Disc authentication by grayscale image

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.

This application claims the benefit, under 35 U.S.C. §365 of International Application PCT/US2006/023252, filed Jun. 15, 2006, which was published in accordance with PCT Article 21(2) on Dec. 21, 2007, in English.

BACKGROUND

1. Field of the Invention

The present principles relate to optical disc authentication. More particularly, it relates to a method and apparatus for disc authentication by applying a grayscale image in the data area through modulation rule variation.

2. Description of the Related Art

The modulation rules applied when writing an optical disc are of integral importance when considering copying and unauthorized duplication of the same. Existing binary systems for imaging the data portion of an optical disc have been shown, for example by the Philips Electronics Pit O' Resc system. This system provides a modulation scheme and hardware that enables a binary image to be encoded on the data portion of the disc so as to generate an image on the same.

Binary images have significant limitations in the art, and more particularly do not provide sufficient flexibility so as to provide more than two diffraction patterns (i.e., more than 2 grayscale levels) in order to decrease forging and counterfeiting capability by adding significant more detail to the authentication images applied there to.

It is therefore desirable to have features on an optical disc which are easily visible with the bare eye and are hard to forge, so that it is easy to determine if it is a legitimate replicated disc or a pirated one.

SUMMARY OF THE INVENTION

The present principles are achieved in accordance with one implementation where the method includes modulating data to obtain bits for encoding first and second encoded region lengths on an optical disc, said modulating includes selecting at least three diffraction pattern in a data area on the optical disc and responsive to criteria based on the selected said diffraction patterns.

According to one embodiment, a counter is started upon the initiation of the recording of an optical disc. The counter is read and the varied modulation rules are applied when the counter reaches a multiple of a predetermined number, such as, for example, 2, 3, 4, 5, 6, 7 and 8.

According to yet a further embodiment, the method for applying grayscale imaging to the data area of an optical disc includes modulating the data to obtain a channel bit stream representative of a sequence of first and second encoded region lengths on the optical disc; said modulating further includes determining a number of 3T symbols from primary and secondary sync code tables each time there is a choice between primary and secondary sync code tables or state 1 and state 4 modulation tables; selecting at least three diffraction patterns; and assigning one selected diffraction pattern level for each of the following: 1) when the number of 3T symbols is higher in one of said primary and secondary sync code tables or state 1 and state 4 modulation tables; 2) when the number of 3T symbols is lower in one of the primary and secondary sync code tables or state 1 and state 4 modulation tables; and 3) when the number of 3T symbols is equal between the primary and secondary sync codes tables or state 1 and state 4 modulation tables.

In accordance with yet another embodiment, an apparatus includes a modulator for modulating data where a change in distribution of first and second encoded region lengths representative of bits from the modulated data generates at least 3 different diffraction patterns in the data portion of the optical disc.

A grayscale image controller having one input for receiving grayscale image data, one input connected to a pickup disc motor, and an output connected to the modulator, operates to synchronize the application of the modulation rule variations with geometrical positions on the disc.

The change in distribution includes an identification of different statistical properties in the data bytes and an assignment of a grayscale level according to the different statistical properties. Different ones of the different statistical properties are used depending upon the desired grayscale level. The different statistical properties of pit-land length distribution at least one of maximize and minimize a number of 3T symbols in the data bytes.

DETAILED DESCRIPTION OF PREFERRED IMPLEMENTATIONS

This description illustrates the present principles. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody these principles and are included within its spirit and scope.

Turning toFIG. 1, an exemplary Digital Versatile Disc (DVD) recorder to which the present principles may be applied is indicated generally by the reference numeral100. The DVD recorder100utilizes a recordable disk medium102. The disk medium102is embodied as a DVD in the illustrated embodiment. In many instances, as will be noted, the disk medium can also be, for example, a compact disc (CD), a high definition digital versatile disc (HD DVD), a Blue Ray DVD, and so forth. Moreover, as is readily apparent to one of ordinary skill in this and related arts, the present principles are not applicable to optical disc recorders, but also to systems used for creating masters for read only memory discs, e.g., DVD-ROM. This so-called LBR (laser beam recorder) is similar to the illustrated recorder inFIG. 1, but obtains the record signal feed into block128from a hard disc drive.

