1. Field of the Invention
The present invention relates to an optical disk, and more particularly to an optical disk which enables determination as to whether or not it is an optical disk which has been copied in an unauthorized manner.
2. Description of the Background Art
Conventionally, as a method for preventing unauthorized copying of optical disks, a method is commonly used which previously performs a specific process to an optical disk. Specifically, this method utilizes physical features which are formed on an optical disk through the specific process to determine whether it is an authorized optical disk or not. When an optical disk is copied in an unauthorized manner, only the usual data which is recorded on the optical disk will be copied, without performing the aforementioned specific process. Therefore, an optical disk which has been copied in an unauthorized manner lacks the physical features formed by the specific process. When accessing an optical disk, an optical disk drive checks for physical features to determine whether or not the specific process has been properly performed, thereby determining whether it is an optical disk produced in an authorized manner or an optical disk copied in an unauthorized manner. According to the above method, optical disks copied in an unauthorized manner can be prevented from being used.
For example, according to an invention described in Japanese Patent Laid-Open Publication No. 7-282472, a signal pit array is provided between specific tracks, such that the tracks located on the inner and outer periphery sides of the pit array define pitless areas free of pits. In accordance with an optical disk having such features, it is possible to determine whether or not it is an optical disk produced in an authorized manner, based on the presence or absence of randomly-read portions on the optical disk.
According to an invention described in Japanese Patent Laid-Open Publication No. 9-81938, displaced pits are formed in specific positions. In accordance with an optical disk having such features, it is possible to determine whether or not it is an optical disk produced in an authorized manner based on the presence or absence of displaced pits.
In addition to those described in the above two publications, various methods are conceivable as methods for determining authorized disks, e.g., a method utilizing the number, positions, or size of physical features obtained by performing a specific process for an optical disk, or a method utilizing the reflectance when physical features are irradiated with laser light. The determination as to whether an optical disk has been produced in an authorized manner or not is made based on whether the physical features satisfy a certain determination criterion. For example, in the case where determination is made by utilizing the number of displaced pits, the presence of a certain number or more of displaced pits would constitute a criterion for determining an authorized optical disk. In the case where determination is made by utilizing reflectance, the presence of a certain range of reflectance would constitute a criterion for determining an authorized optical disk.
The determination criterion for an authorized optical disk is decided so that any optical disk on which physical features are formed with a predetermined precision or above will be determined as an authorized optical disk. This is in order to ensure that an optical disk having no physical features formed thereon will be determined as optical disk copied in an unauthorized manner, and that an optical disk having physical features formed with a low precision will also be determined as an optical disk copied in an unauthorized manner. The reason is that an optical disk having physical features formed with a low precision can be easily produced, and therefore could also be produced in an unauthorized manner by imitating its physical features.
Moreover, a security level is decided depending on what degree of precision of the formed physical features will be permitted under the determination criterion. Specifically, the security level is lowered by setting a lenient determination criterion, i.e., by permitting optical disks having physical features formed with a low precision. On the other hand, the security level is increased by setting a severe determination criterion, i.e., by only permitting optical disks having physical features formed with a high precision.
Conventionally, the determination criterion for determining an optical disk produced in an authorized manner is previously set in a reproduction apparatus for optical disks. In other words, in order to change the determination criterion, the setting of the reproduction apparatus for optical disks must be changed. However, it is practically impossible to change the setting of the reproduction apparatus for optical disks owned by every user. Therefore, conventionally, the determination criterion for determining an optical disk produced in an authorized manner is fixed and cannot be changed.
In the actual production of optical disks, it may become necessary to change the security level. For example, consider the case where the security level is to be lowered. By lowering the security level, even optical disks having physical features formed with a low precision will be permitted as optical disks produced in an authorized manner. Setting a low security level results in an increased yield and improved productivity. Therefore, the security level may be set low in the case where productivity is regarded as important, e.g., when it is intended to reduce the production cost or produce large quantities over a short period of time. On the other hand, depending on the value of the contents, a high security level may be set in order to prevent unauthorized copying as much as possible. Furthermore, in the case where a currently-set security level can no longer prevent unauthorized copying, it will be necessary to increase the security level in order to cope with the unauthorized copying. Thus, it would be desirable to employ a changeable security level so as to allow a security level to be set in accordance with the purpose.
