An image sequence transmission method and apparatus transmit a sequence of successive images over a bandwidth limited channel. The transmitter has a motion estimator for estimating the motion displacement between successive image frames of the sequence. The motion estimator divides each image into nonoverlapping blocks, each block including a plurality of picture elements. The apparatus then successively selects, in accordance with a steepest descent estimation technique, an initial value of a motion vector displacement for each successive block. Thereafter, an iterative process determines using the steepest descent approach, successive values of the motion displacement vector for a block and the iteration process is terminated when an iteration error measure, which is associated with the steepest descent method, is less than a predetermined threshold value. In particular embodiments of the invention, an adaptive approach is used wherein the step size parameter is incremented in accordance with a gradient error used in the steepest descent technique. In addition, methods and apparatus for determining an initial motion vector field value based upon of the motion displacements in adjacent blocks advantageously determine the initial displacement vector for a block.
A transmission system for use in digital television has an input for receiving a signal to be encoded, a difference circuit (12) for supplying a differential signal formed by a given number of binary elements representing the difference between the signal to be encoded and a prediction signal, a transmission prediction circuit for supplying the prediction signal, a transmission transcoding circuit (15) for reducing the number of binary elements of the differential signal as a function of a control information, an activity measuring circuit (30) for supplying an activity information, a statistic encoding circuit (22) for variable word length coding of the output signal of the transcoding circuit, a buffer memory circuit (25) for storing the words of the statistic encoding circuit and for supplying them to the output of the system, and an occupation measuring circuit (45) for supplying an occupation information of the buffer memory circuit. This system furthermore includes a combination circuit (50) for supplying the control information in response to the activity information and the occupation information applied thereto.
A method and system for video motion compensation in which an overall interframe motion vector is divided into a relative block motion vector and a subblock motion vector. Image reconstruction is achieved by adjusting the delay between the synchronization pulse and the start of the pixel data according to the subblock motion vector, and accessing stored data from memory according to the relative block motion vector. Accessing memory in a block-quantized format ensures that page mode accesses are confined to the same memory row.
A motion estimator for high definition television transmission comprises a device which operates after motions have been estimated for an image (51), when the motions in a following image (53) are to be estimated. This device associates with a part (R) examined in an image (53) a group (5) of a plurality of parts of the preceding image (51) which group contains the part occupying, in the image, the same position as the examined part and likewise the adjacent parts, and investigates whether one of the nine motions determined for the nine parts of the said group (5) can be applied to the part R. If this is the case, the operation of the estimator is terminated for the part (R) examined and, moreover, the transmission of the motion for this part is then effected not by transmitting the value of the motion, but by designating that one of the parts of the group (5), the motion of which is appropriate.
A process for coding by transformation for the transmission of an image signal, comprises a stage of breaking down the image into blocks, each block containing a set of matrix-organized digital data and representing part of the picture, said process being characterized in that it comprises, for each block a step of detecting the movement of the block by comparing said block of the current image with the corresponding block of the preceding image, transmitting a non-refreshing code for the block and an identification code for the block in the image if the block is fixed, if a movement is detected in the block, breaking down the block into several subblocks, movement detection in each subblock by comparison with the corresponding subblock of the corresponding block of the preceding picture and transmission of a code which is a function of the movement of the subblock, if the block is moving.
Method for extracting a contrasting object in a digital image. The method estimates a threshold S.sub.1 for each picture element, corresponding to a background estimation threshold representing an image contrast. A local contrast function GR(i,j) is determined as a recursive gradient proportional to the difference between the average of a video signal on the line of each picture element, and a function of the averages of the estimated background contrasts and picture elements located on an identical line or a previous line. Using the local contrast function, an estimated background value for each element is determined by comparing the contrast function to the threshold. The difference is taken between the video signal and the estimated background. The result of this difference is compared to a second decision threshold to determine whether or not the picture element belongs to the contrasting object.
