Patent Application
20090052313
The present invention relates to a method and to an apparatus for manufacturing a record carrier having stored a content information, allowing for the post-recording of secondary information.
It is known that ROM optical discs are obtained by a molding process, whereby a plurality of discs having exact replicas of the same content information, or user data, is obtained, the content information being e.g. music, a movie, software, which is often a copy-protected material. For some application it would be desirable that the individual discs would differ at least in some part of the carried information. However this cannot be achieved by said molding process. A straightforward application could be, for example, the possibility to distinguish individual discs as a basis for an authentication, access control, or copy protection scheme, particularly in the context of super distribution.
In WO 02/101733 a so-called post-recording method is described which makes it possible to record a secondary information, such as a Unique Disc ID, onto a read-only optical record carrier after disc production. The method, also called “Postscribed ID” (PID), is also used by Sony for CD-ROM. In PID, lands between the stamped pits can be converted, so as to give a pit-like reflection, using laser ablation. The thin film reflective layer (that usually consists of aluminum for conventional discs) has a special composition to allow ablation of the layer. After ablation, the local reflectance will be low and comparable to a stamped pit. Recording in a pit will not lead to a significant reflectivity change, thus, overwritten pit sections remain ‘pit’ whereas overwritten ‘land’ sections are transformed into ‘pit’ for the read-out process. Using this method it is thus possible to adapt the modulation stream, therefore, a plurality of CD-ROM having the same user-information can be obtained in a first step by a molding process; in a second step, the individual members of the plurality can be differentiated by adding an individual Postscribed ID (a Unique Disc ID; in general, a secondary information) to each disc. In order not to corrupt the content information, a special area of the disc is provided where dummy patterns, not relevant for the user and not part of the content information, are pre-recorded: the secondary information is added here.
It is an object of the present invention to provide a method and an apparatus for manufacturing a record carrier having at predetermined positions patterns of a desired type for being modified by a post-recording process for recording of secondary information, which secondary information can be retrieved in a relatively simple way.
This object is achieved according to the invention by a method as claimed in claim 1 and by an apparatus as claimed in claim 4. Preferred embodiments of the invention are claimed in the dependent claims.
It has to be noted that the secondary information is recorded in the same information channel where the content information is pre-recorded, and thus needs to be retrieved by use of substantially the same demodulation/decoding circuitry.
It also has to be noted that the content information is present in the information carrier in the form of a modulated bitstream obtained from the content information by encoding the content information and modulating the encoded content information.
Encoding the content information comprises a combination of:
Modulating the encoded content information foresees converting each data word into a channel word, representable as a pattern of 1s and 0s, or, in case of an optical record carrier, pits and lands.
The invention is primarily based on the recognition that both in providing an area for being modified in a post-recording process, as well as in having this area modified in the post-recording process, it is potentially introduced on the record carrier some pattern which is not compliant with modulation rules that are foreseen.
The reasons for the presence of a modulation step can be to introduce some redundancy which allows to detect/correct errors while retrieving the recorded content information, and/or to render the information to be recorded in a form which is compatible with the bandwidth constraints imposed by a particular recording system, like for example in Optical Storage where a Run-Lenght Limited (RLL) encoding is used.
In Optical recording systems like for example according to the CD, DVD or BD standards, in particular, the modulation step comprises a step of associating to a data word of n bits a channel word of m bits, with m>n. As a consequence, in the space of channel words, i.e. all the 2m channel words obtainable with m bits, only some are foreseen by the relevant modulation algorithm (EFM for CD, EFM+ for DVD and 17PP for BD), whereas the other are non-valid channel words. In contrast, the channel words to which a data word can be associated are herein referred to as valid channel words. In a reproduction apparatus the detection of a non-valid channel word gives rise to marking that channel word as erroneous during demodulation. Therefore, the dummy patterns predisposed for being modified in a post-recording process, need to be compliant with the modulation rules employed, i.e. they need to be valid patterns, or corresponding to valid channel words, otherwise, as non-valid patterns, they would oblige to an adaptation of the demodulation. Moreover, as non-valid patterns, the dummy patterns could violate the RLL (read: bandwidth) constraints of the channel, putting even more burden on the analog pre-processing of the High Frequency signal retrieved from the record carrier and on the demodulation in general in order to correctly detect these patterns.
