Using a modulation transfer function of a device to create digital content for the device

A modified modulation transfer function of a device is determined. The modified modulation transfer function includes intentional deviations from a nominal modulation transfer function of the device. A digital content object is modified based on the modified modulated transfer function to optimize playback of the digital content object on the device, and the modified digital content object is distributed to the device.

BACKGROUND

Digital Rights Management (DRM) is a great concern for digital content owners, such as owners of songs, movies, electronic books, documents and other types of digital media. Content owners try to sell and/or distribute their content in such a way to prevent the illegal copying of their content. For example, content, such as movies are widely sold and distributed on digital video discs (DVDs). To prevent illegal copying, DVDs typically include copy protection mechanisms that prevent users from making copies.

It has currently become very convenient and popular to purchase and download digital content, such as purchasing and downloading songs or other types of digital content via the Internet. In practice, most online content delivery stores also use some form of DRM technology to protect against unauthorized copying.

Typically, the DRM protection downloaded content or content distributed via DVD or CD includes controlling the copying of the bits contained in the digital content. For example, hardware or software in devices operable to play the digital content, such as portable media players, DVD players, compact disc (CD) players, personal computers (PCs), etc., may include built-in protections that do not allow the device to play the digital content or copy the digital content unless playing or copying is authorized, for example, by purchasing the content. However, because of these protections, the device may prevent playing or copying of some content that would not be a violation of an owner's rights, such as playing or copying home-made movies or other home-made content. Furthermore, even though the distributed content includes copy protection mechanisms, just as many mechanisms exist that can make unauthorized copies of the copy-protected content.

DETAILED DESCRIPTION

For simplicity and illustrative purposes, the principles of the embodiments are described. However, one of ordinary skill in the art would readily recognize that the same principles are equally applicable to, and can be implemented using variations of the described embodiments.

According to an embodiment, a modulation transfer function (MTF) of a device operable to play digital content is modified from a nominal MTF. Digital content may include audio, video, still images, text, or other types of media, or any combination of different types of content, such as multimedia content. An MTF for a device is a measure of the transfer of modulation (or contrast) from the digital content to the playback of the digital content on the device. In other words, the MTF measures how faithfully the digital content is reproduced on the device during playback.

Each class of device typically has a nominal MTF. For example, speakers and headsets for devices operable to play content are designed to play each frequency at a predetermined output. One example of audio frequency vs output in a nominal MTF may be that the frequencies representing a music note of low-C have an output of 7 decibels (dB) on every device given a tolerance. In another example, displays have a nominal MTF for visual frequencies. The nominal MTF may be predetermined for each class of device or output type, such as speakers or display, for a device so digital content played on different devices sounds similar.

According to an embodiment, the MTF for each device is modified so the output of the same digital content played on each device is different. That is each device has a modified MTF, which is an MTF modified from a nominal MTF. For example, a modified MTF for a device causes certain audible frequencies to be louder or softer than nominal. For example, one device has a modified MTF playing a low-C at 3 dB and another device plays a low-C at 10 dB. In another example, the modified MTF causes certain visible frequencies of an image to be brighter or dimmer than nominal.

The deviations from nominal are intentional deviations, and may be used to create digital content optimized for each device to prevent unauthorized use of the digital content on other devices. Digital content to be played on a device with a modified MTF is also modified based on the modified MTF. For example, a modified version of the digital content is created from an original, unmodified version of the digital content. The modified version of the digital content is optimized for playback on the device with the modified MTF. For example, if the modified MTF causes a certain audible frequency to be louder, then that audible frequency in the digital content is modified to play softer. In another example, if modified MTF causes a certain visible frequency of an image to be brighter, then that visible frequency in the digital content is modified to be dimmer. If a device with an MTF different than the modified MTF plays the version of the digital content, the quality of the playback of the digital content is degraded. For example, a song is downloaded for a first user's device, and the song is modified for optimal playback based on the modified MTF of the first user's device. If the user makes an unauthorized copy for playback on a second user's device, the fidelity of the song played on the second user's device will be degraded because the second user's device has a different MTF than the first user's device. Assuming every device has a different modified MTF, then any copy made for playback on another device would be degraded during playback. The quality degradation may be such that playback would be unsatisfactory for a user.

This approach to protecting digital content sidesteps the difficult problem of trying to generate a bit-copying protection scheme, through encryption or other form of DRM protection, which cannot be cracked. Furthermore, creating a modified version of the digital content optimized for playback on a device with a certain modified MTF creates a version of the digital content with a particular signature. That is, the modified version of the digital content is varied based on a particular modified MTF. The modified version of the digital content may be associated with the device having the modified MTF, for example, using a database or other tracking technique. Then, if an unauthorized copy of the modified digital content is found, the unauthorized copy can be associated with the device having the modified MTF. This may be used to identify a user or device making unauthorized copies.

