Progressive image transmission

An image transmission system (FIG. 1) including at a transmitting terminal a scanning device (10), an addressable memory (11) for storing black and white binary values corresponding to each picture element of an image to be transmitted, a transmission channel (15) for such image, at a receiving terminal an image display device (20) and at each of such transmitting and receiving terminals of signal processor (13,17) characterized in that

• a processor (13) at the transmitting terminal first encodes cells of binary values from said memory (11) representing basic image areas of uniform size and shape according to the number of picture elements therein of a predetermined binary kind and next forms a multilevel hierarchical tree with nodal values derived from a comparison of pairs of such values on lower levels until a single value on the top level is reached according to whether the members of a pair are both black, both white or mixed, each nodal value representing the shade of an equal-area subdivision for each level of such tree;
• the transmitter (14) sends the nodal values level-by-level over said channel (15) beginning with said single top level value but skips any white or black value repeated to a lower level;
• and
• the processor (17) at a receiving terminal decodes nodal values received over said channel (15) from the single topmost value, corresponding to the overall image shade, of the hierarchical tree through each lower level causing said display device (20) to reconstruct the transmitted image in progressively finer detail until transmission is stopped at any level or is continued to completion.

In an image transmission system (FIG. 1) including at a transmitting terminal a scanning device (10), an addressable memory (11) for storing black and white binary values corresponding to each picture element of an image to be transmitted, a transmission channel (15) for such image at a receiving terminal, an image display device (20), and at each of such transmitting and receiving terminals a signal processor (13,17) the method for coding and decoding picture element information for progressive transmission over such channel characterized in that

• in a first step processor (13) interactively with memory (11) forms picture elements into cells of uniform size and shape;
• in a second step counts the number of picture elements of a predetermined binary kind in each group:
• in a third step forms the base of a multilevel hierarchical tree from nodal values derived from a comparison of pairs of numbers in adjacent cells of the second step, said nodal values being both alike of one binary kind, both alike of the other binary kind, or mixed;
• in a fourth step forms the remaining levels of the hierarchical tree from nodal values of lower levels according to the same code until a single value at the apex of the tree is reached, said nodal values being such that areas once determined to be all of one binary kind need not be further subdivided;
• in a fifth step transmits the nodal values level by level through said transmission channel;
• and
• in a sixth step in said processor (17) at receiving terminal interactively with said display device (20) decodes received nodal values from the apex value corresponding to the overall image shade through the nodal values of each lower level and reconstructs the transmitted image in successively finer detail until transmission is stopped at any level or continued to completion.