Method and apparatus for authenticating printed documents that contains both dark and halftone text

A computer program product comprising a computer usable non-transitory medium having a computer readable program code embedded therein for controlling a data processing apparatus, the computer readable program code configured to cause the data processing apparatus to execute a document authentication process which comprises:

• (a) obtaining an original grayscale image representing an original document, the original grayscale image including one or more halftone text areas and one or more non-halftone text areas, wherein each halftone text area includes a plurality of halftone dots, each halftone dot being formed by a plurality of pixels, each pixel being a smallest unit of the original grayscale image and each pixel having a grayscale pixel value;
• (b) separating the halftone text areas and the non-halftone text areas of the original grayscale image;
• (c) separately binarizing the halftone text areas and the non-halftone text areas generated by step (b);
• and
• (d) down-sampling only the binarized non-halftone or dark text areas generated by step (c) which correspond to the non-halftone or dark text areas of the original grayscale image, without down-sampling the binarized halftone or light text areas which correspond to the halftone or light text areas of the same original grayscale image, whereby a binarized original image is generated.

A computer program product comprising a computer usable non-transitory medium having a computer readable program code embedded therein for controlling a data processing apparatus, the computer readable program code configured to cause the data processing apparatus to execute a document authentication process which comprises:

• (a) obtaining a target grayscale image representing a hardcopy target document, the target grayscale image including one or more halftone text areas and one or more non-halftone text areas, wherein each halftone text area includes a plurality of halftone dots, each halftone dot being formed by a plurality of pixels, each pixel being a smallest unit of the original grayscale image and each pixel having a grayscale pixel value;
• (b) separating the halftone text areas and the non-halftone text areas of the target grayscale image;
• (c) separately binarizing the halftone text areas and the non-halftone text areas generated by step (b);
• (d) down-sampling only the binarized non-halftone text areas generated by step (c) which correspond to the non-halftone text areas of the target grayscale image, without down-sampling the binarized halftone text areas which correspond to the halftone text areas of the same target grayscale image, whereby a binarized target image is generated;
• and
• (e) comparing the binarized target image with a binarized image of an original document to determine whether the target document is an authentic copy of the original document.