising a mobile
terminal.
13. The apparatus of claim 6 further comprising a sensor for
sensing a spectrum of ambient light for providing a sensed
spectrum, wherein a reference spectrum is selected at least partly
based on the sensed spectrum.
Description
CROSS-REFERENCE AND RELATED APPLICATIONS
[0001] This patent application is a continuation application of
U.S. Pat. No. 8,598,798, issued on Dec. 3, 2013 (U.S. patent
application Ser. No. 12/322,709 filed on Feb. 4, 2009), which
claims benefit to U.S. Patent Application Ser. No. 61/072,151 filed
on Mar. 28, 2008.
BACKGROUND
[0002] The disclosure relates generally to illumination for both
photography and general lighting and, in particular, to camera
flash. An illumination source is largely characterized by luminous
flux (lumen) and spectral power distribution (W/nm). The former is
a metric of the perceived brightness whereas the latter determines
the color of the light via multiplication with the color matching
functions. The color of white light can be expressed both by CIE
chromaticity coordinates and by the correlated color temperature
(CCT), that is, the temperature of a black-body radiator resulting
in a spectrum which, when multiplied by the color matching
functions, yields the same color as the original illumination
source. For example, an incandescent light bulb has a spectrum
corresponding to a CCT of 3200.degree. K whereas a Xenon camera
flash typically has a CCT of 9000.degree. K. The CCT of daylight
varies by weather, location and time of the day and year.
[0003] The human vision adapts to the illumination so an object
with flat reflection spectrum looks white under many different
illumination sources. In contrast, a film-based camera is not able
to adapt. In a digital camera, the sensor usually has fixed RGB
(red, green, blue) filters, post-processing of the raw image data
can be used to adjust the white balance to a predefined value,
usually expressed in CCT. In particular, in consumer cameras, this
process is automated via automatic white balancing (AWB)
algorithms, i.e. the white point of the image is adjusted after it
has been recorded. These algorithms are often very intricate and
advanced but the result is always implemented by adjusting the
relative gain in the red, green, and blue channels.
SUMMARY
[0004] A method and an apparatus for spectrum synthesis for use in
a flash unit are provided. The spectrum synthesis comprises
combining a plurality of emissive light sources in order to provide
a combine output beam and producing the output spectrum for the
combined output beam at least based on a reference spectrum. The
reference spectrum can be obtained by sensing the spectrum of
ambient light or selected from a plurality of stored spectra. It is
possible that a user can determine the type of ambient light source
and select the reference spectrum based on the determined type. The
flash unit has at least two emissive light sources and each of the
light sources can be adjusted relative to each other so that the
outputs from the light sources can mimic a selected illumination
scenario. When the number of the light sources in the flash unit is
too small, the difference between the synthesized spectrum and the
spectrum of the selected illumination scenario can be significant.
It is possible to use a mixture of quantum dots to tailor each
light source so that the combined spectra from different light
sources can reasonably mimic a number of frequently used
illumination scenario. In general, the difference between the
synthesized spectrum and the spectrum of the selected illumination
scenario can be reduced by increasing the number of the light
sources in a flash unit. In any case, the minimum number of the
light sources is two.
[0005] Thus, in accordance with the various aspects of the
invention, a method for spectral synthesis is disclosed. According
to one aspect, the method includes providing at least a first
emissive light source and a second emissive light source for a
camera flash, wherein the first emissive light source is configured
for producing a first light output with a first spectral
distribution, and the second emissive light source is configured
for producing a second light output with a second spectral
distribution different from the first spectral distribution; and
providing electrical access to the first and second emissive light
sources such that at least the first light output is adjustable
relative to the second light output for producing a combined light
output with a third spectral distribution.
[0006] Another aspect is a flash module. According to one
embodiment, the flash unit includes at least a first emissive light
source configured for producing a first light output with a first
spectral distribution; and a second emissive light source
configured for producing a second light output with a second
spectral distribution different from the first spectral
distribution, wherein at least the first light output is adjustable
relative to the second light output for producing a combined light
output with a third spectral distribution for a camera flash. The
adjustment of the light output can be achieved by controlling the
amplitude of the electrical current or by controlling the
pulse-width in a pulse-width modulated current.
