Method for mismatch detection between the frequency of illumination source and the duration of optical integration time for imager with rolling shutter
First Claim
1. A method for achieving flickerless operation of imagers using a rolling shutter comprising the steps of:
- first detecting flicker in an image frame caused by an illumination source having a non-zero light intensity period; and
adjusting an integration time such that said integration time is an integer multiple of said non-zero light intensity period,wherein said first detecting step further comprises the steps of;
calculating an expected frequency of a sine wave, said sine wave representing a spatial period of said flicker in said image frame;
second detecting a sine wave intensity fluctuation in a difference of two image frames; and
third detecting a sine intensity pattern in a direction of a scan.
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Abstract
A method for achieving flickerless operation of imagers using a rolling shutter, including the steps of detecting flicker in an image frame and adjusting an integration time such that the integration time is an integer multiple of a light intensity period, is described. The method reduces the task of detecting flicker to detecting a spatial sine wave in the image frame by subtracting two image frames from each other. The subtraction reduces or eliminates image content from the image frames and makes the detection process independent of image content. This method can be practiced based on a very short sequence of image frames (as few as two image frames) and is virtually insusceptible to motion of the image content. Adjustments to the integration time are made by changing the horizontal blanking time of the imager and, thereby extending the duration time of each row of said image frame.
34 Citations
68 Claims
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1. A method for achieving flickerless operation of imagers using a rolling shutter comprising the steps of:
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first detecting flicker in an image frame caused by an illumination source having a non-zero light intensity period; and adjusting an integration time such that said integration time is an integer multiple of said non-zero light intensity period, wherein said first detecting step further comprises the steps of; calculating an expected frequency of a sine wave, said sine wave representing a spatial period of said flicker in said image frame; second detecting a sine wave intensity fluctuation in a difference of two image frames; and third detecting a sine intensity pattern in a direction of a scan. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. An image processor for achieving flickerless operation of images comprising:
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an imager using a rolling shutter; and a flicker avoidance circuit, wherein said flicker avoidance circuit performs the following functions; first detecting flicker in an image frame caused by an illumination source having a non-zero light intensity period; and adjusting an integration time such that said integration time is an integer multiple of said non-zero light intensity period, wherein said first detecting step further comprises the steps of; calculating an expected frequency of a sine wave, said sine wave representing a spatial period of said flicker in said image frame; second detecting a sine wave intensity fluctuation in a difference of two image frames; and third detecting a sine intensity pattern in a direction of a scan. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
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35. An image processing system comprising:
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a processor; a memory device coupled to said processor; and an image device coupled to said processor, said image device further comprising; an image processor using a rolling shutter; and a flicker avoidance circuit, wherein said flicker avoidance circuit performs the following functions; first detecting flicker in an image frame caused by an illumination source having a non-zero light intensity period; and adjusting an integration time such that said integration time is an integer multiple of said non-zero light intensity period, wherein said first detecting step further comprises the steps of; calculating an expected frequency of a sine wave, said sine wave representing a spatial period of said flicker in said image frame; second detecting a sine wave intensity fluctuation in a difference of two image frames; and third detecting a sine intensity pattern in a direction of a scan. - View Dependent Claims (36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51)
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52. An image processing system comprising:
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a CPU; an image system coupled to said CPU, said image system comprising an image processor, said image processor comprising; a rolling shutter; and a flicker avoidance circuit, wherein said flicker avoidance circuit performs the following functions; first detecting flicker in an image frame caused by an illumination source having a non-zero light intensity period; and adjusting an integration time such that said integration time is an integer multiple of said non-zero light intensity period, wherein said first detecting step further comprises the steps of; calculating an expected frequency of a sine wave, said sine wave representing a spatial period of said flicker in said image frame; second detecting a sine wave intensity fluctuation in a difference of two image frames; and third detecting a sine intensity pattern in a direction of a scan. - View Dependent Claims (53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68)
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Specification