Cryptography – Video cryptography – Video electric signal modification
Reexamination Certificate
1996-12-18
2001-04-24
Buczinski, Stephen C. (Department: 3662)
Cryptography
Video cryptography
Video electric signal modification
C380S245000
Reexamination Certificate
active
06222926
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to display devices and in particular to scrambling and encrypting devices and methods which prevent a signal “in the clear” at the display device.
2. Description of Related Art
To avoid pirating of video, video is scrambled or encrypted by the provider to protect against unauthorized viewing. The term “scrambling” typically means the altering of an analog signal such that it cannot be displayed in a conventional sense without the proper descrambling operation. Examples of scrambling techniques include but are not limited to sync suppression, active line rotation, and line shuffling. The term “encryption” typically is used to describe the operation of altering a digital sequence usually by multiplying it by a pseudo-random sequence. In order to recover the original signal, a “key” is required. An example of this technique is the Data Encryption Standard (DES).
An example of a typical MPEG display system without encryption is shown in FIG.
1
. An example of a typical MPEG display system with encryption is shown in
FIG. 2
, where it should be noted that an encrypted sequence “BLCFADGIHEKJ” is created.
A video signal is often scrambled or encrypted so that without proper authorization, it is in an unusable form. However, if the consumer premises are granted authorization, then typically at interfaces which are accessible to the consumer, such as at the output of a cable converter box or the “video output” jacks of a receiver, the video signal is descrambled or decrypted and hence is “in the clear” (See FIG.
3
). There are many types of display devices available today. There is the generally well known cathode ray tube display devices (CRT), and discrete display devices such as digital light modulators or deformable mirror spatial light modulator (DMD), liquid crystal displays (LCD), and plasma displays. Each of these displays have the problems associated with an unauthorized user simply recording the video “in the clear” from the output of the cable converter box or the “video output” jacks of a television receiver. For ease of description reference will be had to the operation of a LCD.
A liquid crystal display device includes liquid crystal picture elements (“pixels”) arrayed in rows and columns. In an LCD display system, the discrete display device is illuminated on a “row” or line basis, due to the matrix addressing scheme typically employed. Hence, a particular row is illuminated and then another row is illuminated until an entire frame is created. For example, in a particular Philips LCD display device there are 480 columns by 480 rows worth of pixels. To load the 480 pixels required for a given row, column drivers are required. The 480 rows are then activated sequentially to create a picture (or a frame).
FIG.
4
(
a
) shows a schematic diagram of an LCD display device. Referring to FIG.
4
(
a
), the display device, which is intended to display video, for example television pictures, includes an active matrix liquid crystal color display panel
10
. The panel
10
comprises two spaced, transparent and insulating supporting plates, for example of glass, with twisted nematic liquid crystal disposed therebetween and has a large number of liquid crystal picture elements with associated switching elements and memory elements (e.g. capacitors) arranged in rows and columns which are addressed via first and second sets of crossing address conductors with each picture element being connected with a respective address conductor of each set. The first set comprises row address conductors extending in the row direction. Conductors of the second set extend generally in the column direction and hereinafter will be referred to as column address conductors. Each column address conductor is connected with a respective picture element in each row.
In known active matrix liquid crystal display devices, the row address conductors serve as scanning electrodes and are controlled by a row driver circuit
15
, comprising a shift register circuit, which applies a selection signal to each row conductor sequentially in turn during a respective row address period. In synchronism with the selection signals, achieved by means of the timing and control circuit
16
, data (video) signals, obtained by sampling a TV line with serial to parallel conversion, are applied to the column address conductors from a column driver circuit
17
connected to the output of a video processing circuit
18
to produce a required display effect from the rows of picture elements as they are scanned. Thus the video information for a single line is loaded into the column driver circuit
17
and depending on the row addressed by the row driver circuit
15
, this row is loaded with video information. The individual display effects of the picture elements, addressed one row at a time, combine to build up a complete picture in one field, the picture elements being addressed again in a subsequent field. This sequential loading of the array
10
provides a signal “in the clear” which is easily pirated.
SUMMARY OF THE INVENTION
It is an object of the invention to eliminate the signal “in the clear” in an LCD display device.
It is another object of the invention to eliminate the signal “in the clear” without requiring substantial modification of the LCD display device.
A further object of the invention is to eliminate the signal “in the clear” while minimizing temporal artifacts.
Achievement of these and other objects is based on the realization that to load the memory elements with pixel data it is not necessary to do so in a sequential order. Instead the memory elements are loaded in an encrypted sequence in accordance with an encryption “key”.
These objects are achieved in a first embodiment of the invention by encrypting the pixel data within a line or row of the display device and placing it in a register or other storage device of the column driver circuit and decrypting the pixel data by causing the register or other storage device to place decrypted data, decrypted in accordance with a decryption key, in the appropriate locations of the column driver circuit.
In a second embodiment of the invention, the row sequence or time order of the display of the rows is encrypted so that the row driver circuit must load the appropriate row in accordance with the decryption key.
In a third embodiment of the invention both the pixel sequence within a row and the row sequence are encrypted and both the row and column decoders load the LCD line by line in accordance with the encryption key.
In a fourth embodiment of the invention the encryption is performed to limit the temporal artifacts that occur due to varying the row sequence. This is achieved by partitioning each frame of video into a plurality of partitions. Each partition having the rows within the partition in an encrypted sequence but the time order of the display of the partitions is controlled.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.
REFERENCES:
patent: 5208857 (1993-05-01), Lebrat
patent: 5297201 (1994-03-01), Dunlavy
patent: 5321747 (1994-06-01), Lindholm
patent: 5321748 (1994-06-01), Zeidler et al.
patent: 5621799 (1997-04-01), Katta et al.
patent: 5636279 (1997-06-01), Katta et al.
Basile Carlo
Cavallerano Alan
Goldenberg Jill Forer
Buczinski Stephen C.
Gathman Laurie E.
Philips Electronics North America Corporation
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