[0007] Another aspect is a stand-alone camera or a camera in an
electronic device such as a mobile phone, the camera having a flash
unit, wherein the flash unit includes at least a first emissive
light source configured for producing a first light output with a
first spectral distribution; and a second emissive light source
configured for producing a second light output with a second
spectral distribution different from the first spectral
distribution, wherein at least the first light output is adjustable
relative to the second light output for producing a combined light
output with a third spectral distribution for a camera flash. The
camera can be a digital camera or a film-based camera.
[0008] Various embodiments will become apparent upon reading the
description of the drawings taken in conjunction with FIGS. 1 to
7.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1a is a block diagram showing a digital camera.
[0010] FIG. 1b is a block diagram showing a film-based camera.
[0011] FIGS. 2a-2d show various illumination modules.
[0012] FIGS. 3a-3b show emissive light sources.
[0013] FIG. 4 shows a flash unit.
[0014] FIG. 5 shows an example of synthesized flat spectra from the
output of 20 LEDs.
[0015] FIG. 6 shows an example of an arbitrary synthesized spectra
from the output of 20 LEDs
[0016] FIG. 7 is a flowchart for minimizing the spectral error of
the synthesized spectrum.
DETAILED DESCRIPTION
[0017] The optimization of the transmission spectra of the color
filters in a digital camera assumes a standard illuminant, standard
object reflectance spectrum, standard object preference, or a
combination thereof. This means that the camera is, from a
sensitivity point of view, sub-optimized for most illumination
sources, especially for camera flash light. In order to perform
AWB, the gain factors need to be adjusted for each R, G, and B
channel to achieve the desired white balance (CCT). Increased gain
inevitably results in larger image noise and a grainier image.
[0018] If the photograph is taken in the illumination for which the
sensor is spectrally optimized, gain can be minimized. In most
situations, however, the illumination is a superposition of several
sources so the resultant spectrum, and hence the CCT, is not well
defined across the image. This situation occurs, for example,
indoors close to a window where the object is illuminated by both
daylight and artificial light (incandescent bulbs, fluorescent
lamps, light-emitting diode (LED) lamps etc). The same problem
occurs when using a conventional flash in ambient light.
[0019] A problem with both LED and Xenon flashes is the low color
rendering index (CRI) which is caused by their discontinuous
emission spectrum (pseudo-white LEDs have only blue and yellow
light). This results in missing colors or depth when taking
photographs or poor light quality when the mobile phone flash is
used in torch mode.
[0020] Image noise generated by gain is typically reduced by
low-pass or other filtering in the image-processing chain of the
camera but this leads to artifacts and reduced sharpness.
[0021] The problem of mixed illumination sources and a white point
CCT varying within the image has been solved by applying filters to
one or several of the sources. For example, a blue filter can be
attached to incandescent lamps to give the same CCT as daylight.
However, the spectra are still not identical which can confuse the
AWB algorithm. Also, it is not practical to carry and attach blue
filters every time a photo is to be taken. AWB algorithms are not
perfect and objects with extreme color distributions often appear
with the wrong color balance. If instead the actual illumination
spectrum can be identified, more accurate white balancing can be
achieved.
[0022] Accordingly, in one embodiment, the first step is to
determine the type of ambient light source. The subsequent step is
to adjust the spectrum of the flash so that the spectrum and,
therefore, the CCT coincide with that of the ambient light. When
shooting occurs in darkness or in dim ambient light where the
majority of the illumination comes from the flash, the flash
spectrum is adjusted to that of the camera/film to achieve maximum
camera/film speed. The synthesized/identified spectrum is fed back
to the AWB algorithm to achieve the actual white point without
analyzing the image or adjusting the RGB gain factors which leads
to reduced color artifacts. When used in the torch mode of the
flash or in general lighting, a spectrum of any light source can be
synthesized. This is useful for accurate rendering of surface
colors.