Instead, if the dummy patterns are valid patterns, no modifications at demodulation level and analog pre-processing are necessary at all; the upper layer—the decoding level—instead, has to be adapted, because it has to know where the dummy patterns are supposed to be, and how they are supposed to look like, with or without modification. During decoding there must not be an attempt to correct the patterns that have been modified in the post-recording process. However this adaptation is a relatively simple one. In practice, the dummy patterns are placed at predetermined locations; a unit in a decoder will check one by one if the patterns present at the predetermined locations have been modified or not, thereby retrieving the secondary information which has been recorded.
Thus, in order to allow the recording, or “post-recording” as is sometimes referred, of a secondary information, which can be individual to each record carrier, such as a Unique Disc ID, a record carrier has to be provided which has dummy patterns, which correspond to valid channel words, at predetermined location. The secondary information can then be stored on the record carrier by selectively modifying said dummy patterns in said post-recording process.
It is clarified that, in the context of this document, the expressions “dummy pattern” and “dummy channel word” are not used to refer a pattern or a channel word of no value at all, but rather a pattern or a channel word which is not carrying any content information. I.e., the dummy pattern or dummy channel word are indeed irrelevant, or “dummy”, from the point of view of the content information, nevertheless the are relevant to the secondary information, since a dummy pattern or channel word, whether modified or not stores a piece of said secondary information. The distinction between pattern and channel word is clarified hereinafter.
In the case of a ROM record carrier, i.e. a, record carrier where the content information is pre-recorded and is not modifiable by the user, the dummy patterns and the patterns encoding the content information are preferably formed by means of a unique step, for example a molding process. Therefore it is possible to create a plurality of record carriers having prerecorded the same content information, where differentiated secondary information can then be recorded. However the invention can also be applied to record carriers recordable by the user, where the method according to the invention can be used to pre-record an individual code on the record carrier, which can be useful according to some models of distribution of copy-protected content.
The present invention is thus based on the further recognition that it is not possible to generate a modulated bitstream having desired patterns at predetermined positions by simply modifying the pattern present in a modulated bitstream at the predetermined positions, because this would, in general, cause a violation of the modulation rules (i.e. the RLL constraints). Instead, according to the invention a modulated bitstream having desired patterns at predetermined positions is obtained by inserting data words corresponding to the desired patterns in the succession of data words, before the modulation takes place.
The invention will now be explained in more detail with reference to the drawings in which:
While in the examples shown in
A method like this is used according to CD, DVD and also BD standards. The exact sequence and algorithm for ECC generation, shuffling and scrambling varies from standard to standard though, as well as the particular modulation employed.
Thus, the replacing 34 takes place between the encoding step 21 and the modulation step 26. The reason why the replacing 34 takes place before the modulation step 26 has already been explained above and is due to the fact that by doing so it is made sure that no patter is introduced in the modulated bitstream 29 which violates the encoding rules. However it is also advantageous that the replacing 34 takes place after the encoding step 21, for the following reasons:
Any valid patterns can be used in principle as desired patterns (also referred herein as dummy patterns, or patterns for being modified by the post-recording process), a valid pattern being a pattern which may result from the modulation of a data word. However, preferably, the dummy patterns must have the following property: there must be a modification mask such that the result of the logical operation OR between the dummy pattern and the modification mask is also a pattern corresponding to a valid channel word, where the modification mask extends over the pattern to be modified, the modification mask being represented by the value 1 in correspondence to a point to be modified and 0 elsewhere, the dummy pattern being represented by the value 1 in correspondence to a pit and 0 elsewhere. This reflects a modification of the dummy patterns which is effected by laser ablation, whereby pits remain pits and that lands are modified into pits.
