Method For Acquiring And Controlling Automatic Exposure Control Parameters And Imaging Device

• US 20070263097A1
• Filed: 12/26/2006
• Published: 11/15/2007
• Est. Priority Date: 04/30/2006
• Status: Active Grant

• Current Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Inventors: Wei, Xiaoxia, Wang, Jing, Yang, Haitao, Zhao, Guangyao, Chang, Yilin
• Granted Patent: US 7,688,359 B2
• Time in Patent Office: Days
• US Class Current: 348/221.100
• 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

The present invention discloses a method for acquiring automatic exposure control parameters and a method for controlling automatic exposure control parameters and an imaging device. The core idea is to take the brightness weighted average value obtained according to brightness distribution weighted statistics of the image as the exposure control parameter. Then through adjusting the weighted coefficient of pixels in different brightness regions, control the influence of the pixel concentrated brightness regions on the brightness average value. Because the brightness distribution is the basis for determining weighted statistics, the control method of the present invention is not influenced by the scene assumption. Rather it can be universally adapted to a variety of different scenes, and the exposure control effect is not influenced by the position of scenes in the actual bright region/dark region and block distribution.

Claims

1. A method for acquiring a control parameter in automatic exposure control characterized by including:

1) computing a brightness distribution of an exposure image;

2) partitioning into different brightness regions according to the brightness distribution;

3) assigning corresponding weighted coefficients for different brightness regions;

4) computing a weighted average value of brightness of the exposure image as said control parameter.

2. The method for acquiring a control parameter in automatic exposure control according to claim 1, wherein said step 1) includes:

1a) dividing the degree of brightness into a number of bins;

1b) computing distribution of pixels for the exposure image in each bin.

3. The method for acquiring a control parameter in automatic exposure control according to claim 2, wherein said step 2) includes:

2a) partitioning bright regions with specific widths and focusing on bins with peak values, at least partitioning the highest peak region and the second highest peak region in an entire brightness distribution.

4. The method for acquiring a control parameter in automatic exposure control according to claim 2, wherein said step 1) also includes:

1c) using a moving window with a specific width to compute a moving average and a moving accumulation of the pixel distribution in each bin;

said step

     2) includes;

2a) partitioning each peak region of pixel distribution in each bin based on a brightness region corresponding to a peak value by moving computation, at least partitioning the highest peak region and the second highest peak region in an entire brightness distribution.

5. The method for acquiring a control parameter in automatic exposure control according to claim 3, wherein said step 2) also includes:

2b) judging whether the highest peak region overlaps with the second highest peak region, if they overlap, then, taking a third highest peak region as the second highest region, and so on and so forth, until the highest peak region and the second highest peak region do not overlap.

6. The method for acquiring a control parameter in automatic exposure control according to claim 3, wherein a weighted coefficient for pixels of a peak value region is smaller than weighted coefficients of other regions.

7. The method for acquiring a control parameter in automatic exposure control according to claim 6, wherein the weighted coefficient assigned to the peak value region decreases with increase of pixel distribution in the peak value region, and after decreasing to a smallest weighted coefficient, maintains steady or increase, or increases after maintaining steady in a specific region.

8. The method for acquiring a control parameter in automatic exposure control according to claim 7, wherein the smallest weighted coefficient corresponding to a peak value region with higher brightness of said highest peak region and second highest peak region increases with increase of a current relative photoelectric gain, and the smallest weighted coefficient corresponding to a peak value region with lower brightness decreases with increase of the current relative photoelectric gain.

9. A method for controlling automatic exposure characterized by including:

1) obtaining a weighted average value of brightness for a current exposure image;

2) comparing said weighted average value of brightness with a brightness reference value;

3) performing an adjustment of a relative photoelectric gain based on a result of the comparing, so that the weighted average value of brightness for the exposure image after undergoing the adjustment approaches the brightness reference value.

10. The method for controlling automatic exposure according to claim 9, wherein said brightness reference value increases with increase of a ratio of the current weighted average value of brightness to the relative photoelectric gain.

11. The method for controlling automatic exposure according to claim 9, characterized by setting a proper threshold, a buffer threshold, and a rapid change threshold as gradual expanding ranges centering said brightness reference value;

when said weighted average value of brightness falls into the proper threshold, or the proper threshold enters the buffer threshold and changes within the buffer threshold, not performing the adjustment of the relative photoelectric gain;

when said weighted average value of brightness exceeds the buffer threshold but still falls within the rapid change threshold, adjusting the relative photoelectric gain with a small step length, so that said weighted average value of brightness returns within the proper threshold;

when said weighted average value of brightness exceeds the rapid change threshold, adjusting the relative photoelectric gain with a large step length, so that said weighted average value of brightness returns within the rapid change threshold.

12. The method for controlling automatic exposure according to claim 9, wherein when performing the adjustment of the relative photoelectric gain, the following strategies are adopted:

adjusting a shutter time as the first priority, if the adjustment requirement is not met, continuously adjusting an aperture, and finally adjusting an amplifier gain;

or,

adjusting the aperture as the first priority, the shutter time as the second priority, and the amplifier gain as the last priority;

or,

fixing one or two types of parameters, only adjusting other parameters.

13. An imaging device, including a photosensitive device, an aperture, a shutter, an amplifier, a relative photoelectric gain adjustment module, and an image processing module characterized by also including a brightness distribution computing module, a weighted computing module, and a compensation control module;

said photosensitive device converts light passing through the aperture and the shutter into an analog current signal;

said amplifier amplifies an output from the photosensitive device;

said image processing module converts the output of said amplifier into a digital image signal;

said brightness distribution computing module computes a brightness distribution of the digital image signal;

said weighted computing module distributes corresponding weighted coefficients for different brightness regions based on a computation result of said brightness distribution computing module, and computes a brightness weighted average value of said digital image signal;

said compensation control module determines an adjustment target of a relative photoelectric gain based on a difference between said brightness weighted average value and a brightness reference value;

said relative photoelectric gain adjustment module performs an adjustment of an aperture size and/or a shutter time and/or an amplifier gain, based on the adjustment target of the relative photoelectric gain determined by said compensation control module.