| 摘要 |
<p>The present principles provide a way to place a multilevel grayscale image, visible with the bare eye in the data area of an optical disc. This feature can be used to authenticate a legitimate disc, since the image features are lost when copying a disc either with a PC recording drive or by a pirate creating a data set to be used on a laser beam recorder to produce forged ROM discs. The modulation rules are selectively varied during disc writing in a way to change the distribution of pit/land lengths, so that the at least three (3) different diffraction properties are generated, and therefore produce at least three (3) distinct looks to the bare eye.</p> |
