Image sensor method and apparatus having hardware implemented edge detection processing
First Claim
1. A method for detecting edges in an image using an image sensor that comprises a two-dimensional array of addressable pixels, with each of said pixels providing a data value indicative of a portion of the image sensed by that pixel, the method comprising the steps of:
- (a) sensing the image using the image sensor; and
(b) carrying out the following steps for each of a number of selected pixels using a two-dimensional localized group of pixels surrounding each selected pixel, wherein each of the localized groups of pixels comprises a plurality of one-dimensional sets of pixels, each one-dimensional set being orthogonally offset from the other one-dimensional sets in the group;
(b1) accessing a one-dimensional set of pixels contained within the localized group of pixels;
(b2) reading the data values associated with the pixels accessed in step (b1);
(b3) determining an intermediate data value using a smoothing function that is applied to the data values read in step (b2);
(b4) repeating steps (b1) through (b3) for each of the one-dimensional sets of pixels contained within the localized group to thereby produce a set of said intermediate data values; and
(b5) determining a final data value for the selected pixel using a differencing function that is applied to the set of intermediate data values;
wherein step (b) further comprises processing the selected pixels sequentially such that, for each selected pixel, steps (b1) through (b5) are carried out for that selected pixel prior to carrying out any of the steps (b1) through (b5) for the next selected pixel.
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Abstract
An image sensor comprising an integrated circuit chip that includes both a pixel array and edge detection circuitry hardwired together on the chip. The pixel array provides an addressable, non-destructive readout of the pixel data, with the edge detection circuit providing a hardwired implementation of a pair of n×n masks that are convolved with the pixel array data to thereby generate horizontal and vertical edge data that is combined together and outputted by the image sensor. The masks are implemented as a pair of one-dimensional filters, with one of the filters being a one-dimensional Gaussian filter used to smooth the pixel data along one axis and the other filter providing a first derivative Gaussian function to detect edges along the other, orthogonal axis. The non-destructibility of the readout from the pixel array eliminates the need for buffering large amounts of pixel data and the use of separable, one-dimensional filters permits each mask to be implemented using only n simultaneous outputs from the array, 2n weights, and n−1 buffers for temporary storage of the smoothed pixel data.
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Citations
26 Claims
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1. A method for detecting edges in an image using an image sensor that comprises a two-dimensional array of addressable pixels, with each of said pixels providing a data value indicative of a portion of the image sensed by that pixel, the method comprising the steps of:
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(a) sensing the image using the image sensor; and (b) carrying out the following steps for each of a number of selected pixels using a two-dimensional localized group of pixels surrounding each selected pixel, wherein each of the localized groups of pixels comprises a plurality of one-dimensional sets of pixels, each one-dimensional set being orthogonally offset from the other one-dimensional sets in the group; (b1) accessing a one-dimensional set of pixels contained within the localized group of pixels; (b2) reading the data values associated with the pixels accessed in step (b1); (b3) determining an intermediate data value using a smoothing function that is applied to the data values read in step (b2); (b4) repeating steps (b1) through (b3) for each of the one-dimensional sets of pixels contained within the localized group to thereby produce a set of said intermediate data values; and (b5) determining a final data value for the selected pixel using a differencing function that is applied to the set of intermediate data values; wherein step (b) further comprises processing the selected pixels sequentially such that, for each selected pixel, steps (b1) through (b5) are carried out for that selected pixel prior to carrying out any of the steps (b1) through (b5) for the next selected pixel. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An image sensor for use in sensing an image and outputting image data that identifies edges contained within the image, comprising:
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an array of addressable pixels, each of which provides a non-destructive readout of an analog signal indicative of a portion of the image sensed by that pixel; and an edge detection circuit comprising; a smoothing filter circuit connected to said array, said smoothing filter circuit having an output for supplying filtered output data and having one or more inputs for receiving a plurality of the analog signals from said pixels; and a differencing filter circuit having an input coupled to the output of said smoothing filter circuit to receive the filtered output data, said differencing filter circuit having an output for supplying image data that identifies edges contained within the image. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A method for detecting edges in an image using an image sensor that comprises a two-dimensional array of pixels, with each of said pixels providing a data value indicative of a portion of the image sensed by that pixel, the method comprising the steps of:
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providing a mask that comprises a one-dimensional Gaussian function applied to groups of the image data values in a first direction to thereby produce intermediate data values that each represent a combination of the image data values contained in one of said groups, said mask further comprising a separate one-dimensional, first derivative Gaussian function applied to sets of the intermediate data values; and convolving the mask with the image to produce edge data for each of a number of selected pixels. - View Dependent Claims (24, 25, 26)
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Specification