Conventionally, however, it is impossible to change the security level because the determination criterion cannot be changed. Therefore, once a security level is set, it cannot be changed later, so that it is impossible to set a security level depending on the purpose.
Therefore, an object of the present invention is to provide an optical disk which allows the security level against unauthorized copying to be easily changed.
The present invention has the following features to attain the object above.
A first aspect of the present invention is directed to an optical disk subject to determination by an optical disk reproduction apparatus as to whether it is an optical disk produced in an authorized manner or not, the optical disk comprising a feature forming area and a criterion recording area. The feature forming area has formed therein a physical feature to be used by the optical disk reproduction apparatus for determining whether it has been produced in an authorized manner or not. The criterion recording area has recorded therein a determination criterion by which it is determined as having been produced in an authorized manner if the physical feature is formed with a predetermined precision or above.
In accordance with the above configuration, a determination criterion is recorded on an optical disk for determining whether it has been produced in an authorized manner or not. The determination criterion can be changed by changing the information which is recorded on the optical disk. This can be easily done because there is no need to change the setting of the optical disk reproduction apparatus. Therefore, the security level against unauthorized copying can be easily changed by changing the determination criterion. As a result, the security level may be lowered for improved optical disk productivity, e.g., in the case where the optical disk productivity is regarded as important. The security level may be increased, e.g., in the case where prevention of unauthorized copying is regarded as important. Thus, the security level can be easily changed depending on the purpose.
The criterion recording area may be contained in an area where data is subsequently writable. In this case, the determination criterion recorded in the criterion recording area is decided based on the physical feature formed in the feature forming area.
In accordance with the above configuration, the determination criterion is decided based on the physical features formed on the very optical disk on which the determination criterion is recorded. Therefore, it is possible to decide a determination criterion for each single optical disk produced. As a result, a determination criterion which is appropriate for each optical disk can be recorded.
Moreover, a plurality of kinds of physical features may be formed in the feature forming area. In this case, the determination criterion is recorded in the criterion recording area with respect to each of the plurality of kinds of physical features.
In accordance with the above configuration, it is possible to make a determination by using a plurality of determination methods, so that not only the determination criterion but also the determination method can be changed. Therefore, if security is broken with respect to some of the plurality of determination methods, it is possible to switch to other methods. For example, consider the case where determination methods A and B are used. If the security provided by determination method A is broken through unauthorized copying, the determination method can be switched to determination method B to prevent unauthorized copying. Thus, in accordance with the above structure, when security is broken, the determination method can be switched to another method, so that a higher level of security can be provided than by changing the determination criterion.
A second aspect of the present invention is directed to an optical disk reproduction apparatus for reproducing data recorded on an optical disk, the optical disk reproduction apparatus comprising: a feature detection section (corresponding to step S403 in the embodiment), a criterion reading section (corresponding to step S401 in the embodiment), and a determination section (corresponding to step S407 in the embodiment). The feature detection section detects from an optical disk a physical feature used for determining whether it has been produced in an authorized manner or not. The criterion reading section reads from the optical disk a determination criterion by which it is determined as having been produced in an authorized manner if the physical feature is formed with a predetermined precision or above. The determination section determines whether the optical disk has been produced in an authorized manner or not, depending on whether the physical feature detected by the determining the feature detection section satisfies the determination criterion read by the criterion reading section or not.
In accordance with the above configuration, the determination criterion is recorded on the very optical disk which is subjected to determination, and is not set in the optical disk reproduction apparatus. Since a determination criterion is set for each optical disk, the optical disk reproduction apparatus can change the determination criterion for each optical disk. Therefore, the optical disk reproduction apparatus can easily change the security level against unauthorized copying by changing the determination criterion. As a result, the security level may be lowered for optical disks which are produced with priority attached to optical disk productivity, for example, whereas the security level may be increased for optical disk which are produced with priority attached to the prevention of unauthorized copying, for example. Thus, the security level can be easily changed depending on the optical disk.
