Extended dynamic imaging system and method

• US 6,101,294 A
• Filed: 06/02/1997
• Issued: 08/08/2000
• Est. Priority Date: 06/02/1997
• Status: Expired due to Term

• Current Assignee: Sarnoff Corporation (SRI International, Inc.)
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: McCaffrey, Nathaniel Joseph, Levine, Peter A., Sauer, Donald Jon, Pantuso, Francis P.
• Primary Examiner(s): Couso, Jose L.
• Assistant Examiner(s): Do, Anh Hong
• Application Number:
  US08/867,652
• Time in Patent Office: 1,163 Days
• Field of Search: 382/312, 377/58, 377/60, 257/236, 257/246, 257/250, 348/243, 250/330
• US Class Current: 382/312
• CPC Class Codes: G11C 27/04 Shift registers
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/741 by increasing the dynamic range of the image compared to the dynamic range of the electronic image sensors
• CPC Class Codes: H04N 25/575 with a response composed of multiple slopes

Abstract

A imager has an array of photodetectors, each of which accumulates charge during an integration period as a result of light detected during said integration period, said array having a charge capacity which increases during the integration period. A charge capacity controller coupled to said imager adjusts how the imager increases the charge capacity of the array based upon the brightness distribution detected by said imager during at least one previous integration period.

Claims

1. An imaging system, comprising:

(a) an imager having an array of photodetectors, each of which accumulates charge during an integration period as a result of light detected during said integration period, wherein;

the array has a charge capacity which determines the maximum charge each photodetector of the array can accumulate;

the charge capacity is controlled by a charge capacity control voltage applied to the array; and

the imager increases the charge capacity control voltage during the integration period in a predetermined maimer in accordance with a function and function information to cause a corresponding increase in the charge capacity during the integration period; and

(b) a charge capacity controller coupled to said imager which provides the function information to the imager wherein the function information is based upon the brightness distribution detected by said imager during at least one previous integration period.

2. The imaging system of claim 1, wherein:

the imager provides a video frame after the integration period in accordance with the charge accumulated by each photodetector; and

the charge capacity controller comprises a function generator which generates the function information in accordance with the brightness distribution of at least one previous video frame provided by the imager.

3. The imaging system of claim 2, wherein the charge capacity controller further comprises a histogrammer coupled to the imager and to the function generator, wherein the histogrammer receives video frames provided by the imager and provides a histogram containing the brightness distribution to the function generator.

4. The imaging system of claim 3, wherein the charge capacity controller further comprises a histogram equalization/projection block coupled to the histogrammer and to the imager, wherein the histogram equalization/projection block uses the histogram for a current video frame to optimally display the informational content of the video frame on a monitor.

5. The imaging system of claim 2, wherein the charge capacity controller further comprises a contrast corrector, wherein:

the function generator generates inverse function information; and

the contrast corrector receives video frames provided by the imager, receives the inverse function information provided by the function generator, and uses the inverse function information to remove the effect in video frames caused by the charge capacity of the array of photodetectors being increased during the integration period.

6. The imaging system of claim 2, wherein the function is a two-step non-linear function, wherein the imager increases the charge capacity of the array of photodetectors during the integration period by applying a first charge capacity control voltage to the array of photodetectors during a first portion of the integration period and a second charge capacity control voltage to the array of photodetectors after the first portion, wherein the length of the first portion is determined in accordance with the function information provided by the function generator and the second charge capacity control voltage is greater than the first charge capacity control voltage.

7. The imaging system of claim 2, wherein:

the function generator generates the function information in accordance with the brightness distribution of the most recent previous video frame provided by the imager; and

the function information is generated by the function generator so that light having a brightness level of the brightest object in the most recent previous video frame and impinging upon a photodetector of the imager during the integration period will not cause charge to accumulate in excess of the charge capacity of the photodetector at the end of the integration period.

8. The imaging system of claim 7, wherein the function information is generated by the function generator so that the light will cause charge to accumulate that just reaches but does not exceed the charge capacity of the photodetector at the end of the integration period.

9. The imaging system of claim 1, wherein the imager is a complementary metal-oxide semiconductor imager having an array of virtual gate buried n-channel photodetectors, wherein each photodetector has a charge capacity related to the magnitude of a charge capacity control voltage applied to the photodetector.

10. The imaging system of claim 1, wherein the imager comprises an array charge-coupled device (CCD) photodetectors, wherein each CCD photodetector has a charge capacity related to the magnitude of a charge capacity control voltage applied to the CCD photodetector.