[0023] Synthesizing an arbitrary flash spectrum can be accomplished
by combining two or more individually addressable LEDs with
different spectra. The modulation of each LED is done either by
current, pulse width, or a combination thereof. The emission could
originate either from the LED itself, LED+broadband phosphor, or
LED+any photoluminescent material, including quantum dots (QD),
which allow precise spectral design over the entire visible range
when combined with deep purple or UV exciting LEDs. The emission
can also solely be originated from the photoluminescent material.
The emission spectrum can be simply a Gaussian distribution with
the peak wavelength determined only by the QD size. Typical
full-widths at half-maximum (FWHM) are 10-15 nm and peak wavelength
controllability within +/-1 nm. By mixing QDs of several sizes and
tuning their number ratios, a tailored spectrum for each LED can be
obtained.
[0024] Another way to synthesize the flash spectrum is using a fast
spatial light modulator (SLM) below which QDs or mixtures of QDs
corresponding to the different spectra are printed. The QDs can
then be excited by a single LED and the duty of each wavelength is
controlled by the SLM. SLMs with microsecond response can be
implemented with both ferroelectric liquid crystals (FLCs) and
micro electro-mechanical systems (MEMS). In both cases, a
rotationally symmetric structure and separate Fresnel lenses for
each emitting region is required to distribute the light from each
emitter uniformly.
[0025] To reproduce the approximate spectra of all possible
illumination scenarios (sunlight, cloudy sky, tungsten lamp,
fluorescent light, etc), the fluent weights of the base spectra are
iteratively adjusted until the difference between the illuminant
spectrum and the synthesized spectrum converges to a minimum. When
the base spectral weights
[0026] (current and/or pulse widths) have been determined, they are
stored in a look-up table (LUT) along with an illuminant look-up
index.
[0027] The illuminant indices are determined from the spectrally
calibrated sensor response. The sensor could be a spectrometer,
trichromatic sensor, or a two-channel sensor (see Table 1), or the
camera itself.
[0028] The LUT also contains pre-calculated CCTs of the light
sources which are fed into the white-balancing algorithm (this
already uses CCT as an input parameter). In this way, color
artifacts from determining the white point via image analysis can
be avoided.
TABLE-US-00001 TABLE 1 Example of Relative Response from A
Two-Channel Ambient Light Sensor LIGHT SOURCE CCT CHANNEL RATIO F11
(Fluorescent lamp) 3700K 0.127860953 F12 (Fluorescent lamp) 2800K
0.133593675 Daylight simulator 5600K 0.100576456 Halogen lamp 2600K
0.567822155
[0029] In order to minimize the risk for temporal color artifacts
in scanning sensor systems, e.g. CMOS sensors, current modulation
is preferred over temporal modulation. It is also possible to
distribute energy of the shortest pulse throughout a burst of
multiple pulses, the width of which corresponds to the longest
pulse width of all emitters.
[0030] In sum, according to various embodiments, the spectrum of a
flash is synthesized by using two or more emissive light sources,
at least one of the light sources has a different spectrum from the
other. The flash can be used in a digital camera, a film-based
camera, or a separate unit. A block diagram of a digital camera,
according to one embodiment of the invention is shown in FIG.
1a.
