| 摘要 |
Correction of PCM digital image data by encoding of the redundancy present in blocks of the data may be subject to faulty encoding for certain amounts of redundancy. This occurs at the boundaries where the data values change from 255-256, 127-128 and 63-64, because all the binary bits of the representation change at these values. The improved apparatus of the invention encodes the redundancy in blocks of data by assignment of check bits in terms of the data magnitudes, and does not rely on the PCM binary representation to express the redundancy. Upon decoding, the recovered data redundancy is compared to the redundancy represented by the received check bits, and its magnitude is used to determine the data in error. The value in error is replaced by the average of the data values in the same block.
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