Digital exposure circuit for an image sensor
First Claim
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1. A device comprising:
- an analog to digital converter for producing a plurality of digital outputs comprising a plurality of bits, each of said digital outputs indicative of an output of at least one pixel of an image sensor;
a first counter which counts a number of said digital outputs indicating overexposure during an image frame;
a second counter which counts a number of said digital outputs indicating underexposure during said image frame;
at least one threshold detector for comparing counting results of said first and second counters with desired thresholds; and
a decision element for making a decision to either increase, decrease, or maintain an exposure of a next frame of said image sensor based on comparison results from the at least one threshold detector.
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Abstract
Automatic exposure adjusting device considers the image on a pixel-by-pixel basis. Each pixel is characterized according to its most significant bits. After the pixels are characterized, the number of pixels in any particular group is counted. That counting is compared with thresholds which set whether the image is over exposed, under exposed, and can optionally also determine if the image is seriously over exposed or seriously under exposed. Adjustment of the exposure is carried out to bring the image to a more desired state.
67 Citations
36 Claims
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1. A device comprising:
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an analog to digital converter for producing a plurality of digital outputs comprising a plurality of bits, each of said digital outputs indicative of an output of at least one pixel of an image sensor; a first counter which counts a number of said digital outputs indicating overexposure during an image frame; a second counter which counts a number of said digital outputs indicating underexposure during said image frame; at least one threshold detector for comparing counting results of said first and second counters with desired thresholds; and a decision element for making a decision to either increase, decrease, or maintain an exposure of a next frame of said image sensor based on comparison results from the at least one threshold detector. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of controlling exposure comprising:
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obtaining from a current frame a plurality of digital values representing values of pixels of an image sensor; reviewing only most significant bits of each of said digital values from the current frame to determine if each digital value indicates an overexposed pixel or an underexposed pixel; comparing results of said determination with desired thresholds; and adjusting exposure of a next frame of said image sensor by; decreasing said exposure if a number of overexposed pixels is greater than or equal to a first threshold; and increasing said exposure if a number of underexposed pixels is greater than or equal to a second threshold. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21)
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22. A device comprising:
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an analog to digital converter for producing a plurality of digital outputs, each of said digital outputs indicative of an output of at least one pixel of an image sensor; a first counter which counts a number of said digital outputs indicating overexposure during at least one image frame; a second counter which counts a number of said digital outputs indicating underexposure during said at least one image frame; at least one comparator for comparing counting results of said first and second counters; and a decision element for making a decision to either increase, decrease, or maintain an exposure of a next frame of said image sensor based on factors including comparison results from the at least one comparator. - View Dependent Claims (23, 24, 25, 26, 27)
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28. A method of controlling exposure comprising:
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obtaining a plurality of digital values from a current frame representing values of pixels of an image sensor; reviewing each of said digital values to determine if each digital value indicates an overexposed pixel or an underexposed pixel; comparing a number of digital values determined to indicate overexposed pixels and a number of digital values determined to indicate underexposed pixels in said determination with desired thresholds; and adjusting exposure of a next frame of said image sensor according to factors including said comparison. - View Dependent Claims (29, 30, 31, 32, 33, 34)
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35. A device comprising:
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an analog to digital converter for producing a plurality of digital outputs comprising a plurality of bits, each of said digital outputs indicative of an output of at least one pixel of an image sensor; a first counter which counts a number of said digital outputs indicating overexposure during an image frame; a second counter which counts a number of said digital outputs indicating underexposure during said image frame; a third counter which counts a number of seriously underexposed pixels, wherein said at least one threshold detector further compares counting results of said third counter with desired thresholds; at least one threshold detector for comparing counting results of said first and second counters with said desired thresholds; and a decision element for making a decision to either increase, decrease, or maintain an exposure of a next frame of said image sensor based on comparison results from the at least one threshold detector wherein said desired thresholds including a first value indicative of what percentage of said plurality of digital outputs, when counted by said first counter, indicate serious overexposure, a second value indicative of what percentage of said plurality of digital outputs, when counted by said first counter, indicate moderate overexposure, a third value indicative of what percentage of said plurality of digital outputs, when counted by said third counter, indicate serious underexposure, and a fourth value indicative of what percentage of said plurality of digital outputs, when counted by said second counter, indicate moderate underexposure. - View Dependent Claims (36)
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Specification