Exposure control for an imaging system

• US 20090027545A1
• Filed: 07/16/2008
• Published: 01/29/2009
• Est. Priority Date: 07/25/2007
• Status: Active Grant

• Current Assignee: Candela Microsystems (S) Pte., Ltd.
• Original Assignee: Candela Microsystems (S) Pte., Ltd.
• Inventors: Yeo, Yunn-En, Tay, Hiok-Nam
• Granted Patent: US 8,264,594 B2
• Time in Patent Office: Days
• US Class Current: 348/362
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/92 based on global image properties
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation
• CPC Class Codes: H04N 23/73 by influencing the exposure time
• 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 25/57 Control of the dynamic range

Abstract

A device that analyzes an image. The device includes a circuit that receives an image that includes a plurality of pixels. The circuit creates a histogram of the image and analyzes the histogram to determine an acceptable exposure of the image. The histogram may include a plurality of bins versus a population of pixels associated with each bin. By way of example, the bins may be associated with an intensity of light. The images and histograms may include data defined by low dynamic range number of bits and/or an extended dynamic range number of bits. Certain features and criteria of the image may be determined and analyzed to determine whether the image has an acceptable exposure. If the image is unacceptable, an exposure characteristic can be changed and the process can be repeated until an acceptable image is obtained.

Claims

1. A device that analyzes an image, comprising:

a circuit that receives an image that includes a plurality of pixels, creates a histogram of said image and analyzes said histogram to determine an acceptable exposure of said image.

2. The device of claim 1, wherein said circuit is a processor.

3. The device of claim 1, wherein said histogram includes a plurality of bins that relate to an image characteristic versus a population of pixels.

4. The device of claim 1, wherein said circuit converts said image into a low dynamic range image defined by a first number of bits.

5. The device of claim 4, wherein said circuit generates a plurality of low dynamic range images each at a different exposure time.

6. The device of claim 5, wherein said circuit generates an extended dynamic range image defined by a second number of bits from said plurality of low dynamic range images.

7. The device of claim 6, wherein said circuit generates a low dynamic range image at a selected exposure from said extended dynamic range image and generates a low dynamic range histogram from said low dynamic range image.

8. The device of claim 6, wherein said circuit generates an extended dynamic range histogram from said extended dynamic range image.

9. The device of claim 8, wherein said circuit generates a low dynamic range histogram at a selected exposure from said extended dynamic range image.

10. The device of claim 8, wherein said circuit generates a plurality of low dynamic range images each at a different exposure time from said extended dynamic range histogram, generates a plurality of low dynamic range histograms from said low dynamic range images and selects a low dynamic range histogram at a selected exposure.

11. The device of claim 6, wherein said circuit generates a plurality of low dynamic range images each at a different exposure time from said extended dynamic range image, generates a plurality of low dynamic range histograms from said low dynamic range images and selects a low dynamic range histogram at a selected exposure.

12. The device of claim 6, wherein said circuit generates a plurality of low dynamic range images each at a different exposure time from said extended dynamic range histogram, selects a low dynamic range image at a selected exposure and generates a plurality of low dynamic range histograms from said low dynamic range images.

13. The device of claim 5, wherein said circuit generates a plurality of low dynamic range histograms from said low dynamic range images, generates an extended dynamic range histogram from said low dynamic range histograms and generates a low dynamic range histogram at a selected exposure from said extended dynamic range histogram.

14. The device of claim 1, wherein said circuit detects a sky-peak within said image.

15. The device of claim 14, wherein said circuit utilizes said sky-peak to determine a sky-contrast and determines whether said sky-contrast is below a threshold.

16. The device of claim 1, wherein said circuit detects a right-peak within said image.

17. The device of claim 16, wherein said circuit utilizes said right-peak to determine a peak-contrast and determines whether said peak-contrast is below a threshold.

18. A device that analyzes an image, comprising:

image generating means for generating an image that includes a plurality of pixels;

histogram means for generating at least one histogram of said image; and

,

analyzing means for analyzing said histogram to determine an acceptable exposure of said image.

19. A method for analyzing an image, comprising:

receiving an image that includes a plurality of pixels;

creating a histogram of the image; and

,

analyzing the histogram to determine an acceptable exposure of the image.

20. The method of claim 19, wherein the histogram includes a plurality of bins that relate to an image characteristic versus a population of pixels.

21. The method of claim 19, wherein creating the histogram includes converting the image into a low dynamic range image defined by a first number of bits.

22. The method of claim 21, wherein creating the histogram includes generating a plurality of low dynamic range images each at a different exposure time.

23. The method of claim 22, wherein creating the histogram includes generating an extended dynamic range image defined by a second number of bits from the plurality of low dynamic range images.

24. The method of claim 23, wherein creating the histogram includes generating a low dynamic range image at a selected exposure from the extended dynamic range image and generating a low dynamic range histogram from the low dynamic range image.

25. The method of claim 23, wherein creating the histogram includes generating an extended dynamic range histogram from the extended dynamic range image.

26. The method of claim 25, wherein creating the histogram includes generating a low dynamic range histogram at a selected exposure from the extended dynamic range image.

27. The method of claim 25, wherein creating the histogram includes generating a plurality of low dynamic range images each at a different exposure time from the extended dynamic range histogram, generating a plurality of low dynamic range histograms from the low dynamic range images and selecting a low dynamic range histogram at a selected exposure.

28. The method of claim 23, wherein creating the histogram includes generating a plurality of low dynamic range images each at a different exposure time from the extended dynamic range image, generating a plurality of low dynamic range histograms from the low dynamic range images and selecting a low dynamic range histogram at a selected exposure.

29. The device of claim 23, wherein creating the histogram includes generating a plurality of low dynamic range images each at a different exposure time from the extended dynamic range histogram, selecting a low dynamic range image at a selected exposure and generating a plurality of low dynamic range histograms from the low dynamic range images.

30. The method of claim 22, wherein creating the histogram includes generating a plurality of low dynamic range histograms from the low dynamic range images, generating an extended dynamic range histogram from the low dynamic range histograms and generating a low dynamic range histogram at a selected exposure from the extended dynamic range histogram.

31. The method of claim 19, wherein analyzing the histogram includes detecting a sky-peak within the image.

32. The method of claim 31, wherein analyzing the histogram utilizing the sky-peak to determine a sky-contrast and determining whether the sky-contrast is below a threshold.

33. The method of claim 19, wherein analyzing the histogram detecting a right-peak within the image.

34. The method of claim 33, wherein analyzing the histogram utilizing the right-peak to determine a peak-contrast and determining whether the peak-contrast is below a threshold.

35. A device that analyzes an image, comprising:

a circuit that receives an image that includes a plurality of pixels and determines a number of dark pixels and a number of mid-range pixels, said circuit determines a proportion of said dark pixels versus a combination of dark and mid-range pixels and determines whether said proportion is below a threshold.