GB2249689A

GB2249689A - Encryption of film

Info

Publication number: GB2249689A
Application number: GB9024126A
Authority: GB
Inventors: Terrence William Mead
Original assignee: Rank Cintel Ltd
Current assignee: Rank Cintel Ltd
Priority date: 1990-11-06
Filing date: 1990-11-06
Publication date: 1992-05-13
Anticipated expiration: 2010-11-06
Also published as: GB9024126D0; GB2249689B

Abstract

Photographic or cinematographic film is exposed in a film writer under the control of a video signal. Pixels of image data are exposed in a pseudo-random manner either by writing the film in a pseudo-random sequence in which case a pseudo-random sequence is applied to the scan control of the film writer or by applying the pseudo-random sequence to the pixels of the video signal using a frame store and writing with a conventional scan. A telecine programmed with the encryption key is used to decrypt the film either by programming the scan control or by using a frame store. <IMAGE>

Description

ENCRYPTION OF FILM This invention relates to methods and apparatus for encrypting picture information such as video signals on film, in particular by means of a flying spot scanner such as a telecine and a film writer.

With the advent of DBS (Direct Broadcasting by Satellite) considerable effort was directed towards encrypting video signals to prevent viewing by unauthorised parties. An example of this is pay-TV which is transmitted in an encryted form. The user requires a decoder and smart card to descramble the signal to be able to view the transmitted programme.

One example of video signal encryption is rotation scrambling in which the luminance and chrominance components of a MAC type signal are cut and rearranged. The cut point varies according to an algorithm which is available to the decoder to restore the scrambling signal. This technique is described more fully in BBC research report RD 1985/12.

The present invention aims to encrypt film and in its broadest form provides apparatus which writes encrypted film from decrypted or encrypted video signal. More specifically the invention provides apparatus for producing encrypted cinematographic or photographic film from a video signal comprising a film writer having a flying spot scanner for scanning unexposed film and means for modulating the scanning spot with the video signal to be modulated, and means for causing the pixels constituting images represented by the video signal tcr' to be exposed onto the film in a predetermined pseudo-random sequence.

The invention also provides a method of producing encrypted cinematographic or photographic film from a video signal comprising scanning unexposed film with a film writer, the film writer having a flying spot scanner to scan the film and means for modulating the flying spot with the video signal to be written onto the unexposed film, and causing the pixels constituting images represented by the video signal to be exposed onto the film in a predetermined pseudo-random sequence.

An embodiment to the invention will now be described with reference to the accompanying drawing which shows, in schematic form, the basic elements of a digital flying spot telecine.

The telecine illustrated is well known and a detailed description of the various elements will not be given. Briefly, exposed film 10 is scanned by an electron beam produced by cathode ray tube (CRT) 12. The scan is driven by linear amplifier 14 which, in turn, is controlled by digital scan control 16. The scan control supplies a stream of X and Y co-ordinates from look-up tables which control the position of the electron beam. The scan is usually a left to right scan with flyback but the scan control may be programmed to generate a variety of scan effects. The scan addresses from the scan control are also fed to an 8 Mbyte shading memory 18 which applies a variety of corrections to the signals obtained from the scanning of the film on a pixel by pixel basis.

Light transmitted through the film on scanning is split into its R, G and B components each of which is amplified in a respective photomultiplier 20. After pre-amplification and A to D conversion, at 22, the colour components are passed as 14 bit digital signals to the shading memory as described. After shading connections have been applied the signals are processed in the video channel 24 at which time colour processing occurs.

This includes colour masking, gamma correction and light gain control. The output is a 10 bit signal which is then secondary colour corrected at 26. The secondary corrector forms a matrix of the R, G and B signals into 6 colour separation signals, red, yellow, green, cyan, blue and magenta which are then processed to give corrected R, G and B signals. The colour matrix then converts these R, G and B signals to digital Y, (R-Y) and (B-Y) signals are used by the frame store 28. The final stage is a D to A convertor which provides signals suitable for use with analog display and transmission systems.

Returning now to the digital scan control 16, this may be used to provide an encrypted video signal by programming the control with a pseudo-random scanning sequence. This would result in a video signal which, if played back in a normal manner would be unintelligible. The signal could only be decrypted in a decoder if a digital frame store was either supplied with the encryption key to reorder data as it is written into the store, or to reorder data as it is read from the store. Two frames of storage are needed so that one frame can be read out while the other is being written in with the next frame.

Alternatively, a separate frame store may be provided for the encryption process. The film is scanned using the conventional scanning pattern and the output loaded into a frame store under control of the encryption key. The data is then read out of the frame store sequentially producing an encrypted signal. Again, the frame store must be two frames in capacity and the decoder will have to be the same size and provided with the encryption key.