The DVD recorder100is capable of writing onto and reading from recordable DVD media, in this example, a DVD102. The device comprises a mechanical assembly104, a control section120, a video/audio input processing path140, and a video/audio output processing path170. The allocation of most of the blocks to different sections or paths is self-evident, whereas the allocation of some of the blocks is made for purposes of convenience and is not critical to understanding the operation of the device.

The mechanical assembly104includes a motor106for spinning the disk102and a pickup assembly108that is adapted to be moved over the spinning disk. The pickup108and the motor106are controlled by a servo110. The servo110can receive a playback signal of data which can be read from a spiral track of the disk102as a first input. The playback signal also can be an input to an error correction circuit130, which can be considered part of the control section or part of the video/audio output processing path.

When reading data from the disk102, a laser on the pickup assembly108can direct laser light at an interior layer surface of the disk102. Depending upon the data stored on the disk102, the laser light can be mostly reflected or mostly absorbed. The pickup assembly108can interpret reflected light as one type of electrical signal while light absorbed by the interior layer surface of the disk102can be interpreted as a second type of electrical signal. In the preferred embodiment, transitions between reflectivity and non-reflectivity are mapped to a digital signal referred to as the playback signal which corresponds to the data stored on the disk102.

By comparison, during recording, a laser on the pickup assembly burns spots onto a spiral track on the disk102in order to digitally record video and/or audio program material. More particularly, the disk102, which can include at least one interior crystalline recording layer, can exhibit two distinctive states, amorphous or crystalline, each having different reflectivity characteristics. Those different levels of reflectivity can be detected by optical sensors in the pickup assembly108.

Prior to recording, the interior recording layer of the disk102is in a crystalline state exhibiting high reflectivity. The light intensity of a laser beam can be modulated to write amorphous data marks on the surface of tracks in the interior crystalline recording layer. Specifically, the energy of a laser pulse can quickly raise the surface temperature of the interior crystalline recording layer above the layer melting point. Once above the melting point, the interior layer can transition from a crystalline state of high reflectivity to an amorphous state of low reflectivity. Subsequently, the rapid cooling of the layer prevents the molecular structure of the interior layer from reorganizing into a crystalline state. Hence, digital data can be mapped to a series of laser pulses which can write a digital code to the disk102which can correspond to the digital data.

Notably, depending upon capacity requirements, the disk102can have either one or two recordable sides. Additionally, the disk102can have multiple recordable layers per side. However, for purposes of understanding the present principles, the number of sides and layers is irrelevant. Moreover, in the event of a double-sided recording, it also is irrelevant whether the recording of both sides of the disk102occurs from one or both sides of the disk102.

Returning now toFIG. 1, the control section120preferably includes a controller122and a navigation data generation circuit126. The controller122supplies a first input signal to the navigation data generation circuit126and the servo110supplies a second input signal to the navigation data generation circuit126. The servo can also be considered part of the control section120. The navigation data generation circuit126supplies a first input signal to the multiplexer (MUX)154, which forms part of the video/audio input processing path140. The output of the MUX154is an input to an error correction coding circuit128. The output of the error correction coding circuit128is a recordable input signal supplied to the pickup108, which will be “burned” onto the spiral track of the disk102by the laser.

The controller122also preferably has access to the data included in the track buffer172and record buffer152as shown inFIG. 1. The controller122can delete, modify, and reformat video data stored in the track buffer172and record buffer152for the purpose of implementing the inventive arrangements. Control and data interfaces are also preferably provided for permitting the controller122to control the operation of packet video encoder144and audio encoder148. Suitable software or firmware is provided in memory for the conventional operations performed by controller122. In addition, program routines for the advanced features134are provided for controlling the controller122.

A control buffer132for functions capable of being activated by a user indicates functions such as, e.g., play, record, reverse, fast forward, pause/play and stop. The pause is a counterpart to pause operation in a VCR, for example manually interrupting the play back of a prerecorded program or interrupting the recording of a viewed program to eliminate commercials from the recording. A separate pause buffer136is provided to receive commands for performing the pause during record and playback function.