Moreover, the optical disk reproduction apparatus may further comprise a reproduction section (corresponding to S409 in the embodiment). The reproduction section reproduces contents data recorded on an optical disk only if the optical disk is determined by the determination section to have been produced in an authorized manner.
In accordance with the above configuration, contents data are reproduced only the optical disk is confirmed to have been produced in an authorized manner. As a result, it is possible to prohibit the use of optical disks which are produced through unauthorized copying.
Moreover, the determination section may determine, even before all the physical features that are necessary for determination are detected by the feature detection section, an optical disk to have been produced in an authorized manner if the determination criterion is satisfied. In this case, if an optical disk is determined by the determination section to have been produced in an authorized manner, the reproduction section begins reproduction of the contents data even before all the physical features that are necessary for determination are detected by the feature detection section.
In accordance with the above configuration, the determination is completed, and the reproduction of the contents data is begun, as soon as the optical disk is determined to have been produced in an authorized manner, i.e., as soon as the determination criterion is satisfied. For example, in the case of a determination method which requires an area having physical features formed therein to be detected 10 times, the reproduction of the contents data is begun if the determination criterion is satisfied upon the seventh detection. Thus, the wait time required for determination before the execution of the contents can be reduced, thereby reducing the awkwardness felt by the user.
A third aspect of the present invention is directed to an optical disk recording apparatus for recording data on an optical disk, the optical disk recording apparatus comprising: a feature formation section, a determination criterion storing section (corresponding to a storage section 51 in the embodiment), and a criterion recording section (corresponding to a data recording section 52 in the embodiment). The feature formation section forms on the optical disk a physical feature to be used for determining whether it has been produced in an authorized manner or not. The determination criterion storing section previously stores a determination criterion by which it is determined as having been produced in an authorized manner if the physical feature is formed with a predetermined precision or above. The criterion recording section records the determination criterion stored in the determination criterion storing section on the optical disk.
In accordance with the above configuration, it is possible to produce an optical disk having recorded thereon a determination criterion as to whether the optical disk has been produced in an authorized manner or not. Since the determination criterion is recorded on the optical disk produced in this manner, it is possible to easily change the determination criterion for each optical disk. Therefore, through changing the determination criterion, it is possible to produce optical disks which allow the security level against unauthorized copying to be easily changed. As a result, the security level may be lowered in the case where optical disk productivity is regarded as important, and the security level may be increased in the case where prevention of unauthorized copying is regarded as important, for example. Thus, an optical disk which allows the security level to be easily changed depending on the purpose can be produced.
Moreover, the determination criterion stored in the determination criterion storing section may be decided based on the physical feature on the optical disk formed by the feature formation section. In this case, the criterion recording section records the determination criterion stored in the determination criterion storing section in a subsequently-writable area of the optical disk.
In accordance with the above configuration, the determination criterion recorded on the optical disk is decided based on the physical features formed on the very optical disk on which the determination criterion is recorded. Therefore, an optical disk recording apparatus sets a determination criterion for each optical disk. As a result, the optical disk recording apparatus can record a determination criterion which is appropriate for each optical disk.
The determination criterion stored in the determination criterion storing section may be decided based on the physical feature formed on a prefabricated optical disk specialized for inspection purposes.
In accordance with the above configuration, a determination criterion is decided by using a prefabricated optical disk specialized for inspection purposes. Therefore, a determination criterion will be decided based on the precision with which the physical features are actually formed. If a determination criterion is set independently of the precision with which the physical features are actually formed, it may be possible for the proportion of the produced optical disks which satisfy the determination criterion to significantly decrease due to a high determination criterion being set too high. In contrast, in accordance with the above configuration, a determination criterion can be decided in accordance with the performance of the production equipment. Therefore, any significant deterioration in the optical disk productivity due to an excessively high determination criterion can be prevented.