FIG. 1illustrates a system100, according to an embodiment, operable to distribute a modified version of digital content to a device. The system100includes a content provider120, devices110a-nand a trusted third party130that may communicate with each other via a network140.

The content provider120includes a data storage121storing digital content objects. A digital content object is a unit of digital content, which may include a file or some other data structure for storing digital content. The data storage121may also store MTFs for each of the devices110a-n.

The content provider120includes a transformation module122and an MTF receiving module123. A module may include software, hardware or a combination of hardware and software. The transformation module122creates a modified digital content object for a device using a modified MTF for the device. For example, the device110arequests a digital content object151from the content provider120. The content provider120receives a modified MTF150for the device110a. Each of the devices110a-nhas a different modified MTF. The modified MTF150for the device110amay be transmitted from the device110aor the third party130and is received by the MTF receiving module123at the content provider120, which is described in further detail below.

The transformation module122uses the digital content object151and the modified MTF150as inputs to create the modified digital content object152. The digital content object151may be stored in the data storage121and retrieved by the transformation module122or another module in the content provider120in response to the received request from the device110a. The data object151is the original, unmodified digital content object, which may be provided from the content owner. For example, if the digital content object151is a song, the digital content object151may be the digital reproduction of the song generated by the producer of the song, and the content provider120may be an online music store selling the song. The digital content object151may be optimized for playback on a device with a nominal MTF.

The transformation module122creates a modified digital content object152from the digital content object151and the modified MTF150for the device110a. The modified digital content object152is distributed to the device110a, for example, via the network140.

The modified digital content object152is a modified version of the digital content object151. Like the digital content object151, the modified digital content object152is bits representing the content. However, the modified digital content object152is optimized for playback on a device with the modified MTF, such as the device110a.

FIG. 2shows an example of modifying a digital content object, according to an embodiment. The modifying of the digital content object may be performed by the transformation module122shown inFIG. 1.FIG. 2shows a graph200of a nominal MTF210and a modified MTF220for a device. The graph200includes an x-axis representing frequency and a y-axis representing output. The MTF210and the modified MTF220, in this example, substantially overlap because the MTFs210and220are substantially the same except where intentional deviations from the nominal MTF210were introduced to create the modified MTF220. For example, at section201, the output of frequencies for the modified MTF220is higher than nominal. At sections202and203, the output of frequencies for the modified MTF220is lower than nominal. The difference between the two curves representing MTF210and the modified MTF220are the modifications that are applied to the digital content to create modified digital content that is optimized for the device having the modified MTF220.

In one example, the graph200represents the modified MTF150for a speaker of the device110a, and the x-axis represents audio frequencies in a digital content object, such as a song or a video, and the y-axis represents output of the audio frequency in decibels. If section201represents frequencies around the music note A, then the modified MTF150indicates that note A plays louder than nominal on the device110a. If sections202and203represent frequencies around the music notes B and C respectively, then the modified MTF150indicates that notes B and C play softer than nominal on the device110a.

In another example, the graph200represents the modified MTF150for a display of the device110a, and the x-axis represents visual frequencies in a digital content object, such as a still image, and the x-axis represents output of the video frequency, such as luminance or brightness of colors of pixels represented by the frequencies. If section201represents frequencies around the color red, then the modified MTF150indicates that shades of red are brighter in an image displayed on the device110a. If sections202and203represent frequencies around the colors green and blue respectively, then the modified MTF150indicates that shades of green and blue are dimmer in an image displayed on the device110a.

The transformation module122shown inFIG. 1is operable to transform digital content to match the modified MTF. For example, if the digital content object151is a song and the graph200represents the modified MTF150for a speaker of the device110awhere output around notes A-C are modified, the digital content object151is modified so frequencies around the music note A play softer to compensate for the deviations shown inFIG. 2at section201. Also, the digital content object151is modified so frequencies around the music notes B and C play louder to compensate for the deviations shown inFIG. 2at sections202and203.

In the other example, where the graph200represents the modified MTF150for a display of the device110a, the transformation module122modifies the digital content object151so shades of red are dimmer to compensate for the deviations shown inFIG. 2at section201. Also, the digital content object151is modified so shades of green and blue are brighter to compensate for the deviations shown inFIG. 2at sections202and203.

In one embodiment, the transformation module122modifies the digital content object151to match the modified MTF150of the device110ato create the modified digital content152using well known digital signal processing techniques. For example, Fourier transform may be used to convert the digital content object151to the frequency domain, and the output of certain frequencies are modified to match the modified MTF150. For video, the frequencies of each frame may be modified as needed.

After creating the modified digital content152, the content provider120distributes the modified digital content152to the device110a. The modified digital content152may be downloaded from the content provider120via the Internet or other network, represented by the network140. The modified digital content152may be distributed on a physical medium, such as a DVD or CD or otherwise provided to the device110a.

