Patent US 4,965,845

A scheme for compressing and reconstructing multi-color high resolution navigation image data, such as aeronautical chart images provides an effective bit rate of one bit per pixel. Data representative of the image of a color aeronautical chart is sampled for a plurality of aerial grid points of the image (corresponding to pixels of the displays) each sample being digitized to provide an original color-representative matrix of data points, each resolved to some number of digital bits per basic color, per sample point. The color data is transformed into data representative of luminance (Y) and in-phase and guadrature chrominance (I, Q) components thereof. The Y, I, Q values are compressed using a clustering process that produces, for an aeronautical chart, sixteen clusters of combinations of colors and shades in the Y, I, Q domain. Then, for each sample point, a four bit code representative of the centroid of the three dimensional (Y, I, Q) cluster in which its transformed color/shade value is located is generated, resulting in a preliminary bit rate of six-to-one (four bits per pixel). This preliminarily compressed color image data is further processed using a four-to-one compression code-table to obtain the desired one-bit/pixel bit rate.