The video/audio input processing path140is a signal processing circuit for converting a conventional television signal, for example NTSC or PAL, into digitized packet data, for example MPEG-1 or MPEG-2, for digital recording by the DVD recorder100. The input path140includes an NTSC decoder142and video encoder, for example MPEG-1 or MPEG-2,144for video in, and includes an audio analog-to-digital converter (A/D)146and an audio encoder, for example MPEG-1 or MPEG-2,148. The digitized signals are combined in a multiplexer150and stored in a record buffer152until an entire packet has been constructed. As each packet is constructed, each packet is combined with the output of the navigation data generation circuit in the MUX154and sent to the error correction coding circuit128. Error correction coding circuit128can also be deemed to be part of the input path140.

The output processing path170includes a track buffer, or output buffer,172, in which data read from the disk is assembled into packets for further processing. The packets are processed by conditional access circuit174that controls propagation of the packets through demultiplexer176and into respective paths for video and audio processing. The video is decoded by decoder178, for example from MPEG-1 or MPEG-2, and encoded as a conventional television signal by TV encoder180, for example NTSC or PAL. The audio is decoded by circuit182, for example MPEG-1 or MPEG-2, and converted to analog form by audio digital-to-analog (D/A) converter184. The output processing path170can be deemed to include the error correction circuit130, as noted.

The DVD recorder100can represent a machine having, for example, but not limited to, a 1× read and 1× write capability. Such devices can typically have maximum data rates for recording or playing back of approximately 11 megabits/second.

A multi-level, varying rule based modulator199and/or demodulator198implements the varying rules based modulation in accordance with the present principles, so as to embed a second level code of the optical disc. As is shown, the modulator is disposed between the error correction coding circuit128and pickup108, and the demodulator198is disposed between the pickup108and the error correction circuit130. The modulator199includes an input for grayscale image controller signals from the grayscale image controller195. The grayscale image controller has an input for the image data and an input from the pickup disc motor to synchronize the application of the modulation rule variations with the geometrical position on the disc.

As noted above, the present principles are directed to a method and apparatus for disc authentication by implementing grayscale images onto the data area of an optical disc. Advantageously, in accordance with the present principles, the grayscale image is lost if the optical disc is copied with an optical drive or is reproduced by a professional pirate on the user data level. Thus, the absence of the grayscale image may be used to indicate that an optical disc is illegitimate such as in the case of a pirated copy.

The present principles utilizes specific sets of rules to convert (modulate) data bytes into a channel bit stream, which is the sequence of pits and lands on an optical disc. In accordance with the present principles, different statistical properties of pit-land length distributions may be used to generate three (3) or more grayscale levels for imaging the data portion of the optical disc, without changing the readability performance of the data area since the proposed sets of modulation rules are compatible with the demodulation process used in standard optical disc drives.

All channel codes for optical discs provide a certain degree of redundancy to control the DC component of the bit sequences. Such DC component control is used to guarantee reliable data detection and a sufficient differential phase tracking signal for all possible bit combinations. This redundancy can also be used to select codewords with specific statistical run length distribution properties, resulting in different diffraction patterns that have a distinct look to the bare eye.

The modification to be performed for an optical disc (such as, e.g., a DVD) to obtain more than two different diffraction patterns for each synchronization (sync) frame can be implemented using the following procedure. Every time there is a choice between primary and secondary synchronization (sync) code tables or between state 1 and 4, it shall be determined which one produces more 3T symbols in the bit stream. If the grayscale level is 0, then the case with the higher number of 3T symbols is chosen. If the grayscale level is 1, then the case with the lower number of 3T symbols is chosen. If the number of 3T symbols is the same for both cases, then the usual Digital Sum Value (DSV) control rules are applied as specified. Since most of the time the number of 3T symbols is the same for both cases, the DSV control still works sufficiently. The preceding procedure is further described with respect to the embodiments disclosed inFIGS. 2aand2b.

Turning toFIG. 2a,an exemplary method for generating 3 grayscale levels for imaging the data portion of an optical disc without altering the readability of the data recorded thereon is indicated generally by the reference numeral200. The method200results in the generation of at least 3 different diffraction patterns, thus resulting in the production of 3 grayscale levels for imaging the data portion of the disc. It will be clear from the following that the presented such that the different sets of modulation rules are constructed so as to change or alter the distribution of pit/land lengths, which in turn results in different diffraction patterns that have a distinct look to the bare eye.