The system100inFIG. 1shows multiple devices110a-n. Each of the devices110a-nhas a different modified MTF. The deviations from a nominal MTF for each device may be randomly selected or selected using other techniques such that each of the devices110a-nhas a different modified MTF. Thus, a modified digital content object for one device will not play satisfactorily on another device. Although not shown, the system100may include multiple content providers and trusted third parties.

As described above, the content provider120may include an MTF receiving module123for receiving a modified MTF for a device. According to an embodiment, the modified MTF for each of the devices110a-nis protected from unauthorized access. If an unauthorized user obtains the modified MTF150for the device110aand the modified digital content object152for the device110a, the unauthorized user may be able to convert the modified digital content object152back to the digital content object150so the digital content object150may be played on any device with a nominal MTF. Thus, the modified MTF for each of the devices110a-nis protected from unauthorized access.

In one embodiment, the modified MTF150is securely transmitted from the device110aor the trusted third party130to the content provider120using encryption. For example, the device110aencrypts the modified MTF150with a public key of the content provider120, and the MTF receiving module123at the content provider120decrypts the modified MTF150with a corresponding private key of the content provider120and may store the modified MTF150in the data storage121. Instead of using the public key of the content provider120, the device110amay encrypt the modified MTF150with the public key of the trusted third party130, such as the device manufacturer, and sends the encrypted modified MTF150to the trusted third party130. The trusted third party130sends the decrypted modified MTF150to the content provider120and the content provider120.

In another embodiment, it may not be necessary to transfer a device's modified MTF to the content provider120if the modified MTF and the rendering software can be protected from the device owner, such as with a trusted platform module (TPM) in the device. A TPM is tamper resistant hardware that has some software. A TPM may have a processor or processing circuitry and a limited amount of volatile and nonvolatile memory. The TPM may be a chip in the device that is separate from other hardware in the device. The TPM may store keys and have the ability to perform cryptographic operations, such as creating and deleting encryption keys and encryption/decryption, and create and sign digital certificates. Standards and specifications for TPMs may be provided by the Trusted Computing Group (TCG) organization. A TPM is one type of trusted hardware that may be used in this embodiment. It will be apparent to one of ordinary skill in the art that other types of trusted hardware may instead be used. Trusted hardware may include hardware that is tamper resistant and that can be authenticated.

In this embodiment, the transformation module122may be provided in a TPM in a device, such as the device110a. The TPM receives the digital content object151and converts it to the modified digital content object152. The modified digital content object151is then stored outside the TPM or otherwise made available to a media player outside the TPM. The digital content object151may be encrypted prior to sending the digital content object151to the device110a, and the TPM is operable to decrypt the digital content object151. The TPM is shown inFIG. 6illustrating a block diagram of a device, according to an embodiment.

Users may have their own digital content, such as home movies, digital pictures, audio recordings, etc., that they wish to play on a device with a modified MTF. To playback personal digital content without giving the user access to the modified MTF, the personal digital content may be converted in the TPM to modified personal digital content matching the modified MTF. Alternatively, the user may send the personal digital content to a trusted party, such as the device manufacturer, for conversion to the modified personal digital content.

FIG. 3illustrates a flow chart of a method of using an MTF of a device to create a modified digital content object for distribution to the device, according to an embodiment. The method300is described with respect toFIGS. 1 and 2by way of example and not limitation.

At step301, a modified MTF for a device is determined. This may include receiving the modified MTF and/or retrieving the modified MTF from storage. For example, the modified MTF150for the device110ashown inFIG. 1is received at the content provider120. The modified MTF150may be encrypted with a cryptographic key for securely sending the modified MTF150to the content provider120to prevent unauthorized access to the modified MTF150. In another embodiment, the device110astores the modified MTF150in a TPM or other trusted hardware in the device110aand the modified MTF150may be retrieved for creating the modified digital content object152at the device110a.

The modified modulation transfer function includes intentional deviations from a nominal modulation transfer function for the device. For example, as described with respect toFIG. 2, X's in sections201-203in the graph200represent intentional deviations from a nominal modulation transfer function.

The modified MTF may be determined at step301in response to receiving a request for a digital content object and payment for the digital content object. For example, a user of the device110amay purchase a song or other digital content from the content provider120. Once payment is received and a determination is made that the payment is received, the content provider120creates the modified digital content object152for distribution to the device110a, for example, via the Internet.

At step302, a digital content object is modified based on the modified MTF for the device. For example, the modified digital content object152is created from the digital content object151using the modified MTF150for the device110a. The modified digital content object152is optimized for playback on the device110abecause the modified digital content object152is created using the modified MTF150of the device110a.

At step303, the modified digital content object is distributed to the device. For example, the modified digital content object152is distributed via a network or using a physical medium, such as a CD or DVD, to the device110a. In another example, where the modified digital content object152is created in a TPM in the device, distributing may include providing the modified digital content object to a media player outside the TPM.

