Image compression technique
First Claim
1. The machine method of automatically compressing a fingerprint image represented by a field of binary pixels comprising the steps of:
- optically imaging a finger surface or a continuous fingerprint to provide an input image of said fingerprint, said input image being a field of binary value pixels, each of said pixels having either a first value or a second value,designating each mutually exclusive m pixel by n pixel box in said imput image as a unit set, m and n each having a value greater than one,associating a subfield greater than the unit set as an associated subfield for said unit set, the unit set being centered in its associated subfield,assigning a binary value to each of said unit sets as a function of the number and position of the first value pixels and of the second value pixels in said associated subfield, andassigning said binary value of each of said unit sets as the value of a single pixel in an output image, said single pixel having substantially the dimensions of a pixel of said input image to provide said output image no more than one-fourth the size of said input image.
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Accused Products
Abstract
An optical and electronic scan produces an image composed of binary value pixels. An automatic picture compression routine reduces the number of pixels in the image. A first stage four to one reduction in the number of pixels is achieved by treating each mutually exclusive four pixel unit as a separate set. A binary value is assigned to each four pixel set. That binary value is assigned to a single pixel in a first output image. The same process is repeated a second time to provide a final output image that has one-sixteenth the number of pixels as has the original input image. The value assigned to each four pixel unit set is a weighted function of the binary value of each of the sixteen pixels in a four pixel by four pixel subfield in which the unit set is centered. The greatest weight is give to the center pixels, that is, to the four pixels of the unit set. Lesser weight is given to the peripheral pixels. Among the peripheral pixels, lesser weight is given to the four corner pixels than is given to the eight side pixels between the corners. In the weighting process, the significance of the binary value of the sixteen pixels in the subfield is in part a function of the total pattern of the pixel values in the subfield.
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Citations
14 Claims
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1. The machine method of automatically compressing a fingerprint image represented by a field of binary pixels comprising the steps of:
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optically imaging a finger surface or a continuous fingerprint to provide an input image of said fingerprint, said input image being a field of binary value pixels, each of said pixels having either a first value or a second value, designating each mutually exclusive m pixel by n pixel box in said imput image as a unit set, m and n each having a value greater than one, associating a subfield greater than the unit set as an associated subfield for said unit set, the unit set being centered in its associated subfield, assigning a binary value to each of said unit sets as a function of the number and position of the first value pixels and of the second value pixels in said associated subfield, and assigning said binary value of each of said unit sets as the value of a single pixel in an output image, said single pixel having substantially the dimensions of a pixel of said input image to provide said output image no more than one-fourth the size of said input image. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. The machine method of automatically compressing an image represented by a field of binary pixels into an output image with reduced number of pixels comprising the steps of:
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scanning a predetermined object to provide an input image consisting of a field of pixels, designating each mutually exclusive two pixel by two pixel box as a four pixel unit set in the input image and a single pixel in the output image, associating a four pixel by four pixel subfield with each of said four pixel unit sets, said unit set being centered in the sixteen pixels of said subfield, assigning to each of said unit sets a binary value determined by a weighted contribution from the pixels of said subfield including the pixels of said unit set within said subfield, and assigning said binary value of each of said unit sets as the value of a single pixel in an output image, said single pixel having substantially the dimensions of a pixel of said input image to provide said output image one-fourth the size of said input image. - View Dependent Claims (12)
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13. Apparatus for automatically compressing a fingerprint image represented by a field of binary pixels comprising:
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means to optically image a finger surface or a continuous fingerprint to provide an input image of said fingerprint, said input image being a field of binary value pixels, each of said pixels having either a first value or a second value, means for designating each mutually exclusive m pixel by n pixel box in said input image as a unit set, m and n each having a value greater than one, means for associating a subfield greater than the unit set as an associated subfield for said unit set, the unit set being centered in its associated subfield, memory means responsive to the number and positions of the first value pixels and the second value pixels in said associated subfield to assign a binary value to each of said unit sets and to a single pixel representing each of said unit sets in an output image each of said output image pixels having substantially the dimensions of a pixel of said input image to provide an output image no more than one-fourth the size of said input image. - View Dependent Claims (14)
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Specification