A fourth aspect of the present invention is directed to an authorized disk determination method for determining whether an optical disk to be reproduced has been produced in an authorized manner or not, the authorized disk determination method comprising a feature detection step (corresponding to step S403 in the embodiment), a criterion reading step (corresponding to step S401 in the embodiment), and a determination step (corresponding to step S407 in the embodiment). The optical disk has recorded thereon a physical feature used for determining whether it is an optical disk produced in an authorized manner or not, and a determination criterion by which it is determined as having been produced in an authorized manner if the physical feature is formed with a predetermined precision or above. The feature detection step detects the physical feature from the optical disk. The criterion reading step reads the determination criterion from the optical disk. The determination step determines whether the optical disk has been produced in an authorized manner or not based on whether the physical feature detected by the feature detection step satisfies the determination criterion read by the criterion reading step or not.
In accordance with the above configuration, the determination criterion is recorded on the very optical disk which is subjected to determination, and is not set in the optical disk reproduction apparatus. Since a determination criterion is set for each optical disk, the determination criterion can be changed for each optical disk in the determination of an authorized disk. Therefore, the security level against unauthorized copying can be easily changed by changing the determination criterion. As a result, the security level may be lowered for optical disks which are produced with priority attached to optical disk productivity, for example, whereas the security level may be increased for optical disk which are produced with priority attached to the prevention of unauthorized copying, for example. Thus, the security level can be easily changed depending on the optical disk.
A fifth aspect of the present invention is directed to a method for producing an optical disk such that the optical disk to be reproduced is capable of being determined as having been produced in an authorized manner or not by an optical disk reproduction apparatus, comprising: a feature formation step(corresponding to a feature formation section 53 in the embodiment), a criterion deciding step (corresponding to a storage section 51 in the embodiment), and a criterion recording step (corresponding to a data recording section 52 in the embodiment). The feature formation step forms on the optical disk a physical feature to be used for determining whether it has been produced in an authorized manner or not. The criterion deciding step decides, based on the physical feature, a determination criterion by which it is determined as having been produced in an authorized manner if the physical feature is formed with a predetermined precision or above. The criterion recording step records on the optical disk the determination criterion decided by the criterion deciding step.
In accordance with the above configuration, it is possible to produce an optical disk having recorded thereon a determination criterion as to whether the optical disk has been produced in an authorized manner or not. Since the determination criterion is recorded on the optical disk produced in this manner, it is possible to easily change the determination criterion for each optical disk. Therefore, through changing the determination criterion, it is possible to produce optical disks which allow the security level against unauthorized copying to be easily changed. As a result, the security level may be lowered in the case where optical disk productivity is regarded as important, and the security level may be increased in the case where prevention of unauthorized copying is regarded as important, for example. Thus, an optical disk which allows the security level to be easily changed depending on the purpose can be produced.
Moreover, the criterion deciding step may decide the determination criterion based on the physical feature formed by the feature formation step. In this case, the criterion recording step records the determination criterion decided by the criterion deciding step in a subsequently-writable area of the optical disk.
In accordance with the above configuration, the determination criterion recorded on the optical disk is decided based on the physical features formed on the very optical disk on which the determination criterion is recorded. Therefore, a determination criterion is set for each optical disk. As a result, a determination criterion which is appropriate for each optical disk can be recorded.
The criterion deciding step may decide the determination criterion based on the physical feature formed on a prefabricated optical disk specialized for inspection purposes.
In accordance with the above configuration, a determination criterion is decided by using a prefabricated optical disk specialized for inspection purposes. Therefore, a determination criterion will be decided based on the precision with which the physical features are actually formed. If a determination criterion is set independently of the precision with which the physical features are actually formed, it may be possible for the proportion of the produced optical disks which satisfy the determination criterion to significantly decrease due to a determination criterion which is set too high. In contrast, in accordance with the above configuration, a determination criterion can be decided in accordance with the performance of the production equipment. Therefore, significant deterioration in the optical disk productivity due to an excessively high determination criterion can be prevented.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.