Electronic image acquistion system with image optimization by intensity entropy analysis and feedback control

• US 5,387,930 A
• Filed: 01/25/1993
• Issued: 02/07/1995
• Est. Priority Date: 05/25/1990
• Status: Expired due to Fees

• Current Assignee: Millennium Ventures Group
• Original Assignee: European Visions Systems Centre Limited
• Inventors: Toh, Peng S.
• Primary Examiner(s): Razavi, Michael T.
• Assistant Examiner(s): Greening, Wendy R.
• Application Number:
  US07/934,668
• Time in Patent Office: 743 Days
• Field of Search: 358/227, 358/228, 358/166, 358/174, 358/169, 358/209, 358/213.11, 358/213.28, 348/207, 348/222, 348/229, 348/362
• US Class Current: 348/222.1
• CPC Class Codes: G06T 1/0007 Image acquisition
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation
• CPC Class Codes: H04N 23/72 Combination of two or more compensation controls

Abstract

An image acquisition system is arranged to optimize the information in an acquired image. Parameters associated with the system, such as any of the lens aperture, the lens focus and image intensity, are adjusted. Incoming image data is processed to determine the entropy of the image and with this information the aperture can be optimized. By determining the dynamic range of the scene the black and white levels thereof can be identified and the gain and offset applied to the image adjusted to minimize truncation distortion. Specular highlights can be detected by calculating the ratio of changes in maximum and minimum intensities between different but related images.

Claims

1. An image acquisition system comprising:

(a) an electronic camera having a lens with a selectively adjustable aperture control;

(b) an amplifier coupled to said camera to receive image data therefrom, said amplifier having selectively adjustable gain and offset controls;

(c) a digitizer coupled to said amplifier to receive amplified image data therefrom; and

(d) a processor coupled to said digitizer to receive digitized image data therefrom, said processor having outputs coupled to said amplifier gain and offset controls for selectively adjusting the same, and an output connected to said lens aperture control for selectively adjusting the same;

(e) said processor being adapted to process said digitized image data received from said digitizer to calculate therefrom an intensity entropy of an image and, in response thereto, to provide outputs selectively to said amplifier gain and offset controls and said lens aperture control for selectively adjusting the same to optimize the acquired image information, said intensity entropy of said image being defined as H_n, where;

##EQU12## and n=the number of quantized intensity levels of the digitizer, and

P_i =the probability of the i^th intensity level occurring in the image and is defined by p_i =f_i /N where f is the frequency of occurrence of the i^th intensity level in the digitized image data and N is the total number of pixels in the digitized image data.

2. An image acquisition system as claimed in claim 1, wherein said processor is adapted to derive a histogram of the image intensities in the digitized image data received from the digitizer and to calculate the intensity entropy H_n of the image from said histogram.

3. An image acquisition system as claimed in claim 1, wherein said processor is further adapted to identify specular reflections in the digitized image and, in response thereto, to provide outputs selectively to said amplifier gain and offset controls and said lens aperture control for selectively adjusting the same.

4. An image acquisition system as claimed in claim 3, wherein said processor is adapted to identify specular reflections as digitized image intensity values above a predefined intensity threshold.

5. An image acquisition system as claimed in claim 4, wherein said processor is adapted to determine the dynamic range of the image by determining the ratio of image intensity changes in two captured images acquired under different settings of said amplifier gain and offset controls and said lens aperture control, and to determine said predetermined intensity threshold as a function of the determined dynamic range.

6. An image acquisition system as claimed in claim 5, wherein said processor is adapted to determine said dynamic range from the maximum and the minimum intensity values in said two captured images.

7. An image acquisition system as claimed in claim 3, wherein said processor is adapted to process image data associated with detected specular reflections to determine a color content thereof and, in response thereto, to normalize the color content of acquired images to compensate for color variations between images caused by changes in image illumination.

8. An image acquisition system as claimed in any one of claims 1 to 7, wherein the lens of said electronic camera also has a selectively adjustable focus control, and said processor also has an output coupled to said focus control for selectively adjusting the same to optimize the acquired image information.

