Full-spectrum flash for electronic devices
Introduced here are light sources for flash photography configured to produce high-fidelity white light that is tunable over a broader range of correlated color temperatures (CCTs) than conventional flash technologies. The light source can include multiple independently controllable color channels representing illuminants (e.g., light-emitting diodes) of different colors with varying degrees of saturation. Operating collectively, the multiple color channels can produce a high spectral quality white light corresponding to different CCTs (e.g., “warm” white light having a red hue, “cool” white light having a blue hue). Operating independently, these same color channels can be pre-flashed in a variety of prescribed sequences to probe the spectral characteristics of a scene, thereby allowing for an enhanced, spectrally matched white flash as well as collecting per-pixel reflectivity data that can be later used in during post processing of the captured image.
1. An electronic device comprising:
an image sensor configured to generate images from light collected through a lens;
a light source that includes at least three color channels,
wherein each color channel includes one or more illuminants configured to produce a substantially similar color, and
wherein each color channel is separately addressable to produce light of a different color;
a memory configured to store multiple color mixing models associated with multiple correlated color temperatures (CCTs),
wherein each color mixing model specifies a driving current to be provided to each color channel of the at least three color channels to achieve the corresponding CCT; and
a processor configured to:
receive input indicative of a request to capture an image of an ambient environment viewable through the lens;
determine that the image is to be captured in conjunction with a flash produced by the light source; and
generate a signal that prompts simultaneous illumination of each color channel to produce white light having a CCT of at least 1650K and no more than 10000K.
2. The electronic device of claim 1 , wherein the light source includes four color channels configured to produce red light, blue light, green light, and amber light.
3. The electronic device of claim 1 , wherein the light source includes five color channels configured to produce red light, blue light, amber light, cyan light, and lime light.
4. The electronic device of claim 1 , wherein the processor is further configured to:
identify, based on a color characteristic of the image sensor or the light source, a color mixing model from amongst the multiple color mixing models; and
determine an operating parameter to drive the at least three color channels of the light source based on the color mixing model.
5. The electronic device of claim 4 , wherein the color characteristic is derived from thermal feedback generated by a heat sensor, optical feedback generated by an optical sensor, or a reference image created by the image sensor in conjunction with a reference flash produced by at least one color channel.
6. An electronic device comprising:
an image sensor configured to generate images from light collected through a lens;
a light source that includes at least three color channels,
wherein each color channel includes one or more illuminants configured to produce a substantially similar color, and
wherein each color channel is separately addressable to produce light of a different color; and
a processor configured to:
receive input indicative of a request to capture an image of an ambient environment viewable through the lens;
determine that the image is to be captured in conjunction with a flash of white light produced by the light source;
cause a series of colored flashes to be produced in which each color channel is separately illuminated;
cause a series of images to be captured in conjunction with the series of colored flashes;
identify a spectral characteristic of each color channel by examining the image in the series of images that is captured in conjunction with the corresponding colored flash;
examine the spectral characteristics to establish a spectral property of the light source; and
generate a signal that prompts simultaneous illumination of each color channel to produce the flash of white light having a correlated color temperature (CCT) of at least 1650K and no more than 10000K.
7. The electronic device of claim 6 , wherein the signal is based on the spectral property of the light source.
8. An electronic device comprising:
an image sensor configured to generate images from light collected through a lens;
a light source that includes at least three color channels,
wherein each color channel includes one or more illuminants configured to produce a substantially similar color, and
wherein each color channel is separately addressable to produce light of a different color; and
a processor configured to:
receive input indicative of a request to capture an image of an ambient environment viewable through the lens;
determine that the image is to be captured in conjunction with a flash of white light produced by the light source;
cause a reference flash to be produced in which the at least three color channels are simultaneously illuminated;
cause a reference image to be captured in conjunction with the reference flash;
cause a series of flashes to be produced in which all color channels except one are simultaneously illuminated;
cause a series of images to be captured in conjunction with the series of flashes;
identify a spectral characteristic of each color channel by estimating a corresponding discoloration effect,
wherein the corresponding discoloration effect for a given color channel is estimated by comparing the image in the series of images that is captured in conjunction with the flash in which the given color channel was not illuminated to the reference image;
examine the spectral characteristics to establish a spectral property of the light source; and
generate a signal that prompts simultaneous illumination of each color channel to produce the flash of white light having a correlated color temperature (CCT) of at least 1650K and no more than 10000K.
9. The electronic device of claim 8 , wherein the signal is based on the spectral property of the light source.
10. A light source designed to improve color reproducibility, the light source comprising:
an illuminant array that includes at least three color channels,
wherein each color channel includes one or more illuminants configured to produce a substantially similar color, and
wherein each color channel is separately addressable to produce light of a different color; and
a controller configured to—
select a color mixing model corresponding to a particular correlated color temperature (CCT) from amongst multiple color mixing models, and
determine, based on the color mixing model, an operating parameter to simultaneously drive the at least three color channels to produce a flash of white light having the particular CCT.
11. The light source of claim 10 , wherein the illuminant array has a tunable CCT range of 1650K to 8000K.
12. The light source of claim 10 , wherein the illuminant array has a diameter of less than four millimeters (mm).
13. The light source of claim 10 , further comprising:
at least three linear field-effect transistor-based (FET-based) current regulated drivers,
wherein each linear FET-based current regulated driver is configured to drive a corresponding color channel of the at least three color channels.