[0031] As shown in FIG. 1a, the digital camera 1 has a single lens
or a lens system 10 for forming an image on a sensor 20, such as a
solid-state sensor. Under the control of a processor 30, an image
is captured by the user taking a picture. The captured image can be
stored in a memory 40. The camera 1 also has a flash unit 50 with
at least two emissive light sources 52 and 54 for emitting lights
with different spectral ranges or distributions. The flash unit 50
is operatively connected to a control module 60 so that the light
sources 52 and 54 can be separately controlled or addressed by the
control module 60. An LUT is operatively connected to the control
module 60 and the processor 30. The camera 1 also has a
user-interface 80 to allow a user to choose the settings of the
camera, including the choice of illumination scenarios. The camera
1 may have a light spectrum sensing unit 90 for determining the
spectral distribution of ambient light, for example. The sensing
unit 90 typically has a diffusing light collecting lens to average
the illumination from many different directions. Alternatively, the
camera itself is used as a light sensor by temporarily defocusing
to achieve the same effect. The sensing unit 90 is calibrated
against all possible illumination sources and the calibration data
is written into the LUT. The signals from the sensing unit for an
arbitrary illumination are then compared to the LUT, the
corresponding base spectrum weighs are loaded, and the flash is
driven with the corresponding weighs. If the sensor signal is below
a pre-defined value, the flash unit is identified as the main
illumination, and the emitter weights are selected to produce a
spectrum corresponding to the maximum spectral sensitivity of the
sensing unit.
[0032] A film-based camera is shown in FIG. 1b. As shown in FIG.
1b, the camera 1 allows a section of a photographic film 22 to be
placed at the image plane of the lens or lens system 10 for
recording an image. A shutter 24, under the control of the
processor 30 and a shutter release driver 26, is used to control
the exposure on the film.
[0033] In spectrum synthesis, the output of the light sources 52
and 54 is controlled by the electrical current. As shown in FIG.
2a, the control unit 60 has at least a first current source 62 and
a second current source 64 to separately provide electrical current
112 and electrical current 114 to the light sources 52 and 54. The
electrical power source can be a battery 160 or a transformer
connected to another power source, such as an electrical outlet.
According to another embodiment, the output of the light sources 52
and 54 is controlled by the pulse-width of two pulse-width
modulation power supplies 66 and 68, as shown in FIG. 2b. The
current 112' and the current 114', as shown in FIG. 2b, are
pulse-width modulated currents.
[0034] According to yet another embodiment, the flash unit 50 has a
battery 160 and the current sources 62 and 64 to provide electrical
current to the light sources 52 and 54, as shown in FIG. 2c. The
flash unit 50 also has electrical connectors for receiving control
signals 116 and 118 from an external controlling processor 61 so as
to control the output of one or both of the light sources.
[0035] According to a different embodiment, the flash unit 50 does
not include a battery 160. Instead, the flash unit 50 has
electrical connectors 162 for connecting to an external
battery.
[0036] FIG. 3a shows an emissive light source for use in the flash
unit 50. As shown, the emissive light source 52, 54 has a
light-emitting diode encased in a transparent body with a lens for
beam forming Alternatively, an optically excitable material is
placed between the beam forming lens and the light-emitting diode
so that the material can be used as a secondary emissive source, as
shown in FIG. 3b. For example, the optically excitable material can
be a broadband phosphor or a photoluminescent material, including
quantum dots. The light-emitting diode in this arrangement, can be
the diode that emits light in the deep purple or UV. The output of
the light source as shown in FIG. 3a and FIG. 3b can be controlled
by the input current to the light emitting diode as illustrated in
FIG. 2a. Alternatively, the output is controlled by pulse width
modulation, as illustrated in FIG. 2b.
[0037] FIG. 4 shows an emissive light source, according to another
embodiment. As shown in FIG. 4, the flash unit 10 may comprise one
or more exciting light emitting diodes, a plurality of quantum dots
arranged in an array, and one or more spatial light modulators
placed between the light emitting diodes and the quantum dots in
order to control the light output from the quantum dots. For
example, the UV/NUV light emitting diodes can be used to excite
single-size quantum dots, each of which gives a Gaussian or
near-Gaussian spectrum. It is also possible that a mixture of
quantum dots are used to produce a combined spectrum with a
particular spectral distribution, for example.
[0038] FIG. 5 shows an example of synthesized flat spectra from the
output of 20 LEDs, wherein each of the LEDs produces a Gaussian or
near-Gaussian spectrum of a different wavelength.
[0039] FIG. 6 shows an example of an arbitrary synthesized spectra
from the output of 20 LEDs.
[0040] FIG. 7 is a flowchart illustrating an exemplary procedure in
determining the synthesized spectrum, according to one embodiment.
