Exposure control for an imaging system

• US 8,264,594 B2
• Filed: 07/16/2008
• Issued: 09/11/2012
• Est. Priority Date: 07/25/2007
• Status: Expired due to Fees

• Current Assignee: Candela Microsystems (S) Pte., Ltd.
• Original Assignee: Candela Microsystems (S) Pte., Ltd.
• Inventors: Yeo, Yunn-En, Tay, Hiok-Nam
• Primary Examiner(s): SELBY, GEVELL V
• Application Number:
  US12/218,742
• Publication Number:
  US 20090027545A1
• Time in Patent Office: 1,518 Days
• Field of Search: 348/221.1, 348/222.1, 348/229.1, 348/234, 348/362
• 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 method for analyzing a daytime image in a device, comprising:

receiving an image that includes a plurality of pixels into the device;

computing a histogram of the image; and

,

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

wherein said analyzing the histogram includes;

determining whether, in the histogram between a first summit and an adjacent second summit lower in intensity value than the first summit, there is a bin whose population is below a first threshold that is below the first summit, the first summit being highest in intensity value among all summits in the histogram and being associated with pixels with dominant brightness of a sky region in the image.

2. The method of claim 1, wherein said determining includes:

determining a Sky Contrast, the Sky Contrast being a ratio of a population of a minimum between the first and second summits to a population of the first summit; and

,

comparing the Sky Contrast with the first threshold.

3. The method of claim 1, wherein the first threshold is defined as a predetermined percentage of a population of the first summit.

4. A method for analyzing a daytime image in a device, comprising:

receiving an image that includes a plurality of pixels into the device;

computing a histogram of the image; and

,

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

wherein said analyzing the histogram includes;

determining whether, in the histogram and higher in intensity value than a first summit that is highest in intensity value among all summit(s) not associated with pixels with dominant brightness of a sky region in the image in the histogram, there is a bin having a population below a first threshold that is below the first summit.

5. The method of claim 4, wherein said determining includes:

determining a Peak Contrast, the Peak Contrast being a ratio of a population of a minimum adjacent to the first summit and higher in intensity value than the first summit to the population of the first summit; and

,

comparing the Peak Contrast with the first threshold.

6. The method of claim 5, wherein the first threshold is defined as a predetermined percentage of the population of the first summit.

7. A method for analyzing a daytime image in a device, comprising:

receiving an image that includes a plurality of pixels into the device;

computing a histogram of the image; and

,

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

wherein said analyzing the histogram includes;

comparing a population of a plurality of darker bins of the histogram with a threshold defined to be proportional to a combined population of the plurality of darker bins and a plurality of brighter bins,

wherein the brighter bins do not include a summit associated with a sky region in the image, if this summit exists, nor any bins brighter than this summit.

8. A method for analyzing a daytime color image in a device, comprising:

receiving a daytime color image that includes a plurality of pixels;

creating a plurality of histograms of the image; and

,

analyzing the plurality of histograms to determine an acceptable exposure of the image,

wherein said analyzing the plurality of histograms includes either or both of;

detecting a Right Peak, said Right Peak being tallest among a plurality of rightmost summits that each is rightmost among all summit(s) in a different one among the plurality of histograms and not associated with pixels with dominant brightness of a sky region in the image; and

,

detecting a Significant Peak, said Significant Peak being rightmost among a plurality of tallest summits that each is a tallest among all summit(s) not associated with pixels with dominant brightness of a sky region in the image and in a different one among the plurality of histograms.

9. The method of claim 8, wherein a bin value where one of the Right Peak is located at in one of the plurality of histograms is compared with a predetermined threshold.

10. The method of claim 8, wherein a bin value where the Significant Peak is located at in one of the plurality of histograms is compared with a predetermined threshold.

11. A method for analyzing a daytime image in a device, comprising:

receiving an image that includes a plurality of pixels into the device;

computing a histogram of the image; and

,

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

wherein said analyzing the histogram includes;

determining a ratio of a population of a minimum between a first summit and a second summit to a population of the first summit, the first summit being highest in intensity value among all summits in the histogram and being associated with pixels with dominant brightness of a sky region in the image, the second summit being adjacent to and lower in intensity value than the first summit; and

,

comparing the ratio with a predetermined threshold.

12. A method for analyzing a daytime image in a device, comprising:

receiving an image that includes a plurality of pixels into the device;

computing a histogram of the image; and

,

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

wherein said analyzing the histogram includes;

determining a ratio of a population of a minimum in the histogram to a population of a first summit in the histogram, the first summit being highest in intensity value among all summit(s) not associated with pixels with dominant brightness of a sky region in the image in the histogram, the minimum being adjacent to and higher in intensity value than the first summit; and

,

comparing the ratio with a predetermined threshold.