Abstract: Interframe compression of moving image data is achieved by a combination of vector coding and scalar coding of transform coefficient differences formed by the subtraction of previous image transform coefficients from corresponding present image transform coefficients along a Zig-Zag path in the arrays of coefficients. More efficient scalar codes are used instead of vector codes for transmission of coefficient data where the previous image coefficients are non-zero along the path. Vector codes are used where a non-zero value in the previous image transform array has not been established but a non-zero value coefficient occurs in the present image transform array. Vector coding efficiency is improved by modified run length coding.

Abstract: An integrated receiver decoder (IRD), commonly called a set-top box, has a global positioning system (GPS) receiver. The GPS receiver checks to see if the IRD is at an authorized location and allows descrambling of video signals only if the location is authorized. A central access control system, remote from the customers/viewers, has a high quality GPS receiver and sends some GPS data in the transmission medium used to send video signals to the customers. This GPS data, referred to herein as indirect GPS data, is used by the IRD such that it requires less complexity than otherwise. The IRD introduces a pseudo-random time delay in generating certain signals such that spoofing (i.e., providing phony signals to the IRD) is much more difficult. Various components of the IRD are in a common sealed container such as an integrated circuit or a smart card such that tampering with the components and spoofing are more difficult.

Abstract: A companding technique takes advantage of spatial masking in order to avoid problems from noise and/or distortion introduced when storing or transmitting video signals. A forward companding or encoding part of the technique divides a video frame into separate portions. A local average is calculated for each portion. For each pixel or picture element within a portion, the average of that portion is subtracted and the result is subjected to a non-linear forward process which emphasizes those video signals which are close to the local average and which de-emphasizes those video signal portions which are relatively different from the local average. An encoded output is applied to a medium and, upon recovery from the medium, the recovered signal is subjected to a decode process including a non-linear reconstruction process which is the inverse of the non-linear process applied at the encode stage.