| 摘要 |
A series of bits which represent the intensity values of elements of a facsimile picture are preprocessed to eliminate runs of length one, and then applied to a predictive encoder which treats values for alternate pels in two distinct ways. Specifically, the value of every odd pel is predicted, based upon the intensity values of some surrounding picture elements. Each prediction is compared with the true intensity value to yield an error signal. The encoder is also arranged to generate a reference signal which indicates whether the confidence in each prediction for odd pels is high or low. The error values for odd pels within a predefined reordering interval are then sorted or reordered into two groups, dependent upon the reference value. On the other hand, the intensity values of even pels are predicted only when the values cannot be precisely determined from the two previous and subsequent values; the error values for even pels are assembled into a third group. When data for an entire reordering interval has been processed, each of the groups is run length coded for transmission. By encoding even pel values only when they are needed, the amount of data required to represent the facsimile picture is reduced, at the expense of only a slight loss in detail, which is not objectionable. Further, since the statistics of the groups formed by reordering are different, different code dictionaries can be used for run length coding.
|