It has to be said that due to the modulation used according to optical disc standards it is in general not known a priori with which polarity a given channel word appears in the modulated bitstream 29. Since with the known post-recording method it is only possible to convert ‘lands’ into ‘pits’, it follows that it is necessary to control the polarity of the generated modulated bitstream 29. This need for a control of the polarity in the modulation bitstream can be dispensed with in an embodiment of the method of the invention, according to which regardless of the polarity with which a channel word appears in the modulated bitstream, a modification is applied which modifies the dummy pattern into another pattern corresponding to a valid channel word. That is, the modification mask and the dummy pattern have the further property that the pattern obtainable as the result of the logical operation OR between the negative of the dummy pattern and the modification mask is also a pattern corresponding to a valid channel word. Obviously this restricts the possible choice of dummy patterns and modification masks. In this case it is correct to talk about dummy channel word.
The method according to the invention can be used in conjunction with EFM, EFM+ or 17PP. According to EFM and EFM+, the data words are individually converted into channel words. According to 17PP instead, the conversion of a data word into a channel word (and vice-versa), depend also on the previous and next data word (channel word) in the sequence of encoded data words 25 (sequence of channel words 27′). Therefore, when applying the invention in conjunction with 17PP, preferably the dummy patterns are chosen so as to have the characteristic that during demodulation the dummy patterns as well as the dummy patterns modified are converted into respective data words regardless of the content of the previous and following channel words.
The initial sequence of data words 30 may be for example the content information with appended a sub-sequence of words of irrelevant value, for example all zeroes or random, of an adequate size for storing the secondary information. Then, in the step of replacing 34 only the encoded subsequence is affected, i.e. the data words of irrelevant value are those words, in the encoded initial sequence of data words 31, that can be replaced in the step of replacing 34, without altering the content information.
The advantage of this approach is that it makes possible to provide the final sequence of data words 42 to a legacy apparatus where usual encoding step 21 and modulation step 26, and possibly mastering step, take place.
In this case the initial sequence of data words 30 may be of an adequate size for storing the secondary information and the content information, and may consist entirely of data words of irrelevant value. The content information may then be inserted in the merging step 40.
In a further alternative the initial sequence of data words 30 may be of an adequate size for storing the content information only, of data words of irrelevant value. The content information may then attached be inserted in the merging step 40.
Preferably, said predetermined positions do not interfere with the content information, for example by being located in the lead-in, at the beginning of one or more recording frames or ECC frames or after the frame sync of a recording frame (for instance in an application of the invention in a BD system), This makes it easy to detect and decode the post-recorded secondary information.
For the general understanding of the invention, in
Each of these data words is checked against its original value (value associated to the dummy pattern) or the value that may have the dummy pattern when modified by a post-recording process. By establishing if a dummy pattern has been modified or not the secondary information 119 is retrieved. No error correction is applied while retrieving the secondary information, however: if the error correction unit was not disabled, the error correction unit 116 would detect the modifications and correct them to the initial values, thus erasing the effect of the post-recording (if the error level does not exceed the capabilities of the ECC).
The advantage of having both the dummy patterns and the dummy patterns modified as valid patterns is that the demodulation unit 111 can be the same as in a legacy apparatus.
In the Figure it is shown as an example that a data word is checked first against the value 75h (dummy channel word), and if not it is then checked against the value 25h or 01h (dummy channel word modified, according to the polarity), thereby retrieving one bit of information, 0 for dummy channel word not modified or 1 for dummy channel word modified, or vice versa, whichever convention has been made in advance. Briefly summarized, it is essential for an apparatus for reproducing secondary information that it:
The invention can be summarized as follows. The present invention relates to a method and to an apparatus for manufacturing a record carrier having stored a content information in the form of a modulated bitstream obtained from the content information by encoding and modulating. The record carrier has a number of dummy patterns at predetermined locations, allowing for the post-recording of secondary information, like an individual code, whereby the secondary information is recorded by selectively modifying the dummy patterns. The method and apparatus according to the invention foresee that the modulated bitstream with dummy patterns at the predetermined positions id obtained by inserting data word corresponding to the dummy patterns in a sequence of data words before the modulation takes place, so as to make sure that the dummy patterns are compliant with the modulation employed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 04105641.7 | Nov 2004 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB05/53608 | 11/4/2005 | WO | 00 | 5/2/2007 |