Both the methods described encrypt a digital video signal by encoding the order in which picture locations are read. In one method the order in which the locations are scanned is controlled and in the other method the order in which the information is stored after scanning is controlled.

The techniques described can be used to produce encrypted film if applied to a film writer. It has been proposed in our corresponding patent application GB 8928991 to produce a flying spot non-real time film writer. The contents of that application is incorporated herein by reference. The film writer is similar to the telecine shown in the figure but instead of reading exposed film the flying spot writes onto unexposed film under the control of the video signal.

To write encrypted film, either the video signal which modulates the flying spot or the scan control must be encrypted.

Alternatively a different encryption key could be applied to each. The scan control is encrypted in the manner described previously and the video signal is encrypted using a frame store as discussed. No store would be needed if the video signal was supplied in an encrypted form.

Because the scanning sequence is pseudo-random, the flying spot may be required to move from one side of the CRT to the other in one pixel period. Existing scanning circuits are not able to move the spot this quickly and it is necessary to slow down operation of the apparatus to perhaps 1/100th real time scanning speed.

The exposed, encrypted film, which may be either single images or moving sequences, can be decoded by the telecine of the figure. That is, the film can either be scanned under the control of the digital scan control supplied with the encrytion key or it can be scanned normally and the pixels reordered in the frame store. The latter possibility is preferable in terms of speed as the scanning could be performed in real time.

Film encoded according to the invention has the advantage of security and may be used for military and other purposes.

Film represented as an encoded video signal has the advantage that films can be distributed electronically without the possibility of hacking.

Although using frames stores has the advantage of real-time operation, it would require special design of the frame store to give truly random access at video speeds.

Claims

1. Apparatus for producing encrypted cinematographic or photographic film from a video signal, comprising a film writer having a flying spot scanner for scanning unexposed film and means for modulating the scanning spot with the video signal to be modulated, and means for causing the pixels constituting images represented by the video signal to be exposed onto the film in a predetermined pseudo-random sequence.

2. Apparatus according to Claim 1, wherein the means for causing pseudo-random pixel exposure comprises a digital scan control for controlling the flying spot scan, the scan control being programmed to cause the flying spot to scan the film in the said predetermined pseudo-random sequence.

3. Apparatus according to Claim 1, wherein the means for causing pseudo-random pixel exposure comprises means for encrypting the video signal modulating the flying spot with the pseudo-random sequence.

4. A method of producing encrypted cinematographic or photographic film from a video signal comprising scanning unexposed film with a film writer, the film writer having a flying spot scanner to scan the film and means for modulating the scan with the video signal to be written onto the unexposed film, and causing the pixels constituting images represented by the video signal to be exposed onto the film in a predetermined pseudo-random sequence.

5. A method according to Claim 4, wherein the step of causing pseudo-random pixel exposure comprises controlling the flying spot scan with a digital scan controller and programming the controller to produce scan co-ordinates for the flying spot in the pseudo-random sequence.

6. A method according to Claim 4, wherein the step of causing pseudo-random pixel exposure comprises encrypting the video signal modulating the flying spot with the pseudo-random sequence.

7. Apparatus for converting encrypted cinematographic or photographic film into decrypted video signals comprising a telecine having means for scanning the encrypted film and means for re-ordering the pixels of the scanned images to be scanned in accordance with the encryption key with which the film was encrypted.

8. Apparatus for decrypting cinematographic or photographic film encrypted according to the method of any of Claims 1 to 3, comprising a telecine for scanning the film and decrypting means supplied with the encryption key by which the film was encrypted for rearranging the image data into a decrypted format.

9. Apparatus according to Claim 8, wherein the decrypting means comprising the telecine scan control programmed to scan the film in the pseudo-random sequence in which it was exposed.

10. Apparatus according to Claim 8, wherein the decrypting means comprises a frame store which writes into or reads out video data from the telecine scanner in the pseudo-random sequence in which the film was exposed.

11. A method of decrypting cinematographic or photographic film encrypted according to the method of any of claims 1 to 3, comprising scanning encrypted film with the scanning means of a telecine, and decrypting the image data by rearranging the data under control of the encryption key under which the film was encrypted.

12. A method according to claim 11, comprising programming the telecine scan control to scan the film in the pseudo-random sequence in which it was exposed.

13. A method according to claim 11, comprising writing video data into, or reading video data from a frame store in the pseudo-random sequence in which the film was exposed.

14. Apparatus for producing encrypted cinematographic or photographic film from a video signal, substantially as herein described with reference to the accompanying drawing.

15. A method of producing encrypted cinematographic or photographic film from a video signal, substantially as herein described with reference to the accompanying drawing.

16. Apparatus for decrypting encrypted cinematographic or photographic film substantially as herein described with reference to the accompanying drawing.

17. A method of decrypting encrypted cinematographic or photographic film substantially as herein described with reference to the accompanying drawing.