Differential PCM video transmission system employing horizontally offset five pixel groups and delta signals having plural non-linear encoding functions

A method for compressing digital data in the form of time-sequential television pixels representing successive raster lines, each pixel including N bits comprising the recurrent steps of:

• organizing said pixels into recurrent groups of first, second, third, fourth and fifth time-sequential pixels, each group of pixels of a given raster line being offset horizontally by two pixel positions with respect to a group of pixels of a preceding line
• transmitting each second pixel of each group with a resolution of N-bits;
• comparing said first and third pixels with said second pixel located therebetween for each said group to produce first and second M-bit delta signals representing the difference between said second pixel and said first and third pixels, respectively;
• where M is a number of bits less than N;
• transmitting each said M-bit first delta signal of a given group before transmitting said second pixel of said given group;
• transmitting each said M-bit second delta signal of said given group after transmitting said second pixel of said given group;
• comparing said fourth pixel of said given group with said second pixel having a corresponding horizontal position on one of the next upper and next lower horizontal lines to produce an M-bit third delta signal representing the difference between said fourth and second vertically adjacent pixels;
• transmitting said third delta signal immediately after said second delta signal of said given group;
• comparing said fifth pixel of said given group with said second pixel having a corresponding horizontal position on the other of said next upper and next lower horizontal lines to produce an M-bit fourth delta signal representing the difference between said fifth and second vertically adjacent pixels;
• and
• transmitting said fourth delta signal immediately after said third delta signal of said given group.

A method for compressing digital picture information, comprising:

• transmitting a first pixel-representative word at full bit depth;
• comparing a second pixel-representative word with said first pixel-representative word to form a difference word representative of the amplitude difference between said first and second words;
• encoding said difference word to form a delta word having less than said full bit depth, said encoding comprising subjecting said difference word to a plurality of non-linear encoding transfer functions, each said transfer function having a first region representing small amplitude increments when said amplitude difference represented by said difference word is small and having at least one second region representing large amplitude differences when said amplitude difference represented by said difference signal is large and
• selecting a given one of said transfer functions for encoding said difference word as a function of the amplitude of said first pixel-representative word to thereby provide an encoded delta word having greater accuracy for small differences over a range of values of said amplitude of said first pixel representative word.

A method for transmitting N-bit digital television representative signals through a transmission path, comprising:

• organizing said digital signals into recurrent groups of five time-adjacent samples representative of horizontally-adjacent pixels on each one of a plurality of lines of said television representative signal;
• offsetting each group of samples by two pixel positions from line-to-line;
• comparing first and second samples of a group of a first one of said lines with a second sample of said group to form first and second difference signals, respectively;
• comparing a fourth sample of said group with the second sample of a group on a second horizontal line adjacent said first horizontal line to form a third difference signal;
• comparing a fifth sample of said group with the second sample of a group on a third horizontal line adjacent said first horizontal line to produce a fourth difference signal;
• representing each of said first, second, third and fourth difference signals by words of M bits, where M is less than N bits;
• transmitting said first, second, third and fourth difference signals of M bits and said N-bit second signal.

A method for reconstituting digital picture information encoded in a format in which a first pixel is transmitted in unencoded form as an N-bit word and a second pixel is transmitted in an encoded form as an M-bit delta word, M being less than N, said delta word being encoded as given one of a plurality of non-linear functions of an amplitude difference between said first and second pixels, said given non-linear function being selected in accordance with the amplitude of said N-bit word, comprising:

• receiving said N-bit pixel and M-bit delta words;
• selecting one of a plurality of decoding transfer functions in accordance with a given number of most significant bits of said N-bit pixel word;
• applying said M-bit delta word to said transfer function selected by said N-bit word to regenerate said amplitude difference between said first and second pixels;
• and
• combining said N-bit word with said regenerated amplitude difference to reconstitute said second pixel with a resolution of N-bits.