CCD camera with adaptive compression control mechanism

• US 5,982,424 A
• Filed: 04/23/1997
• Issued: 11/09/1999
• Est. Priority Date: 04/23/1997
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta Incorporated (Cisco Systems, Inc.)
• Inventors: Rodriguez, Arturo A., Simerly, Timothy W., Patel, Neilesh R.
• Primary Examiner(s): Garber, Wendy
• Assistant Examiner(s): Harrington, Alicia M.
• Application Number:
  US08/838,948
• Time in Patent Office: 930 Days
• Field of Search: 348/394, 348/399, 348/402, 348/412, 348/364, 348/229, 348/61, 348/207, 348/211, 348/222, 348/295, 348/299
• US Class Current: 348/229.1
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/72 Combination of two or more compensation controls

Abstract

A charge coupled device (CCD) camera includes a CCD imager circuit, a compression engine, and a control circuit coupled to both the CCD imager circuit and the compression engine. The CCD imager circuit is characterized by an integration time defined by clock pulses from the control circuit. The compression engine generates successive frame requests. The control circuit generates the clock pulses to define the integration time based on a time between the sucessive frame requests. The camera further includes a histogram accumulator and an automatic gain controlled (AGC) amplifier coupled between the CCD imager circuit and the histogram accumulator. The CCD imager circuit is characterized by a predetermined maximum imager dynamic range and generates successive frames of imager data values, each successive frame of imager data values being characterized by an imager data value dynamic range and each frame of imager data values being generated based on a corresponding integration time. The AGC amplifier is characterized by an AGC gain defined by a gain control signal and characterized by a maximum output dynamic range. The AGC amplifier processes the successive frames of imager data values into corresponding successive frames of gain controlled data values, each successive frame of gain controlled data values being characterized by a gain controlled data value dynamic range. The histogram accumulator processes a first frame of gain controlled data values to determine a first frame result. The control circuit generates the clock pulses based on the first frame results to define the integration time that corresponds to a second frame of imager data values so that the integration time is maximized while the imager data value dynamic range is less than the maximum imager dynamic range, and the control circuit further generates the gain control signal based on the first frame results and the maximum imager dynamic range to minimize the AGC gain required so that the gain controlled data value dynamic range is equal to a predetermined range within the maximum output dynamic range.

Claims

1. A charge coupled device (CCD) camera, comprising:

a CCD imager circuit;

a compression engine; and

a control circuit couples to both the CCD imager circuit and the compression engine,

wherein;

the CCD imager circuit is characterized by an integration time defined by clock pulses from the control circuit;

the compression engine generates successive frame requests; and

the control circuit generates the clock pulses to define the integration time based on a time between the successive frame requests.

2. The camera of claim 1, further comprising a histogram accumulator and an automatic gain control (AGC) amplifier coupled between the CCD imager circuit and the histogram accumulator wherein:

the CCD imager circuit generates successive frames of imager data values, each frame of imager data values being generated based on a corresponding integration time;

the AGC amplifier processes the successive frames of imager data values into corresponding successive frames of gain controlled data values;

the histogram accumulator processes a first frame of gain controlled data values to determine a first frame result; and

the control circuit generates the clock pulses based on the first frame results to define the integration time that corresponds to a second frame of imager data values.

3. The camera of claim 2, wherein:

each successive frame of gain controlled data values is characterized by a gain controlled data value dynamic range;

the AGC amplifier is further characterized by a maximum output dynamic range; and

the control circuit generates the gain control signal based on the first frame results to control the AGC gain so that the gain controlled data value dynamic range is equal to a predetermined range within the maximum output dynamic range.

4. The camera of claim 3, wherein the predetermined range is substantially equal to the maximum output dynamic range.

5. The camera of claim 4, further comprising a gamma correction circuit and a color space transform circuit coupled between the AGC amplifier and the gamma correction circuit wherein:

the color space transform circuit processes successive frames of gain controlled data values into successive frames of luminance data values; and

the gamma correction circuit transforms a first luminance data value into a corrected first luminance value based on a linearizing function defined to make linear a response by an associated monitor to the corrected first luminance value.

6. The camera of claim 3, wherein the predetermined range plus a predetermined range margin equals 100% of the maximum output dynamic range.

7. The camera of claim 6, further comprising a gamma correction circuit and a color space transform circuit coupled between the AGC amplifier and the gamma correction circuit wherein:

the color space transform circuit processes successive frames of gain controlled data values into successive frames of luminance data values;

the gamma correction circuit transforms a first luminance data value into a corrected first luminance value based on a linearizing function defined to make linear a response by an associated monitor to the corrected first luminance value when the first luminance data value is within the predetermined range; and

the gamma correction circuit transforms the first luminance data value into the corrected first luminance value based on a compression function when the first luminance data value is not within the predetermined range, the compression function mapping the first luminance data value into a value within the predetermined range margin.

8. The camera of claim 1, further comprising a histogram accumulator and an automatic gain controlled (AGC) amplifier coupled between the CCD imager circuit and the histogram accumulator wherein:

the CCD imager circuit generates successive frames of imager data values;

the AGC amplifier is characterized by an AGC gain defined by a gain control signal and processes the successive frames of imager data values into corresponding successive frames of gain controlled data values;

the histogram accumulator processes a first frame of gain controlled data values to determine a first frame result; and

the control circuit generates the gain control signal based on the first frame results.

9. The camera of claim 8, wherein:

each frame of imager data values is generated based on a corresponding integration time; and

the control circuit generates the clock pulses based on the first frame results to define the integration time that corresponds to a second frame of imager data values.