As shown in the flowchart 300, the goal is to obtain a synthesized
spectrum S' (.lamda.) in reference to an illuminant or source
spectrum S(.lamda.). At step 301, the source spectrum S(.lamda.) is
obtained from the sensing unit 90 or retrieved from the LUT 70 in
the camera (see FIGS. 1a and 1b). For simplicity, it is assumed
that the source spectrum is normalized such that its peak is set
equal to 1. If the number of light sources in the flash unit is n,
then the synthesized spectrum is S'(.lamda.) which is expressed as
the sum of W.sub.nS.sub.n(.lamda.), with S.sub.n(.lamda.) being the
base spectra of the light sources, and W.sub.n being the fluent
weights. At step 302, each fluent weight W.sub.n is set equal to 1.
At step 303, the wavelength .lamda..sub.p at which the spectral
power distribution of S(.lamda.) reaches a maximum is determined,
either from measurement or from the LUT. At step 304, the
synthesized spectrum S'(.lamda.) is normalized to become
S'(.lamda..sub.p), in each iteration, so that the peak in the
normalized synthesized spectrum S'(.lamda..sub.p) is equal to 1.
During the normalization process at step 304, the weight W.sub.n of
each of the base spectra is adjusted to W.sub.n'. At step 305, the
relative error .epsilon.=S'(.lamda..sub.n)/S(.lamda..sub.n) for
each base spectrum is computed, where .lamda..sub.n is the peak
wavelength of that base spectrum. At step 306, the weight W.sub.n'
is adjusted based on the relative error .epsilon. so that the error
vanishes after the adjustment. After the weight W.sub.n' of each of
the base spectrum has been adjusted, as determined at step 307, an
interim synthesized spectrum is computed at step 308. Since the
base spectra have finite distributions, there will be errors for
other wavelengths in each base spectrum. These errors may be
minimized by iteration. At step 309, if it is determined that the
sum of errors has reached a predetermined value, the interim
synthesized spectrum is used as the final synthesized spectrum. The
weight W.sub.n' for each base spectrum can be used to adjust the
output of the light source.
[0041] It should be noted that when a particular illuminant
spectrum S(.lamda.) is stored in the LUT and the base spectra of
the light sources in the flash unit are known, it is possible to
store the fluent weights for the base spectra in the LUT once a
synthesized spectrum is determined. For example, once a synthesized
spectrum of a candle-lit scenario has been determined according to
the base spectrum of the light sources in the flash unit, the
fluent weights for this particular synthesized spectrum can be
stored in the camera. If the user chooses to take a picture with
this synthesized candle-lit spectrum through the user interface 80
(see FIGS. 1a and 1b), the control module 60 will adjust the output
of the light sources in the flash unit 50 using the stored fluent
weights in the LUT 70, for example.
[0042] In sum, a method and an apparatus for spectrum synthesis for
use in a flash unit are provided. The flash unit has at least two
emissive light sources and each of the light sources can be
adjusted relative to each other so that the outputs from the light
sources can mimic a selected illumination scenario. The emissive
light sources can be LEDs or other adjustable light sources, or a
combination thereof. Furthermore, one or more non-adjustable light
sources, such as Xenon flash lights, can be used in combination
with one or more adjustable light sources in a flash unit. When the
number of the light sources in the flash unit is too small, the
difference between the synthesized spectrum and the spectrum of the
selected illumination scenario can be significant. It is possible
to use a mixture of quantum dots to tailor each light source so
that the combined spectra from different light sources can
reasonably mimic a number of frequently used illumination scenario.
In general, the difference between the synthesized spectrum and the
spectrum of the selected illumination scenario can be reduced by
increasing the number of the light sources in a flash unit. In any
case, the minimum number of the light sources is two.
[0043] Accordingly, the method for spectral synthesis, according to
one embodiment, comprises combining a plurality of emissive light
sources for providing a combined output beam; and producing the
output spectrum for the combined output beam at least partially
based on a reference spectrum. The method further comprises sensing
a spectrum of ambient light for providing the reference spectrum.