11. An imaging system, comprising a charge capacity controller coupled to an imager having an array of photodetectors, each of which accumulates charge during an integration period as a result of light detected during said integration period, said array having a charge capacity which determines the maximum charge each photodetector of the array can accumulate, wherein the charge capacity is controlled by a charge capacity control voltage applied to the array, wherein the imager increases the charge capacity control voltage during the integration period in a predetermined manner in accordance with a function and function information to cause a corresponding increase in the charge capacity during the integration period, wherein the charge capacity controller provides the function information to the imager, wherein the function information is based upon the brightness distribution detected by said imager during at least one previous integration period.

12. The imaging system of claim 11, wherein:

the imager provides a video frame after the integration period in accordance with the charge accumulated by each photodetector; and

the charge capacity controller comprises a function generator which generates the function information in accordance with the brightness distribution of at least one previous video frame provided by the imager.

13. The imaging system of claim 12, wherein the function is a two-step non-linear function, wherein the imager increases the charge capacity of the array of photodetectors during the integration period by applying a first charge capacity control voltage to the array of photodetectors during a first portion of the integration period and a second charge capacity control voltage to the array of photodetectors after the first portion, wherein the length of the first portion is determined in accordance with the function information provided by the function generator and the second charge capacity control voltage is greater than the first charge capacity control voltage.

14. In an imager having an array of photodetectors, each of which accumulates charge during an integration period as a result of light detected during said integration period, wherein the array has a charge capacity which determines the maximum charge each photodetector of the array can accumulate and the charge capacity is controlled by a charge capacity control voltage applied to the array;

and a method for increasing the dynamic range of the imager, the method comprising the steps of;

(a) increasing the charge capacity control voltage during the integration period during the integration period in a predetermined manner in accordance with a function and function information to cause a corresponding increase in the charge capacity during the integration period; and

(b) providing the function information to the imager, wherein the function information is based upon the brightness distribution detected by the imager during at least one previous integration period.

15. The method of claim 14, wherein the function information is provided by a charge capacity controller coupled to the imager, the method comprising the further steps of:

providing, with the imager, a video frame after the integration period in accordance with the charge accumulated by each photodetector; and

generating, with a function generator of the charge capacity controller, the function information in accordance with the brightness distribution of at least one previous video frame provided by the imager.

16. The method of claim 15, wherein the function is a two-step non-linear function, wherein the imager increases the charge capacity of the array of photodetectors during the integration period by applying a first charge capacity control voltage to the array of photodetectors during a first portion of the integration period and a second charge capacity control voltage to the array of photodetectors after the first portion, wherein the length of the first portion is determined in accordance with the function information provided by the function generator and the second charge capacity control voltage is greater than the first charge capacity control voltage.

17. The method of claim 15, comprising the further steps of:

generating inverse function information with the function generator; and

receiving, with a contrast corrector of the charge capacity controller, video frames provided by the imager, the inverse function information and using the inverse function information to remove the effect in video frames caused by the charge capacity of the array of photodetectors being increased during the integration period.

18. An imaging system, comprising:

(a) means for increasing a charge capacity control voltage of an array of photodetectors of an imager during an integration period in a predetermined manner in accordance with a function and function information to cause a corresponding increase in the charge capacity during the integration period, wherein each photodetector accumulates charge during the integration period as a result of light detected during said integration period, wherein the array has a charge capacity which determines the maximum charge each photodetector of the array can accumulate and the charge capacity is controlled by the charge capacity control voltage applied to the array; and

(b) means for providing the function information to the imager, wherein the function information is based upon the brightness distribution detected by the imager during at least one previous integration period.

19. The imaging system of claim 18, wherein:

the imager provides a video frame after the integration period in accordance with the charge accumulated by each photodetector; and

means (b) comprises a function generator which generates the function information in accordance with the brightness distribution of at least one previous video frame provided by the imager.

20. The imaging system of claim 19, wherein the function is a two-step non-linear function, wherein the imager increases the charge capacity of the array of photodetectors during the integration period by applying a first charge capacity control voltage to the array of photodetectors during a first portion of the integration period and a second charge capacity control voltage to the array of photodetectors after the first portion, wherein the length of the first portion is determined in accordance with the function information provided by the function generator and the second charge capacity control voltage is greater than the first charge capacity control voltage.