14. The light source of claim 10 , further comprising:
a heat sensor configured to measure thermal feedback;
wherein the controller is further configured to:
determine, for each color channel, an effect of the thermal feedback; and
adjust the color mixing model responsive to a determination that the effect has exceeded a predetermined threshold for at least one color channel.
15. The light source of claim 10 , further comprising:
multiple optical sensors configured to measure optical feedback at different wavelength ranges;
wherein the controller is further configured to:
determine, for each color channel, whether color shift has occurred by examining the optical feedback; and
adjust the color mixing model responsive to a determination that color shift has exceeded a predetermined threshold for at least one color channel.
16. The light source of claim 10 , wherein the controller is further configured to:
identify a color feature of an image captured by an electronic device in conjunction with the flash of white light; and
adjust the color mixing model based on the color feature.
17. The light source of claim 10 , further comprising:
a circular substrate to which the illuminant array is mounted,
wherein the circular substrate is comprised of a material able to dissipate heat generated by the illuminant array.
18. A method for producing white light with a multi-channel light source having at least three color channels, each color channel including one or more illuminants configured to produce a substantially similar color, the method comprising:
characterizing a spectral property of the multi-channel light source by
producing a series of flashes in which each color channel is separately illuminated,
causing a series of images to be captured in conjunction with the series of flashes,
identifying a spectral characteristic of each color channel by examining the image in the series of images captured in conjunction with the corresponding flash, and
examining the spectral characteristics to discover the spectral property of the multi-channel light source;
identifying a color mixing model based on the spectral property; and
causing the multi-channel light source to produce white light having a particular correlated color temperature (CCT) by separately driving each color channel of the at least three color channels in accordance with the color mixing model.
19. A method for producing white light with a multi-channel light source having at least three color channels, each color channel including one or more illuminants configured to produce a substantially similar color, the method comprising:
characterizing a spectral property of the multi-channel light source by
producing a reference flash in which the at least three color channels are simultaneously illuminated,
causing a reference image to be captured in conjunction with the reference flash,
producing a series of flashes in which all color channels except one are simultaneously illuminated,
causing a series of images to be captured in conjunction with the series of flashes,
identifying a spectral characteristic of each color channel by estimating a corresponding discoloration effect,
wherein the corresponding discoloration effect for a given color channel is estimated by comparing the image in the series of images that is captured in conjunction with the flash in which the given color channel was not illuminated to the reference image, and
examining the spectral characteristics to discover the spectral property of the multi-channel light source;
identifying a color mixing model based on the spectral property; and
causing the multi-channel light source to produce white light having a particular correlated color temperature (CCT) by separately driving each color channel of the at least three color channels in accordance with the color mixing model.
20. A method comprising:
accessing a memory that associates color mixing models with spectral properties of a multi-channel light source,
wherein the multi-channel light source includes at least three color channels, each color channel including one or more illuminants configured to produce a substantially similar color;
characterizing a spectral property of the multi-channel light source;
identifying an appropriate color mixing model in the memory based on the spectral property; and
causing the multi-channel light source to produce light having a particular correlated color temperature (CCT) by separately driving each color channel of the at least three color channels in accordance with the appropriate color mixing model.
21. The method of claim 20 , wherein the multi-channel light source includes at least five color channels.
22. The method of claim 20 , wherein the multi-channel light source includes at least seven color channels.
23. The method of claim 20 , wherein the multi-channel light source is housed within an electronic device.
24. The method of claim 23 , wherein the memory is accessible to the electronic device across a network.
25. The method of claim 23 , wherein the memory is housed within the electronic device.
26. A light source comprising:
a first color channel that includes a first illuminant configured to produce red light that is located on a first die;
a second color channel that includes a second illuminant configured to produce blue light that is located on a second die;
a third color channel that includes a third illuminant configured to produce cyan light that is located on a third die;
a fourth color channel that includes a fourth illuminant configured to produce amber light that is located on a fourth die;
a fifth color channel that includes a fifth illuminant configured to produce lime light that is located on a fifth die; and
a controller configured to produce white light having different correlated color temperatures (CCTs) by controllably distributing electrical current amongst the first color channel, the second color channel, the third color channel, the fourth color channel, and the fifth color channel.
27. The light source of claim 26 , wherein the first color channel, the second color channel, the third color channel, the fourth color channel, or the fifth color channel includes multiple illuminants.
28. The light source of claim 26 , wherein each illuminant is a light-emitting diode (LED).
29. The light source of claim 28 , wherein the intra-die spacing is no more than 0.1 millimeters (mm).
30. The light source of claim 26 , further comprising:
a substrate configured to dissipate heat generated by the first illuminant, the second illuminant, the third illuminant, the fourth illuminant, and the fifth illuminant.
31. The light source of claim 30 , wherein the substrate is comprised of woven fiberglass cloth with an epoxy resin binder.
32. The light source of claim 30 , wherein the substrate is comprised of ceramic, metal, or any combination thereof.
33. The light source of claim 30 , further comprising:
a protective cover comprised of a transparent material.