Method and apparatus for registering color separation film
First Claim
1. In a method of registering a pair of color separation films containing halftone dot detail and macroscopic edges which align when the films are registered, the steps of:
- selecting one of the films as a reference film;
recording first and second pictures of the reference film centered at spaced apart first and second locations, respectively;
recording third and fourth pictures of the other film centered at locations thereon which approximately correspond to but may be offset from the respective first and second locations;
extracting from said first and third pictures the locations of corresponding macroscopic edges on the reference film and on the other film;
extracting from said second and fourth pictures the locations of corresponding macroscopic edges on the reference film and on the other film; and
determining the offset between the edge locations on the reference film and the corresponding edge locations on the other film to thereby determine the positional adjustment of the other film necessary for registration with the reference film.
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Abstract
An algorithmic based method and apparatus for registering halftone color separations using edge based registration techniques. Digital pictures are taken at two locations on each film, and, following optimal thresholding of the data, the edges are located by application of a Laplacian of a Gaussian edge detection operator. Sampling is used to reduce the computational requirements, and full resolution is restored by interpolation. The edge locations are corrected for operator edge bias, and the corrected edge points are linked into segments which are registered by the parameter space method. The initial offset is corrected for size differences by application of least squares correction techniques.
135 Citations
39 Claims
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1. In a method of registering a pair of color separation films containing halftone dot detail and macroscopic edges which align when the films are registered, the steps of:
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selecting one of the films as a reference film; recording first and second pictures of the reference film centered at spaced apart first and second locations, respectively; recording third and fourth pictures of the other film centered at locations thereon which approximately correspond to but may be offset from the respective first and second locations; extracting from said first and third pictures the locations of corresponding macroscopic edges on the reference film and on the other film; extracting from said second and fourth pictures the locations of corresponding macroscopic edges on the reference film and on the other film; and determining the offset between the edge locations on the reference film and the corresponding edge locations on the other film to thereby determine the positional adjustment of the other film necessary for registration with the reference film. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. Apparatus for effecting registration between a pair of color separation films containing halftone dot detail and macroscope edges which align when the films are registered, said apparatus comprising:
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a digital camera operable to record digital pictures at locations on each film with the locations on the respective films corresponding but possibly being offset; means for extracting from each digital picture the locations of macroscopic edges thereon; and means for calculating the offset between the edges on corresponding pictures of the films thereby determining the relative movement necessary to bring the films into registration. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36)
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37. In a method of registering a pair of color separation films containing halftone dot detail and macroscopic edges which align when the films are registered, the step of:
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selecting one of the films as a reference film; recording first and second pictures of the reference film centered at spaced apart first and second locations, respectively; recording third and fourth pictures of the other film centered at locations thereon which approximately correspond to but may be offset from the respective first and second locations; extracting from said first and third pictures the locations of corresponding macroscopic edges on the reference film and on the other film; extracting from said second and fourth pictures the locations of corresponding macroscopic edges on the reference film and on the other film; determining the offsets between the edge locations on the reference film and the corresponding edge locations on the other film required to separately move the first picture into registration with the third picture and the second picture into registration with the fourth picture; constructing a imaginary line vector extending from a tail point at one selected location on the reference film and a tip point at another selected location on the reference film; computing a tail point on the other film by subtracting the corresponding offset from the coordinates of said one selected location; computing a tip point on the other film by subtracting the corresponding offset from the coordinates of said other selected location; and constructing an imaginary line vector extending from said tail point on the other film to said tip point on the other film whereby the positional adjustment of the other film necessary to register it with the reference film can be effected by aligning the vector on the other film with the vector on the reference film. - View Dependent Claims (38, 39)
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Specification