Canon Kabushiki Kaisha

Canon Information Systems Research Australia Pty. Ltd.

Ross Alexander Donelly

Stamatios Demetriou

Jim Mulhearn

A method of determining an indicator for the presence of an image is disclosed in which the image is comprised of a two dimensional array of pixels. The method finds particular use in the prevention of fraudulent copying of images, such as bank notes using colour laser copiers and printers. The method firstly imposes a grid of cells over a portion of the image. Then a representative value for each of the cells is determined. Next, a measure of the difference between the representative values of adjacent cells of the grid is determined over the whole of the grid. The first three steps are then repeated for substantially all possible positions of the grid of cells to determine a grid position having an overall maximum positional difference. Finally, the grid position and the representative value for each of said cells is used as a representation of the image. The representation can thus comprise a template used in an image detection system.

Template formation method and apparatus

An image detection system is disclosed for the detection of an image in an input pixel stream. An image is input as a input pixel stream and accumulated and converted into cells which are formed into cell data portions from regions of a corresponding image of the input pixel stream. A template storage ROM stores at least one template that comprises a multiplicity of cell data entries derived form an desired image to be detected. A comparator matrix is connected to the cell converter and the template ROM for comparing the cell data portions with a multiplicity of cell data entries to derive a template detection signal when a predetermined number of the cell data portions match with the multiplicity of said cell data entries. The system finds particular use in the prevention of fraudulent copying of images, such as bank notes using colour laser copiers and printers.

Image detection system

The present invention provides a method and apparatus for error diffusing a series of images, each of said images being made up of component pixels. The method comprises, for each of said pixels determining a current error diffused value for said pixel; adding an error margin to each current error diffused value to produce a marginalised error diffused value, said marginalised error diffused value being a translation of said current error diffused value in a direction towards that of a previous output value for said pixel; utilising said marginalised error diffused value to determine a closest possible output value to said marginalised error diffused value; and error diffusing the difference between said closest possible output value and said error diffused value to adjacent pixels.

Digital halftoning of a continuous tone image using error diffusion

Computer based images are normally provided in the form of large amounts of data on a pixel by pixel basis. Method and apparatus (25) are disclosed for converting this pixel based data (7,8,9-16,17) to spline based data (FIG. 5) wherein the characteristics present in the pixel based data are substantially retained in the spline based version of the image.

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West Ryde, Australia

Ross Alexander Donelly