Low bandwidth video teleconferencing system and method

Claim 1

A bandwidth compression method for frames of gray scale digital video image data including lines of pixels comprising, calculating the two dimensional mean gray scale level of a predetermined plurality of pixels located about a pixel in question, calculating the two dimensional activity level of a plurality of pixels relative to the pixel in question, comparing a predetermined combination of the activity level and the mean to a threshold, turning the pixel in question either black or white in response to the results of the comparison, determining the intraframe correlation of the lines of the frame, determining a first interframe correlation between the lines of the present frame and the corresponding lines of the previous frame, generating a plurality of displaced versions of the previous frame, each displaced version being shifted by one or more pixels in either the lateral, vertical or diagonal directions, determining additional interframe correlations between the lines of the present frame and the corresponding lines of each of the displaced versions of the previous frame, comparing the intraframe correlation and interframe correlations and selecting as a reference the frame having the best correlation with the present frame, run length encoding in two dimensions the present frame with respect to the reference.