Optical disc comprising a watermark and a method and recorder for recording such a disc
AssigneeKoninklijke Philips Electronics N.V.
InventorsJacobus Maarten Den Hollander, Josephus Arnoldus Henricus Maria Kahlman
Life of this patent
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Abstract
A visible pattern is obtained by modulating the digital sum value. Because the digital sum value modulation allows the choice of several different channel bits groups between DC control points, the selection of a group of channel bits resulting in a change of reflection. This creation of a visible pattern is highly suitable for Blueray as the parity preserving property of the channel code guarantees disparity inversion by the DC-control bit, which keeps the DSV excursions between hard limits. As a result only small DSV deliberate variations are required to produce a grating, which will not deteriorate the bit-detection margin of the optical disc.
Claims17
An optical disc comprising
- a track,
- a plurality of marks located in the track representing channel bits,
- the plurality of channel bits having a Digital Sum Value,
- the Digital Sum Value having a set point determined by a DC control,
- the DC control being limited within a DC Control range
- characterized in that the optical disc further comprises:
- diffractive elements in a limited contiguous area,
- a diffractive structure formed by the diffractive elements,
- each diffractive element being formed by an alignment of a plurality of marks across a plurality of radially at least partially adjacent sections of the track, where the set point is a modulated set point, diverting from a default set point in the limited contiguous area, the modulated set point being correlated to the alignment of the plurality of marks across the plurality of radially adjacent sections of the track.
A method of producing an optical disc comprising
- a track,
- a plurality of marks located in the track representing channel bits,
- the plurality of channel bits having a Digital Sum Value,
- the Digital Sum Value having a set point determined by a DC control,
- the DC control being limited within a DC Control range,
- the method comprising the step of replicating the optical disc from a master,
- characterized in that the optical disc further comprises:
- diffractive elements in a limited contiguous area,
- a diffractive structure formed by the diffractive elements,
- each diffractive element being formed by an alignment of a plurality of marks across a plurality of radially at least partially adjacent sections of the track, where the Digital Sum Value is a modulated Digital Sum Value diverting from the set point in the limited contiguous area, the modulated Digital Sum Value being correlated to the alignment of the plurality of marks across the plurality of radially adjacent sections of the track.
A method of inspecting an optical disc to find illegally copied optical discs, comprising the steps of:
- locating a diffractive structure on the optical disc,
- illuminating, when found, the diffractive structure,
- observing a diffractive characteristic of the diffractive structure,
- declaring the optical disc an illegally copied optical disc when no diffractive nature of the diffractive structure is observed.
Dependencies are inferred from the claim text.