The method200includes a start block that passes control to a function block202. The function block202determines which sync code table or state table produces more 3T symbols in the bitstream each time there is a choice between the primary and secondary sync code tables or between the state 1 and state 4 tables, and passes control to a decision block204. The decision block204determines whether or not the number of 3T symbols is the same for both cases (i.e., whether the output of the function block202was indeterminate). When the answer is “yes”, the standard DSV modulation rules are applied to that portion of the data recording. When the answer is “no” at decision block204, a subsequent decision block206determines whether the target grayscale level is equal to “0”, “1” or “2”. When the grayscale level is to be 0, the sync code table or state table with higher than 3T symbols is selected to write the data to the disc (212). When the grayscale level is to be 1, the standard modulation rules are used.

When the grayscale level is to be 2, the sync code table or state table with lower than 3T symbols is use. Once this determination is made, the data is written to the optical disc using the varied modulation scheme (216).

The function block212selects the sync code table or the state table with the higher number of 3T symbols (or uses the standard Digital Sum Value (DSV) modulation rules when the output of the function block210is indeterminate), and passes control to the writing function block216.

The function block214selects the sync code table or the state table with the lower number of 3T symbols (or uses the standard DSV modulation rules when the output of the function block210is indeterminate), and passes control to the writing function block216.

The writing function block216places the modulated bits into the output buffer to be transferred to the pickup and passes control to an end block. This decision sequence (200) has to run once per primary code data or sync byte.

The preceding description is directed to modulation rules for embedding a 3 or more grayscale levels imaged onto the data portion of an optical disc by changing the diffraction patters of the pits and lands during the modulation process used during recording.

However, given the teachings of the present principles provided herein, one of ordinary skill in this and related arts will readily comprehend that the present principles are also readily applied to other optical disk modulation rules including, but not limited to, compact disc (CD), high definition digital versatile disc (HD DVD), and Blu-Ray Disc (BD) modulation rules.

In accordance with further embodiments of the present principles, additional grayscale levels can be achieved by using the modified modulation rules only in every other case (resulting in 5 grayscale levels), or in one of every three cases (resulting in 7 grayscale levels).

By way of example,FIG. 2bshows an embodiment of the present principles where a counter302and a decision block304are added to the beginning of the method. The counter is started, and decision block304determines whether the counter is at a multiple of 3 (e.g., in the case of 7 grayscale levels). When “yes” the decision block304passes operation onto the varied modulation method of the present principles. When decision block304says “no”, the standard DSV modulations rules are selected and applied. The remainder of the process remains the same as described above with reference toFIG. 2a.Those of ordinary skill in the art will recognize that the interval or multiple number used by decision block304is shown as an exemplary implementation and can be can be changed or varied without departing from the spirit of the present principles.

Turning toFIG. 3, an exemplary graph for the distribution of runlengths when data modulation rule variation for the above described grayscale level 0 and 2 is applied to a DVD bitstream with grayscale image bit length corresponding to one sync frame of first level data is indicated generally by the reference numeral400. In the graph400, the horizontal axis denotes the number of consecutive sync frames, and the vertical axis shows the number of symbols with the various runlengths. It is easily seen that the number of 3Ts varies between higher and lower values. If the modulation process is conducted as described in the DVD specifications, then the average number of 3Ts per sync frame is approximately 105.

FIG. 4shows a two dimensional plot how a binary image can be created on the disc surface by coloring the 3T occurrence in different colors. This binary imaging has been performed by the known Philips Pit O Resc technology and shows the current state of the art for binary imaging the data portion of the disc. This concept is limited to binary imaging and shows conceptually that the 3 or more grayscale levels generation for data area imaging of the present principles can be performed as disclosed.

These and other features and advantages of the present principles may be readily ascertained by one of ordinary skill in the pertinent art based on the teachings herein. It is to be understood that the teachings of the present principles may be implemented in various forms of hardware, software, firmware, special purpose processors, or combinations thereof.

While there has been shown, described and pointed out fundamental novel features of the present principles as applied to preferred implementations thereof, it will be understood that various omissions, substitutions and changes in the form and details of the methods described and devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the present principles. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the present principles. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or implementation of the present invention may be incorporated in any other disclosed, described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.