Alternatively, the reference spectrum is selected from a plurality
of stored spectra. In one embodiment, the stored spectra are
representable by a plurality of weighting values for said
combining. In another embodiment, the method further comprises:
sensing a spectrum of ambient light for providing a sensed
spectrum; and selecting the reference spectrum at least partly
based on the sensed spectrum. In general, the plurality of emissive
light sources comprise: a first emissive light source arranged to
provide a first light beam of a first spectrum; and a second
emissive light source arranged to provide a second light beam of a
second spectrum, wherein at least part of the second spectrum is
different from the first spectrum, and wherein at least one of the
first emissive light source and the second emissive light source is
adjustable for producing the output spectrum. In one embodiment, at
least one of the first emissive light source and the second
emissive light source is arranged to receive a pulse-width
modulated power for producing a corresponding light beam, and
wherein pulse width of the modulated power is changed for adjusting
said at least one of the first emissive light source and the second
emissive light source. In another embodiment, each of the plurality
of emissive light sources is arranged to receive an electric
current for producing a corresponding light beam, and wherein
amplitude of the electric current received by at least one of said
plurality of emissive light sources is adjustable for producing the
output spectrum.
[0044] To state it differently, the method comprises
[0045] providing a first emissive light source and a second
emissive light source for a camera flash, wherein the first
emissive light source is configured for producing a first light
output with a first spectral distribution, and the second emissive
light source is configured for producing a second light output with
a second spectral distribution different from the first spectral
distribution; and providing electrical access to the first and
second emissive light sources such that at least the first light
output is adjustable relative to the second light output for
producing a combined light output with a third spectral
distribution. Likewise, the apparatus, according to one embodiment,
includes a first emissive light source configured for producing a
first light output with a first spectral distribution; and a second
emissive light source configured for producing a second light
output with a second spectral distribution different from the first
spectral distribution, wherein at least the first light output is
adjustable relative to the second light output for producing a
combined light output with a third spectral distribution for a
camera flash.
[0046] According to various embodiments, the electrical current
adjustment can be achieved by adjusting the amplitude of the
current or by changing the pulse width in a pulse-width modulation.
Moreover, one or more weighting values can be stored so that the
adjustment can be based on at least one stored weighting value in
order to produce the combined light output with the third spectral
distribution.
[0047] It is possible to store a plurality of illuminant spectral
distributions so as to allow a user to select the third spectral
distribution from the illuminant spectral distributions. According
to various embodiments, the method further comprises obtaining a
reference spectral distribution so that the adjustment can be at
least partially based on the reference spectral distribution,
wherein the reference spectral distribution is obtained by sensing
the ambient light or obtained from a memory, such as a look-up
table.
[0048] The method, according to various embodiments, can be carried
out by a software program embedded in a computer readable storage
medium or embedded in a processor having programming codes to carry
out the various steps as described above.
[0049] The camera flash unit, according to various embodiments,
comprises a plurality of emissive light sources for providing a
combined output beam; and a power receiver for receiving electric
current to power each of the plurality of emissive light sources,
wherein the electric current to power at least some of the
plurality of emissive light sources is adjustable so as to produce
an output spectrum for the combined output beam at least partially
based on a reference spectrum. The plurality of emissive light
sources comprise:
[0050] a first emissive light source arranged to provide a first
light beam of a first spectrum; and
[0051] a second emissive light source arranged to provide a second
light beam of a second spectrum, wherein at least part of the
second spectrum is different from the first spectrum, and wherein
at least one of the first emissive light source and the second
emissive light source is adjustable for producing the output
spectrum. The flash unit may include a battery for providing
electrical current to the first and second emissive light sources.
The flash unit may also include
[0052] a first current source for providing electrical current to
the first emissive light source, and a second current source for
providing electrical current to the first emissive light source.
