Abstract: The present invention relates to the field of vector quantization of transmitted imagery. In particular, the invention is a method for automatically generating a codebook for use in the transmitter and receiver components of an amplitude-adaptive normalized differential vector quantization system based upon a specified signal-to-noise ratio goal. In accordance with this method, the specified signal-to-noise ratio goal automatically derives the amplitude thresholds and other required data to determine the tradeoff between image quality and data compression for the transmitted imagery.

Abstract: A method for data compression provides for an improved digital facsimile document transmission system. The mixed mode method provides that symbols can be located both individually and as a part of a line of symbols in order to provide for efficient operation for both the symbol and graphic portions of a document to be transmitted without requiring that the symbols be organized in lines or that each location be conveyed independently of all other locations of symbols.

Abstract: A method is provided for data compression and image enhancement in a digital facsimile document transmission system. The method permits images containing gray scale content to be reproduced using conventional facsimile equipment. An irregularly shaped matrix of thresholds is employed in an adaptive approach to convert each multilevel gray scale pixel to a bilevel (black/white) pixel. The adaptive thresholding approach employed provides improved image quality in images containing both gray scale and high contrast information, e.g., identification cards. Compression performance is enhanced by an image rearrangement process in which pixels thresholded with similar threshold values are grouped together prior to run length encoding.

Abstract: A method for data compression provides for an improved digital facsimile ument transmission system. The mixed mode method provides that symbols can be located both individually and as a part of a line of symbols in order to provide for efficient operation for both the symbol and graphic portions of a document to be transmitted without requiring that the symbols be organized in lines or that each location be conveyed independently of all other locations of symbols.

Abstract: A method of error processing is disclosed in which the first erroneous line etected in a facsimile transmission is decoded, and printed in the normal manner, up to the point in the line where an error is detected. An erroneous portion of the line is then defined to be the point in the line from which the error is detected as well as four color changes to the left. This erroneous portion is replaced by the corresponding picture elements in the immediately preceding line. The resulting "corrected" line is then used as a new "previous line" and the process is repeated with the erroneous portion of each subsequent line being replaced with white until a full line is properly decoded.

Abstract: A method and apparatus are provided for data compression in a digital facile document transmission system. In accordance with the method, only alternate scan lines are transmitted, i.e., every other line is deleted in transmission, and at the receiver, the missing scan lines are interpolated from the transmitted data. This compression technique provides a fixed compression ratio of 2 to 1 regardless of the complexity of the input document. The interpolation method relies on comparing, for each picture element to be interpolated, the colors of one or more pairs of adjacent picture elements of the transmitted scan lines and making a decision as to the color of the picture element to be interpolated on this basis.