Video telecommunication system and method for compressing and decompressing digital color video data

Claims

I claim:

1. A method for compressing digital color video data in a video telecommunication system having means for generating a color video signal for a plurality of video picture frames, with each picture frame comprising a plurality of scan lines composed of a plurality of pixels, and each pixel in said picture frame comprising three digital color components, said method comprising the steps of:

(a) determining a luminance function for each pixel based upon at least one of said three digital color components;

(b) determining at least one decision parameter for at least a substantial portion of the pixels in the scan lines of a current picture frame based upon the difference of said luminance function between pixels a predetermined distance from at least one other pixel on each scan line;

(c) comparing said at least one decision parameter with a corresponding threshold value to determine starting pixels and ending pixels for run lengths of sequentially related pixels in said scan lines, said run lengths being of a first digital word size, and said three color components being of second, third, and fourth digital word sizes, respectively;

(d) encoding all of said digital color components in said picture frame according to a look up table of digitally compressed color codes of the most visually significant color combinations of a fifth digital word size smaller than the sum of said second, third and fourth digital word sizes;

(e) encoding a plurality of combination of said run lengths and digitally compressed color codes representing at least a portion of said picture frame;

(f) comparing said run lengths and digitally compressed color codes of said current picture frame with the run lengths and digitally compressed color codes of a previous picture frame to determine changes from said previous picture frame to said current frame; and

(g) encoding said changes from said previous picture frame to said current picture frame for at least a portion of said picture frames, whereby once an initial picture frame is encoded, only those changes in subsequent picture frames are encoded.

2. The method of claim 1, wherein said step of comparing said at least one decision parameter with a threshold value comprises determining the rate of change of said differences for each of said pixels for which said luminance function difference has been determined; and comparing said rates of change of differences with a predetermined adaptive difference rate of change threshold to determine which of said pixels represent points of change of said luminance function.

3. The method of claim 1, wherein said step of comparing said at least one decision parameter with a threshold value comprises comparing a plurality of decision parameters with a corresponding plurality of thresholds to determine which of said pixels represent points of change of said luminance function.

4. The method of claim 1, wherein said three digital color components represent red, green and blue color video components, and said first, second, and third digital word sizes are equal.

5. The method of claim 1, wherein each said combination of run length and color components is coded as at least a sixteen bit digital word.

6. The method of claim 1, further including the step of concatenating run lengths in said plurality of combinations of run lengths and color components for combinations having color components whose differences are less than a predetermined color difference threshold.

7. The method of claim 1, further including the step of encoding a table of run lengths and compressed color codes representing only those differences from one scan line to the next adjacent scan line in a picture frame in one direction, for each picture frame.

8. The method of claim 1, wherein said step of encoding changes from one picture frame to the next picture frame includes determining distinctive edges of an image segment that has moved as at least one sequence of combinations of run length and compressed color codes in at least one scan line for each picture frame, and encoding in said table of changes the changes in at least one of said sequences between distinctive edges as a table representing a movement of said image sequence from one frame to another frame sequentially.

9. The method of claim 8, wherein said movement encoded is selected from the group consisting of horizontal shifting, shrinking, growing, vertical displacement, horizontal shifting and shrinking, horizontal shifting and growing, horizontal shifting and vertical displacement, vertical displacement and shrinking, and vertical displacement and growing.

10. The method of claim 1, wherein the step of determining said luminance function comprises summing said three digital component signals.

11. The method of claim 10, wherein said luminance function has a digital word size of eight bits.

12. The method of claim 10, wherein the step of determining said luminance function includes weighting of the sum of said three digital color component signals with respect to one of said three digital color component signals.

13. The method of claim 1, wherein the digital word size of each of said digital color components from which said luminance parameter is determined is six bits.

14. The method of claim 13, wherein the digital word size of said color components is reduced to four bits in said combinations of run lengths and color components.

15. The method of claim 14, wherein each said combination of run length and color components is coded as at least a sixteen bit digital word.

16. A system for compressing digital color video data in a video telecommunication system having means for generating a color video signal for a plurality of video picture frames, with each picture frame comprising a plurality of scan lines composed of a plurality of pixels, and each pixel in said picture frame comprising three digital color components, said system comprising:

(a) means for determining a luminance function for each pixel based upon at least one of said three digital color components;

(b) means for determining at least one decision parameter for at least a substantial portion of the pixels in the scan lines of said picture frame based on the difference of said luminance function between pixels a predetermined distance from at least one other pixel on each scan line;

(c) means for comparing said at least one decision parameter with a corresponding threshold value to determine starting pixels and ending pixels for run lengths of sequentially related pixels in said scan lines, said run lengths being of a first digital word size, and said three color components being of second, third and fourth digital word sizes, respectively;

(d) means for encoding all of said digital color components in said picture frame according to a table of digitally compressed color codes of the most visually significant color combinations of a fifth digital word size smaller than the sum of said second, third and fourth digital word sizes;

(e) means for encoding a plurality of said run lengths and digitally compressed color codes representing at least a portion of said picture frame;

(f) means for comparing said run lengths and digitally compressed color codes of said current picture frame with the run lengths and digitally compressed color codes of a previous picture frame to determine changes from said previous picture frame to said current frame; and

(g) means for encoding said changes from said previous picture frame to said current picture frame for at least a portion of said picture frames, whereby once an initial picture frame is encoded, only those changes in subsequent picture frames are encoded.

17. The system of claim 16, wherein said means for comparing said at least one decision parameter with a threshold value comprises means for determining the rate of change of said differences for each of said pixels for which said luminance function difference has been determined; and means for comparing said rates of change of differences with at least one predetermined difference rate of change threshold to determine which of said pixels represent points of change of said luminance parameter.

18. The system of claim 16, wherein said means for comparing said at least one decision parameter with a threshold comprises means for comparing a plurality of said decision parameters with a corresponding plurality of thresholds to determine which of said pixels represent points of change of said luminance function.

19. The system of claim 16, wherein said three digital color components represent red, green, and blue color video components, and said first, second, and third digital word sizes are equal.

20. The system of claim 16, wherein each said combination of run length and color components is coded as at least a sixteen bit digital word.

21. The system of claim 16, further including means for concatenating run lengths in said plurality of combination