The flash unit may include a control module configured to provide
electrical current to each of the first and second emissive light
sources, wherein at least the electrical current to the first
emissive light source is adjustable. The electrical current to the
first emissive light source can be provided in a pulse-width
modulation mode and the electrical current to the first emissive
light source is adjustable by changing pulse width in the
modulation mode. In a camera having an above-described flash unit,
it is possible to include a look up table configured for storing
weighting values to allow the control module to provide electrical
current to each of the first and second emissive light sources
based on the weighting values. The look up table can be configured
to store a plurality of weighting values indicative of a plurality
of illumination scenarios. The camera can be a digital camera
having a solid-state sensor for capturing an image formed at the
image plane of a lens module, or a film-based camera configured for
placing a section of photographic film at the image plane for image
capturing.
[0053] An apparatus is provided which comprises a connector for
receiving a flash unit, wherein the flash unit comprises a
plurality of emissive light sources arranged to receive electric
current for producing a combined light output; and a processor
configured to adjust the electric current so as to produce an
output spectrum of the combined light output at least based on a
reference spectrum. In one embodiment, the apparatus comprises a
sensor for sensing a spectrum of ambient light for providing the
reference spectrum. In another embodiment, the apparatus comprises
a memory for storing data indicative of a plurality of stored
spectra, wherein the reference spectrum is selected from the stored
spectra. The reference spectrum can be selected based on the sensed
spectrum or by a user who determines the type of ambient light
source at the time of picture taking. In one embodiment, the stored
spectra are representable by a plurality of weighting values for
producing the combined light output.
[0054] In one embodiment, the apparatus comprises a first emissive
light source configured for producing a first light output with a
first spectral distribution; a second emissive light source
configured for producing a second light output with a second
spectral distribution different from the first spectral
distribution, wherein at least the first light output is adjustable
relative to the second light output for producing a combined light
output with a third spectral distribution for a camera flash;
electrical connectors for providing electrical access to the first
and second emissive light sources so as to adjust at least the
first light output, and/or a battery for providing electrical
current to the first and second emissive light sources, and/or a
first current source for providing electrical current to the first
emissive light source, and a second current source for providing
electrical current to the first emissive light source.
[0055] The apparatus may have a control module configured to
provide electrical current to each of the first and second emissive
light sources, wherein at least the electrical current to the first
emissive light source is adjustable, wherein the electrical current
to the first emissive light source is provided in a pulse-width
modulation mode and the electrical current to the first emissive
light source is adjustable by changing the pulse width in the
modulation mode.
[0056] The apparatus may have a look up table configured for
storing weighting values to allow the control module to provide
electrical current to each of the first and second emissive light
sources based on the weighting values, wherein the look up table is
configured to store a plurality of weighting values indicative of a
plurality of illumination scenarios.
[0057] The apparatus can be a stand-alone camera, or an electronic
device, such as a mobile terminal. In one embodiment, the apparatus
comprises a memory for storing a software program having
programming codes for carrying out the method of producing an
output spectrum of a flash unit as described above. In a different
embodiment, the programming codes are embedded in a processor. In
yet another different embodiment, the apparatus is configured to
receive a memory unit, such as a computer readable storage medium
for storing the afore-mentioned software program.
[0058] Also provided are a camera, comprising a lens module for
forming an image at an image plane; an apparatus for providing
illumination; and an image forming medium for capturing the image
formed at the image plane, wherein the image forming medium
comprises a solid-state image sensor or a photographic film. The
apparatus comprises a mobile terminal.
[0059] Briefly, a method and apparatus for spectrum synthesis in a
flash unit are provided. The flash unit has two or more emissive
light sources with different spectral distributions. Each of the
light sources can be adjusted relative to each other so that the
outputs from the light sources can be combined to mimic the
spectral distribution of a selected illumination scenario. A
look-up table is used to store a plurality of weighting values so
that different weighting values can be used to produce various
synthesized spectra from the different spectral distributions of
the emissive light sources. It will be understood by those skilled
in the art that the foregoing and various other changes, omissions
and deviations in the form and detail thereof may be made without
departing from the scope of this invention.
* * * * *