9. An image acquisition system comprising:

(a) an electronic camera having a lens with a selectively adjustable aperture control;

(b) an amplifier coupled to said camera to receive image data therefrom, said amplifier having selectively adjustable gain and offset controls;

(c) a digitizer coupled to said amplifier to receive amplified image data therefrom; and

(d) a processor coupled to said digitizer to receive digitized image data therefrom, said processor having outputs connected to said amplifier gain and offset controls for selectively adjusting the same and an output connected to said lens aperture control for selectively adjusting the same;

(e) said processor being adapted to process said digitized image data received from said digitizer to calculate therefrom an intensity gradient entropy of said image and, in response thereto, to provide outputs selectively to said amplifier gain and offset controls and said lens aperture control for selectively adjusting the same to optimize the acquired image information, the intensity gradient entropy of the image being defined as H_g, where;

##EQU13## and the intensity gradient magnitude being defined as g, where;

space="preserve" listing-type="equation">g=(I.sub.x.sup.2 +I.sub.y.sup.2).sup.1/2

and the intensity partial derivatives I_x and I_y are ##EQU14## and m=the number of levels spanned by the gradient magnitude distribution of the quantized intensity levels of the digitizer; and

p_g =the probability of the g^th intensity gradient level occurring in the image and is defined by p_g =F_g /N, where f_g is the frequency of occurrence of the g^th intensity gradient level in the digitized image data and N is the total number of pixels in the digitized image data.

10. An image acquisition system as claimed in claim 9, wherein said processor is adapted to derive a histogram of the image intensities in the digitized image data received from the digitizer and to calculate the intensity gradient entropy Hg of the image from said histogram.

11. An image acquisition system as claimed in claim 9, wherein said processor is further adapted to identify specular reflections in the digitized image and, in response thereto, to provide output selectively to said amplifier gain and offset controls and said lens aperture control for selectively adjusting the same.

12. An image acquisition system as claimed in claim 11, wherein said processor is adapted to identify specular reflections as digitized image intensity values above a predetermined intensity threshold.

13. An image acquisition system as claimed in claim 12, wherein said processor is adapted to determine the dynamic range of the image by determining the ratio of image intensity changes in two captured images acquired under different settings of said amplifier gain and offset controls and said lens aperture controls and to determine said predetermined intensity threshold as a function of the determined dynamic range.

14. An image acquisition system as claimed in claim 13, wherein said processor is adapted to determine said dynamic range from maximum and minimum intensity values in said two captured images.

15. An image acquisition system as claimed in claim 11, wherein said processor is adapted to process image data associated with detected specular reflections to determine a color content thereof and, in response thereto, to normalize the color content of acquired images to compensate for color variations between images caused by changes in image illumination.

16. An image acquisition system as claimed in any one of claims 9 to 15, wherein the lens of said electronic camera also has a selectively adjustable focus control, and said processor also has an output coupled to said focus control for selectively adjusting the same to optimize the acquired image information.

17. An image acquisition system comprising:

(a) an electronic camera having a lens with a selectively adjustable aperture control;

(b) an amplifier coupled to said camera to receive image data therefrom, said amplifier having selectively adjustable gain and offset controls;

(c) a digitizer coupled to said amplifier to receive amplified image data therefrom; and

(d) a processor coupled to said digitizer to receive digitized image data therefrom, said processor having outputs connected to said amplifier gain and offset controls for selectively adjusting the same, and an output connected to said lens aperture control for selectively adjusting the same;

(e) said processor being adapted to process said digitized image data received from said digitizer to derive a histogram of the image intensities in said digitized image data and to calculate therefrom the variance of the image intensities from a reference histogram and, in response thereto, to provide outputs selectively to said amplifier gain and offset controls and said lens aperture control for selectively adjusting the same to optimize the acquired image information, said variance being defined as σ

_h², where ##EQU15## and n=the number of quantized intensity levels of the digitizer f_i -the frequency of occurrence of the i^th intensity level in the digitized image data, and

μ

_h =N/n, where N is the total number of pixels in the digitized image data.

18. An image acquisition system as claimed in claim 17, wherein said processor is further adapted to identify specular reflections in the digitized image and, in response thereto, to provide outputs selectively to said amplifier gain and offset controls and said lens aperture control for selectively adjusting the same.

19. An image acquisition system as claimed in claim 18, wherein said processor is adapted to identify specular reflections as digitized image intensity values above a predefined intensity threshold.

20. An image acquisition system as claimed in claim 19, wherein said processor is adapted to determine the dynamic range of the image by determining the ratio of image intensity changes in two captured images acquired under different settings of said amplifier gain and offset controls and said lens aperture control, and to determine said predetermined intensity threshold as a function of the determined dynamic range.

21. An image acquisition system as claimed in claim 20, wherein said processor is adapted to determine said dynamic range from maximum and minimum intensity values in two captured images.

22. An image acquisition system as claimed in claim 18, wherein said processor is adapted to process image data associated with detected specular reflections to determine a color content thereof and, in response thereto, to normalize the color content of acquired images to compensate for color variations between images caused by changes in image illumination.

23. An image acquisition system as claimed in any one of claims 17 to 22, wherein the lens of said electronic camera also has a selectively adjustable focus control, and said processor also has an output coupled to said focus control for selectively adjusting the same to optimize the acquired image information.