10. The camera of claim 9, wherein:

each successive frame of gain controlled data values is characterized by a gain controlled data value dynamic range;

the AGC amplifier is further characterized by a maximum output dynamic range; and

the control circuit generates the gain control signal to control the AGC gain so that the gain controlled data value dynamic range is equal to a predetermined range within the maximum output dynamic range.

11. The camera of claim 10, wherein the predetermined range is substantially equal to the maximum output dynamic range.

12. The camera of claim 11, further comprising a gamma correction circuit and a color space transform circuit coupled between the AGC amplifier and the gamma correction circuit wherein:

the color space transform circuit processes successive frames of gain controlled data values into successive frames of luminance data values; and

the gamma correction circuit transforms a first luminance data value into a corrected first luminance value based on a linearizing function defined to make linear a response by an associated monitor to the corrected first luminance value.

13. The camera of claim 10, wherein the predetermined range plus a predetermined range margin equals 100% of the maximum output dynamic range.

14. The camera of claim 13, further comprising a gamma correction circuit and a color space transform circuit coupled between the AGC amplifier and the gamma correction circuit wherein:

the color space transform circuit processes successive frames of gain controlled data values into successive frames of luminance data values;

the gamma correction circuit transforms a first luminance data value into a corrected first luminance value based on a linearizing function defined to make linear a response by an associated monitor to the corrected first luminance value when the first luminance data value is within the predetermined range; and

the gamma correction circuit transforms the first luminance data value into the corrected first luminance value based on a compression function when the first luminance data value is not within the predetermined range, the compression function mapping the first luminance data value into a value within the predetermined range margin.

15. The camera of claim 1, further comprising:

a color space transform circuit;

an automatic gain controlled (AGC) amplifier coupled between the CCD imager circuit and the color space transform circuit; and

a color balance circuit circuit coupled to the color space transform circuit.

16. The camera of claim 15 wherein:

the CCD imager circuit generates successive frames of imager data values;

the AGC amplifier processes the successive frames of imager data values into corresponding successive frames of gain controlled data values;

the color space transform circuit processes successive frames of gain controlled data values into successive frames of red chrominance data values and successive frames of blue chrominance data values; and

the color balance circuit processes red and blue chrominance data values into corresponding balanced red and blue chrominance values.

17. The camera of claim 16, wherein:

the balanced red chrominance values are proportional to corresponding red chrominance data value based on a first proportional constant;

the balanced blue chrominance values are proportional to corresponding blue chrominance data value based on a second proportional constant; and

the color balance circuit includes a memory storing predetermined first and second proprotional constants.

18. The camera of claim 16, further comprising a calibration lamp disposed to cast light on the CCD imaging circuit wherein:

the CCD imaging circuit generates imager data values corresponding to light from the calibration lamp and generates imager data values corresponding to light from a scene casting light upon the CCD imaging circuit;

the balanced red chrominance values are proportional to corresponding red chrominance data value based on a first proportional constant;

the balanced blue chrominance values are proportional to corresponding blue chrominance data value based on a second proportional constant;

the color balance circuit includes a memory storing predetermined first and second proprotional constants;

the control circuit includes circuitry to measure a known color balance from the imager data values corresponding to light from the calibration lamp and to measure an unknown color balance from the imager data values corresponding to light from the scene; and

the control circuit further determines the first and second proportional constants based on the known color balance and the unknown color balance.

19. The camera of claim 1, further comprising a histogram accumulator and an automatic gain controlled (AGC) amplifier coupled between the CCD imager circuit and the histogram accumulator wherein:

the CCD imager circuit is characterized by a predetermined maximum imager dynamic range and generates successive frames of imager data values, each successive frame of imager data values being characterized by an imager data value dynamic range, each frame of imager data values being generated based on a corresponding integration time;

the AGC amplifier is characterized by an AGC gain defined by a gain control signal and characterized by a maximum output dynamic range, the AGC amplifier processing the successive frames of imager data values into corresponding successive frames of gain controlled data values, each successive flame of gain controlled data values being characterized by a gain controlled data value dynamic range;

the histogram accumulator processes a first frame of gain controlled data values to determine a first frame result;

the control circuit generates the clock pulses based on the first frame results to define the integration time that corresponds to a second frame of imager data values so that the integration time is maximized while the imager data value dynamic range is less than the maximum imager dynamic range; and

the control circuit further generates the gain control signal based on the first frame results and the maximum imager dynamic range to minimize the AGC gain required so that the gain controlled data value dynamic range is equal to a predetermined range within the maximum output dynamic range.

20. The camera of claim 19, wherein the predetermined range is substantially equal to the maximum output dynamic range.

21. The camera of claim 20, further comprising a gamma correction circuit and a color space transform circuit coupled between the AGC amplifier and the gamma correction circuit wherein:

the color space transform circuit processes successive frames of gain controlled data values into successive frames of luminance data values; and

the gamma correction circuit transforms a first luminance data value into a corrected first luminance value based on a linearizing function defined to make linear a response by an associated monitor to the corrected first luminance value.

22. The camera of claim 19, wherein the predetermined range plus a predetermined range margin equals 100% of the maximum output dynamic range.

23. The camera of claim 22, further comprising a gamma correction circuit and a color space transform circuit coupled between the AGC amplifier and the gamma correction circuit wherein:

the color space transform circuit processes successive frames of gain controlled data values into successive frames of luminance data values;

the gamma correction circuit transforms a first luminance data value into a corrected first luminance value based on a linearizing function defined to make linear a response by an associated monitor to the corrected first luminance value when the first luminance data value is within the predetermined range; and

the gamma correction circuit transforms the first luminance data value into the corrected first luminance value based on a compression function when the first luminance data value is not within the predetermined range, the compression function mapping the first luminance data value into a value within the predetermined range margin.