A quantization parameter for use in encoding a region of an image is developed from a) a categorization of the region into one of a predetermined plurality of perceptual noise sensitivity (PNS) classes, b) a level of psycho-visual quality that can be achieved for the encoded version of the image, the level being selected from among a plurality of predetermined levels, and c) a prestored empirically derived model of the relationship between the PNS classes, the psycho-visual quality levels and the values of the quantization parameter. PNS indicates the amount of noise that would be tolerable to a viewer of the region, i.e., the perceptual sensitivity of the region to noise. Some characteristics on which PNS classes may be based are: spatial activity, speed of motion, brightness of the region, importance of the region in a particular context, the presence of edges within the region and the texture of the region, e.g., from "flat" to "highly textured". PNS classes that include combinations of the characteristics of a region of the image may also be defined. The PNS classes employed are selected by the implementor and may be determined empirically. The psycho-visual quality of an encoded image is the quality, as perceived by a viewer, of the version of the image that is reconstructed from the encoded image. It is determined from the complexity of the image and the bit-rate available to encode the image.

A vector coding scheme for video transform coefficients is provided. A vector is generated to identify a group of coefficients from a block of transform coefficients that qualify for transmission according to predetermined criteria. In an illustrated embodiment, only coefficients having nonzero amplitudes are transmitted. The vector is encoded to provide a vector code word for transmission. The coefficients from the group qualifying for transmission are encoded to provide coefficient code words for transmission. The vector code word correlates the coefficient code words to coefficient locations in the block. In a preferred embodiment, the block is divided into a plurality of regions containing subsets of coefficients. A separate vector is transmitted for each region, correlating the coefficient code words to coefficient locations in the corresponding region of the block.

Disclosed herein is a method of lossy decoding of bitstream data. The method comprises the steps of decoding the bitstream data having a plurality of symbols to provide an image stream having a plurality of image blocks, marking an image block with a first identifier having a spatial position associated with a location when an invalid symbol is encountered, discarding the bitstream data until a resynchronization code is decoded, marking the image block associated with the resynchronization code with a second identifier, decoding the image stream to provide a plurality of display frames having a plurality of display blocks, comparing the display blocks of a display frame for similarity between the display blocks of a previous display frame to determine display blocks having errors, and replacing the display blocks having errors with previous display blocks corresponding to a similar spatial position.

A digital video signal converting apparatus for converting a first digital video signal having a first resolution to a second digital video signal having a second resolution higher than the first resolution, comprises; block segmentation circuit for converting the first digital video signal into a block format, memory having a mapping table stored therein and having address terminals to which the first digital video signal in a block format is supplied and output terminals from which the second digital video signal in block format is output, and block separation circuit for converting the second digital video signal in a block format into a digital video signal in a raster scan order, wherein the mapping table in the memory is generated by training utilizing a plurality of images the training step being performed by generating first and second digital video signal corresponding to each of the plurality of images, converting each of the first and second digital video signals into a block format, and selecting the first digital video signal in a block format is an address signal for the mapping table and inputting the second digital video signal in a block format to a memory area corresponding to the address, and generating data of the mapping table from the signal stored in the memory area.