Adaptive control of an electronic imaging camera

• US 5,185,671 A
• Filed: 06/21/1991
• Issued: 02/09/1993
• Est. Priority Date: 06/21/1991
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Downes, Philip, Lieberman, Laurence A.
• Primary Examiner(s): Razavi, Michael T.
• Assistant Examiner(s): Greening, Wendy R.
• Application Number:
  US07/720,271
• Time in Patent Office: 599 Days
• Field of Search: 358/99, 358/95, 358/211, 358/213.19, 358/228, 358/174, 358/909, 358/209
• US Class Current: 348/229.1
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation
• CPC Class Codes: H04N 23/74 by influencing the scene brightness using illuminating means
• CPC Class Codes: H04N 7/185 from a mobile camera, e.g. for remote control

Abstract

A CCD imaging camera is adaptively controlled by: illuminating a reflectance field of view, selectively sensing a desired image field area within the field of view and generating an image signal thereof, reducing low frequency components of the sensed area image signal, generating a contrast signal from the image signal, generating an average or mean signal from a plurality of image contrast signals, comparing the mean signal with a reference signal corresponding to a predetermined contrast maximum value, and thereafter controlling the light level or the range of the camera to the object field.

Claims

1. A method for adaptively adjusting the camera lighting level and distance between a camera and a light reflectance object plane including a reflectance field of view, comprising the steps of:

illuminating a reflectance field of view;

sensing a desired image field within the reflectance field of view;

generating an image signal of said image field;

generating a plurality of image parameter signals from the image signal;

generating a means image parameter signal from said plurality of image parameter signals;

comparing said mean image parameter signal with a predetermined reference signal and generating a difference signal therefrom;

initially reducing the camera lighting when the mean image parameter signal is less than said predetermined reference signal,

reducing said distance between the camera and the light reflectance object plane when the mean image parameter signal is greater than said predetermined reference signal;

thereafter repeating said comparing step; and

again reducing the camera lighting when the mean image parameter signal is less than said predetermined reference signal but increasing the camera lighting to a predetermined previous level set when the mean image parameter signal is greater than said reference signal.

2. A method for adaptively adjusting the camera lighting level and distance between a camera and a light reflectance object plane including a reflectance field of view, comprising the steps of:

illuminating a reflectance field of view;

sensing a desired image field within the reflectance field of view;

generating an image signal of said image field;

generating a plurality of contrast parameter signals from said image signal, said contrast parameter signals being a function of intensity of luminance of the image field;

generating a mean contrast parameter signal;

comparing said mean contrast parameter signal with a reference signal corresponding to a predetermined contrast level and generating a contrast difference signal;

initially reducing the camera lighting when the mean contrast parameter signal is less than said predetermined contrast level,

reducing said distance between the camera and the light reflectance object plane when the mean contrast parameter signal is greater than said predetermined contrast signal;

repeating said comparing step; and

then reducing the camera lighting when the mean contrast parameter signal is less than said predetermined contrast value but increasing the camera lighting to a predetermined previous level set when the mean contrast parameter signal is greater than said predetermined contrast value.

3. The method of claim 2 wherein said step of generating a mean contrast parameter signal includes the step of reducing low frequency components in said image signal.

4. The method of claim 3 wherein said step of reducing said low frequency components includes the step of homomorphically filtering said image signal.

5. The method of claim 3 wherein said step of reducing said low frequency components includes the step of high pass filtering said image signal.

6. The method of claim 5 and additionally including the step of low pass filtering said image signal, and dividing the high pass filtered image signal by the low pass filtered image signal and generating a normalized image signal.

7. The method of claim 2 and further including the steps of mounting said camera on a water vehicle and viewing the sea floor.

8. The method of claim 7 wherein said water vehicle comprises an underwater vehicle and said image area lies on or in the vicinity of the sea floor.

9. The method of claim 8 wherein said camera comprises an electronic camera.

10. The method of claim 9 wherein said electronic camera comprises a CCD electronic camera.

11. A method for adaptively adjusting the camera lighting level and distance between a camera and a light reflectance object plane including a reflectance field of view, comprising the steps of:

illuminating a reflectance field of view;

sensing a desired image field within the reflectance field of view;

generating an image signal of said image field;

homomorphically filtering said image signal for reducing low frequency components therefrom;

generating at least one contrast parameter signal from the filtered image signal, said contrast parameter signal being a function of intensity or luminance of the image field;

comparing said at least one contrast parameter signal with a reference signal corresponding to a predetermined contrast level and generating a contrast difference signal; and

controlling the light level or the distance between the camera and the light reflectance object plane as a function of said contrast difference signal.

12. The method of claim 11 wherein said step of homomorphically filtering includes the further steps of:

converting the components of said image signal to logarithmic image components,

adding said logarithmic image components to from a logarithmic composite image,

performing a Fourier transform on said composite image,

high pass filtering the transformed composite image,

performing an inverse Fourier transform on the filtered composite image, and

applying an exponential transfer function to the inverse transformed composite image to provide an output image signal having enhanced reflectance characteristics and attenuated illumination characteristics.

13. Apparatus for adaptively adjusting the camera lighting level and distance between a camera and a light reflectance object plane including a reflectance field of view, comprising:

means for illuminating a reflectance field of view;

means for sensing a desired image field within the reflectance field of view;

means for generating an image signal of said image field;

means for generating a plurality of image parameter signals from the image signal, said contrast parameter signal being a function of intensity of luminance of the image field;

means for generating a mean contrast parameter signal from said plurality of contrast parameter signals;

means for comparing said mean contrast parameter signal with a reference signal corresponding to a minimum contrast level and generating a contrast difference signal; and

means for controlling the light level or the distance between the camera and the light reflectance object place as a function of said contrast difference signal.

14. The apparatus of claim 13 wherein said means for generating a mean contrast parameter signal includes means for reducing low frequency components in said image signal.

15. The apparatus of claim 14 wherein said means for reducing said low frequency components includes means for reducing homomorphically filtering said image signal.

16. The apparatus of claim 14 wherein said means for reducing said low frequency components includes means for high pass filtering said image signal.

17. The apparatus of claim 16 and additionally including,

means for low pass filtering said image signal, and

means for dividing the high pass filtered image signal by the low pass filtered image signal to generate a normalized image signal.

18. The apparatus of claim 13 and additionally including means for mounting said camera on a water vehicle nd viewing the sea floor.

19. The apparatus of claim 18 wherein said water vehicle comprises an underwater vehicle and said image area lies on or in the vicinity of the sea floor.

20. The apparatus of claim 18 wherein said camera comprises an electronic camera.

21. The apparatus of claim 20 wherein said electronic camera comprises a CCD electronic camera.