Adjustable spectrum flash lighting for image acquisition

• US 7,667,766 B2
• Filed: 12/18/2003
• Issued: 02/23/2010
• Est. Priority Date: 12/18/2003
• Status: Active Grant

• Current Assignee: Epistar Corporation (Ennostar, Inc.)
• Original Assignee: Avago Technologies ECBU IP Singapore Pte Limited (Broadcom, Inc.)
• Inventors: Lau, Yue Hoong, Lee, Joon Chok, Chua, Janet Bee Yin, Seah, Teoh Teh, Lee, Kian Shin
• Primary Examiner(s): Jerabek, Kelly L
• Application Number:
  US10/742,310
• Publication Number:
  US 20050134723A1
• Time in Patent Office: 2,259 Days
• Field of Search: 348/370, 348/371, 362/11, 362/231, 362/260, 396/155, 396/176, 257/89, 257/98
• US Class Current: 348/370
• CPC Class Codes: G03B 15/02 Illuminating scene
• CPC Class Codes: H04N 23/74 by influencing the scene brightness using illuminating means
• CPC Class Codes: H04N 23/88 for colour balance, e.g. white-balance circuits or colour temperature control

Abstract

A light module associated with the camera provides flash light having a spectral content that is adjustable according to one or more drive signals. The light module includes one or more emitters of light of at least two different colors that are individually accessible to the one or more drive signals. The flash light is a mixture of the light from the one or more emitters.

Claims

1. An image acquisition system, comprising:

a light emitting system, comprising;

a plurality of red light emitters;

a plurality of green light emitters; and

a plurality of blue light emitters;

a driver system, comprising;

a first set of drivers configured to provide a first set of drive signals for driving each of the plurality of red light emitters;

a second set of drivers configured to provide a second set of drive signals for driving each of the plurality of green light emitters; and

a third set of drivers configured to provide a third set of drive signals for driving each of the plurality of blue light emitters;

a first manual control operable by a user of the image acquisition system to control the driver system for varying an amplitude of at least one of the first, second or third set of drive signals thereby adjusting the spectral content of light emitted by the light emitting system; and

a second manual control operable by the user to control the driver system for varying the intensity of light emitted by the light emitting system without varying the spectral content.

2. The image acquisition system of claim 1, wherein varying the intensity of light emitted by the light emitting system without varying the spectral content comprises varying the first, second, and third drive signals collectively.

3. The image acquisition system of claim 1, wherein each of the first and second manual controls is a hardware control.

4. The image acquisition system of claim 3, wherein each of the red, green, and blue emitters is a light emitting diode (LED), and wherein each of the first, second, and third drive signals is a current.

5. The image acquisition system of claim 4, wherein varying the intensity of light emitted by the light emitting system without varying the spectral content comprises varying the first, second, and third drive currents collectively thereby keeping the ratio between the red, green, and blue components in the emitted light, constant.

6. The image acquisition system of claim 1, further comprising:

a color-sensitive photodetector configured to detect a spectral content present in ambient light when the light emitting system is inhibited from emitting light.

7. The image acquisition system of claim 6, further comprising:

a look-up table configured to map the spectral content present in the ambient light to a set of drive values for generating the first, second, and third set of drive signals for driving each of the plurality of red, green, and blue light emitters.

8. The image acquisition system of claim 7, wherein the look-up table is configured to incorporate a curve-fitting technique for mapping the spectral content present in the ambient light to the set of drive values.

9. The image acquisition system of claim 6, wherein the light emitting system, the driver system, the first manual control, and the second manual control are parts of a digital camera that further comprises an image capture sensor, and wherein the image capture sensor is configured to operate as the color-sensitive photodetector for detecting the ambient level when the light emitting system is inhibited from emitting light.

10. The image acquisition system of claim 6, wherein the light emitting system, the driver system, the first manual control, and the second manual control are parts of a digital camera, and wherein the color-sensitive photodetector is an external module that is coupled to the digital camera.

11. An image acquisition system, comprising:

a light emitting system operable to emit a flash light L_F, the light emitting system comprising a set of light emitters, the set of light emitters comprising a first sub-set of red light emitters, a second sub-set of green light emitters, and a third sub-set of blue light emitters;

a multi-functional light sensor, the multi-functional light sensor configurable in a first mode of operation to detect light L_R received from an object to be imaged, and in a second mode of operation to detect ambient light L_A and generate therefrom, a first control signal corresponding to a spectral content present in the detected ambient light L_A;

a look-up table that maps each of a plurality of control signal values to a corresponding set of drive values S_R, S_G, S_B for driving the set of light emitters; and

a driver system configured to receive the first control signal from the multi-functional light sensor and to use the look-up table for identifying a set of drive values that are stored in the look-up table in correspondence to the first control signal, the driver system further configured to use the identified set of drive values for configuring the first sub-set of light emitters to emit red light at a first intensity, and the second sub-set of light emitters to emit green light at a second intensity that is different than the first intensity.

12. The image acquisition system of claim 11, wherein the light emitting system is configured to inhibit the emission of the flash light L_F during the second mode of operation.

13. The image acquisition system of claim 11, wherein configuring the first sub-set of light emitters to emit red light at a first intensity comprises activating a first number of red light emitters, and configuring the second sub-set of light emitters to emit green light at a second intensity comprises activating a second number of green light emitters, wherein the second number is different than the first number.

14. The image acquisition system of claim 11, wherein configuring the first sub-set of light emitters to emit red light at a first intensity comprises providing a first drive signal for driving a first number of red light emitters, and configuring the second sub-set of light emitters to emit green light at a second intensity comprises providing a second drive signal for driving a second number of green light emitters, wherein the second number is the same as the first number and wherein the second drive signal is different than the first drive signal.

15. The image acquisition system of claim 11, further comprising an intensity control that is operable to collectively vary the overall intensity of the emitted light without varying the ratio between the emitted red light and green light.

16. A method of image acquisition using an image acquisition system, the method comprising:

emitting a pre-flash of light L_F from the image acquisition system;

sensing a spectral content of ambient light during the pre-flash emission, thereby obtaining a sensed spectral content measurement comprising a combination of ambient light L_A and the pre-flash of light L_F;

emitting thereafter, a flash of light from the image acquisition system, the emitting comprising;

using the sensed spectral content measurement to determine a pre-flash control signal value;

identifying a set of drive signal values by referring the pre-flash control signal value against a look-up table that maps each of a plurality of control signal values to a corresponding plurality of drive signal values S_R, S_G, S_B;

using the set of drive signal values for driving a plurality of light emitters that generate colored light having a spectrum that compensates for an undesirable spectral characteristic of the ambient light L_A, wherein driving the plurality of light emitters comprises;

providing a first sub-set of drive signals that configure each of a first sub-set of the light emitters to emit light of a first color at a first intensity; and

providing a second sub-set of drive signals that configure each of a second sub-set of the light emitters to emit light of a second color at a second intensity that is different than the first intensity; and

acquiring an image of an object illuminated by the generated color light.

17. The method of claim 16, wherein the undesirable spectral characteristic of the ambient light comprises one of an undesired color content or an undesired color temperature.

18. The method of claim 17, wherein the ambient light is daylight and the undesired color temperature is a cooler temperature of daylight.

19. The method of claim 16, wherein a light sensor is used at a first instant for sensing the spectral content in ambient light and thereafter, the light sensor is again used at a second instant, for acquiring the image of the object.