FIG. 4illustrates a flow chart of a method400, according to an embodiment. The method400may be described with respect toFIGS. 1 and 2by way of example and not limitation.

At step401, a modified MTF for a device is stored. For example, the content provider120shown inFIG. 1stores the modified MTF150for the device110ain the data storage121.

At step402, a copy of the modified digital content object is received. For example, the content provider120receives a copy of the modified digital content object152. This may include a copy of the modified digital content object152made by the device110a.

At step403, a modified MTF is determined from the copy of the modified digital content object and an original version of the digital content object. For example, the transformation module122shown inFIG. 1may determine the modified MTF for the copy using the copy of the modified digital content object152and the original digital content object151.

At step404, a device is associated with the copy of the modified digital content object based on the determined modified MTF for the copy. For example, the data storage121may include a database storing an identification or representation of each of the stored modified MTFs and an identification of the corresponding device of the devices110a-nfor each stored modified MTF. The modified MTF determined at step403is compared to the stored modified MTFs. If a match is found, an identification for the corresponding device is retrieved from the database.

The method400may be used to identify a device creating unauthorized copies of a digital content object. For example, the device110ais making unauthorized copies of the modified content object152. If an unauthorized copy is received at the content provider120, its modified MTF150is determined from the copy. Then, a database lookup or a table lookup may be performed to match the modified MTF150with the device110a.

FIG. 5illustrates a block diagram of a computer system500, according to an embodiment. The computer system500shown may be used as a platform for the content provider120or any of the devices110a-n. The computer system500includes one or more processors, such as processor802, providing an execution platform for executing software. Instead of a processor, other circuits may be used to perform the functions described herein, such as an ASIC or other circuits designed to perform the functions. Commands and data from the processor502are communicated over a communication bus504. The computer system500also includes a main memory506, such as a random access memory (RAM), where software may be resident during runtime, and a secondary memory508. The secondary memory508includes, for example, a hard disk drive, removable storage, or other type of storage device. Other examples of the secondary memory508include ROM (read only memory), EPROM (erasable, programmable ROM), EEPROM (electrically erasable, programmable ROM).

The computer system500may include user interfaces comprising one or more input/output (I/O) devices512, such as a keyboard, a mouse, a stylus, display, speakers, and the like. A network interface510may be provided for communicating with other computer systems.

If the computer system500represents a device, such as one of the devices110a-nshown inFIG. 1, then modified MTF for the device may be representative of the output of speakers or a display, shown as I/O devices812, for the device. Software stored and executed on the device may include a media player for playing digital content, such as songs, video, images, etc.

If the computer system500represents the content provider120shown inFIG. 1, the computer system500may include components of a server. Also, the content provider120executes software including the modules shown inFIG. 1.

FIG. 6illustrates a block diagram of a device600with a TPM, according to an embodiment. The device600may be one of the devices110a-nshown inFIG. 1. The device600includes many of the components shown and described above with respect toFIG. 5. In addition, the device600includes a TPM614. The TPM614may include processor circuitry615and a memory816.

In this embodiment, the transformation module122and the modified MTF150may be stored in the TPM614to prevent unauthorized access to the transformation module122and the modified MTF150. For example, the TPM614receives the digital content object151and converts it to the modified digital content object152. The modified digital content object151is then stored outside the TPM, such as in the main memory606and/or the secondary memory608, and made available to a software media player outside the TPM614, which may also be stored in the main memory606and/or the secondary memory608and executed by the processor602.

It will be apparent to one of ordinary skill in the art thatFIGS. 5 and 6illustrate generic computer systems. One or more components shown inFIGS. 5 and 6may or may not be used. The computer systems shown inFIGS. 5 and 6may include more or less features depending on the complexity of the system needed.

One or more of the steps of the methods300and400and other steps described herein may be implemented as software embedded or stored on a computer readable medium. For example, one or more of the steps may be software stored in the memories shown inFIG. 5or6. The software may be executed by a processor or processor circuitry, also shown inFIG. 5or6. The steps may be embodied by a computer program, which may exist in a variety of forms both active and inactive. For example, there may exist as software program(s) comprised of program instructions in source code, object code, executable code or other formats for performing some of the steps when executed, for example, by a processor. Any of the above may be stored on a computer readable medium, which include storage devices, in compressed or uncompressed form. Examples of suitable computer readable storage devices include conventional computer system RAM (random access memory), ROM (read only memory), EPROM (erasable, programmable ROM), EEPROM (electrically erasable, programmable ROM), and magnetic or optical disks or tapes. Concrete examples of the foregoing include distribution of the programs or content on a CD ROM or via Internet download. It is therefore to be understood that those functions enumerated herein may be performed by any electronic device capable of executing the above-described functions.