Digital exposure circuit for an image sensor
First Claim
Patent Images
1. A camera comprising:
- an image sensor having a plurality of pixels, and further having an exposure adjustment capability;
an analog to digital converter which produces a digital output comprising a plurality of bits, said digital output indicative of an output of each pixel of said image sensor;
at least one first counter which counts a number of overexposed parts of said digital output;
at least one second counter which counts a number of underexposed parts of said digital output;
at least one threshold detector for comparing counting results of said first and second counters with desired thresholds;
an exposure decision element, which is capable of making a decision to either increase or decrease a next frame of exposure of said image sensor based on a detected relation of said counting results with said thresholds.
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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.
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Citations
22 Claims
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1. A camera comprising:
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an image sensor having a plurality of pixels, and further having an exposure adjustment capability; an analog to digital converter which produces a digital output comprising a plurality of bits, said digital output indicative of an output of each pixel of said image sensor; at least one first counter which counts a number of overexposed parts of said digital output; at least one second counter which counts a number of underexposed parts of said digital output; at least one threshold detector for comparing counting results of said first and second counters with desired thresholds; an exposure decision element, which is capable of making a decision to either increase or decrease a next frame of exposure of said image sensor based on a detected relation of said counting results with said thresholds. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An automatic exposure adjusting CMOS image sensor device, comprising:
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an image sensor, including a plurality of adjustable photoreceptors, each photoreceptor defining a pixel of the image, and said image sensor having an adjustable exposure which when increased, increases an amount of exposure for a next frame of the image, and when decreased, decreases an amount of exposure for said next frame of the image; an analog to digital converter which obtains an analog output from said image sensor and produces a digital output indicative of said analog output to thereby produce a plurality of digital outputs for said plurality of pixels; a pixel characterization element, representing certain most significant bits of at least a plurality of said digital outputs, to thereby characterize said pixel according to its exposure characteristic; a counter element, which counts numbers of pixels characterized by said pixel characterization element and compares said count with certain thresholds; and an image adjusting element, for adjusting said exposure based on said count. - View Dependent Claims (15)
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16. A method of operating a camera, the method comprising:
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obtaining a plurality of digital values, said plurality of digital values representing values of pixel signals of an image sensor; setting a first variable threshold for overexposed pixels; setting a second variable threshold for underexposed pixels; characterizing said digital values according to a number of most significant bits of said pixels and not all bits of said pixels and investigating said most significant bits to determine if they represent overexposed pixels, normally-exposed pixels, or underexposed pixels; counting said characterized digital values; and if the number of overexposed pixels is greater than said first threshold, then decreasing an exposure for a next frame and if the number of under exposed pixels is greater than said second threshold then increasing the exposure for the next frame. - View Dependent Claims (17, 18, 19, 20, 21, 22)
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Specification