Systems and methods for creating full-color image in low light

• US 9,177,988 B2
• Filed: 12/17/2012
• Issued: 11/03/2015
• Est. Priority Date: 12/16/2011
• Status: Active Grant

• Current Assignee: Chromatra, LLC
• Original Assignee: Chromatra, LLC
• Inventors: Jones, Peter W. J., Cargill, Ellen, Purcell, Dennis W.
• Primary Examiner(s): Vaughn, Jr., William C
• Assistant Examiner(s): PEREZ FUENTES, LUIS M
• Application Number:
  US13/717,198
• Publication Number:
  US 20130329053A1
• Time in Patent Office: 1,051 Days
• Field of Search: 348/164
• US Class Current: 1/1
• CPC Class Codes: G02B 5/208 for use with infrared or ultraviolet radiation, e.g. for separating visible light from infrared and/or ultraviolet radiation
• CPC Class Codes: G06F 18/22 Matching criteria, e.g. proximity measures
• CPC Class Codes: G06T 7/90 Determination of colour characteristics
• CPC Class Codes: H01L 27/14645 Colour imagers
• CPC Class Codes: H04N 23/10 for generating image signals from different wavelengths
• CPC Class Codes: H04N 23/11 for generating image signals from visible and infrared light wavelengths
• CPC Class Codes: H04N 23/555 for picking-up images in sites, inaccessible due to their dimensions or hazardous conditions, e.g. endoscopes or borescopes
• CPC Class Codes: H04N 23/843 Demosaicing, e.g. interpolating colour pixel values
• CPC Class Codes: H04N 23/88 for colour balance, e.g. white-balance circuits or colour temperature control
• CPC Class Codes: H04N 25/11 Arrangement of colour filter arrays [CFA]; Filter mosaics
• CPC Class Codes: H04N 25/135 based on four or more different wavelength filter elements
• CPC Class Codes: H04N 25/585 with pixels having different sensitivities within the sensor, e.g. fast or slow pixels or pixels having different sizes
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20
• CPC Class Codes: H04N 9/77 Circuits for processing the brightness signal and the chrominance signal relative to each other, e.g. adjusting the phase of the brightness signal relative to the colour signal, correcting differential gain or differential phase circuits for matrixing H04N9/67

Abstract

Full-color images of low-light scenes are generated by the systems and methods described herein using only two light channels. An array of photosensitive pixels includes two sets of pixels, the first sensitive only to light associated with a first light channel, the second only to light associated with a second light channel. Thus the first set of pixels generate a first set of electrical signals in response to incident light within the first light channel, and the second set of pixels generate a second set of electrical signals in response to incident light within the second light channel. An image processor receives the first and second sets of electrical signals and generates a full-color image of the scene by processing only signals generated by the first and second sets of pixels.

Claims

1. A low-light color imaging system, comprising:

an array of photosensitive pixels configured to generate electrical signals in response to incident light from a scene, including

a first plurality of pixels, each sensitive only to light associated with a first light channel including a first band of wavelengths of light,

such that the first plurality of pixels generate a first set of electrical signals indicative of the first light channel only in response to incident light having wavelengths within the first light channel, and

a second plurality of pixels, each sensitive only to light associated with a second light channel including a second band of wavelengths of light, such that the second plurality of pixels generate a second set of electrical signals indicative of the second light channel only in response to incident light having wavelengths within the second light channel;

an image processor connected to the array of photosensitive pixels and having circuitry configured to receive the first set of electrical signals indicative of the first light channel and the second set of electrical signals indicative of the second light channel and

generate a full-color image of the scene based on only the first and second set of electrical signals, thereby using only two light channels to generate a full-color image of a low-light scene;

a color database associating a first signal associated with the first light channel and a second signal associated with the second light channel with one of a set of predetermined reference colors; and

a color processor to identify a color in the full-color image as an element of the set of predetermined reference colors.

2. The system of claim 1, wherein the image processor is configured to generate full-color images of a scene having an ambient light intensity of less than about 0.2 lux at a rate of fifteen images per second.

3. The system of claim 1, wherein a full-color image allows a viewer to distinguish between predetermined colors within at least one of a set of primary colors, natural colors, and artificial colors.

4. The system of claim 1, wherein the first and second pluralities of pixels are configured such that, in a color space having axes corresponding to signals from the first and second pluralities of pixels, the distances between elements of a predetermined set of reference colors is no smaller than a predetermined threshold.

5. The system of claim 1, wherein at least one of the first or second pluralities of pixels are selected from a predetermined set of possible pixels.

6. The system of claim 1, wherein the first plurality of photosensitive pixels and the second plurality of photosensitive pixels have substantially the same sensitivity to infrared radiation.

7. The system of claim 1, wherein the image processor is further configured to scale a signal generated by a first photosensitive pixel as a function of distance between the first photosensitive pixel and a photosensitive pixel generating a strong signal.

8. The system of claim 1, wherein the second plurality of photosensitive pixels comprises a third and a fourth plurality of photosensitive pixels, wherein a pixel of the third plurality generates a weaker signal than a pixel of the fourth plurality in response to a substantially identical light input.

9. The system of claim 1, wherein the photosensitive pixels of the first plurality and the photosensitive pixels associated with the second plurality are arranged in a substantially checkerboard pattern.

10. A method for generating a color image in low-light conditions, comprising:

providing an array of photosensitive pixels connected to an image processor;

exposing the array of photosensitive pixels to light associated with a scene;

generating, by a first plurality of pixels of the array, a first set of electrical signals indicative of a first light channel as a function of only incident light associated with the first light channel, wherein a light channel includes at least one band of wavelengths of light;

generating, by a second plurality of pixels of the array, a second set of electrical signals indicative of a second light channel as a function of only incident light associated with the second light channel;

generating a full-color image of the scene based on only the first set of electrical signals indicative of the first light channel and the second set of electrical signals indicative of the second light channel,

thereby using only two light channels to generate a full-color image of a low-light scene;

associating a combination of a first signal associated with the first light channel and a second signal associated with the second light channel with one of a set of predetermined reference colors from a color database; and

identifying a color in the full-color image as an element of the set of predetermined reference colors.

11. The method of claim 10, wherein a full-color image allows a viewer to distinguish between predetermined colors within at least one of a set of primary colors, natural colors, and artificial colors.

12. The method of claim 10, further comprising generating full-color images of a scene having an ambient light intensity of less than about 0.2 lux at a rate of fifteen images per second.

13. The method of claim 10, wherein the array of pixels is provided such that, within a color space having axes corresponding to signals from the first and second pluralities of pixels, the distances between elements of a predetermined set of reference colors is no smaller than a predetermined threshold.

14. The method of claim 10, further comprising converting the full-color image into an RGB image.

15. The method of claim 10, wherein a plurality of wavelengths included in the first light channel are substantially included in the second light channel.

16. The method of claim 10, further comprising scaling a signal generated by a first photosensitive pixel by a function of a distance between the first photosensitive pixel and a photosensitive pixel generating a strong signal.

17. The method of claim 10, wherein processing signals includes estimating the intensity of light associated with the second light channel incident on a pixel associated with the first light channel.